摘要:

/- one-stop immediate access to all atomic spectrometry literature published since 7 985 including conference papers. jAASbase is a unique database that provides a fully comprehensive up-to-date source of over 23,. 000 analytical atomic spectrometry references. It is designed to meet every atomic spectroscopists information needs - a convenient desktop tool. As a subscriber you will enjoy the following benefits of JAASbase @ Simplicity of use even for the non-specialist @ Economy of effort and expense @ A vast store of references @ Flexibility that fosters thorough searches @ Adaptability - you can add your own data @ Helpdesk and user literature gives added assurance that you can quickly master JAASbase Idealist Software f 21 0.00 $368.00 1994 Subscription Details JAAS Backfile (1 986-93) jAASbase Updates EC €99.00 EC €280.00 EC USA $174.00 USA $490.00 USA (VAT chargeable in the UK) To order JAASbase and for further information please contact Sales and Promotion Department Royal Society of Chemistry Thomas Graham House Science Park Milton Road Cambridge CB4 4WF United Kingdom. TeI +44 (0)223 420066.Fax +44 (0)223 423623. ROYAL SOCIETY OF Information Services/- one-stop immediate access to all atomic spectrometry literature published since 7 985 including conference papers. jAASbase is a unique database that provides a fully comprehensive up-to-date source of over 23,. 000 analytical atomic spectrometry references. It is designed to meet every atomic spectroscopists information needs - a convenient desktop tool. As a subscriber you will enjoy the following benefits of JAASbase @ Simplicity of use even for the non-specialist @ Economy of effort and expense @ A vast store of references @ Flexibility that fosters thorough searches @ Adaptability - you can add your own data @ Helpdesk and user literature gives added assurance that you can quickly master JAASbase Idealist Software f 21 0.00 $368.00 1994 Subscription Details JAAS Backfile (1 986-93) jAASbase Updates EC €99.00 EC €280.00 EC USA $174.00 USA $490.00 USA (VAT chargeable in the UK) To order JAASbase and for further information please contact Sales and Promotion Department Royal Society of Chemistry Thomas Graham House Science Park Milton Road Cambridge CB4 4WF United Kingdom.TeI +44 (0)223 420066. Fax +44 (0)223 423623. ROYAL SOCIETY OF Information Services/- one-stop immediate access to all atomic spectrometry literature published since 7 985 including conference papers.jAASbase is a unique database that provides a fully comprehensive up-to-date source of over 23,. 000 analytical atomic spectrometry references. It is designed to meet every atomic spectroscopists information needs - a convenient desktop tool. As a subscriber you will enjoy the following benefits of JAASbase @ Simplicity of use even for the non-specialist @ Economy of effort and expense @ A vast store of references @ Flexibility that fosters thorough searches @ Adaptability - you can add your own data @ Helpdesk and user literature gives added assurance that you can quickly master JAASbase Idealist Software f 21 0.00 $368.00 1994 Subscription Details JAAS Backfile (1 986-93) jAASbase Updates EC €99.00 EC €280.00 EC USA $174.00 USA $490.00 USA (VAT chargeable in the UK) To order JAASbase and for further information please contact Sales and Promotion Department Royal Society of Chemistry Thomas Graham House Science Park Milton Road Cambridge CB4 4WF United Kingdom.TeI +44 (0)223 420066. Fax +44 (0)223 423623. ROYAL SOCIETY OF Information Services/- one-stop immediate access to all atomic spectrometry literature published since 7 985 including conference papers. jAASbase is a unique database that provides a fully comprehensive up-to-date source of over 23,. 000 analytical atomic spectrometry references. It is designed to meet every atomic spectroscopists information needs - a convenient desktop tool. As a subscriber you will enjoy the following benefits of JAASbase @ Simplicity of use even for the non-specialist @ Economy of effort and expense @ A vast store of references @ Flexibility that fosters thorough searches @ Adaptability - you can add your own data @ Helpdesk and user literature gives added assurance that you can quickly master JAASbase Idealist Software f 21 0.00 $368.00 1994 Subscription Details JAAS Backfile (1 986-93) jAASbase Updates EC €99.00 EC €280.00 EC USA $174.00 USA $490.00 USA (VAT chargeable in the UK) To order JAASbase and for further information please contact Sales and Promotion Department Royal Society of Chemistry Thomas Graham House Science Park Milton Road Cambridge CB4 4WF United Kingdom. TeI +44 (0)223 420066. Fax +44 (0)223 423623. ROYAL SOCIETY OF Information Services

ISSN:0267-9477    

DOI:10.1039/JA99409BP007

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

1995 European Winter Conference on Plasma Spectrochemistry 8-13 January 1995 CAMBRIDGE UK Short Courses A series of short courses of one half day duration will take place on Sunday 8th January. Notes and tuition material will be distributed with each course. Courses 1 and 2 Short Courses on ICP-MS Professor R.S. Houk Ames Laboratory Iowa State University USA Course 1 (AM) Instrumentation and Theory The course will cover fundamental aspects of ICP-MS including:- a) Molecular beam sampling b) Quadrupole and high resolution c) Vacuum technology d) Ion sources e) Detection systems and data hand1 ing f) Sample introduction technologies analys ers Course 2 (PM) Advanced Topics The course will cover more advanced topics on ICP-MS particularly relevant to problem solving. Each topic will be illustrated with relevant applications examples.a) Interferences (spectroscopic and non-spectroscopic and methods of alleviation b) Isotopic analysis c) Chromatographic methods d) Overview of commercial instrumentation Course 3 (PM) Sample Preparation for ICPs Dr S.J. Haswell Hull University UK The course will focus on important aspects of sampling and sample preparation with particular emphasis on ICP measurements. a) Batch methods f o r wet oxidation b) Recent trends in microwave preparation for ICP-MS atomic spectrometry general analytical techniques c) On-line sample preparation d) Extraction methods e) On-line chemical processing f) Miniaturization Course 4 (PM) Speciation Professor O.X. Donard University of Bordeaux France The course will focus on practical aspects of speciation analysis with particular emphasis on ICP and other plasma sampling systems.Sample collection and handling preservation and preparation prior to injection into hyphenated systems using atomic spectrometry and ICP-AES or ICP-MS as detectors will be illustrated with applications from current topical fields . a) Sampling and sample pretreatment b) Separative techniques Differential chemistry Gas liquid ion and SCF c ) Interfacing chromatography techniques to ICPs and other plasma sources and detectors chromatographies Course 5 (AM) Quality Systems in the Laboratory Professor L. Ebdon Dr E.H. Evans University of Plymouth UK The course will discuss how high quality analytical data can be produced in the laboratory that are accurate reliable and adequate f o r the intended purpose.a) Quality assurance principles b) Sampling and sample preparation c) Personnel aspects d) Statistics for quality control e Use of reference materials and f) Equipment and records maintenance g) Audits and accreditation. traceability Course 6 (AM) Sample Presentation for ICPS Dr C McLeod Sheffield Hallam University UK The course is intended as a problem solving workshop and will attempt to rationalise the choice of sampling system for ICP spectrometries by use of practical examples. a) Nebulisation techniques Traditional and high efficiency The role of desolvation Hydride Other vapour techniques e . g . b) Vapour generation Hg oso c) Microsampling systems d) Flow injection e) Laser ablation1995 European Winter Conference on Plasma Spectrochemistry 8-13 January 1995 CAMBRIDGE UK Short Courses A series of short courses of one half day duration will take place on Sunday 8th January. Notes and tuition material will be distributed with each course.Courses 1 and 2 Short Courses on ICP-MS Professor R.S. Houk Ames Laboratory Iowa State University USA Course 1 (AM) Instrumentation and Theory The course will cover fundamental aspects of ICP-MS including:- a) Molecular beam sampling b) Quadrupole and high resolution c) Vacuum technology d) Ion sources e) Detection systems and data hand1 ing f) Sample introduction technologies analys ers Course 2 (PM) Advanced Topics The course will cover more advanced topics on ICP-MS particularly relevant to problem solving. Each topic will be illustrated with relevant applications examples.a) Interferences (spectroscopic and non-spectroscopic and methods of alleviation b) Isotopic analysis c) Chromatographic methods d) Overview of commercial instrumentation Course 3 (PM) Sample Preparation for ICPs Dr S.J. Haswell Hull University UK The course will focus on important aspects of sampling and sample preparation with particular emphasis on ICP measurements. a) Batch methods f o r wet oxidation b) Recent trends in microwave preparation for ICP-MS atomic spectrometry general analytical techniques c) On-line sample preparation d) Extraction methods e) On-line chemical processing f) Miniaturization Course 4 (PM) Speciation Professor O.X. Donard University of Bordeaux France The course will focus on practical aspects of speciation analysis with particular emphasis on ICP and other plasma sampling systems.Sample collection and handling preservation and preparation prior to injection into hyphenated systems using atomic spectrometry and ICP-AES or ICP-MS as detectors will be illustrated with applications from current topical fields . a) Sampling and sample pretreatment b) Separative techniques Differential chemistry Gas liquid ion and SCF c ) Interfacing chromatography techniques to ICPs and other plasma sources and detectors chromatographies Course 5 (AM) Quality Systems in the Laboratory Professor L. Ebdon Dr E.H. Evans University of Plymouth UK The course will discuss how high quality analytical data can be produced in the laboratory that are accurate reliable and adequate f o r the intended purpose. a) Quality assurance principles b) Sampling and sample preparation c) Personnel aspects d) Statistics for quality control e Use of reference materials and f) Equipment and records maintenance g) Audits and accreditation. traceability Course 6 (AM) Sample Presentation for ICPS Dr C McLeod Sheffield Hallam University UK The course is intended as a problem solving workshop and will attempt to rationalise the choice of sampling system for ICP spectrometries by use of practical examples. a) Nebulisation techniques Traditional and high efficiency The role of desolvation Hydride Other vapour techniques e . g . b) Vapour generation Hg oso c) Microsampling systems d) Flow injection e) Laser ablation

ISSN:0267-9477    

DOI:10.1039/JA99409FX049

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

1995 European Winter Conference on Plasma Spectrochemistry 8-13 January 1995 CAMBRIDGE UK Short Courses A series of short courses of one half day duration will take place on Sunday 8th January. Notes and tuition material will be distributed with each course. Courses 1 and 2 Short Courses on ICP-MS Professor R.S. Houk Ames Laboratory Iowa State University USA Course 1 (AM) Instrumentation and Theory The course will cover fundamental aspects of ICP-MS including:- a) Molecular beam sampling b) Quadrupole and high resolution c) Vacuum technology d) Ion sources e) Detection systems and data hand1 ing f) Sample introduction technologies analys ers Course 2 (PM) Advanced Topics The course will cover more advanced topics on ICP-MS particularly relevant to problem solving. Each topic will be illustrated with relevant applications examples.a) Interferences (spectroscopic and non-spectroscopic and methods of alleviation b) Isotopic analysis c) Chromatographic methods d) Overview of commercial instrumentation Course 3 (PM) Sample Preparation for ICPs Dr S.J. Haswell Hull University UK The course will focus on important aspects of sampling and sample preparation with particular emphasis on ICP measurements. a) Batch methods f o r wet oxidation b) Recent trends in microwave preparation for ICP-MS atomic spectrometry general analytical techniques c) On-line sample preparation d) Extraction methods e) On-line chemical processing f) Miniaturization Course 4 (PM) Speciation Professor O.X. Donard University of Bordeaux France The course will focus on practical aspects of speciation analysis with particular emphasis on ICP and other plasma sampling systems.Sample collection and handling preservation and preparation prior to injection into hyphenated systems using atomic spectrometry and ICP-AES or ICP-MS as detectors will be illustrated with applications from current topical fields . a) Sampling and sample pretreatment b) Separative techniques Differential chemistry Gas liquid ion and SCF c ) Interfacing chromatography techniques to ICPs and other plasma sources and detectors chromatographies Course 5 (AM) Quality Systems in the Laboratory Professor L. Ebdon Dr E.H. Evans University of Plymouth UK The course will discuss how high quality analytical data can be produced in the laboratory that are accurate reliable and adequate f o r the intended purpose.a) Quality assurance principles b) Sampling and sample preparation c) Personnel aspects d) Statistics for quality control e Use of reference materials and f) Equipment and records maintenance g) Audits and accreditation. traceability Course 6 (AM) Sample Presentation for ICPS Dr C McLeod Sheffield Hallam University UK The course is intended as a problem solving workshop and will attempt to rationalise the choice of sampling system for ICP spectrometries by use of practical examples. a) Nebulisation techniques Traditional and high efficiency The role of desolvation Hydride Other vapour techniques e . g . b) Vapour generation Hg oso c) Microsampling systems d) Flow injection e) Laser ablation1995 European Winter Conference on Plasma Spectrochemistry 8-13 January 1995 CAMBRIDGE UK Short Courses A series of short courses of one half day duration will take place on Sunday 8th January. Notes and tuition material will be distributed with each course.Courses 1 and 2 Short Courses on ICP-MS Professor R.S. Houk Ames Laboratory Iowa State University USA Course 1 (AM) Instrumentation and Theory The course will cover fundamental aspects of ICP-MS including:- a) Molecular beam sampling b) Quadrupole and high resolution c) Vacuum technology d) Ion sources e) Detection systems and data hand1 ing f) Sample introduction technologies analys ers Course 2 (PM) Advanced Topics The course will cover more advanced topics on ICP-MS particularly relevant to problem solving. Each topic will be illustrated with relevant applications examples.a) Interferences (spectroscopic and non-spectroscopic and methods of alleviation b) Isotopic analysis c) Chromatographic methods d) Overview of commercial instrumentation Course 3 (PM) Sample Preparation for ICPs Dr S.J. Haswell Hull University UK The course will focus on important aspects of sampling and sample preparation with particular emphasis on ICP measurements. a) Batch methods f o r wet oxidation b) Recent trends in microwave preparation for ICP-MS atomic spectrometry general analytical techniques c) On-line sample preparation d) Extraction methods e) On-line chemical processing f) Miniaturization Course 4 (PM) Speciation Professor O.X. Donard University of Bordeaux France The course will focus on practical aspects of speciation analysis with particular emphasis on ICP and other plasma sampling systems.Sample collection and handling preservation and preparation prior to injection into hyphenated systems using atomic spectrometry and ICP-AES or ICP-MS as detectors will be illustrated with applications from current topical fields . a) Sampling and sample pretreatment b) Separative techniques Differential chemistry Gas liquid ion and SCF c ) Interfacing chromatography techniques to ICPs and other plasma sources and detectors chromatographies Course 5 (AM) Quality Systems in the Laboratory Professor L. Ebdon Dr E.H. Evans University of Plymouth UK The course will discuss how high quality analytical data can be produced in the laboratory that are accurate reliable and adequate f o r the intended purpose. a) Quality assurance principles b) Sampling and sample preparation c) Personnel aspects d) Statistics for quality control e Use of reference materials and f) Equipment and records maintenance g) Audits and accreditation. traceability Course 6 (AM) Sample Presentation for ICPS Dr C McLeod Sheffield Hallam University UK The course is intended as a problem solving workshop and will attempt to rationalise the choice of sampling system for ICP spectrometries by use of practical examples. a) Nebulisation techniques Traditional and high efficiency The role of desolvation Hydride Other vapour techniques e . g . b) Vapour generation Hg oso c) Microsampling systems d) Flow injection e) Laser ablation

ISSN:0267-9477    

DOI:10.1039/JA99409BX051

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 213 R ATOMIC SPECTROMETRY UPDATE-ADVANCES IN ATOMIC ABSORPTION AND FLUORESCENCE SPECTROMETRY AND RELATED TECH N IQU ES Steve J. Hill* Department of Environmental Sciences University of Plymouth Plymouth Devon UK PL4 8AA John B. Dawson Department of lnstrurnentation and Analytical Science UMlST P.O. Box 88 Manchester UK M60 IQD W. John Price Ellenmoor East Budleigh Budleigh Salterton Devon UK EX9 7DQ Philip Riby School of Biological and Chemical Sciences University of Greenwich Wellington St. Woolwich London SE18 UK Ian L. Shuttler Bodenseewerk Perkin-Elmer GmbH Postfach 101 767,D-88647 Uberlingen Germany Julian F. Tyson Department of Chemistry University of Massachusetts Box 34510 Amherst MA 01003-4570 USA Summary of Contents 1 Atomic Absorption Spectrometry 1 .la Flame Atomizers 1.1.1 Fundamental studies 1.1.2.Interference studies 1.1.3. Sample introduction 1.1.3.1. Discrete procedures 1.1.3.2. Atom-trapping techniques 1.1.3.3 Sample introduction by flow injection 1.1.3.4. Solid sample introduction 1.1.3.5. Thermospray introduction 1.1.3.6. High-pressure nebulization 1.1.4. Sample pre-treatment 1.1.5. Chromatographic detection 1.1.6. Plasma atomizers 1.2. Electrothermal Atomizers 1.2.1. Atomizer design and surface modification 1.2.2. Sample introduction 1.2.3. Fundamental processes 1.2.4. Interferences 1.2.5. Developments in technique 1.3. Chemical Vapour Generation 1.3.1 Hydride generation 1.3.1.1. Fundamental studies 1.3.1.2. General developments in instrumentation and technique 1.3.1.3.Determination of individual elements 1.3.2. Mercury by cold vapour generation 1 -3.3. Volatile organo-metallic compound generation and metal vapour separation 1.4.1. Light sources 1.4.2. Optics 1.4.3. Detectors 1.4.4. Continuum source and simultaneous multi-element AAS 1.4.5. Background correction in AAS 1.5. Instrument Control and Data Processing 1.5.1. Instrument control 1.5.2. Data processing 1.5.3. Chemometrics 1.4. Spectrometers 2. Atomic Fluorescence Spectrometry 2.1 Discharge Lamp-excited Atomic Fluorescence 2.2. Laser-excited Atomic Fluorescence 2.3. Studies of Flames Plasmas and Atomic Vapours Using Laser-induced Fluorescence 2.4. Coherent Forward Scattering (Atomic Magneto-optical Rotation Spectrometry) 3. Laser Enhanced Ionization214R JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL.9 This review follows on from last year’s review (J. Anal At. Spectrorn. 1993 8 197R) and describes the developments in atomic absorption and atomic fluorescence spectrometry since that time. Included in this review are fundamental processes and instrumentation in the areas of atomic absorption and atomic fluorescence spectrometry together with advances in related techniques such as atomic magneto-optical rotation spectrometry and laser-enhanced ionization. The review of ‘Atomic Emission Spectrometry’ may be found in JAAS Volume 9 Issue 4. The full references names and addresses of authors can be readily found from the Atomic Spectrometry Updates References in the relevant issue of JAAS. However as an additional service to readers an abbreviated form of each reference quoted (except for those of Conference Abstracts) is given at the end of the review.Comments as to possible improvements for future reviews are welcomed by the review coordinator. 1. ATOMIC ABSORPTION SPECTROMETRY 1.1. Flame Atomizers Research activity in the area of flame atomizers is now mainly concerned with the ever-present problems of sample introduc- tion and pre-treatment. There is also still a considerable amount of literature concerned with the application of FAAS to the analysis of real samples much of which is concerned with some novel sample pre-treatment procedure. The relevant subject-based Updates should be consulted for information relating to applications. A survey of some novel pre-treatment procedures is provided in this Update (see section 1.1.4.).The geographical origins of work on interference effects suggest that some problems already discussed in the western literature are being rediscovered. Only limited coverage of this material has been provided in this Update. Work on funda- mental processes in combustion flames is now at a low level of activity in contrast to activity related to the coupling of sample pre-treatment directly with the spectrometer mainly by FI techniques (see section 1.1.3.3.). There has been little change in the activity relating to sample introduction by discrete procedures and atom-trapping procedures but there is possibly a discernable increase in the use of thermospray introduction (section 1.1.3.5.) and hydraulic nebulization (sec- tion 1.1.3.6.).Whilst the interest in the use of atomic spec- trometry techniques as element specific detectors for chromatography is at a high level there has been limited use of FAAS because of the relatively poor detection limits in comparison with other techniques. A perceptive and entertaining overview of the use of atomic spectrometry techniques for environmental analyses has been provided by Cresser (94/552). Much of the review is concerned with FAAS and the author points out that one of the factors which led to the general acceptance of the technique was the greatly improved analytical performance in an analysis of considerable practical interest; the determination of Mg in agricultural materials. A survey of contributions to practical FAAS by the author and his research group is also provided.These include a number of methods of error detection. 1.1.1. Fundamental studies It is possible to measure combustion species at trace concen- trations with good spatial resolution with a variety of optical probe techniques. Nyholm et al. (93/2881) studied the distri- bution of OH in pre-mixed 02-C2H2 and air-C,H flames using non-linear laser polarization spectroscopy. Reckers et al. (93/2880) have made measurements of both temperature and species concentrations in a pre-mixed air-H flame. The pro- cedure involved detection of the Raman and Rayleigh scattered light from a KrF excimer laser with a high throughput spectrometer and a gated intensified two-dimensional charge- coupled detector.The density profiles of N 02 H 2 0 and H were established. The two-line method has also been used (94/1134) for the measurement of temperature. The light emitted by potassium atoms at 404.4 and 766.5 nrn was coupled to a rapid scanning spectrometer by a 3 mm diameter optical fibre. Values ranging from 1910 to 2530 K were calculated. Further results from the model calculations reported in last year’s Update (see J. Anal. At. Spectrom. 1993 8 197R) are now available (93/3202) still in the Russian literature. The temperature and composition of various flames including air-C,H and N20-CzH2 were calculated for a wide range of fuel-to-oxidant ratios. At the optimum ratio detection limits for 58 elements were calculated. The formation of pyrocarbon films on aerosol particles was discussed.Zaranyika (94/268) has presented a modified steady-state kinetic model for calcu- lation of the fraction of atoms excited and the fraction ionized based on both thermal excitation and ionization and collisional charge transfer interactions. The results of the model calcu- lations for percentage ionization are in agreement with litera- ture values. 1.1.2. Interference studies As can be seen from the material reviewed in this section over the years there is a continual refinement in our understanding of interference effects in flame atomizers. Two well-known effects namely a solute uolatilization interference stable com- pound formation (93/3244) and a vapour-phase interference ionization (93/3967) have been studied by Lueke. In the first of these studies the effect of aluminium on the signals for Ca and Mg has been examined.As has been reported previously (see J. Anal. At. Spectrom. 1992 7 215R) the extent of interference with increasing aluminium passes through a mini- mum in the presence of chloride. In contrast to the previous report the mechanism proposed by Lueke (93/3244) is the formation of only pure aluminium oxides which releases the analyte elements. The effect is observed in both the presence and absence of caesium (added as an ionization buffer). From a practical standpoint the addition of lanthanum as a releaser and the use of the N,O-C2H2 flame are advocated. In the second study (93/3967) the ionization behauiour of the alkaline earth elements in both the air-C,H and N,O-C,H flames were studied.It was pointed out that the degree of ionization is dependent not only on the element and the temperature but also on the concentration of the analyte. Furthermore in the case of many real samples the concomitant presence of alkali metals causes a variable degree of ionization. Values for the extent of ionization of the various elements in the two flames were reported based on the assumption that the increase in signal obtained on the addition of caesium represents complete suppression of ionization. Results at vari- ance with some of those reported by Amos and Willis (Spectrochim. Acta 1966 22 1325) were obtained. Interference effects in the determination of Au have been studied by the inhibition-release titration method (93/3977). It was found that the effect of several complexing agents could be overcome by the addition of NaDDC.The interference of iron and manganese on the determination of Co Cu and Ni (94/758) and of manganese on the determination of Fe (93/3562) have been studied. In the first study it was shown that the overall interference could be computed from previously established element-element interactions and the method was applied to the analysis of marine nodule samples. In the secondJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 215R study it was shown that the interference could be overcome by either the addition of chelating agents (EDTA or quinolin- 8-01) or inorganic ligands (cyanide or fluoride) forming strong complexes with the iron. Chinese workers have noticed (94/682) that the presence of an interference can possibly be deduced from the proportional change in signal obtained on dilution.After a year’s lull more work concerning the role ofsurfac- tants has appeared during this review period. As was noted two years ago (J. Anal. At. Spectrum. 1992 7 215R) there is a possible role for the molecule chain length in determining the time to re-equilibrate with new surfaces formed during droplet production (93/3414). Results were presented for K as the analyte in the presence of 11 surfactants which supported this theory in that it was observed that the longest surfactants did not modify drop-size distribution and thus did not lead to an improvement in sensitivity although under equilibrium measurement conditions they lowered the surface tension the most.It was concluded that for any given surfactant the increase in sensitivity observed was a consequence of the decrease in the aerosol mean drop size which in turn led to improved transport into and atomization in the flame. A Meinhard nebulizer was used with an uptake rate of 1.3 ml min-l. As the nebulizer clogged at concentrations in excess of 0.5 mol l-l the critical micelle concentration (CMC) was not exceeded for some surfactants. Workers at Huazhong Normal University (93/3282) have considered rnicelleforrnation to be important and proposed that below the CMC enhance- ment is due to analyte enrichment in the aerosol droplets due to a surface interaction effect; whereas above the CMC the enhancement is due to binding of analyte species to the micelles in the bulk solution.This group also proposed that the increased carbon loading in the flame led to greater atomiz- ation because of the increased reducing power of the atomizer. A group at the Dalian Medical Officer’s school reported (93/3176) on the effect of 10 surfactants on the signal for Sr. The best enhancement was caused by sulfosalicylic acid (which also decreased the effects of various concomitant ions) whereas sodium dodecylsulfate and sodium dodecylbenzenesulfonate had no effect. The group at Shanxi University investigated (93/4013) the effect of three organic solvents five organic reagents and eight surfactants in the determination of some first row transition elements and Cd Mg Pb and Sr and concluded that acetone was the best.Workers at Nankai have reviewed (93/3288) the role of various sensitization reagents in the determination of Yb (see J. Anal. At. Spectrum. 1993 8 197R). Chinese workers have also rediscovered (94/948) that phosphorus depresses the Ca signal but that the effect is removed on the addition of lanthanum. Korean workers reported (93/3259) that mineral acids (both type and concen- tration) affect the FAA signal of a number of metals and Argentinian workers noted (93/3484) similar effects in the determination of V. Japanese workers exploited (94,4321 ) a selective enhancing eflect ofcarbon black on the signal derived from the oxides of Sn” and Sn” to determine both species in oxide powders. 1.1.3. Sample introduction While the ability to handle liquid samples successfully was one of the features that made FAAS such an attractive technique when first introduced it is limitations in the processes involved in the production of atoms from sample solutions that continue to attract considerable research and development activity. The area has been reviewed by Sneddon (94/338).Work discussed in the previous section on the use of organic additives to improve the sensitivity (and presumably also detection limits) is clearly aimed at improving sample introduction character- istics as well as overcoming some interference effects. Several publications describing analytical methods in which a liquid- liquid extraction (LLE) procedure is used followed by nebuliz- ation of the organic phase have appeared during the review period. Some of these involve the use of new chelating agents with familiar solvents such as IBMK (93/2715 93/3103 93/3195 94/56) butyl acetate (94/818) and isoamyl acetate (93/3963).Others are concerned with the introduction of less commonly used solvents some of which may raise safety issues such as dimethylbenzene (93/3531) nitrobenzene (93/2197) and di-isobutyl ketone DIBK (93/3093). In this latter work DIBK is used for the extraction of APDC complexes of Cu and Ni from strongly acidic media rather than IBMK as the decomposition of the Cu complex in the extract could be suppressed allowing its extraction from either 4 mol 1-l nitric acid or 8 mol 1-1 hydrochloric acid. The ability of this combination of chelating agent and solvent to extract from highly acidic solutions would appear to be of considerable use in analytical procedures which involve acid digestion sample pre-treatment as it is not necessary to add reagents to raise the pH prior to the separation and preconcentration stage.Mixed organic solvents have also been nebulized. Metals extracted as DDC complexes into chloroform or carbon tetra- chloride (94/1122) were introduced after ultrasonication with a mixture of butyl acetate and acetone. Chloroform has also been introduced (93/3415,94/65,94/120,94/1195) by a discrete procedure (see section 1.1.3.1.). Spray chamber modifications have been described for use with oil and petrol samples. By introducing the C,H tangen- tially into the chamber (94/1100) and modifying the baffle design the ability of the premixed gases to transport engine oil droplets into the flame was investigated. A sample introduc- tion system and atomizer for the determination of Pb in petrol has been devised (93/3204) in which the petrol sample acts as the fuel.Qi et al. (94/11) used a ‘high-performance concentric pneumatic nebulizer’ with a Model WFX-1 B spectrometer from the Beijing Second Optical Instrument Factory in a procedure for the determination of Au by FAAS with FI preconcentration. The publication i s concerned with the optim- ization of the FI system and no further information about the nebulizer is available. There appears to have been an increase in the number of publications describing high pressure nebulization and thermo- spray devices during the present review period and these are dealt with in separate sections (see sections 1.1.3.5.and 1.1.3.6.) 1.1.3.1. Discrete procedures. There has been a slight revival of interest in the use of pulse nebulization or ‘one drop’ techniques as shown by the numbers of publications in the current review period. It is tempting to view this procedure as an inferior alternative to flow injection introduction (see sec- tion 1.1.3.3.) as the reasons for using the technique are often given (see for example 94/120) as the ability to handle micro- samples containing high dissolved solids or organic solvents. However the precision may be poor. Relative standard devi- ations of 8% were obtained for the determination of Ca Cu Mg Pb and Zn in serum (94/120). A split capillary system with two reservoirs one for sample and one for a releaser or ionization buffer has been described (94/1064). The system was also used for hydride generation.In addition to these two groups a further three Chinese groups are active in this area. Methods for the determination of trace elements in human hair (94/1214) K and Na in ores (94/1155) and Sr in wild cabbage (93/3176) have been described. A number of procedures have been developed by workers at the Nagoya Institute of Technology in Japan. Following a sealed vessel microwave digestion in a mixture of nitric perchloric hydrochloric and hydrofluoric acids (20:3:1:1 total volume 2.5 ml) Ca Cu Fe Mg Mn and Zn were accurately determined in several biological and botanical reference mate- rials (93/3143). The procedure was extended to elements present at lower concentrations by the addition of a liquid- liquid extraction step in which metals were extracted as the APDC complexes into trichloromethane and a 40pl sub- sample nebulized (93/3415 94/65).A method for the determi-216R JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 nation of leachable Pb from lead-glazed ceramic ware was also developed (94/1195). 1.1.3.2. Atom-trapping techniques. As with discrete pro- cedures most of the published work in the area of atom trapping emanates from Chinese laboratories. All the papers in the present review period are concerned with slotted tube atom retarders (STARS). Various combinations of sample introduction (such as flow injection and chemical vapour generation) with a STAR were investigated by Gao et al.(94/392) for the determination of As Au and Pb. Detection limits of 3.0 0.2 and 1.6 ngml-I respectively were obtained. By using FI introduction Xu et al. (93/3086 see also J. Anal. At. Spectrom. 1993 8 197R) extended the lifetime of the tube by a factor of 5-6 in comparison with that obtained for continuous aspiration. The impact systems could be removed from the spray chamber providing larger enhancement factors (between 3- and 5-fold) with no loss of precision. Thorburn Burns et al. (94/226) obtained a 2-3-fold enhancement in sensitivity for the determination of Sn in zirconium alloys. The STAR had a longitudinal base slot of 10 x 3 mm with six 6 mm diameter holes 15 mm apart at 180". The detection limit was 0.55 pg ml-I. Accurate results for two reference alloys were obtained.A similar improvement in sensitivity was reported by Zhen et al. (94/85 1) for the determination of Mn in drinking water beverages and human hair. By combining a STAR with a preliminary liquid-liquid extraction of the APDC complexes of Sb*** and SbV into IBMK a sensitivity enhancement of 100 was obtained (94/261). Qi et al. (94/11) used a STAR to improve sensitivity in the determination of Au by a FI precon- centration procedure (see section 1.1.3.3.). A brief review oftrapping devices (water cooled silica tubes and STARs) has appeared in the Russian literature (93/2199). Chinese workers (94/396) obtained a 270-fold sensitivity enhancement by the use of a water cooled quartz tube for the determination of Cd. For a 1-min trapping period a precision of 4.1% RSD was obtained for a concentration of 0.4 ng ml-I.1.1.3.3. Sample introduction by flow injection. There continues to be a sustained interest in the coupling of FI sampling handling procedures with atomic spectrometry instrumentation and yet again the current review period contains more publi- cations in this area than in any other. In addition to the substantial numbers of publications describing FI procedures for preconcentration and separation of analyte and matrix species there have been more publications in this review period concerned with the micro-sampling and on-line dilution capa- bilities of FI. It should be noted that most of the high pressure nebulization and thermospray devices described in sections 1.1.3.5. and 1.1.3.6. were used with sample injection. In this way the sample does not pass through the high pressure pump used for carrier stream delivery.As usual there have been a number of overview papers (93/273 1,93/3923,93/3929,94/80) and a book chapter (94/43 1). The essence of these publications is the extreme versatility of FI sample handling and that the combination of FI with atomic spectrometry (AS) leads to enhanced performance (93/2731). It was even suggested that the FIAS combination could be regarded as a new analytical methodology analogous to the techniques encompassed by the terms such as HPLC in the vocabulary of analytical methodology for molecular species. Fang has pointed out (93/C3057 93/C3058) that by the implementation of FI dilution and preconcentration pro- cedures the useful working range of FAAS can be increased from about 3 to about 7 orders of magnitude.Some further information on the coupling of discontinuous flow analysis (DFA) and FAAS (see J. Anal. At. Spectrom. 1992 7 215R) has appeared from Australia (94/1035). It is still not clear whether DFA offers any distinct advantages over the use of single pumps and concentration gradients produced by controlled hydrodynamics. A detailed comparison of propulsion systems has been made (93/3253) in which it was found that good precision could be obtained from a peristaltic pump in the short term but over three days the precisions of a dual piston reciprocating pump and a dual syringe sinusoidal pump were superior (see J. Anal. At. Spectrom. 1993 8 197R). There has been relatively little activity in the area of sample dissolution in this review period.Chinese workers have described (94/210) an on-line electrolytic dissolution procedure for the determination of magnesium in metal alloys. The signal was a linear function of either electrolysis time or current and precisions of between 3 and 5% RSD were obtained. Information on the stopped flow pressurized micrpwave system of Gluodenis and Tyson mentioned last year is now available (93/578). The slurried sample was transported into a glass reactor in the microwave field and heated for 5 min. The pressure was controlled at 2.8 MPa. As the sample volume of the 15% m/v slurries was only 200 pl the possibility of a contribution to the overall variance from sample inhomogen- eity was tested by the analysis of variance (ANOVA). No evidence for sample inhomogeneity was found.A method for the determination of Cu and Zn in whole blood pumped directly from the patient's arm has been described (Burguera et al. At. Spectrosc. 1993 14 90). The sample was merged with an anticoagulant (EDTA) and nitric acid before a sub- sample was injected into a carrier stream for transport through a microwave oven operated at 70 W in which the residence time was 20 s. After passage through a gas diffusion cell (to remove evolved gases) the solution was delivered to the nebul- izer of the spectrometer Good agreement between the results obtained by several methods was obtained and the recovery of spikes added to pooled whole blood samples was 98%. Flow injection has a number of attractive features as a microsampling technique among which are possibilities for implementation of S/N enhancement strategies based on the the known peak shape of FI signals and the known time window in which the signal occurs.Trojanowicz and Szostek (93/3928) used a low-pass Chebyshev Type 11 real-time digital filter to improve the precision and detection limit of a number of FI methods including FAAS. Sperling et al. (93/3926) improved the detection limits for Ca Cu and Zn by the use of ensemble summation of signals in conjunction with gated inte- gration and Savitsky-Golay peak smoothing (see also J. Anal. At. Spectrom. 1993 8 197R). In a study of diflerent sample digestion procedures for the determination of Cd and Ni in rice Morales-Rubio et al.(93/3194) used a single line manifold with a 1OOpl injection volume to deliver the digests to the spectrometer. It was found that complete dissolution was not necessary and satisfactory results were obtained from the introduction of the stirred suspension or supernatant produced on reaction with nitric acid and hydrogen peroxide at room temperature. Other inhomogeneous samples that have been introduced by FI include milk (94/1126) and cement slurries (93/3380). In the former determination (for Ca and Mg) the sample was injected into a carrier stream of strontium nitrate and in the latter for the determination of K and Mg a merging zones manifold was used to add lanthanum solution to the injected sample. The slurry concentration was 0.2% m/v in 0.13 mol 1-1 nitric acid and 100 pl(0.2 mg of cement) of sample was injected.The particles were all less than 70 pm in diameter. The manifold incorporated a well-stirred mixing chamber to provide an on-line dilution of 22. Aqueous standards were used and the results were in agreement with those obtained by FAAS after fusion with lithium carbonate. Ceramic samples (94/735) were fused with lithium metaborate and after dissolu- tion in nitric acid sub-samples were injected into a single line FI manifold using a variable volume injector (see Burguera et al. Anal. Chim. Acta 1990 234 253). The detection limits for Ca Fe and Mg were 70 50 and 8 ng ml-' respectively. No external pump was used the flow was controlled by varying the nebulizer suction. The sample injection volume was varied by both this parameter and the time for which the switching valve was in the sample introduction position.Precisions ofJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 217R between 0.5 and 2% RSD were obtained. The materials (porcelain feldspar kaolin varnish clay and stoneware) were also analysed for Na and K by FAES. Despite the focus of many research projects in atomic spectrometry on the need for improved detection limits many real samples for analysis require reliable dilution prior to presentation to the spectrometer. Two FI procedures were incorporated into the methods described above namely a well- stirred tank (93/3380) and variable volume injection (94/735). In addition a peristaltic pump can always be used to dilute sample continuously (93/3510).An FI system based on a variable-volume mixing chamber (see J. Anal. At. Spectrom. l992,7,215R) was used (93/3397) to extend the working range for Ca and Cu by factors of about 100. Two injection valves in series were used to inject air (10.5 ml) and sample (50 pl). The air followed the sample plug into the dilution volume the inlets of which were positioned so that the air bubbled through the sample and carrier providing efficient mixing. The diluted sample was then presented to the spectrometer and a flat topped peak obtained as the air prevents further mixing of the diluted solution with the carrier. To overcome the effect of the variation in flow rate that occurs as the air slug was being compressed which would give rise to a varying signal a 30 cm delay coil was included in the manifold.Air Compensation was used as the nebulizer suction was not balanced by the pressure from the external peristaltic pump. The air was introduced at a T-piece located immediately in front of the nebulizer. A method based on sequential injections of increasing volumes was used by dos Reis et al. (94/990) to minimize the amount of sample actually introduced into the spectrometer. Each successive sample peak was measured and once a peak was recorded which exceeded a preset threshold the remainder of the sample zones in the manifold were diverted to waste. The procedure was applied to the determination of Mn in rocks and the results were in agreement with those obtained by ICP- AES. These workers have also developed (94/918) a computer controlled FI system for dilution in which the volume injected and the manifold length could be controlled.Results for the determination of Ca in citrus leaves over the range 100-1000mg 1-' in agreement with those of ICP-AES were obtained. A thorough study of the possibilities of achieving high dilution factors (up to 1000) by the use of a stepper motor driven pump to meter small volumes has been made by Fang et a/. (94/692). The authors calculated that if a volume of 30 pl (the smallest volume that can typically be injected by a rotary valve with an external loop) was used the sample throughput with an on-line dilution of 1000 would be 4 h-l. To improve this figure of merit which would be unacceptable for routine use volumes down to 0.7 pl were delivered by a computer controlled pump fitted with the narrowest bore (0.25 mm) of Neoprene tubing (this is more elastic than the more commonly used Tygon material).With the valve in the inject position the connecting tube between the sample reservoir and the valve was flushed by aspirating the sample through to waste. The valve was then turned to the fill position and the desired volume of sample solution drawn into the valve injection loop by controlled rotation of the pump head (1.8" per step). The sample metering pump was stopped and the valve turned to the inject position when the contents of the loop were interca- lated into the carrier stream for delivery to the spectrometer in the normal way. The manifold consisted of 100 cm of 0.5 mm i.d. tubing configured either as a 3 cm coil or a knotted reactor.To achieve the highest dilution factor (1330) this was replaced by 160 cm of 1.3 mm i.d tubing. The precision for this factor was 1.8% RSD. For lower dilutions the precision was approxi- mately 0.5% RSD. The Mg content (7.2% m/m) of an alu- minium alloy was determined directly in a 1% m/v solution of the alloy. Sample throughput was between 60 and 100 h-'. Chinese workers (94/259) have devised a gradient calibration method based on the concentration-time relationship for a single standard. The method was applied to the determination of Cu Pb and Zn in arsenical pyrite. As with previous review periods much of the published work concerns the interface of chemical pre-treatment pro- cedures for preconcentration and separation of analyte and matrix species with the spectrometer using an FI manifold.Procedures include sorbent extraction ion-exchange liquid- liquid extraction and precipitation (93/C3069). By directly coupling a cation resin column to an FAA spectrometer Hewavitharana and Kratochvil(94/1108) were able to measure the amount of free Ca and Mg in solution at micromolar concentrations in the presence of complexing ligands such as citrate and phosphate. The method involves pumping the sample through the resin until equilibrium has been achieved so that the uptake of ions by the resin (confined to about 1% of the resin capacity by the addition of sufficient univalent electrolyte) has not changed the composition of the solution. In 0.1 mol 1-' KNO the amount of metal sorbed onto the resin is proportional to the free metal concentration over the range 1.25 x mol 1-'.The metal was eluted with nitric acid. Salacinski et al. measured A1 in beverages and waters by a procedure in which the A1 was preconcentrated on a strong cation exchange column (a 500 mg commercially available preparative column). Concentrations down to 75 ng ml-' were measured by loading up to 24 ml of sample followed by elution with 250 pl of 4 mol 1-1 HC1. The columns were mounted between the valve and the nebulizer so that all the sample was delivered to the instrument. It was not clear why this design was used instead of placing the column in the loop of the valve (see Tyson et al. Anal. Chim. Acta 1988,214 329). The use of FI cation exchange in the determination of metals in sea-water has been critically reviewed (94/383) and Chinese workers (94/188) obtained detection limits for the determination of Cd Cu Mn Ni Pb and Zn in water of between 0.2 and 5.0 ng ml-'. A sampling frequency of 30 h-' was obtained with sensitivity increases of between 40- and 60-fold in comparison with conventional introduction.Sperling et al. (93/2896) devised a procedure for the determi- nation of both Cr'" and Cr" in waters based on the accumu- lation of the appropriate oxidation state on an alumina column. The relative affinity of the column for the two species was controlled by the pH of the carrier. At pH 7 Cr"' was selectively retained whereas at pH 2 CrV' was retained. Satisfactory recoveries from natural water samples were obtained with detection limits of about 1 mg ml-' for each species (see J.Anal. At. Spectrom. 1993 8 197R). The use of chelatingfunctionalities is of considerable interest as it is likely that the required selectivity for analyte over matrix species can only be achieved with this type of material when the matrix element is present in large excess. In the next stage of their on-going studies (see J. Anal. At. Spectrom. 1993 8 197R) Olbrych-Sleszynska et al. (94/323) have produced a stable acid-resistant material capable of retaining 10 metal ions by immobilizing Eriochrome Blue-Black R on either a non-ionic sorbent (Amberlite XAD-2) or an anion-exchange material (Amberlyst A-26). Nickel for example could be determined at a concentration of 0.1 ngml-'. Hungarian workers (93/3312) have determined Cu Cd and Pb by accumu- lation on silica gel modified with quinolin-8-ol.The procedure was described as 'off-line enrichment and flow injection atomic absorption spectrometry' so may not have involved direct elution of the metals into the spectrometer. The columns were 30 x 2.5 mm and contained 40 mg of silica gel of particle size 30-50 pm with pore diameters of 10 nm. A 100-fold enrichment in Pb concentration was obtained. Murakami et al. (94/133) used a chromatographic grade active carbon impregnated with quinolin-8-01 to determine Cu down to a detection limit of 4.4 ng ml-' with a precision of 2% RSD at 100 ng ml-'. Accurate analyses of some CRMs including pepperbush pond sediment vehicle exhaust particulates low alloy steel and orchard leaves were obtained.Work by Littlejohn et al. to 5 x218R JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 (94/553) on the use of quinolin-8-02 immobilized on controlled pore glass has now been extended to include Ga and In as well as A1 (see J. Anal. At. Spectrom. 1993 8 197R). As for Al it was found that the best buffer for Ga and In was 0.1 mol 1-' malonate at pH 8-10 and 9.2-10 respectively. Thus for loading for 3 min at 6 ml min-' all three elements could be determined with a detection limit of about 3 ng ml-I after elution with a 1 mol 1-' mixture of hydrochloric and nitric acids. Enrichment factors of between 70 and 80 were obtained and the method was applied to the analysis of natural waters. Xu et al. (94/727) have further developed the sorbent extraction procedure based on the use of C material.The sample is merged with diethylammonium-N,N-diet hyldi t hiocarbamate (DDTC) and the resulting neutral complexes are retained on the approximately 100 pl of solid-phase extractant sealed in a small conical column. After loading the derivatives were eluted with methanol which was separated from the aqueous solutions in the lines by an air bubble on the leading and trailing edges. The procedure was applied to the determination of Cd and Cu in some plant and animal tissue reference materials and in urine. Enrichment factors for both elements were 20 but the overall signal enhancements due to the effect of the methanol and removal of the flow spoiler were 126 and 114 for Cd and Cu respectively. Detection limits were 0.15 and 0.2 ng ml-' respectively (see J.Anal. At. Spectrom. 1993 8 197R). A chemically modiJedJibre material has been used by Qi et al. (94/11) for the preconcentration of Au. The material which had a neutral phosphine oxide extractant linked via a functional group to an inert 8531 fibre was prepared by the Department of Applied Chemistry Institute of Costume (presumably in Beijing) and had a capacity for Au of 0.17mmol g-'. The fibre form was found to be superior to the resin in that the release of the trapped Au was more rapid (giving sharper peaks) with the former material. The fibre material also pro- duced very little back pressure when packed in a column a useful characteristic for FI systems which typically use peristal- tic pumps for liquid propulsion. The material retained Au with high efficiency from solutions containing from 5 to 25% aqua regia at flow rates up to 10 ml min- '.As a result of comprehen- sive optimization studies a column of 4Ox2mm was used (containing 80 mg of fibre) with elution by 0.5% m/v thiourea solution at 50 "C. The effects of over 40 potentially interfering species were examined and a method devised for the routine determination of Au in some ores and metals at concentrations around 0.01 g 1-'. The detection limit in solution was 0.2 ng ml-' and sample throughput was 40-60 h-'. In comparison with solid phase extraction (SPE) procedures there is relatively little interest in the use of other separation methods in FIAS systems. However there is a sustained if low level activity in the development of liquid-liquid extraction (LLE) and precipitation (PN) methods.These procedures are often used as part of an indirect method. Further work on this aspect of LLE from Valcarcel's group (93/3398) was concerned with the determination of alkaloids (amylocaine bromhexine hydrochloride and papaverine) by the extraction of ion pairs with either Bi1,- (Dragendorff's reagent) or Co( SCN),2-. A continuous extraction manifold was used in which the ion pairs were extracted into 1,2 dichloroethane and following separation of the phases in a Teflon-assisted gravity T-piece separator 150 p1 of the organic extract was delivered to the spectrometer by an aqueous carrier flowing at approximately 4 ml min-' under the action of nebulizer suction. The working range for the three alkaloids was 0.5-175 pgml-I with a precision of approximately 3% RSD.In comparison with the manual LLE procedure the FI version was more rapid con- sumed less sample and reagent and was between 10- and 50-times more sensitive. Memon and coworkers (93/C3059 94/253) have devised LLE procedures for the determination of Cu in waters and botanical samples. The sample was injected into a carrier flowing at 4 ml min-' which was merged with a stream of 0.1 YO 5,7-dibromo-quinolin-8-01 in xylene flowing at 0.65 ml min-I. After extraction the phases were separated by a Teflon membrane separator and a sub-sample delivered to the spectrometer by a water carrier. The possible beneficial effects of agitating the extraction coil with ultrasound were studied but it was found that this was not necessary provided the coil was about 3 m long.The method which had a enhancement factor of 11 a throughput of 80 h-' a detection limit of 0.02 pg ml-I and a precision of 1.3% RSD at 1 pg rnl-' was applied to the determination of Cu in rain and tap water. The method has been improved (see Memon et al. At. Spectrosc. 1993 14 99) by the use of a toluene-xylene (1 4) mixed solvent for the extraction. The enhancement factor was improved to 16 and the throughput to 180 h-'. Accurate determinations of Cu in some reference materials (wheat flour tomato leaves pine needles and bovine liver) were achieved. To remove the silver matrix in the determination of some minor alloying elements Debrah et al. (94/326) trapped the chloride precipitate in a filter column of nylon fibres in a recirculating loop man$old.Approximately 95% of the silver could be removed allowing accurate determination of Cu Fe Ni and Zn in solutions containing 10% m/v silver. The low back pressure filter column was rapidly regenerated by flushing with ammonia solution. Esmadi et al. (J. Flow Inj. Anal. 1993 10,33) have added the determination of cyanide and thiocyan- ate to the list of anions for which they have developed indirect precipitation methods. The precipitant was silver ions and the resulting salt was retained on a 70 x 2.8 mm packed-bed reactor containing 1.9 mm diameter Pyrex glass beads. To dissolve the precipitates solutions of thiosulfate and cyanide were used for silver cyanide and silver thiocyanate respectively.The respect- ive detection limits were 3 x lop6 and 1 x mol 1-l with a throughput of approximately 17 h-'. The same concept was also applied by these workers to the determination of metals by preconcentration as insoluble inorganic salts (94/365). Cadmium was precipitated as either the carbonate or phos- phate and redissolved in acid Cu was precipitated as the sulfide and redissolved in cyanide solution and Zn was precipi- tated as the carbonate and dissolved in either ammonia cyanide solution or hydrochloric acid solution. For a collection time of 5 min the respective detection limits were 7 40 and 6 ngml-'. An overview of indirect methods in atomic spectrometry covering the relevant literature since 1985 has been provided (93/3558). The article covers both AAS and ICP-AES as well as FI techniques.An entrapped solid copper carbonate reagent material has been prepared by Garcia Mateo and Martinez Calatayud (94/697) for the determination of glycine. When a sample solution flows through the column some of the copper is dissolved by co-ordination with the glycine. The reagent consists of copper carbonate trapped in a matrix of polyester (the reference to the original method is incorrect in this publication; the journal is given as the Analyst whereas it should be Anal. Chim. Acta). The preparation produced a solid mass containing 0.8 gml-' of carbonate which was broken up with the aid of a hammer and a coffee grinder. Particles in the size range 300-400 pm were selected by sieving and packed in a 100 x 0.8 mm column.The extent of dissolution of the reagent increased with decreasing pH from zero at pH 5. Glycine samples (100 p1) were injected into a borax buffer carrier (pH 9.25) flowing at 4.2 ml min-' through the copper reactor to the spectrometer. The detection limit for glycine was 1.2 pg ml-' with a throughput of 180 h - l . The procedure was applied to the determination of glycine in some pharma- ceutical formulations which presumably did not contain mate- rials capable of significant complexation with copper at pH 9.25. The indirect determination of cyanide and thiocyanate (see Esmadi et a!. J. Flow Inj. Anal. 1993 10 33) by a FI precipitation method has already been discussed above as has the determination of three alkaloids by an indirect LLE method (93/3398).Flow injection methods for sample pre-treatment prior toJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 219R determination by graphite furnace AAS have also been reported (see section 1.2.2.) and there is a considerable interest in the use of FI methods for the generation of volatile analyte derivatives (see section 1.3.). There is also some overlapping of the classification boundaries between FI and chromatography and a number of papers discussed in relation to chromato- graphic sample pre-treatment (see section 1.1.5.) also contain material relevant to FI introduction. 1.1.3.4. Solid sample introduction. Japanese workers have developed (94/256) a standard additions method for the deter- mination of Co Cu Mn and Ni in powdered biological samples and another Japanese group has reported a method for the differential determination of tin" oxide and tinIv oxide based on the enhancing effect of carbon black with direct introduction of the powdered samples.Cement slurries have been analysed directly (93/3380) for K and Mg by FI introduc- tion into a merging zones manifold (for the addition of lanthanum) with on-line dilution by passage through a well- stirred mixing chamber (see section 1.1.3.3.). 1.1.3.5. Thermospray introduction. Workers at McGill University (93/2897 93/3240) have reported further develop- ments of the microatomizer device for the atomic absorption detection of selected elements separated by HPLC (see sec- tion 1.1.5.). Earlier designs (see J. Anal. At. Spectrom. 1993 8 197R) for HPLC used the methanol in the mobile phase as fuel.For work with aqueous mobile phases (93/2897) a device incorporating an H2-02 flame was constructed consisting of quartz tubes of which the main body comprised a thermospray inlet tube and a hydrogen inlet (both 10 cm x 4 mm) followed by a combustion chamber with an oxygen inlet. The resulting gases were introduced into the centre of an atomic vapours retainer tube mounted at right angles in the light path of the spectrometer. The thermospray tube was heated to 800-900 "C by 45 coils of Kanthal A-1 wire (4.53 ohm m-') and the mobile phase introduced at 1 ml min-l following ignition of the H,-0 flame. The system was used in the determination of Cd and Cd metallothioneins in biological samples. A version of the device for direct interfacing of an FI or HPLC system with a conventional spray chamber-burner assembly has been constructed (93/3240).Two electrical heating elements were used to heat separately a 50pm silica capillary and the nebulizer gas (air) which were fed through quartz tubes with Swagelok fitting assemblies. The capillary tube was inserted into the sample aspiration needle of the heated nebulizer nozzle. Liquid delivered at a rate of 1 ml min-' was completely nebulized and S/N enhancements of factors of 6-8 were obtained. A thermospray device for the introduction of volatile metal chelates into a flame-heated quartz tube atomizer has been described (93/3241). The volatile chelates were synthesized on-line in an FI system and a 50p1 sub-sample injected into an air carrier stream delivered at 0.41 MPa through an electri- cally heated stainless-steel tube of length 24 cm and i.d.0.5 mm. Sensitivities for Al Co and Cr were improved in comparison with those obtained for conventional nebulization; up to 20-fold in the case of Co. Precision was found to be critically dependent on the position of the capillary outlet in the quartz tube and was worse than values obtained with pneumatic nebulization leading to detection limits that were only superior for the thermospray device in the case of Co. There were also interferences from other elements capable of forming volatile derivatives with the particular reagent used. 1.1.3.6. High-pressure nebulization. Berndt et al. (93/3118) have reported further studies relating to the characterization of the performance of the hydraulic high pressure nebulizer (HHPN).In a study of the droplet size distribution produced by forcing sample solution at 10-40MPa through a 20pm nozzle it was found that in comparison with a conventional pneumatic nebulizer for FAAS and a GMK nebulizer for ICP work the HHPN produced a significantly higher proportion of smaller drops. For a 200 p1 sample volume (injected between the pump and the nozzle) a 5-fold increase in peak area was obtained with a greater freedom from interferences by high salt (sodium chloride) concentrations. Further work (94/270) showed that the improved freedom from solute volatilization interferences was also obtained for samples containing high concentrations of aluminium (3% m/v) iron (15% m/v) and copper (33% m/v).The analytes were Ag Cd Co Cr Cu Mg Mn Ni Pb and Zn and the FI introduction mode was used. For the elements in the aluminium solutions a comparison of detection limits showed an improvement for the HHPN over conventional nebulization by factors ranging from 4 to 10. Some further demonstrations of the reduced effect of high salt concentrations have been described (94/1108). It was also shown (94/729) that HHPN could be used to introduce solutions that were too viscous to be aspirated by conventional nebulization. Solutions containing up to 10% m/v of poly- (ethyleneimine) were analysed for Cd Co Cu Fe and Ni. When 1 0 0 ~ 1 of this solution was injected the pressure rose from 17 MPa to 25 MPa to maintain the constant delivery rate of 2.5 ml min-l.The HHPN device has also been used by incorporation of a suitable HPLC column for the determi- nation of Cr"' and Cr"' in waters and soil extracts (Posta et al. Anal. Chern. 1993 65 2590). Detection limits of 30 and 20 ng ml-' respectively were obtained. By changing the strength of the mobile phase the system was used to preconcen- trate Cr". For a 5 ml sample a detection limit of 0.5 ng ml-' was obtained. A new type of nebulizer designated the single-bore high- pressure pneumatic nebulizer (SBHPPN) has been designed (94/48) in which pressurized gas and liquid streams mix within the nozzle before discharging through the outlet orifice (15 pm in diameter). The gas (air) pressure in the nozzle was varied from 0.5 to 3.0 MPa (flow rates from 0.57 to 0.87 1 min-') for which the corresponding liquid flows delivered by an HPLC pump ranged between 0.6 and 1.2ml min-'.The device was interfaced with the premix chamber of the spectrometer via a Scott-type double pass spray chamber. In comparison with a Meinhard nebulizer improvements in analytical performance (sensitivity and detection limit) were obtained. It is not clear whether the device performed any better than the conventional pneumatic nebulizer and spray chamber combination of the Perkin-Elmer Model 373 spectrometer used. Nor were any comparisons made (or speculated upon) of the relative perform- ance characteristics of the SBHPPN and the HHPN. 1.1.4. Sample pre-treatment Following the format used in last year's review this section provides an overview of some novel sample pre-treatment procedures that may be of interest.Most of the publications are concerned with methods for preconcentration and/or separ- ation of analyte species from potentially interfering matrix species. The majority involve liquid-liquid extraction (LLE) or solid-phase extraction (SPE) but a small number of methods involving precipitation are also included. A further application of the naphthalene SPE method has been reported (93/2726). A small column of naphthalene loaded with tetraphenyl borate was used to retain Co as the 2-( 5-bromo-2-pyridylazo)-5-diethylaminophenol complex from aqueous solutions of pH 3-8. Following loading of the solid phase extractant the entire solid is dissolved in DMF and sprayed into an FAA spectrometer. The procedure was applied to the determination of Co in metal and pepperbush CRMs a Co concentration of 23 pg g-' in pepperbush was accurately determined. Chinese workers (94/1256) have determined Ag after selective preconcentration of the I 10-phenanthroline com- plex on sponge at pH 6-7 in the presence of EDTA.The analyte was removed by 1 moll-' nitric acid. Another Chinese group (93/3136) determined Au by concentration of the AuC1,- onto plastic foam under reduced pressure. The Au was removed by boiling in a solution of 3% (m/v) thiourea and220 R JOURNAL OF ANALY'TICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 16 pg ml-I iron(1Ir). A reference ore was accurately analysed. Myasoedova (93/2181) has reviewed the main characteristics of the complexing sorbents POLYORGS (the trade name for a series of compounds synthesized at the V.I. Vernadsky Institute of the former USSR Academy of Science). These contain pyrazole imidazole amidoxime 2-mercaptobenzo- thiazole thioglycolanilide and arsenazo groups and have high selectivity towards noble heavy and REEs. Properties and some information on methods are tabulated in the paper. An evaluation (in Japanese) of several possible supports for the immobilization of quinolin-8-ol has been made (94/22). It was concluded that azo-bonding to Capcell-NH (silicone coated silica gel with alkyl amino groups) and Sepabeads (polyvinyl polymer with alkyl amino groups) were suitable for the precon- centration of Cd Cu Fe Ni Pb and Zn. As several of the authors of this paper work at the National Research Council of Canada in Ottawa it is to be hoped that the information will be available in English as well.A Chinese polymeric chelating resin (D401) has been used in the determination of Cu Cd Fe Mn Pb and Zn in sea-water (93/3682). For the determination of Cu Ni and Zn in tap water preconcentration on Amberlite XAD- 16 resin has been used (94/737). Recoveries of Cu and Ni were increased to 99% by the addition of 1-(2- pyridylazo)-2-naphthol. For the determination of Au and Pd in manganese and nickel compounds retention on Amberlite XAD-7 resin has been used (94/773). After dissolution in aqua regia and evaporation to near dryness the metals were dis- solved in 0.5 mol I-' HCl containing 0.1 mol I-' KSCN and loaded onto the column. After washing the metals were eluted with acetone.The detection limit for both analytes was 0.07 pg g- '. Three different Chinese groups (93/2150 94/1161 and 94/1260) have used xanthate cotton for preconcentration in methods for the analysis of waters and geological materials. For the determination of Cu (93/2150) and Cu Pb and Zn (94/1260) the cotton was added to the sample solution and after scavenging the metals was then removed and the metals washed out with dilute nitric acid. For the determination of Hg (94/1161) the sample solution was passed through a 30x3 mm column packed with the cotton. The Hg was removed with 50% aqua regia. The same approach has been used for the retention of Ag on sulfydryl cotton (93/3135). The eluent was 0.5 mol 1-1 ammonium thiocyanate. The method was applied to the analysis of high purity copper.A cellulose ion exchanger (Hyphan) has been used (94/1021) for the retention of metal oxyanions (Cr04,- Mn04- and Mo02-) in a procedure for the determination of these metals in various water samples. The complexes with the solid extractant were characterized by IR spectroscopy magnetic measurements and thermal analysis. A liquid membrane emulsion was used (94/730) to preconcen- trate Cd Co Cu Fe Mn Ni Pb and Zn from water beer and soft drinks. The liquid membrane consisted of extraction agents (2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester and di- 2-ethylhexyl phosphoric acid) a surfactant (sorbitan mono- oleate) and an emulsion strengthening agent (not specified) dissolved in an organic solvent (kerosene). This cocktail was mixed to produce a water in oil emulsion in which the water droplets were 1-10 pm in diameter. The emulsion was mixed with the sample so that the kerosene droplets were 0.5-2mm in diameter.Analyte ions in the sample were transferred into the interior of the water drops in the emulsion by interaction with the extractants in the liquid membrane surrounding each drop. After separation and the addition of butanol to clarify the emulsion the organic mixture was nebulized. Goat tissue has been analysed for Cd and Zn (94/414) by a procedure incorporating a liquid ion-exchange extraction with Aliquat 336 in IBMK (for the separation of Cd) and with Aliquat 336 in xylene (for the separation of Zn). The metals were back extracted into 0.1 mol 1-' perchloric acid before introduction to the spectrometer.An indirect procedure for the determination of cocaine has been developed (94/151) in which the analyte was extracted into trichloromethane as a complex with cobalt and thiocyan- ate. After separation the trichloromethane layer was evapor- ated to dryness and the residue taken up in 5% aqueous nitric acid. Trace Ni in geological materials has been determined (94/149) by precipitation with 2,3-butanedione dioxime (dimethylglyoxime) followed by solvent flotation with ethyl acetate. The Ni in the organic phase was back extracted with 1 moll-' HCl solution. After evaporation to near dryness and taking up in dilute HC1 the solution was presented to the spectrometer. There were no interferences from copper iron lead molybdenum tungsten and zinc.The same precipitant has been used (93/3280) to separate the nickel matrix in the determination of Ca Cu Mg Pb and Zn in a nickel salt in the presence of tartaric acid as a masking agent. Two Chinese research groups (93/2148 and 94/543) appear to have published the same procedure for the determination of Pb in urine virtually simultaneously. The method is based on the co-precipitation of Pb with bismuth nitrate from alkaline solution and redissolution in hydrochloric acid. A method for the determination of Cd in hair has been devised (94/1058) in which preconcentration by co-precipitation was achieved by addition of 1-( 2-pyridylazo)-2-naphthol. After centrifugation the precipitate was dissolved in dilute nitric acid. When the matrix forms a strong complexes with the precipitating agent then incomplete recoveries of the trace constituents are obtained.To overcome this problem (93/3428) in the precipi- tation of eleven trace elements from a solution of a copper-tin alloy by hexamethyleneammonium hexamethylenedithiocarba- mate the copper and tin were first separated. Copper was precipitated as copper@) thiocyanate and tin was vaporized as the tetrabromide. The limits of detection were between 0.1 and 2 g-'. 1.1.5. Chromatographic detection Interest in the development and application of coupled chroma- tography and atomic spectrometry remains at a high level mainly for the quantification of the different forms of a particular element in complex samples particularly in environ- mental and biological materials. However as reviewers have pointed out (93/2730 93/C3047) it is the availability of the multi-determinand low detection limit capability of the MIP- AES and ICP-MS that represents the most significant recent development.Flame atom sources are of limited use because of the poorer inherent detection power compared with these plasma sources but do still find some application as detectors for LC separations often via some novel sample introduction system such as thermospray or high pressure nebulizer devices (see sections 1.1.3.5. and 1.1.3.6.). A number of GC-AS combi- nations use AAS as the detection mode though the atom source is rarely an unmodified combustion flame supported on a laminar flow burner. More commonly the atomizer is a heated tube of some sort either a flame or electrically heated quartz tube or an electrothermally heated graphite tube.These last two atomizers are considered in sections 1.3. and 1.2.2. respectively. For many publications the main emphasis of the work is on the chromatographic separation and thus many abstracts do not indicate what type of atomizer was employed only that the mode of detection was AAS. The determination of Cd metallothioneins in horse kidney and mussels by HPLC-FAAS with the use of a thermospray sample introduction device has been described (93/2897 93/3240). The mobile phase was 15 mmol I-' Tris-HC1 buffer adjusted to pH 7.21. The interface could handle up to 100mmol 1-' of this buffer without a deleterious build up of salt but was found to corrode in the presence of 0.1 mol 1-' sodium.The authors proposed to replace the quartz tube with one made of stainless steel. Ion pair HPLC-FAAS has beenJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 221 R used (see Posta et al. Anal. Chem. 1993 65 2590) for the determination of Cr"' and CrV1. The mobile phase was 1.5 x mol I-' tetrabutylammonium phosphate adjusted to pH 3.0-3.2 with phosphoric acid ( 3 . 7 ~ mol I-') in 20% v/v methanol. Sample introduction was via a hydraulic high pressure nebulizer. The method which had detection limits of 30 ngml-' and 20 ngml-' for Cr"' and CrV1 respectively was applied to the analysis of drinking water and soil extracts. An HPLC-FAAS method for the determination of occupational exposure to organotin compounds used in wood preservatives has been described (94/616).The material trapped on glass fibre air filters was leached by sonication for 10 min in 5ml of the HPLC mobile phase. No further sample prep- aration apart from filtering was performed. Hansen has reported (94/484) on the use of ion-exchange and ion-pair reversed-phase HPLC with FAAS for the speciation of up to seven arsenic compounds (see J. Anal. At. Spectrom. 1993 8 197R). For GC-AAS Baxter and Frech (94/710) have derived expressions for the description of the relative values of peak height detector response and the chromatographic efficiency and resolution in terms of the ratio between the residence time of the analyte in the atomizer and the standard deviation of the peak eluting from the GC system (assumed to be Gaussian in shape).They concluded based on the model calculations and experimental results for the determination of alkyllead species that (i) larger volume detector cells are better and (ii) open tubular capillary columns are preferred. Thus quartz tube atomizers are preferred over graphite tube atomizers (leaving atomization considerations aside) for which peak broadening should be reduced when required by increasing the auxiliary gas flow. The determination of various Sn species in several diferent matrices has been a popular activity during this review period. Butyltin compounds in sediments have been determined by Cai et al. (94/15,94/39). In the first of these studies the relative merits of tetrahydroborate and tetraethylborate derivatizations were evaluated. It was found that the ethylation procedure gave good recoveries of di-and tributyl species but lower recovery of monobutyltin (HG gives good recovery of this species). In addition problems due to foaming and interaction with other species extracted from the sediments by the acidified methanol extract were absent in the ethylation method.Detection limits in the dried sediment of 0.2 0.1 and 0.4 ng g-' for mono- di- and tributyltin were obtained. In the second paper (94/39) the ethylation method incorporated a cryogenic trapping stage but curiously the detection limits quoted are 9 38 and 12 ng g-' respectively. It was pointed out that the ethyl derivatives are more stable than the hydrides. Liou et al. (93/4033) described an HG method for the determi- nation of all three species in sea-water.The hydrides were extracted into dichloromethane and concentrated under reduced pressure. An electrically heated quartz furnace atom- izer was used and detection limits of 20 20 and 70 pg ml-' respectively were obtained. The HG approach was also used by Ritsema for the analysis of water samples. After generation the hydrides were purged with nitrogen at 300ml min-' and trapped on the cooled GC column (Chromosorb GNAW 60 to 80 mesh coated with 3% SP2100). It was stated that the method could also be adapted for the determination of As species. Dirkx et al. (94/487) have developed GC-AAS method- ology based on extraction into pentane of the diethyldithiocar- bamate complexes of derivatives formed by reaction of the organotin compounds with a Grignard reagent (such as ethyl- magnesium bromide).The same group have evaluated (94/775) the relative merits of capillary column GC-AAS packed column GC-AAS and capillary column GC-AES for the determination of pentylated organotin compounds. For capil- lary GC with a heated quartz atomizer a detection limit for Sn of 0.35 pg ml-I was obtained. Forsyth and coworkers have devised GC-AAS methods for the determination of Sn species in edible oils (94/756) and fruit juices (94/785). The Sn species were extracted from the oils with 0.05% tropolone in 0.04 mol 1- ' HC1-methanol and methyl derivatives formed by reaction with an appropriate Grignard reagent after cooling in dry ice/ methanol which removed a considerable amount of the non- volatile coextracted compounds. Oils sold in poly (vinyl chlor- ide) containers had ng g-' concentrations of dioctyl- and mono-octyltin. For the fruit juices (94/785) the extractant was 0.05% tropolone in 25 % pentane-diethyl ether.Methyl deriva- tives were formed in a similar manner and butyl and octyltin species were detected. Their presence was confirmed by GC-MS which also detected phenyl- and cyclohexyltin com- pounds at concentrations below the detection limit of the GC-AAS procedure (about 40 pg ml-l). Chakraborti has reviewed (93/3988) the use of GC-AAS methods for the speciation of organolead compounds in the environment. An overview of the determination of alkyllead compounds by GC-AAS has been provided by Dirkx et al. (93/3642). Tetra- alkyllead was determined by cryogenic trapping GC-AAS with a graphite furnace atomizer and ionic alkyllead compounds were converted to tetra-alkyllated butyl derivatives by a Grignard reaction.A simple method for the determination of methylmercury in fish by GC-AAS has been developed by Fischer et al. (93/3436). The sample was extracted with meth- anolic KOH and the ethyl derivative formed by reaction with sodium tetraethylborate trapped on the GC column. The detection limit was 4 ng g-' in the dried tissue. Harms has provided a brief overview (93/3641) of methods for the determi- nation of methylmercury in organic matrices used in the author's lab. It was concluded that problems with the electron capture detector could be overcome by the use of an element specific AA detector. Korean workers (93/3260) have reported on an ion- chromatograhy method 'in conjunction with' AAS for the determination of C1- Na and K in the diagnosis of mastitis.As mastitis proceeded it was found that the CI- and Na ion concentration increased whereas the K concentration decreased. It is not clear from the abstract whether the chromatograph and the spectrometer were directly coupled. A method for the determination of Na by sequential metal vapour elution has been developed (93/3230). The procedure separated Na in a molybdenum capillary tube (1.22 mm i.d.) at tempera- tures between 1520 and 1870 K from aluminium calcium copper molybdenum and zinc vapours. The technique was applied to the determination of Na in some SRMs (oyster tissue citrus leaves and non-fat milk powder). After wet digestion an aliquot of the digest was injected into the system dried evaporated and eluted in a stream of hydrogen.The apparatus is fully described in an earlier paper (see Ohta et al. Spectrochim. Acta Part B 1982 37 343). 1.1.6. Plasma atomizers The performance of an atomic absorption spectrometer with an argon MIP atomizer MAK nebulizer-spray chamber and a desolvation-condensation unit has been evaluated (94/18). Detection limits for twelve elements were established and ranged from 0.04 pg ml-' for Mg to 4 pg ml-' for P. The effect of sodium and phosphate on a 10 pg ml-' Ca solution were investigated and effects very similar to those seen with an air-C,H2 flame were noted though in the case of the phosphate depression this seemed to come as a surprise to the authors. 1.2.Electrothermal Atomizers The period covered by this Update appears to be one of consolidation in the field of electrothermal atomization. While the investigation of fundamental processes within an electro- thermal atomizer continues to generate great interest that of sample introduction seems to be one area where many practical benefits can be gained both in terms of lower detection limits and the reduction of interferences. Workers continue to find222 R JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 novel applications whereby an electrothermal atomizer is the best means of generating gaseous atoms from a sample to allow detection by a variety of spectrometric means. Very few major reviews have appeared in this period. In a short review Rossi (94/792) considered the development of electrothermal atomizers from L'vov to the current Zeeman- effect background corrected instruments and assessed the practical use of the technique with respect to detection power and dynamic range; 46 references were given An overview of the latest innovations in electrothermal atomization was pro- vided by Mariconti (94/479) ranging from transverse heating slurry sampling to coupling of on4ine FI techniques.The discussions continue regarding the relative merits of integrated absorbance or peak absorbance for quantification of transient signals from electrothermal atomizers. In response to the comments from Welz (Spectrochim. Acta Part B 1992 47 1043) who stressed the preference for integrated absorbance Doidge (94/52) argued that both peak absorbance and inte- grated absorbance can be useful for studying atomization mechanisms.In addition the smaller S/N generally obtained at very low analyte concentrations when using integrated absorbance can be a problem. The choice of measurement parameter is not totally clear cut and while from a fundamental consideration of the measurement process integrated absorbance appears to be the preferred option the differences in the commercial instruments available depending upon whether their design has been optimized for either integrated absorbance or peak absorbance does not make the choice easy. However the gereral consensus appears to be towards using integrated absorbance measurements. Fonseca et al. (93/3371) in investigating the mechanisms of vaporization of Ag and Au found that changes in the morphology of the sample before desorption took place affected the shape of the absorption profiles but that the integrated absorbance remained constant.This made the use of integrated absorbance a more accurate tool than peak absorbance for quantitative measurements. Another area that the authors of these Updates have to contend with is the lack of consistency in the choice ofunits often within the same publication! This makes life difficult for everybody in trying to compare and assess the results from a number of papers published in the same area but all using different units. During the period of this Update a revised second edition of Quantities Units and Symbols in Physical Chemistry was published (IUPAC Blackwell Scientific Publications Oxford 1993).Within this Update recommended SI units have been used throughout and results in non-SI units from publications have been converted using the factors pre- sented in this book. The adoption of consistent units enables us to communicate in the same language and avoid confusion. A copy of this book is a recommended reference text for anybody concerned with publishing in the scientific literature. 1.2.1. Atomizer design and surface modijication No radically new graphite atomizer designs were presented during the period of this Update. Present work on atomizer design and surface modification appears to be centred on three areas namely graphite modifications tungsten atomizers and metal carbide coatings. Often the ideas proposed were small modifications to commercially available atomizers for specific applications or research work.Krakovska (94,4039) presented a review concerning the use of tungsten atomizers listing 42 references. Advantages were claimed to be the high chemical resistance mechanical stability and the isothermality of such an atomizer which is considered to be a direct result of the high heating rates seen with these devices. However it was acknowledged that it is not possible to atomize Fe Mo and Si from a tungsten surface. Unfortunately this review was published in Serbo-Croat. Schlemmer et al. (93/CSIGAT-B2) discussed the performance criteria and test procedures for graphite components used in electrothermal atomizers with respect to validating new materials and designs and the precision and long-term stability that can currently be achieved.Pawlik et al. (93/CSIGAT-P1-12) described the design and performance of the second commercially available transverse heated graphite atomizer. Unlike the first commercial design which contains a fixed integrated L'vov platform this atomizer tube design is more conventional and allows two different platform designs to be used either a fork- or ring-type. This is claimed to allow optimum matching between the sample properties and the atomizer. An extension of the graphite platform atomization approach has been proposed by Ziegler (94/505) with a tube-in-tube atomizer machined from one piece of graphite. This consisted of an external furnace tube and an inner tube connected to the furnace body at a single point.A laboratory-constructed graphite tube-in-tube atomizer was applied by Alvarado and Cristiano (94/287) to the determi- nation of Cd Co Fe Ni and Pb in Venezuelan cigarette components. The inner tube was a totally pyrolytic graphite tube measuring 1.8 x 0.4 cm 0.d. with a 0.1 mm wall thickness. Graphite wedges of totally pyrolytic graphite were used to support the internal tube within the conventional Perkin- Elmer pyrolytic graphite coated electrographite tube such that the injection holes of both tubes coincided. The performance of this system was compared with that obtained using a platform. Similar accuracy sensitivity and precision were reported and it would seem that the only advantage of using this arrangement was a slight increase in tube lifetime.However this appeared to be only 50 cycles greater than that obtained for a conventional tube and platform (550 cycles for Cd) which seems marginal in view of the effort required to put the tube-in-tube combination together. While the accuracy of the procedure was confirmed by analysis of NIST SRMs and recovery studies it was necessary to apply the method of analyte additions for quantification though it is noticeable that no chemical modifiers were used. The detection limits (3s) were found to be 0.04 0.8 0.96 and 0.53 pg 1-' for Cd Co Ni and Pb respectively. Dobrowolski and Mierzwa (94/265) applied a special ring chamber tube designed for the Zeiss AAS-3 spectrometer for the determination of Cd Co Ni and Pb in tobacco leaves by solid sampling.Totally pyrolytic graphite tubes were employed by Chinese workers (94/1154) for the determination of Sr in sediment samples with the ammonium salt of EDTA as a chemical modifier. Polish workers (94/177) described procedures for the domestic fabrication of pyrolytic graphite coatings. These were obtained by the thermal decomposition of a C3Hs and C4H gas mixture containing 92-94% CH and 2% C2H on the graphite substrate. It is unclear how worthwhile this activity was as the lifetimes and sensitivities were comparable to those obtained from commercially available atomizer components. The application of a tungsten coil atomizer to the determi- nation of Cd in biological materials discussed in the last Update (see J. Anal. At. Spectrom. 1993 8 197R) as a con- ference report has now been published (94/285).On manual loading of the coil with 10 pl sample aliquots and using short atomizer cycle times (41 s) a peak absorbance characteristic mass for Cd of 0.5 pg was found. While the high heating rates of this atomizer tend to favour the use of peak absorbance for signal measurement these workers did note that for certain RMs better accuracy was obtained with integrated absorbance measurements though in general good agreement was obtained for a range of RMs. Shan et al. (94/559) assessed the applica- bility of the tungsten WETA-90 atomizer for the direct determi- nation of Mn in river- and sea-water RMs. These workers considered that the transverse heating and high heating rates should achieve fairly isothermal conditions within the atomizer which would be an advantage for the analysis of materials that cause non-spectral interferences. Interferences caused by the sea-water matrix were eliminated by the addition of 1% ascorbic acid and 0.2% nitric acid and a purge gasJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL.9 223 R of argon and hydrogen (19+1) was employed. A detection limit (3s) in sea-water of 1.2 pg was found corresponding to 0.12 pg 1-l for a 10 pl sample. Ohta et al. (93/3938 94/227) continued to investigate the use of metal electrothermal atomizers and in recent work have employed molybdenum tubes. These were applied to the direct determination of Mn in biological fluids (93/3938) using slurry sampling with ultrasonic agitation. An argon-hydrogen purge gas was utilized along with the addition of .thiourea as a chemical modifier.This work was extended to the determi- nation of Ag (94/227) also in biological samples such as bovine liver non-fat milk and orchard leaves with thiourea as the chemical modifier but in this case the sample solutions were examined after nitric acid digestion. The method gave an impressive absolute detection limit of 3.7 fg of Ag. The use of tungsten as a su$ace coating for graphite atomizers continues to generate a number of reports and dominates this area of research though coatings of metals or carbides of other elements such as lanthanum hafnium tantalum and zirconium have been described. Iwamoto et al. (94/13) considered the use of a tungsten-coated electrographite atomizer in combination with a palladium chemical modifier to determine Sn in saline water.It was reported that this combination allowed pyrolysis and elimination of the salt matrix and sulfate interference from 2-fold diluted sea-water at a temperature of 1700°C without any serious loss of Sn. For the sea-water matrix a detection limit of 0.08 ng was found with integrated absorbance measure- ments. Tserovsky et al. (93/3410) found that tungsten-impreg- nated graphite tubes and a palladium chemical modifier were the optimum combination for the determination of Cd Co and Pb in chlorine-containing organic solvents. This work compared the use of electrographite tubes pyrolytic graphite coated electrographite tubes tungsten impregnated graphite tubes and tubes with pyrolytic graphite platforms for these determinations.Chinese workers (94/465) combined the use of tungsten-coated graphite tubes with a calcium chemical modifier for the determination of Si in mineral water. With a lanthanum-coated graphite tube and a calcium chloride chemical modifier to overcome sulfate interferences Yang (93,4015) determined Mo in rice and found a detection limit of 0.76 pg 1-I. Liu et al. (93/2171) applied lanthanum-coated platforms to the determination of Cr in human hair to over- come interferences. Zheng and Zhang (93/3119) found that the use of a tungsten- or zirconium-coated graphite tube improved the atomization of Ge. These coatings eliminated the premature loss of Ge as GeO. The conference reports from Benzo and Cecarelli et al. discussed previously (see J.Anal. At. Spectrom. 1992 7 215R) have now been published (93/3395). These workers used vapour deposition-sputter ion plating to coat new and exhausted pyrolytic graphite platforms with tungsten carbide and assessed their performance against uncoated pyro- lytic graphite platforms for measurements of Cd Cu Ge Mo Pb and V. The coated surfaces allowed an increase in the pyrolysis temperature for Cd and Pb and produced an increase in sensitivity for Ge. This was combined with the advantage that the platforms could be regenerated with only the sensitivit- ies for V and Mo being affected. However while these workers concluded that this coating procedure could be an alternative to adding chemical modifiers no results were presented in matrices containing interfering salts and no data presented on the expected lifetime of the coating.Kagaya et al. (94/1030) applied a hafnium-impregnated atom- izer for the determination of Sn" after co-precipitation with gallium phosphate. The gallium phosphate enhanced the signal by 1.7-fold and the hafnium coating eliminated most inter- ferences. The method was applied to the determination of SnIV in water with a detection limit of 0.23 pg I-' in 500ml of sample. Krivan et al. (93/2183) examined the effect of boron nitride-coated tubes along with nickel and mixed palladium- magnesium chemical modifiers on the pre-atomization behav- iour of Se. These workers reported that optimum stabilization was achieved using boron nitride-coated tubes and that after conversion of SeIV into a volatile piazselenol a quantitative pre-atomization separation of SeIV from SeV' in such a coated tube was possible.Ma et al. (93/CSIGAT-P1-5) continued their studies into the application of tantalum tungsten foil platforms and pyrolytic graphite coated tubes lined with a tungsten spiral and tantalum foil for absolute analysis. The use of tantalumfoil as an atomization surface for the determination of Li in renal tubular fluid was investigated by Boer et al. (93/3232). These workers reported no matrix interferences and hence no requirement for background correc- tion and the S/N was improved. Compared with atomization from a graphite surface 10- and 4-fold increases in peak and integrated absorbance measurements respectively were found. The atomization temperature could also be lowered by 300 "C which no doubt considerably reduced emission from the atom- izer.These improvements allowed the determination of Li in 10 nl sample volumes of rat renal tubular fluid. Metal or metal carbide coated second-surface atomizers continued to generate some interest. Hocquellet (93/3966) described a small graphite arch coated with tantalum carbide placed inside a Massmann-type atomizer to achieve second- surface atomization. The atomic vapour produced from the tube wall was trapped on the arch which was coated with tantalum carbide to improve its retention power. Analyte atomization occurred when the arch heated by radiation attained the temperature of the atomizer. The performance of the atomizer was assessed for the determination of As Cd Pb and Zn in simple and complex matrices.The advantages of this approach are not clear as from the data presented compared with using a platform similar sensitivities were found and only in some cases was a reduction in interferences seen. While not concerned with electrothermal atomization using atomic absorption as a detector Holcombe and Scheie (93/CSIGAT-A1) discussed the use of a second-surface atomizer with a tantalum plug as a vaporization device for MS to avoid the need for the ICP. Hungarian workers (93/2692) reported the use of a 'thermally shielded furnace' for the determination of Mo in soil claiming advantages of prolonged atomizer lifetime of up to 250 cycles though no further details concerning the atomizer design were available. The probe atomizer design produces a small number of reports each year though it is clear from the published data that only in a very few instances does this design offer any improvements in performance over what can be obtained with a platform in a standard graphite tube atomizer.Wang and Deng investigated the atomization of Fe (93/3965) and Sn (93/3526) from the graphite probe using X-ray diffraction Auger spectrometry and SEM. In a further study (93/4006) these workers applied probe atomization to the determination of Co in soil and coal fly ash. Other Chinese workers (94/1049) described an unusual and novel coating namely polyethylene for a probe atomizer. The coating was applied as an 80% saturated solution of polyethylene in benzene (though with no mention of the associated safety problems of using benzene especially in an electrothermal atomizer!) to avoid diffusion of the sample into and along the probe surface and reduce permeation into the graphite micro-holes.The analytical characteristics of the polyethylene-coated probe and tube were claimed to be improved though it is unclear what happens to this coating during atomization and whether it has to be re-applied prior to each measurement cycle. Two groups reported on the use of a probe atomizer for the determination of Pb in urine having developed very similar procedures. Gayon et al. (94/583) reported that after diluting one part urine with three parts water it was possible to obtain interference-free determination of Pb without the use of a chemical modifier and aqueous standards for calibration.These workers found a detection limit (3s) of 0.3 pg 1-l and recoveries of 100+5%. Chen and Littlejohn (94/172) diluted two parts urine with 12.5 parts water and determined Pb in urine RMs,224 R JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 quality control and patient samples. This direct method elimin- ated the need for chelation and solvent extraction. The detec- tion limit (3s) was found to be 0.4 and 0.2 pg 1-1 at the 283.3 and 217.0 nm wavelengths respectively and while probe atom- ization removed interferences for integrated absorbance measurements a 10-20% suppression remained for peak absorbance measurements in some samples. 1.2.2. Sample introduction The topic of sample introduction continues to be an area of sustained interest.More workers appear to be experimenting with slurry sampling and when coupled with automated ultra- sonic agitation for preparation of the slurries seem to be convinced of the usefulness of this technique. Miller-Ihli (93/2200 93/CSIGAT-D1 94/732) continues to be active in this area and has proposed a systematic approach to ultrasonic slurry ETAAS (93/2200 93/CSIGAT-D1) for the attainment of optimum analytical conditions including slurry preparation and calibration strategies. Other factors to consider (93/CSIGAT-D1 94/732) are particle size up to 300-500 pm have been shown to be acceptable but heterogeneous samples require very small particle sizes (< 10 pm) density analyte partitioning the power output to the ultrasonic probe and the mixing time.A minimum mass required for the analysis is calculated from the particle size and density of the material. While only one manufacturer E perkin-Elmer) offers an auto- mated ultrasonic probe slurry sampling device for use with its electrothermal atomizer autosamplers based on the design proposed by Miller-Ihli Hoenig and Cilissen (94/98 1) described how they adapted a Gilson 221 sample changer along with an ultrasonic probe to allow automated slurry sampling with a Varian SpectrAA 400 instrument. Ohta et al. (93/3938) determined Mn in biological samples by slurry sampling with ultrasonic agitation using a molybdenum tube atomizer. Other workers have also reviewed the use of slurry/solid sampling in ETAAS (94/154,94/180). Lueker et al. (93/2189) discussed the use of solid sampling electrothermal atomization for the production and characterization of animal tissue reference materials including bovine liver teeth bone muscle blood and equine renal cortex.Sandoval et al. (93/3113) compared the use of impact beads and mechanical and ultrasonic methods for the preparation of sediment slurries. They found that ultrasonic mixing was the best method as it enabled the use of either aqueous or slurry standards and produced superior results. The sediment slurries (2-10 mg of sample) were prepared in 5% nitric acid (1 ml) before mixing for 1 min with a manual ultrasonic probe. Palladium chloride was used as a chemical modifier and atomization from a L'vov platform. For the determination of Cd and Pb RSDs were 3.1-9% and 2.9-7.3% for a calibration established with aqueous standards and 2.4-4.3 YO and 2.7-7.2% with slurry standards respectively.Docekal and Krivan (93/3236) demonstrated one of the advantages of slurry sampling for the direct determination of Ca Co Cr Cu Fe K Li Mg Mn Na and Ni in high-purity molybdenum trioxide where the detection limits in the matrix following a con- ventional sample decomposition are blank limited. Direct determinations by slurry sampling are free of this limitation and detection limits could be improved by two orders of magnitude reaching 2 1 0.5 and 1 ng 8-l for Ca K Mg and Na respectively. The slurries were prepared by suspending 0.1-0.25 g of the molybdenum trioxide powder in 1Oml of ultrapure water with the aid of an ultrasonic bath. The slurries were maintained by automatic mixing via a remote controlled magnetic stirring device prior to 20 pl aliquots being dispensed into the electrothermal atomizer.It would appear that the limitations of the magnetic stirring system applied to current commercially available autosamplers has led one of these workers to develop a simpler stirring device. Docekal(94/589) proposed a small turbine device constructed totally from polymethacrylate glass containing rotating magnetic pieces. The device can be easily incorporated into an autosampler tray and can be driven by compressed air or cooling water. The use of hydrofluoric acid as an aid in the preparation of slurries of glass materials was first suggested by Bendicho and de Loos-Vollebregt (Spectrochim. Acta Part B 1990 45 695) and Lopez Garcia et al.(93/3413) have applied this reagent to the preparation of slurries of diatomaceous earth a material with high silica content for the determination of Cr Cu and Pb. Slurries (particle size < 30 pm) were prepared by suspen- sion in hydrofluoric acid. The slurries were placed in an ultrasonic bath for 5 min and maintained by magnetic stirring while sample aliquots (10-25 pl) were taken into the electro- thermal atomizer. Aqueous standards were used to establish the calibration. The analysis times were reduced by eliminating the pyrolysis and clean-up steps of the atomizer programme. Results for a number of CRMs obtained by this approach compared well with those from acid digestion of the samples. The advantage of using hydrofluoric acid as the suspension agent was a dramatic increase in platform lifetimes compared with diatomaceous earth suspended in water.Bermejo-Barrera et al. (94/1190) determined Pb in mussel slurries using Triton X-100 to stabilize the slurries along with a mixed chemical modifier of palladium-magnesium nitrate. Results from the slurry method were compared with those obtained after a wet-digestion procedure. The detection limit was 0.9 pg 1-1 and within- and between-run precisions were found to be 3.1 and 5.3% respectively with recoveries of 92.1-98.7%. From the same group (93/CSIGAT-D3) a similar procedure was used to determine Pb in slurries of marine sediments. The marine sediments were ground by shaking with zirconia balls for 60 min such that the particle size was reduced to <5 pm and the slurries maintained by mechanical stirring prior to manual sampling into the electrothermal atomizer.Results from the slurry method were compared with those obtained after pressure microwave digestion of the samples in nitric acid. Good agreement was found and the precision and accuracy of the method was assessed using PACS-1 (marine sediment) RM. The detection limit was 0.22 pg 1-l and within- and between-run precisions were found to be 2.3 and 2.5% respectively. Chinese workers have been increasingly active in the field of slurry sampling with investigations into the determination of Pb in wheat and rice flour (93/3564) Cd in soil (93/3137) using an agar solution to stabilize the suspension Cr in suspensions of incompletely digested hair samples (93/2171) and the determination of Cu (94/258) in plant material using a suspension mixture of 1 % ammonium nitrate-10% nitiric acid containing 200 pg ml-' of nickel and 40% ethanol and for soil samples with a solution of hydrofluoric acid-nitric acid-nickel.Recoveries ranged from 94 to 106% with RSDs in the range 6-11% though no indication was given of the concentration levels. Polish workers (94/265) compared the use of solid and slurry sampling for the determination of Cd Co Ni and Pb in tobacco leaves. For solid sampling a ring chamber tube was used. There was acceptable agreement between the results obtained from direct solid sampling slurry sampling and solutions obtained after an acid digestion and the precisions of the measurements by slurry sampling were better than those obtained for solid sampling.Pesch et al. (93/3109) determined the Cd Hg and Pb content of cigarette tobacco by solid sampling into platinum boats (for Hg) or graphite boats (for Cd and Pb) followed by introduction into the electrothermal atomizer. For calibration purposes NIST SRM 1572 was employed and the results for 50 brands of cigarettes from eight different countries statistically analysed. The concentrations found reflected the local environment of the tobacco plants. Results concerning the difficulty of determining Au Pd and Pt in silver and discussed last year (see J. Anal. At. Spectrom. l993,8,197R) have now been published (94/744). Two differentJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL.9 225 R solid sampling methods were compared. The first approach was the in situ dissolution of a solid sample by addition of 25% v/v nitric acid in a cup-in-tube atomizer. A high gas flow removed the large matrix and analyte masses present in the analytical volume during atomization. The lower residence time permitted an expanded dynamic range but with reduced sensitivity compared with conventional electrothermal atomiz- ation. The second approach used a slurry of the silver samples dissolved in nitric acid then agitated to suspend the undissolved elements/matrix. With both procedures calibration was achieved with matrix matched aqueous standards and results compared favourably with a solution determination based on a hydrochloric acid leaching procedure. Hinds et al.(93/CSIGAT-E1) compared dissolution and solid sampling methods for the determination of Si in high-purity gold. The solution method suffered from interferences as increasing amounts of gold were introduced into the atomizer. The solid sample method did not appear to be affected by the amount of gold introduced though the reproducibility of the analytical curve appeared to depend on the condition of the atomizer. A Massmann-type and transverse heated atomizer were com- pared and though the detection limit in the transverse heated atomizer was higher the memory effects from the gold matrix were much reduced compared with the Massmann-type atomizer. One of the major problems with any solid sampling technique is that of establishing a calibration. Hofmann et al.(93/2188) investigated this issue with respect to the determination of Cd with solid sampling Zeeman-effect AAS. Initially different CRMs were analysed for Cd using milk powder CRMs as standards. This gave good results indicating that one reference material can be used to analyse other samples of different compositions on a routine basis. In a second comparison a method of standard additions with solid samples was developed in order to make calibration independent of the CRM. Lyophilised codfish powder was loaded with different amounts of Cd lyophilised again then homogenized. Using an iteration process results were obtained which were no longer dependent upon the CRM. The determination of Pb in solid PVC samples by Belarra et al. and discussed last year (see J.Anal. At. Spectrom. 1993 8 197R) has now been published (93/2080). The solid PVC samples (of the order of 2-5 mg) were introduced directly into the electrothermal atomizer through the sample injection hole which was enlarged to 4mm in diameter. Using integrated absorbance measurements but with wall atomization cali- bration was achieved against aqueous standards and the 364.0 nm wavelength for Pb used to enable measurements with a working range of 0-5Opg of Pb. Results were compared with those obtained for the same PVC samples determined by a dissolution method in N N-dimethylformamide followed by FAAS and good agreement was found however the %RSD obtained by the solid sampling method was 5-10%. The ETAAS method was quicker overall but in view of the poorer precision was recommended only as a simple screening method. Chinese workers determined Co in animal feed (94/116) with solid sampling techniques. While not a 'pure' ETAAS report concerning solid sampling McNew et al. (93/C3003) used a graphite electrothermal furnace to determine Li and other trace elements in lithium aluminate ceramics.The samples of discrete spherical particles weighing less than 1 mg each were analysed individually by sealing them in a small cavity between two porous graphite rods which were then heated to approxi- mately 3000°C. The sample was vaporized and Li and other elements swept by the argon carrier stream into either the flame of an AA spectrometer or the torch of an ICP-AE spectrometer. Ohls et al. (93/2186) employed an Atomsource sputtering chamber combined with AAS to determine trace elements in pg portions of samples.The technique allowed determinations in dust soil and other oxide materials. A method was developed which allowed 1 ng of Hg to be determined in 1 pg of sample. For the coupling of FI techniques to ETAAS a number of groups have been very active over the last few years. What is important to note is that a great many of the conference abstracts discussed in previous ASU reviews have subsequently been published. These efforts are to be applauded as this ensures that the practical details and information required are available to all others interested in applying such coupling techniques. The work of Sperling et al. (93/31 lo) applying an on-line solid sorbent extraction procedure by complexing elements with NaDDC before sorbtion onto a column of bonded silica with octadecyl functional groups and subsequent elution with ethanol into a graphite atomizer partly discussed last year (see J.Anal. At. Spectrom. 1993 8 197R) as a conference abstract has now been published (93/3110). In this procedure Cd Co Cu Ni and Pb were determined in sea- water RMs with detection limits at the ng l-l level and good agreement was obtained with the certified values. Welz et al. (93/3927) discussed the important topic of time-based or volume-based sampling into the graphite atomizer for on-line sorbent extraction procedures. Flow injection on-line precon- centration systems are complicated by the low eluate volume typically less than 50 pl which can be sampled into the graphite atomizer.Even when columns with a small capacity of 15 pl were used it was found impossible to to elute the sorbed analyte completely with an eluate volume that was compatible with the capacity of the graphite atomizer. Two approaches for introducing only the most concentrated fraction of the eluate into the graphite atomizer while discarding the rest were investigated and compared controlling the time interval for collection and introduction of the eluate into the atomizer (time-based sampling) and collection of the eluate fraction of interest in thin tubing of fixed volume followed by introduction of this fraction into the atomizer using a low flow of air (volume-based sampling). The analyte elements investigated were Cd Cu and Ni. A 15-30% greater enhancement factor was obtained for volume-based sampling because dispersion was prevented during sample injection by air segmentation.The short- and long-term reproducibility were also better for volume-based sampling because variations in the pump tubing had no influence on the eluate volume introduced. These combined effects resulted in an improvement in detection limits of the three elements by factors of 1.3-2.0. Sample throughput (23 h-') sample consumption (3ml min-I) and reagent consumption were the same for both approaches. There were no significant differences in the accuracy and precision of the two techniques in the analysis of sea- estuarine- and river- water RMs. The on-line preconcentration procedure described by Azeredo et al. using a 20pl column of quinolin-8-01 immobilized on silica and discussed last year (see J.Anal. At. Spectrom. 1993,8 197R) has now been published (93/3372). The preconcentration of Pd Pt and Rh by on-line sorbent extraction for ETAAS or ICP-AES was discussed by Lee et al. (93/3430). The metals were preconcentrated as bis(carboxy- methy1)dithiocarbamate (CMDTC) chelates on a microcolumn packed with XAD-2 after the off-line addition of solid CMDTC to the sample solution containing tin@) chloride and hydro- chloric acid. The sample rinsing and eluent solutions were segmented by air to prevent dispersion. The eluate was col- lected on-line in a PTFE loop and was forced into either the graphite atomizer by a flow of nitrogen or into the ICP by using a carrier solution. The time for one preconcentration cycle was approximately 10 min.The influence of the acidity of the synthetic sample solution the concentration of the complexing reagent and reducing agent the flow-rate for preconcentration the efficiency of the desorption and the influence of various matrices were also investigated. The detec- tion limits (3s) were 0.03 0.1 and 0.01 pg 1-' for Pd Pt and Rh respectively using ETAAS detection. The procedure was applied to the analysis of polluted biological materials.226 R JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 Yuan et al. (93/CSIGAT-P2-13) compared two different on- line preconcentration column materials quinolin-8-01 immobil- ized on controlled-pore glass and Amberlite XAD-2 for the determination of A1 by directly coupled FI-ETAAS.Both systems were found to be suitable for preconcentration though the chelating kinetics of the quinolin-8-01 immobilized on controlled-pore glass were less favourable than the absorption kinetics of the XAD-2 system. The detection limits (3s) were similar for each system and varied from 15 to 40 ng 1-' depending upon the preconcentration time. A major problem was contamination from A1 in the reagents employed. For concentrations of 1 pg 1-l the within-batch precisions were approximately 3 %. The direct coupling of FI hydride generation and 'in atomizer trapping' of the hydrides continues to be an active area of investigation. One of the problems for successful hydride trap- ping has been what has appeared to be the need for the use of a trapping reagent (often palladium) added as a solution and dried prior to the introduction of the gaseous hydrides. This complicates the overall procedure and reduces the possibilities for automation of the procedure.Shuttler et al. (93/3399) appear to have found a solution. The single manual application of a mixed trapping reagent containing 50 pg of iridium and 50 pg of palladium allows up to 300 complete hydride trapping and atomization cycles. The precision was generally better than 3% and the efficiency of trapping virtually 100% for As Bi and Se. Thomassen et al. (93/CSIGAT-C2) applied the same tech- nique of FI hydride generation and 'in atomizer trapping' of the hydrides within a graphite atomizer to the determination of Sb in body fluids. The trapping efficiency was studied with radioactive 12sSb and showed that with an iridium nitrate coated graphite surface the trapping was 80% and without a coating of iridium nitrate approximately 60%.This coupling procedure allowed the the determination of Sb in whole blood and urine down to 0.2 pg 1-' levels though the detection limit of the procedure was found to be strongly dependent upon the degree of contamination of the reagents with Sb. For an integrated absorbance signal of 0.1 s- ' the reproducibility of the instrumental procedure was 0.5-2% and sequestration of Sb from the sample solutions allowed more accurate results to be obtained than direct analysis of the matrix and calibration against aqueous solutions. A Chinese worker (94/393) appears to have developed a semi-automatic sampling device for FI hydride generation coupled with a graphite atomizer.The device was applied to the determination of As Bi Hg Sb Se and Sn though no further details were available. The determination of As"' and AsV species using the Fleitmann reaction proposed by Burguera and Burguera and discussed last year (see J. Anal. At. Spectrom. 1993,8 197R) has now been published (94/283). An et al. (93/3160) showed that the coupling of hydride generation and 'in atomizer trapping' was an effective method for determining As in the presence of suppresive interferences. The trapping of As on a deposit of reduced palladium was found to be 100% efficient. The addition of L-cysteine permitted full recovery of the As signal in the presence of 100 pg amounts of nickel or platinum.Thiourea was effective at reducing interferences from 100 pg amounts of gold and nickel or 10 pg of palladium contained in 1 ml of solution. Increasing amounts of palladium used to coat the graphite atomizer or quantifi- cation of the signals via integrated absorbance can reduce interferences that occur in the graphite atomizer due to other hydride forming elements. For this determination a detection limit of 36 pg was found. Chinese workers (93/3235) trapped indium hydride in a pre-heated graphite atomizer coated with palladium and found that this greatly improved the sensitivity for the determination of In. Palladium was found to be a very efficient adsorbent for indium hydride and X-ray photoelectron spectroscopy (XPS) was used to characterize the sample deposits on the graphite platform surface. Ni et al.(93/3353) employed 'in atomizer trapping' of sel- enium hydride in a palladium coated graphite tube for the determination of Se in urine. Sample digestion procedures with different acid mixtures were used to decompose selenomethio- nine and selenocystine added to urine. Recoveries were of the order 92-98% and the concentration detection limit found to be 20 ng 1-'. From the same group Yan et al. (94/241) developed a method for the determination of Hg by cold vapour generation and trapping of the Hg vapour in a pal- ladium-coated graphite tube. The Hg vapour generated by using sodium tetrahydroborate was rapidly trapped in the graphite tube coated with palladium chloride at 250°C and atomized at 2200°C.The trapping efficiency for Hg by pal- ladium chloride was better than that obtained by reduced palladium. Reducing the palladium chloride to palladium metal gave less favourable Hg trapping. Calibration was established from aquous solutions. The detection limit was 628 pg 1-l for a 50ml sample volume. The method was applied to the determination of Hg in certified water samples sea- and waste- waters. Though not within the abstracting period for this Update yet recently published and of relevance to the determi- nation of Hg by trapping within a graphite electrothermal atomizer Sinemus et al. (Spectrochim. Acta Part B 1993 48 1719) have applied a similar procedure to that proposed by Shuttler et al. and discussed above to determine Hg after trapping on an iridium-coated surface.The detection limit for a 25 ml sample was 70 pg and at least 300 measurements could be made without degradation of the trapping efficiency. Tao and Fang (93/3227) determined Ge by FI hydride generation followed by trapping in a pre-heated graphite atomizer coated with palladium at 400 "C followed by atomiz- ation at 2500 "C. The sensitivities and interference effects using different concentrations of hydrochloric acid were compared. The tolerance to interferences was improved at high acidities of 3 moll-' hydrochloric acid and also in the FI system when compared with a batch 'in atomizer trapping' system. The sampling frequency was 18 h-l with a detection limit (3s) of 0.004 pg I-' in 0.15 moll-' hydrochloric acid and 0.03 pg I-' in 3 mol 1-' hydrochloric acid for a 4.5ml sample volume.Precisions at 0.3 pg I-' in 0.15 mol I-' hydrochloric acid were 2.0% and 2.5% at 1.5 pg 1-' in 3 mol 1-' hydrochloric acid. The method was applied to the determination of Ge in garlic water ginseng and geological RMs. The determination of Pb in biological materials by microwave assisted mineralization and FI coupled with E TAAS proposed by Burguera and Burguera and discussed last year (see J. Anal. At. Spectrom. 1993,8 197R) has now been published (94/284). The problems of coupling of HPLC with ETAAS presented by Laborda et al. and discussed last year (see J. Anal. At. Spectrom. 1993,8 197R) have now been published (93/3237). Using a sampling procedure based on fraction collection and hot injection into the graphite atomizer with fraction volumes of 0.5ml or lower a detection limit of <1 ng of Se with respect to the sample injected into the chromatograph was found.The procedure was applied to the speciation of Se. The separation of trimethylselenonium selenite and selenate was performed by anion-exchange chromatography using 0.01 mol 1-' ammonium citrate solution with gradient elution from pH 3.0 to 7.0. Citrate suppressed the Se signal but this was reduced by adding nickel (200 pg) and magnesium nitrate (50 pg) as a chemical modifier and matrix-matched standards. Detection limits were found to be 1.67 1.27 and 0.76 ng of Se for trimethylselenonium selenite and selenate respectively. The speciation of butyltin compounds by on-line HPLC-ETAAS was applied to sediment samples by Astruc et al.(94/488). The period of this review has generated a collection of reports concerning electrodeposition onto a variety of supports followed by placement of the support or tube into the atomizer and subsequent analysis. To date nobody appears to have solved the problems of automation and a number of unusual and interesting procedures have been described. The elec-JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 227 R trodeposition of Cr onto a pyrolytic graphite coated electro- graphite L'vov platform was applied by Vidal et al. (93/3243) to the speciation of CrV' and Cr"'. The L'vov platform was employed as the cathode for the selective preconcentration of CrV' or CrlI1 on a mercury film. At pH 4.70 and E,= -0.30 V against a saturated calomel electrode (SCE) CrV' was reduced to Cr"' and accumulated as Cr(OH) by adsorption on the mercury film whereas at an applied potential at E,= - 1.80 V both Crv' and Cr"' were accumulated forming an amalgam with the added Hg" ions.Once the film had been formed the platform was transferred into a graphite tube for the determi- nation of Cr. The detection limit was 0.15 ng 1-' and the recovery of CrV' added to water samples was 105 & 6.2%. The approach of Zhang et al. discussed last year (see J. Anal. At. Spectrom. l993,8,197R) has now been published in English (94,664). The three-coil tungsten wire cathode was used to electrodeposit Cd from 0.1 mol 1-1 sulfuric acid solutions by the application of -1.0 V versus an SCE for 2 min. The cathode was then placed in a graphite atomizer and a normal atomizer programme run.The method was applied to the determination of Cd in urine and river waters. Recoveries at a concentration of 0.1 pg I-' were better than 95% and the detection limit was 0.01 pg 1 - ' . This same group used a similar procedure to preconcentrate Cu from 0.2 mol I-' sulfuric acid (94/401). The method was applied to the determination of Cu in gereral reagent grade potassium chloride and distilled water. A detection limit of 0.01 pg I-' was found. Other Chinese workers (94/395) described an interesting procedure to precon- centrate and determine Au in ores. The Au was preconcentrated electrochemically on the inside wall of the graphite atomizer tube which had been previously modified by a thin coating of polyacrylamidine thiocyanate. Other elements did not interfere and a 100-fold enhancement in analytical sensitivity was found.However it is not clear as to whether the polyacrylamidine thiocyanate coating had to be reapplied after every atomization cycle. Beinrohr et al. (94/889) described an electrochemical flow-through cell made from crushed reticulated vitreous graph- ite and a graphite atomizer tube whereby Mn could be preconcentrated. The sample 0.1-1.0 ml in volume was pneu- matically transported through the system and Mn" ions quanti- tatively deposited both anodically and cathodically over a period of 5-10 min. It would appear that this same group applied similar principles to purify reagents and separate element traces (93/3106). Through a PTFE flow-through cell with a vitreous graphite rod anode mounted inside a commer- cial graphite atomizer tube used as the cathode was pumped the electrolyte-sample at 300 ml min-' for 2 h.The tube was transferred to the atomization unit for ETAAS determination of the deposited metals. Tests with 6oCo in the solution showed that the deposition yield was >99%. The method was used to purify 520% (m/v) ammonium fluoride solutions. The initial concentrations of Co Cu Fe Ni Pb and Zn in a 10% ammonium fluoride solution (4-40 pg 1-') were reduced to < 0.3 pg 1- '. Chinese workers (93/3528) preconcentrated Ag from water samples onto a Nafion-modified tungsten wire by ion exchange without applying an electrode potential. The wire was then placed into the graphite atomizer and Ag determined with a detection limit of 0.04 ng 1-I.This same group determined arginine in pharmaceuticals using a Nafion 11 7 (Du Pont) modified tungsten coated wire coil and determi- nation by a difference procedure. The signals obtained after soaking the Nafion-modified tungsten coil for 3 min in a solution containing Cu both before and after the addition of arginine were compared. The decrease in absorbance was directly proportional to 31-250 nmol 1-' of arginine. The detection limit was 13 nmol 1-'. Another group of Chinese workers (93/3575) applied a Nafion-modified tungsten wire to determine Bi in drugs after preconcentration. Silva et al. (94/586) examined the stabilization ofmetals in organic media. The instability of Cu and Pb in kerosene and in analytical organic solutions is the main problem with their direct determination.When propan-1-01 is added to a mixture of kerosene and water a homogeneous three-component solu- tion is obtained which is stable for up to 24 h and allows direct ETAAS determinations to be performed. The three- component solutions containing purified kerosene and enriched with metallic ions in aqueous solution or with copper or lead cyclohexanebutyrate or tetraethyllead are also stable. In spite of some differences in the absorption pulses the maximum pyrolysis temperatures characteristic masses and precision for the three-component solutions in comparison with aqueous solutions were similar. 1.2.3. Fundamental processes At long last an in-depth review on mechanisms in electrothermal atomization has been published.Styris and Redfield (94/523) are to be congratulated on drawing all this information together and this review is recommended reading for all those interested or wishing to gain an immediate appreciation of how complex this subject is. The advantage of preparing a yearly Update is that one has an ideal vantage point of the trends and current interests within the subject and can see how these vary with respect to time and/or further developments. In previous years the subject of the reduction of oxides by carbides (ROC) mechanism has in this section received a great deal of attention. Last year it appeared that this theory was no longer able to explain the experimental results. The confer- ence report discussed last year (see J.Anal At. Spectrom. 1993 8 197R) concerning the findings by Frech and L'vov regarding the condensation of matrix vapour in a graphite atomizer has now been published (94/306). The appearance of non-specific absorbance signals when pg masses of elements (Ag Au Cu Mg Mn and Pd) are vaporized was studied. This phenomena was found to be common to all types of electrothermal atomizers (end or side heated) and mode of operation (platform or wall atomization) and was interpreted contrary to the previous soot formation hypothesis as proposed by L'vov et al. (Spectrochim. Actu Part B 1991 48 1001) as a result of condensation of metal (or oxide) vapours in the cooler zones of the atomizer with formation of a particle cloud. Owing to temperature inhomogeneity over the cross-section near the injection hole in end-heated HGA-type atomizers conden- sation occurs not only at the tube ends but also at the centre.Very few papers concerned with the production of Al 'spikes' have been published during the period of this review but those that have appeared seem to be the final contributions. By employing high-resolution absorption spectra Ohlsson et al. (94/41) found clear evidence that A1H molecules are present during the spike-like A1 atomic absorption signals obtained when samples containing >500 ng of A1 were slowly heated in a graphite atomizer. The molecules CN or C were not observed though these workers stated that this does not rule out the involvement of Al,C in the spike formation process. The A1H molecules are probably formed in the gas phase from A1 and hydrogen and the partial pressure of the latter was estimated to be 200-600 Pa and appeared to be constant for the duration of the A1 spike.Chinese workers (93/C3075) found negative pulses of atomic absorption signals for precious metals which coincided with the time and shape of A1 spikes. Experimentation by platform atomization of Pt and A1 in the same or different positions showed that the loss of analyte element could be due to the co-vaporization or fine particle inclusion in the course of the sudden vaporization of A1,03. In an effort to clarify some of the results concerning the decomposition of metallic nitrates to oxides McAllister (93/CSIGAT-H3) employed an ETVMS system with transverse rather than end-on sampling of the gas from the atomizer.Much of the previous data concerning the existence of MO species had been obtained with the latter arrangement. With the transverse arrangement no gaseous metal oxides were228 R JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 detected for the thermal decomposition of nitrates of Co Cu Mg Ni and Pb over a range of heating rates from slow drying to rapid atomization. The results were in keeping with thermo- chemical calculations and tended to indicate that the earlier observation of gaseous metal oxides could be attributed to the formation of macromolecular clusters of oxides or nitrates during rapid decomposition then passing into the MS quadrupole. The final parts of the initial series of publications concerned with shadow spectral filming have now been published (94/556 94/766).In one of these Gilmutdinov et al. (94/556) discussed the dynamics of formation and dissipation of an Ag absorption layer in ETAAS with different operating modes such as gas- stop gas-flow and wall and platform atomization. As a test element Ag was selected because of its chemical inertness with respect to the processes within a graphite atomizer and hence allowed the characterization of the influence of the physical factors (mass transfer and adsorption-condensation on the graphite tube wall) during atomization to be assessed. Under gas-stop conditions it was shown that the cross-sectional structure of the Ag absorbed layer was practically uniform. This uniformity indicated the high efficiency of diffusional mass transfer in graphite atomizers.The use of an internal gas flow produced a pronounced distortion of the uniformity and during the atomization process there was a sharp decrease in the gas-phase concentration of Ag from the bottom of the tube to the top. A more detailed study of the dynamics of longitudi- nal propagation was performed by using Hg as the test element in a quartz tube having the same geometry as the graphite tube. The absence of vapour near the cooler ends of the tube was shown. From these results these workers proposed (a) the introduction of a new characteristic atomization parameter the disappearance temperature defined as the temperature below which the analyte cannot exist as vapour near the surface; and (b) a cascade mechanism of the analyte propa- gation in non-isothermal furnaces.The mechanism consists of a number of condensation-vaporization processes of the ana- lyte as the temperature wave propagates along the length of the atomizer during heating. The mechanism is important for fairly low heating rates when the velocity of diffusional propa- gation of the analyte vapour is higher than the velocity owing to temperature propagation. The further improvement of the shadow spectral filming technique by digital imaging of the atomization process using a charge-coupled device (CCD) camera (93/3432) was discussed last year (see J. Anal. At. Spectrom. 1993 8 197R). In a conference report that was discussed last year (see J. Anal. At. Spectrom. 1993 8 197R) Brown and Styris considered the atomization of Sn.This work has now been published (94/55 1) and extended to consider the actual mech- anisms that control the atomization of tin chloride. These were investigated by monitoring mass spectra of the gaseous species generated in pyrolytic graphite coated electrographite atomiz- ers and simultaneously the atomic absorption signal during the atomization cycle using wall atomization. Vacuum and atmospheric pressure vaporization were used to assist in differentiating between homogeneous gas-phase and con- densed-phase interactions. During vacuum atomization free Sn was not observed and the only molecular species detected were SnO(g) and SnCl,(g). During atmospheric pressure vapo- rization the observed molecular species were primarily SnCl,(g) and SnO(g) free Sn as determined by MS was absent from the centre of the atomizer however free Sn was present as determined by AAS.This suggests that atomization occurs at the regions of lowest temperature in the atomizer i.e. the end regions. The thermal decomposition of homo- geneous gas-phase species cannot account for the formation of free Sn because of the paucity of Sn(g) in the centre of the atomizer. However SnO (g) interactions with the cooler surface regions of the graphite atomizer do explain these data. Desorption of the resulting Sn(ad) can then account for the free Sn that was observed as the atomizer temperature increased. This argument was supported by MS results acquired when vaporizing at atmospheric pressure from capil- lary-type graphite cups that were heated to exhibit temperature gradients along their lengths. Appearing to apply this latter technique further Styris and Brown (93/CSIGAT-B1) have investigated the effects of bulk digusion induced analyte losses in pyrolytic graphite coated electrographite.Analyte species Ga and In were vaporized in uacuo and the species that diffused through a 0.3mm thick graphite barrier monitored by MS. Interferences from analyte species that were not involved in the bulk diffusion process were avoided by monitoring species that diffused through the base of inverted capillary tube-type cups. Uniform radiative heating of the cups was provided by the tube atomizer the cups being positioned within the atomizer tube and supported by the injection hole. It would appear that concentration gradients are responsible for the bulk diffusion of Ga as shown by the changes in the relative magnitudes of the diffusing species with varying amounts of analyte being deposited.Bulk movement through the graphite for In appeared to be driven by chemical diffusion. From the results presented these workers argued that it would appear that some atomization of molecu- lar In species occurs within the bulk graphite. In collaboration with Hinds Brown and Styris (93/CSIGAT-E 1) investigated Si atom formation from aqueous and solid gold samples by MS monitoring of the gaseous species. This indicated that Si and SiO were present in the gas phase when both types of sample were atomized. Diatomic Si was observed from the solid samples which was coincident with the appearance of Si and it was concluded that there appeared to be different atomization mechanisms operating for the solid and solution samples.Other workers (93/CSIGAT-H2) have also examined the formation and stab- ility of molecular species of Ge Si and Sn following the vaporization of the pure elements and oxides as slurries from graphite and tantalum surfaces. The molecular metal sulfide originates in the presence of SO2 which is derived from the decomposition of sulfates and in the presence of sulfides such as pyrite. In the case of Si while SiO is observed during the vaporization of a variety of solid samples SiS can be detected during the vaporization of coal slurries having the relevant sulfur content (as sulfate or sulfide). The two-band systems of SiS lying in the UV range (200-250 and 260-330nm) are responsible for the non-specific absorption measured during the determination of trace elements in coal samples at atomiz- ation temperatures above 1800 "C.Gilchrist e t al. (93/3234) have continued their investigations into the mechanisms of atomization of Pb from a pyrolytic graphite probe atomizer. Application of the exposure-time technique whereby dried sample residues on a graphite probe are inserted into the furnace at a given temperature (exposure temperature) for a given time (exposure time) allows the rate of vaporization of molecules within the graphite probe surface to be determined assuming a monolayer or sub-monolayer on the probe surface and hence vaporization occurring as a first- order rate process.Consequently the activation energies can be calculated and these used to gain an insight into the release process for different analyte species. From these studies it was found that vaporization and atomization of Pb are separate processes and Pb is vaporized as a molecular species. The following mechanism was proposed. Prior to atomization of Pb PbO is released from a nitric acid matrix whereas PbCl is released from a hydrochloric acid or sodium chloride matrix into the vapour phase. Atomization of Pb from these matrices occurs by gas-phase thermodynamic equilibrium dissociation of PbO or PbCl molecules. The activation energy for the release of both PbO and PbCl has been found to be about 26 kJ mol-I this activation energy is considered to represent the energy for desorption of PbO or PbCl from the graphite surface.Hydrogen gas was found to be an effective chemicalJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 229 R modifier to remove the gas-phase interference by chlorine on Pb and increases the dissociation of the gas-phase Pb molecular species. The major source of oxygen in the graphite probe atomizer is ambient air which diffuses through the probe insertion slot cut into the graphite tube. The po in the graphite probe atomizer is higher than that in a conventional graphite electrothermal atomizer and is reduced when hydro- gen gas is added as a chemical modifier. The electrothermal atomization of Pb from pyrolytic graphite coated electrographite palladium-coated and zirconium- coated graphite tubes was examined by Yan and Ni (94/1178).The appearance temperatures kinetic orders and activation energies for atomization from these three surfaces following both the direct introduction of Pb as a solution and after trapping of the gaseous hydride were compared. The results showed that the mode of sample introduction did not appear to play a role in governing the analyte release energies. However the nature of the atomizer surface did. A first-order release occurred from pyrolytic graphite coated electrographite indicating that the analyte desorbs from the surface as highly dispersed atoms with an E of 301 & 17 kJ mol-' which these workers considered indicative of the Pb-graphite interaction. For the zirconium-coated tube a fractional order between 0 and 1/3 with E values of 188-201 kJ mol-' suggested the release of Pb from three-dimensional structures in the form of 'caps' or micro-droplets showing weak Pb-zirconium carbide interaction. From the palladium-coated tube first-order kin- etics were found with larger E values of 418-519 kJ mol-' which suggested not surprisingly in view of the effect of palladium as a chemical modifier for Pb a strong interaction between the Pb and palladium.Chinese workers (93/3561) investigated the atomization mechanism of Vfrom a graphite probe surface using XRD SEM and ESCA techniques in addition to AAS measurements. During the pyrolysis step species of V can be converted into stable carbides on the probe surface followed by decompo- sition into free V atoms and carbon during the high tempera- ture atomization step.The study of the mechanisms of vaporization for Ag and Au using electrothermal atomization at atmospheric pressure discussed last year (see J. Anal. At. Spectrom. 1993 8 197R) have now been published (93/3371). Fonseca et al. (93/3371) found that vaporization of Ag or Au appears to occur from varying sizes of microdroplets or from adsorbed atoms depending on the conditions of the analysis. Using as criteria the shifting of the peaks to later times with increasing concen- trations a fractional order of release for both metals was suggested under normal electrothermal atomization analysis conditions. However a first-order process was obtained when formation of adsorbed atoms was expected. The activation energies for desorption of Ag and Au are mass dependent.The decreasing influence of the graphite as the droplet size becomes large could explain the increase in E observed at increasing concentrations. The highest E values obtained for both metals approach the respective AHv values and indicate desorption from the surface of large microdroplets. The lowest E could represent the interaction between individual adsorbed atoms and the graphite surface. The dry and thermal pre-treatment stages affect E and the shape of the absorption profiles because they probably produce changes in the surface topology of these metals before atomization takes place. Chemisorbed O2 seems to reduce the size of the microdroplets in the case of Ag but the effect of Au has not been completely rationalized.The tendency of the Ag and Au microdroplets to disperse on graphite seems to be reduced by mechanical roughening of the surface which probably increases the number of active sites on the graphite. Rohrer and Wegscheider (94/740) considered the atomization of Ag via a Monte Carlo study of the pysical parameters. A model was presented to explain the possible interactions between the analyte and the graphite under differ- ent experimental conditions. Wide variations in frequency factor and activation energy for Ag can be caused by lateral (adsorbed atom-adsorbed atom) and vertical (adsorbed atom- surface) interactions. By applying a simple calculation of the temporal distribution of particles in the atomizer a satisfactory correlation with experimental absorbance profiles was obtained.To investigate the varying results found for Ge by ETAAS Doidge and McAllister (94/558) studied the atomization of Ge in a graphite atomizer with ETAAS and electrothermal MS and by calculation of thermochemical equilibrium. The evol- ution of GeO(g) from alkaline or nitric acid matrices and of GeS(g) from a sulfuric acid solution of Ge at a fairly low temperature during pre-atomization or atomization was confirmed by electrothermal MS. No gaseous germanium carbide was detected in the electrothermal MS experiments. Equilibrium calculations at low carbon activity showed how GeO(g) can be evolved at 800 K by partial reduction of GeO,. Further estimates of equilibrium for sodium germanate and sulfuric acid-GeO matrices in both tube and platform atomiz- ers showed that many of the anomalies observed in the study of Ge by ETAAS could be explained in terms of varying numbers of active carbon sites on the surface in the atomizer which produces differing amounts of GeO(g) depending on the heating rate and the nature of the chemical modifier and pyrolysis temperature.They concluded that for the determi- nation of Ge by ETAAS platform atomization using a pal- ladium chemical modifier provides a more isothermal environment. Rojas (94/304 93/CSIGAT-A2) has continued work on investigations into the use of kinetic parameters to elucidate atomization mechanisms with a detailed study of the electrother- mal atomization of Ni (94/304). The kinetic order of generation of the atomic vapour of Ni was determined as a function of the initial mass of analyte.For masses up to 3.0 ng a kinetic order of one was obtained with atomization and pulse half- width independent of the analyte mass. However for sample mass in the range 4.9-8.0 ng a kinetic order of two was found with a constant atomization energy and a pulse half-width that increased as the initial mass increased. Accordingly a first-order kinetic model was employed to describe the atomiz- ation profiles of analyte masses up to 3.0 ng. To determine the vapour formation and dissipation rate constants kl and k the rate equations for the model were solved using boundary conditions at t the time at which the rate of change of absorbance presents a minimum value and the temperature has already reached its maximum value. Employing the kinetic parameters of this model a good description of the absorbance profiles was achieved and the theoretical behaviour of the peak absorbance and the area of the peak as a function of the analyte mass was predicted.Chinese workers (94/725) exam- ined the atomization of Mn. The order of the atom formation reaction of Mn was verified which starts from first-order then moves to zero-order kinetics as the heating rate decreases. Results from XPS studies showed that the mechanism of atomization of Mn in a graphite atomizer is a thermodynamic process of dissociation of high- to low-valent metal oxides until final formation of the Mn atom. The effects of surface interaction and heating rate on the atomization of Cu was considered by Jackson and Qiao (93/CSIGAT-G2). They found that the signals for Cu atomized from a pyrolytic graphite platform were broader than the profiles obtained from a tantalum platform.In an effort to reduce the effects of platforms with different thermal mass on the heating rate pyrolytic graphite platforms were coated with tantalum carbide. By using combinations of tantalum carbide coated platforms and tantalum carbide coated tubes evidence was presented to indicate interaction of Cu both with the platform surface and tube wall though no effects were seen for Pb and it would seem that surface adsorption and desorp- tion processes are significant when Cu is atomized from a conventional graphite atomizer.230R JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 It would appear that the work considering the use of complete neglect of diferential overlap (CNDO) calculations for investigating the atomization of Mo from pyrolytic graphite and discussed last year (see J.Anal. At. Spectrom. 1993 8 197R) has now been extended and published in more readily available journals (93/3440 94/373). It was found that hydro- chloric and nitric acids produced an enhancement of the Mo AA signal with respect to non-acidified solutions. These effects were assessed by the response surface method and by modelling the Mo-graphite interactions using quantum mechanical calcu- lations. A multivariate optimization approach was carried out using the Doehlert matrix and a cubic equation to estimate the experimental response. The mineral acid enhancement was interpreted as a decrease in the memory effects caused by the presence of the acid which facilitates formation of Mo species that can be more easily atomized.The fractional factorial design however revealed that the pyrolysis ramp was the factor that most influenced the Mo AA signal. These calcu- lations revealed that the adsorption of Mo and MOO occurs on 6-fold centre sites and that protons co-adsorbed on the graphite surface facilitate the migration of Mo species. The use of alloy phase diagrams were considered by Hirokawa et al. (93/3936) to be useful in elucidating the high- temperature reactions during pyrolysis and the beginning of atomization within a graphite atomizer. The origin of double peak signals in the direct atomization of metal samples can be explained the analytical curve for Pb in iron could be utilized for Pb in copper because of their similar phase diagrams and the role of a metal chemical modifier can be considered using phase diagrams between the chemical modifier and analyte elements.The group at the University of Karlsruhe Germany have continued their studies on the efect of oxygen in a graphite atomizer. Hahn et al. (94J282) considered in detail the effect of oxygen on the reaction of T1. By coating the electrographite surface with oxygen at 300 K then flushing with argon at 300 K this ensures that only chemisorbed oxygen remains on the surface and that the gas zone in the atomizer is free of oxygen. An atomization step in argon at 2500 K ensures that all surface oxides are destroyed. This procedure allows a separation between the oxygen treatment step and the subsequent measurement.This method demonstrated that the effects of oxygen are due to a change in the surface properties of the furnace. Thallium forms T1,03 residues in untreated and oxygen-treated atomizers after the drying steps. In untreated atomizers the reduction to TI atoms occurs via the volatile suboxide T120 which is the reason for the losses of T1. Atomizers treated with oxygen avoid the formation of the volatile suboxide owing to the chemically modified graphite surface and consequently the absorbance signal is enhanced. The modification of the graphite surface is caused by chemi- sorption of oxygen on active sites of the graphite which are destroyed in a high-temperature step. Hence the reduction process is shifted to higher temperatures with reduced losses of analyte.An interesting point raised in this paper concerns the mass dependence of the oxygen effect. The oxygen effect was examined with masses of T1 ranging from 1 to 1000 ng. Up to 100 ng the stabilizing effect was constant however between 500 and 1000 ng the stabilizing effect at 1200 K decreased strongly indicating that the stabilizing effect of the oxygen treatment vanishes for masses >1 pg. This indicates clearly that the chemical reactions of p.g amounts of T1 are different to those for ng amounts in an oxygen-treated atomizer. Consequently the results obtained from techniques such as MS XRD and molecular absorption which require relatively high masses with respect to graphite electrothermal atomiz- ation should be considered with caution.These workers found that pyrolysing the T1 on an untreated electrographite surface at 1300 K for 30 s under gas-stop conditions achieved the same effect as that for an oxygen-treated surface. This effect was thought to be due to the ability of the volatile suboxide T1,0 which vaporizes during the pyrolysis time now to have the possibility of hitting the graphite surface several times from which it is further reduced to T1 as opposed to being blown out of the atomizer when a full gas flow is present during the pyrolysis step. Guell et al. (93/3434) applied Monte Carlo simulations along with numerical heat-transfer techniques to evaluate the impact of using atomizers that heat more isothermally than conven- tional tubes which are known to exhibit a thermal gradient from the centre to the end of the tube during the heating cycles.Isothermally heated atomizers whose shapes have been altered to improve the longitudinal temperature distribution (i.e contoured tubes) showed only small changes in the analytical signal magnitude for simple aqueous samples Oxygen and chlorine were used as interferents in separate simulations to consider the formation of molecular CuO and CuCl respectively. Only very small improvements in reduction of interferences were noted when the isothermally heated tubes and contoured tubes were employed. In none of the atomizers studied was the interference eliminated. However in all these simulations atomization was considered from the tube walls. These same workers (94/307) also considered the optimization of the S/N for electrothermal atomizers by employing Monte Carlo techniques.The S/N predicted by the Monte Carlo simulation did not depend strongly upon the heating rate or the nature of the analyte being determined. The optimum atomizer geometry was found to be large with a diameter of approximately 0.5 cm and a length of 4.0cm. While most commercial atomizers have diameters close to the optimum the shorter lengths reflect pragmatic decisions taken with respect to the power supplies required and prolonged heating times which could well reduce the useful tube lifetime. In addition longer tubes could well accentuate non-isothermal temperature distributions. Cathum (93/3092) calculated the atomization eficiencies of the Perkin-Elmer HGA-400 for the production and contain- ment of atomic vapour for Al Ag Au Co Cu Fe Ga and Ni by a method developed under non-isothermal conditions.The method takes into account the residence time and the shape of the absorbance signal profile. It is based on the entire absorption signal profile rather than on any part of it. The uncertainty in the method arises from calculation of the rate constant of atom loss owing to the temperature gradient which has a pronounced effect on the ‘effective’ length of the analysis path when the atomizer is operated under non-isothermal conditions. The average value of the atomization efficiency for the eight elements used for the study was found to be about 0.10. This value is very different to those found previously by Frech and Baxter of 0.69-1.05 (Spectrochim.Acta Part B 1990 45 867) though it would appear that Cathum (93/3092) used very slow heating rates wall atomization and an instrument with a slow response time (time constant of 20 ms) all of which will influence the final atomization efficiency in comparison with Frech and Baxter who employed STPF conditions. Yan et al. (94/1004) proposed a method for the simultaneous determination of the kinetic order activation energy and the frequency factor for atom formation from one single absorbance signal under normal analysis conditions in ETAAS. Both ETAAS experiments and computer simulation techniques (with known kinetic parameters of atom formation) were employed to examine the validity of the proposed method and compari- son with other methods.The results showed that the activation energy values obtained at lower temperatures by previous methods and by the proposed method are almost identical. However the Arrhenius plots obtained by the previous methods often bend at higher temperatures while those obtained by the proposed method exhibit much wider linearity The method was applied to the determination of kinetic parameters for the atomization of Cu and Mn. In addition a method for the simultaneous determination of the diffusion coefficient of gaseous atoms and its temperature dependenceJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 231 R from the decay portion of one single absorbance signal was also proposed. Tserovski et al. (94/1133) calculated activation energies for the atomization of Ca Cu Fe and Pb from aqueous solutions and organic extracts using an APDC-IBMK extrac- tion system.Two atomizer surfaces were studied pyrolytic graphite coated and tungsten-impregnated graphite tubes and the results have been discussed earlier in section 1.2.1. 1.2.4. Interferences This is an area that always generates a vast volume of work and once again this year is no exception. However as the authors of this Update have noted in the past (see J. Anal. At. Spectrom. 1993 8 197R and J. Anal. At. Spectrom. 1991 6 187R) a number of these papers are simply a repetition of what was performed previously finding the same results and often arriving at the same conclusions. Fortunately there are suggestions for new approaches for the application of new techniques to reappraise previous ideas and these publications are a delight to read and study.Only one review (93/3578) concerning the use of chemical modifiers for the determination of heavy metals by ETAAS appeared during this review period in Korean but with 83 references. The group at the University of Sofia Bulgaria have been very active in the last few years and have published some key papers in the field of chemical modification. In continuing this work Mandjukov et a!. (93/2885) have proposed the use of regular solution theory to model analyte losses during sample pyrolysis in the presence of chemical modifiers in ETAAS. The influence of the chemical modifier concentration on the thermal stabilization effect the analyte loss kinetics and the shape of the absorbance signal were studied for the example of Pb determination with a tungsten-containing chemical modifier.The experimental results were found to be in acceptable agreement with the theory of regular solutions. Special atten- tion was paid in the model to interpreting the problem of analyte kinetics as presented in the literature. Previous findings concerning the mechanism of thermal stabilization were criti- cally discussed. This is an interesting paper though difficult to read possibly because of minimal editing. It is disappointing to find this in a major analytical journal published in the English language. The work on Rutherford backscattering spectrometry (RBS) to investigate high-temperature reactions on graphite and which was discussed as conference reports last year (see J .Anal. At. Spectrom. 1993 8 197R) has now been published Majidi and co-workers (94/28 1) showed clearly that RBS indicates that nitrate salts of Ag Cd and Pb (2 pg of the metal placed on the graphite surface) readily migrate to a depth 2 3 pm into the pyrolytic graphite coated electrographite substrate at room temperature. Hence contrary to popular belief pyrolytic graphite coated electrographite is not impervious. With the addition of an aqueous solution of ammonium dihydrogen phosphate as chemical modifier the data again showed that phosphate and analyte readily migrate through the surface. The formation of a 'surface' metal-oxyphosphorus compound was observed with Cd and Pb when these samples were heated to 350 K.The surface bound species for Cd and Pb were lost by 950 and 910K while the analytes were observed in the bulk up to 1010 and 1030 K respectively. In the case of Ag the addition of the chemical modifier did not significantly alter the temperature at which Ag was lost from the bulk and hence Ag is not stabilized by the phosphate chemical modifier. The best fits to the RBS spectra in which the metal-oxyphosphorus surface species was observed yielded an oxygen to phosphorus atom ratio of 2.5. These workers proposed from these data and the fact that the metal to phosphorus ratio varied with temperature that the metal-phosphate interaction results in the formation of an xMO.P,O glass. Because Cd and Pb were not instantaneously lost from the bulk when the surface oxyphosphorus compound decomposed it was also proposed that as part of this mechanism that the glass modified the graphite substrate.This work is of importance as it directly questions a number of widely held concepts in ETAAS studies namely that the analyte is present on the graphite surface either as a monoatomic or molecular layer or as micro- droplets. Most theoretical studies concerning activation ener- gies of atomization assume one of these and it would appear that neither is totally correct. This paper is well worth reading for practical analysts and theoreticians This work has con- tinued as Majidi et al. (93/CSIGAT-G1) have now turned their attention to examining the efect of oxygen ashing on the surface reactions of Ag Cd and Pb. For Pb the effect of oxygen in the gas phase at temperatures of 800 and 1000°C appears to prevent Pb moving into the surface layers of the graphite the Pb remains on the surface.With Cd at these same temperatures and in an oxygen atmosphere Cd diffuses into the 1 pm graphite layer as does Ag. It is clear that oxygen changes the graphite surface and from this work it would appear that the oyxgen thickness on the surface is c 2 0 nm after treatment at 1000 "C. Investigations with material sputt- ered onto the graphite surface rather than applied in solution followed by drying indicated that Au Pb and Pt remain on the surface but Ag migrates. As with many fundamental investigations this work poses more questions than it answers however it would appear that this approach is producing a great deal of information and no doubt the next few years will produce a number of key publications in this area.The collaborative work between L'vov and Frech which was presented as conference abstracts and discussed last year (see J . Anal. At. Spectrom. 1993 8 197R) has resulted in a number of papers (94/50 94/306 94/1183) considering the physical interference efects from matrix vapours in ETAAS. As discussed previously (see section 1.2.3) these workers found non-specific absorbance signals when pg masses of elements such as Ag Au Cu Mg Mn and Pd were vaporized in a graphite atomizer (94/306). Another paper (94/50) investigated these physical interferences in more detail. Two types of interference were identified. The first type concerned analyte trapping in the cooler ends of end-heated H GA-type atomizers. Trapping was investigated using analytes of differing volatilities (Au Cd Ga Mn and Pb) in the presence of a silver matrix.The total decrease in the analyte signal depended on the atomization temperature used and on the volatility of the analyte. These workers claimed that by using a mini-flow of argon internal gas through the atomizer instead of the normal gas-stop conditions trapping could be eliminated. As stated in the Update last year (see J . Anal. At. Spectrom. 1993 8 197R) these results need to be further investigated and clarified because of the contrast with the shadow spectraljilming investi- gations of Gilmutdinov et al. discussed previously (see J . Anal. At. Spectrom. 1993 8 197R and also section 1.2.3) whereby a flow of internal gas during atomization resulted in a pro- nounced distortion of the uniform cross-sectional structure of the absorbing layer found under gas-stop conditions.L'vov and Frech (94/50) considered a second type of interference where the integrated absorbance signals for some elements were increased by up to 15% in the presence of silver compared with aqueous solutions. This type of interference was explained by an increased analyte residence time due to high partial pressures of matrix vapours which changed the diffusion coefficients of the atoms. This type of interference effect was also observed for a potassium sulfate matrix when Ga and A1 were used as analytes. Following on the study of end-heated atomizers Frech and L'vov (94/1183) then turned their attention to side- or transverselheated graphite atomizers ( THGA).They considered that the phenomenon of analyte trapping on the surface of a condensed matrix in cooler zones of the graphite tube is general for both end-heated and side-heated atomizers. In an end- heated graphite atomizer trapping takes place on the tube wall covered with matrix whereas in the side-heated tube this232 R JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 effect occurs in the cloud of condensed matrix particles located near the tube ends in cooler gas phase zones. By adding end- caps with an aperture of 3 mm diameter to the THGA tubes diffusional losses through the tube ends were reduced and interference effects from yg amounts of matrices such as silver cadmium and palladium eliminated.In addition the sensitivity was increased by approximately 1.7-fold with end-capped tubes. Byrne et al. (93/3231) have continued their studies of the mechanisms of chloride interferences in ETAAS investigated by means of ETV coupled with ICP-MS. Attention has now turned to examining the effect of a sodium chloride matrix and ascorbic acid chemical modifier on Mn. The use of the ETV-ICP-MS technique allowed direct observation of the signals of Mn along with matrix components during both the pyrolysis and atomization step of ETAAS and allowed differ- entiation between the loss of Mn from the atomizer during pyrolysis and loss owing to formation of molecular species during atomization. These workers found that the mechanism of sodium chloride interference is independent of the pyrolysis temperature the loss of Mn occurs not during pyrolysis but is due to a vapour-phase interference caused by the formation of manganese chloride during atomization.The addition of ascor- bic acid as a chemical modifier removes the sodium chloride interference at all pyrolysis temperatures by promoting an early release of chloride during the atomization cycle. The appearance temperature of the chloride is approximately 250 “C lower than that of the Mn. In ETAAS this difference in the two temperatures reduces the amount of residual chloride left in the graphite atomizer at the Mn appearance time thereby eliminating the interference of sodium chloride with Mn. Yet another group of workers (93/3416) proposed a method that will eliminate over-correction owing to spectral inter- ferences of iron on Se and hence allow the accurate determi- nation of Se in the presence of iron by continuum source background corrected ETAAS.The pyrolytic graphite L‘vov platform was pre-treated by depositing 10 pl of a 1 mg ml-I solution of platinum and 10 pl of 5% ascorbic acid followed by an ETAAS programme to dry the solution followed by pyrolysis at 1000 “C and atomization at 2200 “C to pre-treat the platform. This procedure was repeated a total of 60 times in the words of these workers ‘to obtain a lasting coating’. A quick calculation of the time this procedure would take assuming an average 20 s delay between pipetting and the start of the furnace programme with a total time of 153 s gives approximately 3 h.As if this is not sufficient of a platinum group metal to have in the atomizer the samples were also pipetted with the addition of 2 pl of a 1 mg ml-’ palladium solution and the samples were prepared in 0.5% ascorbic acid solutions. The ability to determine 50 pg 1-’ of Se in the presence of 2.5 mg ml-’ of iron was claimed. However the success of this procedure must be questioned as precisions were between 3 and 10% and the method of analyte additions for quantitation was needed in addition no samples or reference materials of any description were examined. French workers (93/3218) claim to have found a spectral interference related to the presence of nitrate and nitrogen monoxide in Zeeman-effect background corrected ETAAS measurements.The decomposition of metallic nitrates in the graphite atomizer resulted in evolution of NO which led to an underestimation of Se at 196.0 nm and an overestimation for Se and Zn at 204.0 and 213.9nm respectively. The inter- ference was removed by calcination of the nitrates however for Zn the calcination temperature approached the atomization temperature and therefore care was required. Further work from these same workers (93/CSIGAT-P1-10) discussed over- coming this effect found in the determination of Zn in sea- water by the application of nitric and oxalic acids as chemical modifiers. These reduced the background absorption approxi- mately 10-fold. Oxalic acid was found to be the optimum chemical modifier as the interference was still present when nitric acid was applied.In this latter presentation the inter- ferenc effect is thought to be owing to the splitting on the NO absorption bands produced during the decomposition- reduction step of the different nitrate salts. Kiirfurst and Pauwels (93/CSIGAT-D2) observed an inter- ference on the Pb 283.3 nm line in direct and inverse Zeeman- efSect ETAAS when solid samples with a high sulfur content were atomized. This interference was thought to be due to molecular absorption by S2 molecules as placing a sealed quartz tube containing sulfur in the atomizer and heating to 500 “C showed negative signals. However the interfence could be overcome in an inverse Zeeman-effect instrument by the addition of nitric acid to the sample in the atomizer. Doidge (93/3957) found that the well known autoionizing doublet 2P-2S of A1 was formed in the emission spectrum of an ICP even though these lines are not listed in tables.The use of this doublet to investigate atomizer interferences was proposed. For those of us more concerned with using palladium as a chemical modifier others may have to determine the element. Frigge and Jackwerth (93/3363) found that the two most sensitive lines for Pd at 244.8 and 247.6nm showed spectral interferences from lead. In addition they found that the use of Zeeman-effect background correction at 247.6 nm caused negative signals owing to line splitting however the use of an optimized atomizer temperature programme allowed a 20000-fold excess of lead to be removed prior to atomization. In considering chemical modifiers once again palladium is virtually the only reagent that either analysts are using or publishing papers about! While in earlier Updates this reviewer (I.L.S.) commented that palladium appeared to be becoming the ‘universal’ chemical modifier that had been talked about in the early papers extolling its virtues it would appear that palladium has in fact now become this ‘universal’ modifier.The trick appears to be to find a combination of another reagent with palladium for some particular application and rush into print. The culminating paper (94/3394) in the series considering the use of palladium as a chemical modifier from Welz et al. and assessing its performance for the determination of 21 elements was discussed in detail last year (see J.Anal. At. Spectrum. 1993 8 197R). This reviewer (I.L.S.) accepts that the term ‘chemical modifer ’ is perhaps not the most accurate representation indicating the action of a reagent added to a graphite electrothermal atomizer to assist in both thermally stabilizing the analyte ensuring the various forms of the analyte are in one form prior to atomiz- ation and aiding in removing the matrix during the pyrolysis step. However it is the agreed term recommended by IUPAC for such a reagent and accordingly to avoid ambiguity and confusion it should be used. As a ‘chemical modifier’ can act in a variety of ways not just as an ‘analytical isoformer’ as the latter term proposed by Granadillo et al. (93/3233) seems to suggest then the term ‘chemical modifier’ which to the present author implies either a chemical and/or physical effect on either the analyte and/or matrix and graphite substrate encompasses that suggested by ‘isoformation’.Eventually the argument becomes one of semantics rather than analytical chemistry though I for one am prepared to subjugate my own personal preferences in the interests of the majority. The term ‘chemical modifier’ may not linguistically be the optimum but at least all workers in the field of electrothermal atomization appreciate what the term implies as outlined in the opening sentence of this paragraph. Granadillo et al. (93/3233) discussed and compared the use of palladiumsitric acid and ammonium dihydrogen phos- phate-magnesium nitrate-citric acid mixtures as chemical modi- fiers for Pb in a variety of clinical and environmental samples.In the presence of a carbon monoxide atmosphere the Pb signal was shifted late in time with respect to the signal obtained in the presence of citric acid. It was concluded that this is an indication of a carbon-dependent mechanism for theJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 233 R reduction of the atomic precurser to form Pb atoms with the production of carbon monoxide. From the results obtained a simple method for the determination of Pb in clinical and environmental samples using a mixed chemical modifier con- sisting of 5 ng of palladium and 200 pg of citric acid and applying STPF conditions with oxygen ashing during the pyrolysis step was developed. Even though this mass of pal- ladium is considerably lower than the pg masses normally found to be necessary the data presented in this paper show that 5 ng of palladium were optimum.These workers found that with larger masses of palladium (up to 25 ng) the tube lifetime was considerably reduced. The limit of detection (3s) of the method was found to be 0.1 pg 1-1 for a 10 pl sample injection and the method was validated using human serum freeze-dried urine whole blood pond sediment Chlorella tea leaves vehicle exhaust particulates and Sargasso RMs. Within- and between-run precisions were of the order of 2 and 3% respectively for a concentration range of 10-20 pg I-' of Pb in whole blood and urine. In contrast to this study Penninckx et al. (93/3955) found that a mixed chemical modifer containing a mass of 6 pg of palladium and 15 pg of magnesium nitrate was optimum for the determination of Pb in biological mate- rials and foodstuffs.This chemical modifier enabled the direct determination of Pb in diluted urine milk and whole blood against an analytical curve established with aqueous solutions and an increased linear range was observed when this modifier was employed. The optimum pyrolysis temperature was sample dependent and needed to be determined for each specific sample type. Qiao et al. (Spectrochim. Acta Part B 1993 48 1495) have continued their studies into the mechanism of action ofpalladium and have considered this action in reducing the chloride interferences for the determination of T1. Thermal stabilization of TI in a sodium chloride matrix at 1100 "C was only found to be effective if palladium was pre-pyrolysed on the platform at 900°C prior to introduction of the sample.By this means 1 ng of TI could be determined in the presence of 200pg of sodium chloride without interference. Stabilization was con- sidered to occur through absorption of the analyte by underpotential deposition since the reduction potential for Tl+/Tl (Eo = - 336 V) is more negative than that for Pd2+/Pd (Eo= +0.951 V) on the pre-pyrolysed palladium deposit. The analyte remains adsorbed on palladium until the sodium chloride has volatilized during the 1100 "C pyrolysis stage. During atomization the T1 becomes embedded in molten palladium and then diffuses out. The addition of magnesium to the palladium was found to improve the recovery of T1.These workers claimed that this procedure allowed the determi- nation to be performed with either continuum source back- ground corrected instruments or those employing the Zeeman effect though sadly no analytical results for RMs were pre- sented to demonstrate this. The thermal and temporal impact of magnesium and palladium chemical modifiers on the thermal pre-treatment of Ag and Cu have been assessed (94/1176). For Ag palladium improved thermal stabilization and magnesium and a magnesium-palladium mixed chemical modifier contrib- uted to the temporal stabilization though for Cu palladium and magnesium-palladium chemical modifiers decreased temporal stabilization but magnesium alone gave a slight increase. These effects were correlated with the vaporization of palladium and magnesium by measuring the absorption signals for palladium and magnesium at various pyrolysis temperat ures-times.The work of Laborda et al. (94/584) on comparing the effects of nickel and palladium chemical modifiers on different chemical species of Se and the influence of a urine matrix discussed as a conference report last year (see J. Anal. At. Spectrom. 1993,8 197R) has now been published. Of the main Se species in human urine namely selenite and trimethyl- selenonium these are both stabilized to the same extent and produce an equivalent response when nickel is employed as a chemical modifier. With respect to the two forms of palladium used either reduced (by thermal pre-treatment or by a chemical reducing agent) and non-reduced only the latter produced an effect analogous to that observed for nickel.Trimethylselonium was found to be stabilized to a lesser extent with respect to selenite consequently nickel was the preferred chemical modi- fier. A response for Se independent of the urine matrix with Se recoveries of 96% at a concentration of 44 f 6.9 pg 1-1 was obtained for urine samples diluted 1+4 with water and the addition of 100 pg of nickel though the detection limit (3s) of 20.6 pg 1-1 seems rather high and prevents this method from being used to determine endogeneous levels of Se in urine. Other workers (94/861) investigated the determination of Se in urine and serum. Kao et al. (94/861) diluted urine 1 +9 and employed a mixed chemical modifier of 0.6 pg of palladium 25 pg of nickel and 80 pg of ammonium nitrate. However these workers appear to have a much better detection limit (3s) of 4.9k0.8 pg 1-l and it is difficult to rationalize the differences between the work of Laborda et al.(94/584) and Kao et aE. (94/861). Janssen (94/197) discussed the use of copper and palladium as chemical modifiers for the determi- nation of Se in whole blood. A pyrolysis step with air ashing at 550°C was found to be beneficial. The work of Garcia-Olalla and Aller (93/2131) concerning the use of a mercury-palladium mixed chemical modifer has been discussed previously (see J. Anal. At. Spectrom. 1993 8 197R). This mixed chemical modifier has now been employed to determine Se in coal fly ash after digestion. These workers claimed that wall atomization was used with a high pyrolysis temperature and Smith-Hieftje background correction to elim- inate matrix interferences though it would appear that the method of analyte additions and an analytical curve prepared in matrix-free solutions were both employed for calibration purposes. Values obtained for a coal fly ash RM agreed with the certified value.Xuan (93/3945) employed AAS and XRD measurements to investigate the reactions of Bi Ge and Pb with a mixed palladium-magnesium chemical modifier. For the determination of P with atomization from a platform Chinese workers (93/2239 93/3563) applied a mixture of palladium(11) chloride and calcium nitrate as the chemical modifier. The method was applied to the direct determination of P in biological samples. Klinkenberg et al.(94/752) found that a mixed chemical modifier of palladium Triton X-100 and hydrogen was the optimum for an electrothermal atomiz- ation procedure for the determination of Te in industrial waste water. It was found that only Triton X-100 could assure the uniform atomization of Te. It appeared that the particle size distribution of palladium was much more important than the dispersion of palladium particles in the atomizer. Fourty eight waste-water samples were analysed and the results compared for both ETAAS and ICP-MS as paired samples using a t-test on the differences. At a confidence level of 0.05 both methods gave identical results. The determination of Bi Pb Se Te and T1 in high-temperature alloys was examined by Reichardt (93/3079) and the use of a mixed chemical modifier of pal- ladium and magnesium nitrate compared with that of the in situ nickel chemical modifier present in the alloy samples evaluated.For Bi Pb Te and TI the nickel matrix was sufficient to stabilize the analytes but for Se the palladium and mag- nesium nitrate chemical modifier was recommended. Tserovsky et al. (93/3410) have continued their work on examining the behaviour of Cd Co and Pb in chlorine- containing solvents with respect to atomizer type chemical form of analyte and the chemical modifier employed in ETAAS determinations. The use of tungsten-impregnated atomizer tubes avoided the depression of absorbance signals by solvents such as carbon tetrachloride trichloromethane or 1,2-dichloroethane. The addition of palladium as its ion-association complex bis(methyltriocty1ammonio)- palladium(w) tetrachloride provided an additional stabiliz- ation effect.234R JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL.9 The application of Ag Au Cd Co Cu Fe La Mo Pb Pd Pt and Zn as thermally stabilizing chemical modifersfor the determination of Bi was examined by Brazdes and Fazakas (93/2691). Cadmium and lead improved the peak shape and enhanced both peak absorbance and integrated absorbance signals. Palladium was found to impair the sensitivity. Japanese workers (93/3383) found that a mixed chemical modifier of nickel nitrate aluminium nitrate and the ammonium salt of EDTA was suitable as a chemical modifier for the determi- nation of Te in copper alloy. This mixed chemical modifier removed both chloride and sulfate interferences.The same workers (94/1022) found that a mixed chemical modifier of nickel and copper nitrates plus the ammonium salt of EDTA removed sulfate interferences in the determination of Bi. Imai et al. (94/349) examined the atomization of Pb in the presence of nitrates and sulfates of Al Cu Co Mg Ni and Zn. The interference from sulfate on the Pb signal was considered to be owing to the formation of lead suIfide which is more volatile than lead oxide leading to decreased sensitivity. The interference of sodium chloride and sodium sulfate on the determination of Ag in potable waters was investigated by Bozsai et al. (93/CSIGAT-P2-14). Employing palladium and magnesium nitrate as a mixed chemical modifier and a conven- tional Massman-type atomizer used under STPF conditions in the presence of 2 pg of the interferent salts recoveries of only 75 YO were obtained.With a transverse-heated atomizer these interferences were eliminated for up to 10 pg of the interferent salts. For the determination of Zn in 0.05 mol 1-1 CaC1 soil extracts Bogacz (94/369) found that interferences owing to chloride could be overcome by the addition of 1% v/v phosphoric acid. Chemical modifiers of nitric acid mag- nesium nitrate and sodium tungstate were investigated by Beceiro-Gonzalez et al. (93/3238) for the determination of Cr and magnesium nitrate was found to be optimum. Chinese workers (93/C3077) applied a chemical modijier of lanthanum to the determination of Sc in ilmenite. A sensitivity enhance- ment of 240% was claimed along with no interferences from Al Ca Mg Fe and Ti.Zeng (94/678) employed bariumfluoride as a chemical modifier and lanthanum nitrate coated pyrolytic graphite coated electrographite tubes for the determination of Mo in human liver after a microwave decomposition with nitric acid and hydrogen peroxide though Yang (93/4015) applied a chemical modifier of calcium chloride with a lantha- num-coated graphite tube to overcome sulfate interferences for the determination of Mo in rice. Thiourea was used as a chemical modifier for the determination of Mn (93/3938) and Ag (94/227) in biological samples with a molybdenum tube electrothermal atomizer and in the case of Ag was claimed to eliminate the interferences from aluminim calcium copper iron magnesium lead and zinc.In an interesting procedure Yalei et al. (94/301) discussed the use of zirconium as a chemical modger for the determination of AsV and As"' species in environmental samples. The As species were co-precipitated with zirconium hydroxide from water samples at pH 9.5. The precipitate was dissolved in 9 mol 1-1 hydrochloric acid and 10 pl aliquots of this solution taken. The presence of concentrated hydrochloric acid and pyrolysis at 1100°C converted the As"' into low boiling arsenic(m) chloride and this was volatilized from the atomizer. The zirconium contained within the sample aliquot acted as a chemical modifier and retained AsV which was determined during atomization at 2600°C. By this procedure As"' was selectively removed. The recoveries of As" and AsV were compared from industrial waste- pond- ground- and tap- water samples and were of the order of 90-95%.The direct determination of Cd in sea-water continues to be one of those difficult analyses that generates a different chemical modijier proposed by every analyst who has attempted the determination. Lan (93/2727) proposed the use of sodium hydroxide. It is claimed that this permits a pyrolysis tempera- ture of 1400°C to be used and markedly reduces the back- ground signal caused by the high salt content though a pyrolysis time of 100 s is suggested. The action of the chemical modifier is considered to be via the precipitation of colloidal magnesium hydroxide produced by the addition of 4 pl of 20% m/v sodium hydroxide to 80 p1 of sea-water in the graphite atomizer tube and that trace amounts of Cd were coprecipi- tated with the magnesium hydroxide. Wall atomization was employed at 2100°C.Good agreement was obtained for CASS-1 and CASS-2 sea-water RMs and for an 80 pl sample volume a detection limit (3s) of 0.015 pg 1-' was found. 1.2.5. Developments in technique With a thought provoking lecture entitled 'Analytical measure- ment in GFAAS How much is it correct? Gilmutdinov et al. (93/CSIGAT-G3) questioned the ability of PMTdetectors used in conventional AA spectrometers to provide accurate analyt- ical information. They showed that the absorbances recorded by such systems depended not only on the number of absorbing species but also on their distribution in the atomizer volume. To eliminate this problem they proposed a detection system based on a charged coupled device linear array (CCDLA).The CCDLA was located along the monochromator exit slit and allowed the detection of spatially resolved absorbances. In addition the cross-sectional distributions of intensity of radi- ation from a primary source were shown to be non-uniform and also to affect the measured absorbance. The analytical signal recorded by this system was shown to be proportional to the number of absorbing atoms irrespective of the non- uniformities. This is a novel concept and the publication is awaited with some interest. Simultaneous multi-element ETAAS continues to generate a number of reports. Harnly (94/294) again considered the use of a xenon arc continuum source with linear photodiode array detection (LPDA).This recent paper considered the determi- nation of Cd Cu and Ni. Absorbance noise was found to decrease with wider entrance slits and increase as the number of pixels in the calculation increased. The best LODs were obtained with an entrance slit of 500pm and 16-32 pixels although spectral interference could be a factor with real samples. Gated detection was required to minimize source flicker for larger numbers of pixels and in the presence of background absorbance. Detection limits were found to be comparable to line source AAS. Smith and Harnly (93/CSIGAT-E4) reported that the higher quantum efficiency and application of multiplexing using an LPDA detector improved S/N ratios in the far UV. Detection limits for elements with wavelengths below 250 nm were comparable to line source AAS. These same workers (93/CSIGAT-P1-11) compared the use of pulsed continuum sources with continuous operation to improve UV sensitivity by increasing the intensity of the source.High current pulses were found to increase intensity output and hence improve detection limits. Lifetimes of the pulsed lamps were discussed with reference to normal operation. In contrast to previous work Harnly et al. (93/CSIGAT-P1-3) replaced the LPDA traditionally used in their continuum source device with a charge injection device (CID) to take advantage of the lower noise characteristics of this detector. However problems were encountered from the transmission characteristics of the Cchelle spectrometer used noise from the CID and the controller read rate.Despite this these workers reported that a new system being developed should be able to overcome these problems and provide simultaneous multi-element detection with comparable LODs to conventional AAS. Berglund et al. (94/1184) evaluated a simultaneous multi- element ETAAS system constructed from a transverse-heated graphite atomizer (THGA) with longitudinal Zeeman-effect background correction mounted in an tchelle polychromator. Up to four line sources could be combined using beam splitters. Using multi-element atomization conditions characteristicJOURNAL O F ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 235 R mass values were similar to those obtained with conventional line source ETAAS using a THGA but the LODs were on average an order of magnitude poorer.These resulted from the lower radiation flux through the polychromator and light losses in the optical system though suggestions were made as to how this could be improved. An additional disadvantage was the short working range. The system was applied to the simultaneous determination of Cd Cu and Pb in sea-water samples following preconcentratrion and matrix separation with an FI system. Groll and Niemax (94/751) used six independent diode lasers as primary sources in order to perform simultaenous multi- element determinations of Ba Cs K Li Rb and Sr by ETAAS and Cs K Li and Rb by FAAS. Simultaneous background correction was employed. However it is unclear from the abstract how this was achieved. Limits of detection were similar to those obtained by conventional single-element AA techniques.A further approach to obtain multi-elemental analyses was demonstrated by Nichols et al. (93/CSIGAT-C3) by the appli- cation of hollow cathode FANES with a compact polychromator and two-dimensional dispersion for the determination of Al Ca Cr Cu Fe Mg Mn Ni and Pb in biological samples. Despite the use of various chemical modifiers problems were still encountered with the analysis of urine and these workers concluded that the matrix components such as sodium and magnesium adversely affected the discharge. Foodstuffs were successfully analysed using a palladium modifier following microwave digestion with nitric acid. Papp (93/3660) reported the use of an atomizer for both AE and AA spectrometric analysis. Emission was achieved using a hollow cathode dis- charge presumably in a similar manner to hollow cathode FANES.In further investigations of FAPES Sturgeon et al. (93/CSIGAT-A3) applied a CCD to acquire data on the spatial distribution of the excited state plasma under various discharge conditions. Analyte excitation appears to be incompletely decoupled from analyte atom formation and EIEs distort the discharge but analytical performance was found to be substan- tially enhanced if the system was voltage biased. Sen Gupta (93/3412) applied a commercially available instrument Hitachi 2-9000 for the simultaneous determination of four REEs. This work used pyrolytic graphite coated atomizers with Zeeman-effect background correction and per- mitted the detection of low pg g-' levels of Nd Sm Y and ng 8-l levels of Dy Er Eu Ho Sc Tm and Yb.Good agreement between ICP-AES and ICP-MS was found. The technique was used to analyse SRMs and was applied to the characterization of new geological standards. Heitmann et al. (93/CSIGAT-E2) considered the design and performance characteristics of a LEAFS system designed for operation in the near visible UV spectral range coupled with ETAAS. The system was applied to the determination of Se in whole blood as part of an epidemiological study in Berlin. An LOD of 1.5 ng 1-l of Se was found with a linear range of 5 orders of magnitude. It is not clear why such a non-routine technique was applied to a survey of this nature when this type of determination is performed routinely in many labora- tories by conventional ETAAS or HGAAS.The determination of As and Sb was also examined in aqueous samples. Transverse Zeeman-effect background correction was applied to LEAFS coupled with ETAAS by Irwin et al. (93/3162). These workers employed a modified Perkin-Elmer Zeeman 5100 system designed to give a higher magnetic field than the standard commercial instrument. The Zeeman sigma component energy level splittings were determined for both Co and Pb by measurement of the AF profile. The LODs for Pb and Co were 4 and 500fg respectively and were within a factor of two of those achieved without background correction. The use of background correction was found to have no effect on linear range was capable of correcting for blackbody radiation and background caused by the addition of 20pg of AIC13 to aqueous standards of Co.The technique was applied to the determination of Pb in NIST SRMs such as Estuarine Sediment Coal Fly Ash and Citrus Leaves by slurry analysis with Cali bra tion against aqueous standards with sat isfactory results. Precisions were of the order of 6-14% though no indication was given of the concentration at which these were measured. Owing to the fact that slurry sampling produced matrix interference problems for Co this element was deter- mined after dissolution with the addition of a palladium chemical modifier in Coal Fly Ash and Estuarine Sediment. The topic of linearization of analytical curues obtained by Zeeman-effect ETAAS continues to generate interest and the procedure proposed by L'vov et al.(93/3164) whereby the dip formed in the absorbance at the pulse maximum could be corrected was discussed last year (see J. Anal. At. Spectrom. 1993 8 197R). L'vov (93/CSIGAT-F1) has continued these investigations and has now extended the application of the linearization procedure to the calculation of photometric error in Zeeman-effect ETAAS. In addition to the roll-over absorbance A and a Zeeman sensitivity ratio R three other parameters should be used in the calculations namely the energy value or lamp intensity baseline off-set compensation time (tboc) and the integration time (tint). Using these additional parameters it was shown that the photometric error of the peak area measurements was very small in comparison with sampling and atomization errors.L'vov considered that this explained why the linearization procedure did not degrade the precision of measurements even for signals with roll-over effects. The LODs were calculated to be 10-20 times lower than the characteristic mass with optimized measurement conditions of energy = 65-70 (arbitrary units); tboc of 4 s and tint of 1-2s though it has to be considered that short inte- gration times are not normal for routine ETAAS measurements for many elements. De Loos-Vollebregt et al. (93/CSIGAT-F2) compared the dynamic range of 3-Jield Zeeman-efect measurements in con- trast to the linearization approach of L'vov. These workers considered that the precision required determines the degree of the extension of the analytical curve. Three-field Zeeman- effect measurements were also performed by Chinese workers (94/1051) who found a 10-fold increase in dynamic range and applied the developed system to the determination of Cd and Pb in blood pork liver and urine. Slavin et al.(93/CSIGAT-F3) applied the linearization approach developed by L'vov and co-workers not to extend the linear range of Zeeman ETAAS measurements but to improve the stability of the analytical curve. The procedure was applied to experimental data gener- ated for Ag Cr Cu and T1 as these elements show a wider variation in analytical curves with respect to changes in the experimental conditions than others. These workers found that by correcting the analytical curves for effects due to stray light lamp current spectral slit-width Zeeman-effect correction effects and other effects that resemble stray light the character- istic mass found for any instrument varied by less than 5% from other instruments of similar design.The claimed benefits of this approach are ( i ) fewer calibration standards required (ii) the effect of contamination is more readily apparent as the characteristic mass must be very similar to literature values for instruments of a similar design; and (iii) the opportunity for achieving absolute analysis is increased as instrumental variations can be minimized. Ganeyev et al. (93/3161) compared four Zeeman instrumental conjgurations for the determination of Hg isotopes using either the cell or light source within either a longitudinal or transverse magnetic field. Chinese workers (93/3525) discussed the use of an LPDA as a way of obtaining background corrected data which appears to be based on measuring the atomic absorption coefficients at different wavelengths inside atomic emission line profiles.The technique was used for the determination of Cu in serum and human hair and Rb in soil and leaf samples though more specific details were not available.236R JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 In an interesting move away from measuring atomic lines a number of papers have considered the graphite atomizer as a source for molecular absorption. Ratliff and Majidi (93/2887) designed a system capable of measuring both atomic and molecular absorbance simultaneously with the intention of elucidating atomization mechanisms. This system is based on back-lighting a graphite atomizer with a continuum plasma emission generated by lasers as a source for molecular absorbance.The atomic absorbance is measured by using an HCL as the source that passes through the atomizer in the opposite direction to the continuum light. The laser generated sources produced higher intensities in the UV than conven- tional sources and allowed measurement of the transient molecular species. These workers studied the atomization of nitrates of Al Cu and Pb. Species of these metals were monitored in both tantalum-lined and unlined graphite atomiz- ers. Aluminium showed a number of molecular forms that were unidentified which these workers considered indicated extensive gas-phase reactions. The atomization cycle of Cu was not followed effectively with none of the expected molecu- lar forms being observed and unlike A1 and Pb no AA lines were seen in the molecular spectrum without excess Cu being present.In the case of Pb two molecular species were observed PbO and Pb,. This was confirmed by literature values. Galban et al. (93/3369) also employed the graphite atomizer as a source for what was described as vapour-phase molecular absorption spectrometry to determine As and Sb. This was achieved by the generation of AsCl and SbCl and the measurement of absorbance at 205 and 220 nm respectively. The chlorides were formed during the drying stage using weak hydrochloric acid. No LODs were given but the linear response range was 0.06-3.75 pg of As"' and 0.30-5.0 pg of Sb"'. Although the method was applied to the determination of As in arsenic ore where concentrations are presumably high other halides were found to interfere.Parvinen and Lajunen (94/1137) proposed the determination of organic chlorine by aluminium monochloride molecular absorption spectrometry using a lead atomic line (261.417 nm). This technique employed a carbon rod furnace and deuterium arc background correction. Few reviews have appeared on the topic of absolute analysis although that produced by Zhang and Li (94/1207) containing 48 references will be of more interest to Chinese readers as it is published in Chinese. For investigating and improving the possibility of absolute analysis the construction of a special atomizer by Torsi et al. discussed last year (see J. Anal. At.Spectrom. 1993 8 197R) has now been published (94/1007). The system was applied to the volatile elements Cd Hg and Pb in simple matrices (93/CSIGAT-B3). Absolute analysis was applied by Zheng and Su (94/757) for the determination of Cr in geochemical reference materials. The characteristic mass and atomic absorption coefficient appeared to show less than 10% variation when the atomization temperature was 2500-2800 "C. These same workers (94/1175) determined Ag and Cd in geochemical RMs and compared the results obtained by absolute analysis after calculating the characteristic mass from theoretical considerations with those obtained from a conventional analytical curve. Good agreement was obtained although these workers warned that frequent checking of the characteristic mass values is required as is the use of chemical modification to eliminate interferences. Fundamental optical spectroscopic data (available for absol- ute analysis) were discussed by Doidge (93/CSIGAT-B4) who pointed out that the accuracies of the final results obtained by absolute analysis depend as much on the quality of the data used in the model as on the validity of the model itself. The recent availability of more accurate figures for $values optical damping and hyperfine structure data (much of it produced by astronomers and theorists) would bring the possibility of absolute analysis closer.Ma et al. (93/CSIGAT-Pl-5) con- tinued their investigations into the applications of metallic platforms and coatings to absolute analysis for the determi- nation of Ba Cd Cr Er and Yb in environmental RMs with good agreement being obtained.Hou et al. (94/257) measured the experimental and theoretical characteristic masses of ten elements with a probe atomization system. These workers reported that these values showed an improvement over those obtained from a conventional platform atomizer. LaRue and Tyson (94/982) tackled the problem of tempera- ture calibration in graphite atomizers not at the atomization stage but for the drying and pyrolysis steps. This was achieved by using the known melting-points of a series of compounds over the range 44-220 "C. Russian workers (93/3283) exploited a graphite atomizer for temperature profiling Hg containing minerals. By monitoring the release of Hg using AA as a function of temperature the temperature could be used as a guide to the strength of the Hg bond in the crystals being analysed.In contrast to the comments in the last Update (see J. Anal. At. Spectrom. 1993 8 197R) during the period covered by this Update a number of reports concerning 'fast furnace programmes' have now been published. Hoenig and Cilissen (94/618) compared the use of conventional and fast atomizer programmes for the determination of As Cd Co Cr Cu Mn Ni Pb V and Zn in sea-water soil sediment and plant RMs with either slurry sampling or after acid dissolution. In general for simple matrices good agreement was obtained between the two approaches and with the fast atomizer programme a reduction of up to 40% in the analytical cycle time could be achieved. Differences in peak shape were observed but the use of integrated absorbance measurements generally resulted in acceptable data.However these workers concluded that with difficult matrices such as blood urine and sea-water such samples have to be analysed by conventional atomizer pro- grammes taking advantage of chemical modifiers to reduce or eliminate the effects of the matrices. Another group (93/3413) analysed slurries of diatomaceous earth for Cr Cu and Pb and were able to use rapid atomizer programmes by increasing the drying temperature and removing the ashing and clean- out steps. Li et al. (Spectrochim. Acta Part B 1993 48 1435) applied rapid atomizer programmes with a THGA instrument and found that a total atomizer cycle of 32 s could be achieved for the determination of As Cd Cr Cu Pb Se T1 and V in simple matrices such as acid-digested waters waste waters and biological materials without the need for a pyrolysis step or chemical modifier.For the determination of As and Pb in urine and As in sediments a chemical modifier of palladium and magnesium nitrate and a pyrolysis step was required for accurate results although after careful optimization of the atomizer programme even this programme was only 60 s long. It would appear from the conclusions of Hoenig and Cilissen (94/618) and Li et al. (Spectrochim. Acta Part B 1993 48 1435) that the use of rapid or fast atomizer programmes is beneficial when applied to simple matrices but that even with more complex samples savings in time can be made after careful atomizer programme optimization.1.3. Chemical Vapour Generation Developments in chemical vapour generation are directed at both improving analytical sensitivity and accuracy and provid- ing additional information notably speciation. Improvements in vapour generation are not only of benefit in AAS but also in AES AFS and MS therefore where appropriate experi- ences in vapour generation in the range of spectroscopies will be recorded in this section of the 'Update'. No single outstand- ing development or strong general trend has been identified since the last ASU review (J. Anal. At. Spectrorn 1993,8 197R) and publications once again reflect repetition consolidation and modest developments in technique and understanding.JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL.9 237 R 1.3.1. Hydride generation Though batch processing of samples is widely practised there is accumulating evidence that FI methods benefit from reduced interferences in addition to operational convenience and greater sample throughput. In practice however the choice between batch or FI sample processing will also be influenced by the total number and variety of samples to be analysed. 1.3.1.1. Fundamental studies. Cross interference between hydrideforming elements has been investigated by Borth et al. (93/3145). The amounts of interfering elements required to produce a 10% decrease in the signals from As Bi Sb Se and Te were determined. It was found that a 10% KI solution significantly reduced the interference of Bi''' SeIV and Te" in the determination of Sb"' and the addition of oxygen to the carrier gas reduced the interference of AsV Bi''' Sb"' and Te" in the determination of Se". The efect of solid oxidizers e.g.KBrO or CuO with KH,P04 on the generation of ASH SbH and SnH and on the interference between these hydrides has been studies by HG-AAS (94/646). When KBr03-KH2P04 ( 1 + 4) was used as the oxidizer interferences in the determination of Sn were eliminated. The interference of Cu" in the HG-AF determination of Se has been studied by means of signal shape analysis (93/3960). Mathematical models based on the absence and presence of hypothesized liquid phase interference mechanisms were devised and used in the deconvolution of the observed signal curves. Extension of the approach to analytical applications was suggested.Gas phase efects have been investigated by Welz and Guo (93/3961). The system studied was the decomposition of arsine and stibine in a quartz tube atomizer where low temperature insufficient oxygen and high analyte element concentration led to double peaks. This effect was attributed to hydrogen radical depletion. 1.3.1.2. General developments in instrumentation and tech- nique. A review in Japanese of apparatus for batch and continu- ousflow generation of the hydrides of As Bi Ge Pb Se Sn and Te has been published (94/143). Other workers (93/3056) achieved a 2.5-10 fold improvement in detection limits for the same group of elements when a batch procedure was replaced by an FI system with a sampling frequency of 120 h-l. Two papers by Tsalev et al.(93/2717 93/2718) described the con- struction and use of an on-line microwave pre-treatment system for HG. The system which had a throughput of 10-40 samples h-' was based on a focused microwave oven and a manifold with two coils. A reaction coil and a ballast load coil were placed in the digester to improve long term stability and increase reaction times. Various oxidation mixtures were tested and those based on bromination and persulfate were found to be most appropriate for HG- and cold vapour (CV)-AAS. Conditions were optimized for the determination of As Bi Hg Pb and Sn in urine and natural waters. Limits of detection ranged from 0.01 pg 1-l for Hg with amalgamation to 0.5 pg I-' for As. For the electrochemical generation of hydrides a miniaturized flow cell has been developed (94/557).Platinum electrodes were used and the anode and cathode compartments separated by a Naflon membrane. The small dimensions of the cell minimized reagent consumption and required only small sample volumes (100 pl). The influence of transition metals was investigated and was eliminated for most applications. The efect of quartz tube atomizer design purge hydrogen flow rate and atomizer temperature on HG-AAS determination of As have been investigated by Dedina and Welz (94/46). From experiments and thermodynamic calculations they con- cluded that ( i ) the decay of free analyte atoms was controlled by the pattern of gas flow and in a T-shaped atomizer where there was turbulence at the junction substantial decay occurred; (ii) decayed As species were volatile and could be re-atomized with additional oxygen; and (iii) sensitivity could be enhanced and interference reduced by means of an L-tube atomizer design.In-situ concentration of hydride forming elements on a Pd-coated graphite tube was used with an automatic sampler to achieve a 20-30 fold improvement in sensitivity over conventional HG-AAS for As and Se (94/122). Arsenic and Se were determined in sea-water and detection limits were 30 and 13 pg respectively. 1.3.1.3. Determination of individual elements. In this section of the 'Update' some references will relate to papers where several elements have been determined in such cases the reference will be quoted once only under the element that is first alphabetically. Antimony has been determined in many matrices by several methods all incorporating HG.The concentration of Sb in natural waters is low. A 20-fold preconcentration was achieved using a micro-column packed with quinolin-8-01 immobilized on controlled pore glass (CPG-8Q) chelating ion exchanger and eluted by 4 mol 1-l HCl directly into the HG system (94/376). The detection limit was 1.5 ng 1-'. Chinese workers (94/117) have used solvent extraction with APDC into IBMK followed by HG in ethanolic NaBH which gave a detection limit of 0.68 ng of Sb. An indirect methodfor the determination o f S b based on the release of Hg and the latter's detection by AF has been described by Shi et al. (94/25). The Sb was preconcentrated on a column of sulfhydryl cotton. Methods for the selective determination of Sb'" and SbV have been examined with a view to assessing the bioavailability of Sb in water sediments and soils (94/491).For geological specimens (94/1163) potassium ferrocyanide was used to overcome inter- ferences in the HG determination ofAs Bi and Sb and detection limits of 01,0.05 and 0.04 pg ml-' respectively were obtained. For the determination of Sb in the anode mud leaching liquor following gold extraction the liquor was acidified with HC1 and KI added prior to reaction with KBH4 to convert SbV to Sb"' (93/2172). Little interference was observed and the method was reported to be simple to operate with a detection limit of 0.019 pg m1-I. Hydride generation non-dispersive AFS (94/1259) was used for the determination of As Bi Pb Sb and Sn in iron and steel.The paper was principally concerned with sample dissolution. The sample was dissolved in aqua regia for the determination of As and Sb and in HNO for Bi and Sn. Lead necessitated dissolution in mixed acid followed by extrac- tion into IBMK. There were no interferences from common elements found in steel and recoveries were 90-1 10%. Arsenic infly ash has been determined by direct HG from a slurry ofthe ash (94/160). For the method to be successful the particle size of the ash must be below 8.5 pm. Calibration was by means of aqueous standards and the detection limit was 2.8 ng of As. The procedure for the determination of trace As in river water using NaBH4 bonded on an anion-exchange resin (Diaion SA21A) as devised by Tesfalidot and Irgum (Anal Chem.1989,61 2079) has been automated by Narasaki et al. (94/350). The automated procedure gave satisfactory results provided that silicates were initially decomposed by HF. In several reports on the determination of total As ascorbic acid was used to reduce AsV to As"' (93/3173 94/238 94/1159). As the biological effect of As depends upon the form in which it is present in the sampled medium for some time there has been considerable interest in As speciation. Again this has been achieved by trapping the HG ursine derivatives generated from sea-water in a cold trap of Chromosorb WAW-DMCS (94/482) followed by slow thermal release of the trapped species. By means of the progressive addition of NaBH and pH optimiz- ation similar response factors for AS"' AsV methylarsenic acid and dimethylarsenic acid were achieved. Etched glass beads in a liquid nitrogen trap have also been used to trap HG ursine derivatives (94/481).Detection limits for inorganic mono- and di-methylarsenic lie in the range 19-61 pg of As (19-61 ng 1-l). A study of FI-HG-AAS for the assessment of inorganic arsenic compounds and their metabolites concluded that an analyte addition procedure was necessary if accurate results were to be obtained (93/3084). A sample throughput of 3 min-' and a detection limit of 2.9 pg 1-' were reported.238 R JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 Bismuth and Se have been determined simultaneously by HG gas phase molecular absorption (94/62). The transient signals were measured at 204 and 220 nm (Bi and Se respect- ively) using a diode array detector. The method was used to determine Bi in synthetic ores and pharmaceuticals. The detec- tion limit for Bi was 30 ng.In the determination of Bi by HG-AFS in geological samples thiourea and ascorbic acid were used as masking agents (94/153). The interferences from Au Cu Se and Te were overcome and the tolerance levels to As Hg and Sb greatly increased. Calibration was by the method of analyte addition and recoveries between 91.5 and 98.8% were obtained. Germanium has been determined in environmental samples by FI-HG-AAS (93/3227). The element was preconcentrated in a palladium coated graphite furnace preheated to 400 "C to decompose the hydride and atomized at 2500 "C. Interferences were minimized by use of high acidity (3 mol 1-l HCl) and FI rather than batch processing to give a detection limit of 0.03 pg 1-'.The lowest detection limit 0.004 pg 1-' was obtained in 0.15 mol I-' HCl. The sample throughput rate was 18 h-'. Atomic fluorescence detection was used in the determination of the Ge content of huir (93/2151). The sample was dissolved in HN03-H3P04 with heating and stabilized with 0sv"' in H2S04 prior to HG. The detection limit was 10 ng of Ge which was equivalent to 0.1 pg g-' of hair. In the determination of lead by HG the enhancement of the sensitivity by the presence of oxidants is well established. It has been examined in depth by Wei et al. (93/3560) who found the enhancement by K,Fe(CN) to be higher than that of other oxidants. Chelating agents have also been examined as a means of enhancing sensitivity (93/C3063).Of some 22 reagents examined 1-( 2-pyridylazo)-2-napthol-6-sulfonic acid (PAN-S) was preferred and led to a characteristic concentration of 6.5 ng. Trapping of plumbane in CeIV-KI solution followed by Pb determination with graphite furnace AAS has also been used as a means of enhancing sensitivity (93/3347). A concen- tration factor of =:-fold was achieved and the detection limit was 1 pg 1-' in the original sample. Preconcentration of Pb on chelate forming resin prior to HG has also been used to improve the sensitivity of plumbane-based analytical methods (94/560). The recovery of Pb from the resin was found to be ~ 1 0 0 % and the detection limit was 0.025 pg 1-l for a 1 1 sample treated with 50mg of resin.Methods have been described for the HG-AAS determination of Pb in commercial iron oxide pigments (94/494). No pretreatment was required. Following dissolution with an HCl-HNO mixture or suspension in 0.01 9'0 aqueous solution of sodium hexametaphosphate a solution of (NH,) S208HN03 was added prior to reaction with NaBH,. The detection limits were 0.8 and 0.2 pg g-' for acid dissolution and slurry methods respectively. Selenium is well suited to determination by HG methods. A new design of hydride generator which minimizes HC1 inter- ference and maximizes analytical sensitivity has been described for use with ICP-MS (93/2154). Under optimum conditions the detection limit was 6.4 pg but in routine analysis of biological material it was 1300 pg of Se. A comprehensive study of the interference of As Bi Sb Sn and Te on the HG-AAS determination ofSe has been reported by Welz and Strauss (94/615).They conclude that the hydrogen radical deficiency in the gas phase was the origin of most interference effects. In practical terms batch operations tend to require experimental conditions that produce low densities of hydrogen radicals though the converse is found when FI is used. Further in FI systems owing to kinetic discrimination interferents that react more slowly with the tetraborate than the analyte are carried to waste so that the amount of interferent entering the atomizer may be more than an order of magnitude smaller than with a batch system. Hydride generation methods have been compared with neutron activation (93/3207) and spectro- Juorometry (94/863) and with both methods (93/2195) for the determination of Se in cloud water aerosols foodstuffs and biological samples.Satisfactory agreement was found in all cases. Methods based on HG have also been reported for the determination of Se in human serum and urine with a detection limit of 1.0 and 0.5 ng ml-' respectively (94/742). For Se and Te in nickel the detection limits were 4.5 and 4.0 ng g-' respectively (94/198). Preconcentration of Se has been effected following HG by ( i ) absorption of H,Se in an aqueous solution of 3 mol I-' HClO,-O.O2 mol 1-' KMn0,-0.05 mol 1-' Na oxalate (93/2196) (ii) sweeping H,Se in a stream of argon into a heated Pd coated graphite furnace (200-1000°C) where it was trapped prior to atomization and a detection limit of 20pg was obtained (93/3353) and (iii) by cryogenic trapping of H,Se on silanized quartz wool (93/3090).The last system had a sampling rate of 10 h-' and a detection limit of 2 ng 1-l of Se for a 30 ml sample. Tin has been determined by HG from basic Sn solutions or acidic solutions of EDTA-NaBH (93/3545) with yields of stannane comparable to that from traditional acidic Sn solu- tions. Interference by transition elements in the generation of stannane from NaOH-NaBH solutions was completely elimin- ated when KCN was added to the solution to produce a concentration of 2 x lo- mol 1-' CN- (94/588). Astrac and Pine1 (93/3640) have reviewed HG-GC-AAS methods for the determination of tributyltin ( T B T ) in sediments. Other workers found poor recoveries of butyltin species from environmental samples analysed by HG-GC-AAS (94/786).The effect was particularly associated with sediments having high sulfur hydrocarbon or chlorophyl pigment contents. A method for the determination of tributyltin in sea-water (93/3308) had a detection limit of 3.6 ng 1-l of TBT based on a 500 ml sample. Variable pre-peaks observed by Welz et al. (93/3091) in the FI-HG-AAS determination of Sn were eliminated by the inclusion of 10% H in the Ar purge gas. Best results were obtained when a saturated boric acid solution containing 0.1 mol 1-I HC1 was used for standards samples and carrier solutions. The sensitivity of FI-HG-AAS was improved by trapping on a heated Pd-treated STPF prior to atomization (93/3964). A detection limit of 7 ng 1-' of Sn from a 10ml sample was reported.Solvent extraction of Sn with APDC into IBMK and HG from ethanolic NaBH has been used for the determination of Sn in geological samples (94/1162). 1.3.2. Mercury by cold vapour generation Over the 23 years of the 'Updates' and its predecessor 'Annual Reports on Analytical Atomic Spectroscopy' many papers on the determination of Hg have been recorded and this year is no exception with several dozen more being added to the list. The lowest detection limits of 20 years ago were approximately 0.3 ng of Hg or 50 ng 1-'; present day detection limits are in the region of 1 pg of Hg or 2 ng I-'. In addition to lowering detection limits there have been improvements in precision and in overcoming interferences. Stannous chloride is the most frequently used reducing agent in the CV determination of Hg however I - can interfere with the reduction to Hg'.This problem has been overcome (94/347) by means of apow type electrolytic cell wherein Cr"' was reduced to Cr" which in turn reduced any Hg iodine complex to Hg'. Mercury at the pg 1-' level could be determined without interference in the presence of iodide ions at levels as great as 100 mg 1-l. Iodine inter- ference has also been overcome by use of a reductant containing SnCl and NaBH (94/349). When NaBH is used as the reducing agent in the presence of HNO nitrogen oxides can inhibit the reduction to Hg' by scavenging the reducing agent (94/760). This effect was eliminated by purging the sample with Ar and by use of peak area measurements.The interference produced by Ag Au Co Cu Ni Pb Pd Pt Rh and Ru over a wide concentration range were eliminated by use of cyanide as a complexing agent (94/781). Several authors have reported amalgamation trapping with Au followed by thermal release as a method of preconcentrationJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 239 R to lower detection limits (93/3228 93/3229 94/252 94/720 94/765 94/1005). When detection of Hg by AAS AES and AFS were compared (94/765) the lowest limit of detection and the lowest RSDs were achieved by AAS. Flow injection systems may incorporate an amalgamation trap from which the Hg is released into a separate quartz absorption cell mounted in the sample compartment of a FAAS system (94/252) or the trap may be Au-Pt gauze in a graphite tube furnace (94/1005); the detection limit of the former was 17 pg and of the latter 35 pg.Flow systems require a gas-liquid separator and Hanna et al. (93/3228) have carried out a thorough investigation of the efficiencies of three different designs of separator. The amalgamation step successfully decoupled the kinetic processes occurring in the manifold from the atomic absorption step. Under optimum conditions the best separator achieved 100% efficiency. When SnCl was compared with NaBH as a reducing agent it was concluded that the former is to be preferred to avoid poisoning of the trapping medium. Methods other than amalgamation have been used to pre- concentrate Hg. A microcolumn packed with LiChrospher 100 RP 18 was used by Sarzanini et al.(94/433). The mercury was eluted with aqueous acetonitrile containing APDC and the vapour generated with NaBH,. Other workers (94/355) have used cellulose-hyphan as an ion exchanger for the pre- concentration of Hg. Two methods have been reported for the selective determi- nation of inorganic and methyl Hg. In one (94/422) inorganic Hg was determined by SnC1 reduction and total Hg by reduction after photo-oxidation. The other method (94/327) uses the relatively high afinity of sulfhydryl cotton for MeHg to effect enrichment and separation of Hg species in river water. Solvent extraction with CHC13 (94/286) or toluene (94/489) has been used to separate MeHg from the sample matrix. In the first paper the extract was treated with HN0,-NaBH in DMF to generate Hgo and in the second bromination was used to oxidize the organomercury com- pounds which were extracted into water for FI-CV-AAS determination of HG.1.3.3. Volatile organo-metallic compound generation and metal vapour separation Cadmium has been determined by generating a volatile Cd species probably diethylcadmium using sodium tetraethyl- borate@) (NaTEB) in aqueous solution (94/582). The instru- mentation consisted of a continuous flow vapour generation system with gas-liquid separator interfaced with an argon diluted hydrogen diffusion flame as atom cell. Detection was by non-dispersive AFS with a Cd vapour discharge lamp for excitation and an interference filter with solar blind photomul- tiplier for radiation selection and measurement. Interferences by transition elements were decreased by the use of a citrate buffer as masking agent.The detection limit was 20 ng 1-I. A chromatographic procedure sequential metal vapour elu- tion with detection by AAS has been used for the determination of metals in complex samples (see Section 1.1.5). This approach has been applied to the determination of Cd in river water (94/328) and Nu in biological SRMs (93/3230). Retention times at column and atomizer temperatures of 1870 K were 7.9 15.6 and 6.7 s for Cu Na and Zn respectively. Aluminium Ca and Mg remained in the column. The value of this field of study may be more in the information gained on the behaviour or metal vapours than in providing a practical analytical method. 1.4. Spectrometers This year sees a number of papers relevant to all aspects of spectrometers in AAS including background correction a subject which last year was conspicuously absent.A simple atomic spectrometer most useful one imagines in a teaching context can be built from ‘inhouse components’ and used for measurements in AAS or AES (93/3462). Mermet (94/1250) has made a concise comparison of flame and furnace AAS and ICP/AES; (he believes that interference effects influ- ence ICP the most). 1.4.1. Light sources A general review has appeared (94/1262 in Russian) of the physico-chemical properties of hollow cathode lamps in spec- tral analysis illustrated by their use in AES AAS and AFS. Two papers (94/673,93/4061) refer to the superior performance in AAS of boosted discharge ‘super lamps’ though few analytical data were offered.The lamps contain an additional cathode serving as a source of electrons which excite residual atoms in the ground state and thus decrease the degree of self-absorption within the lamp. L‘vov et al. (94/303) established that differences in the characteristic masses of elements atomized under the same conditions can be related to differences in self-absorption of emission lines in HCLs. With Zeeman-correction spectrometers self-absorption can be checked by measuring the roll-over absorption. Operating conditions for HCLs were recommended with the object of minimizing such sensitivity differences. An atlas of the spectrum of a Pt-Ne HCL has been established over the region 113.0-433.0 nm (93/4050) using both photographic and photoelectric recording.The uncertainty of the photographically measured wavelengths was said to be kO.2 pm while that for photoelectric scans was 1 pm for wavelengths below 203.0 nm and 2 pm at higher wavelengths. 1.4.2. Optics A feature issue of Applied Optics (94/1173) deals with the wide field of optical interference coatings. Early methods of anti- reflection treatment consisted of leaching components in order to reduce the refractive index. Currently the system is to apply a thin film. This can cause problems the reduction of which is the object of newer coating design techniques. A new family of quasi-stigmatic designs for the Rowland circle mounting has been demonstrated by Grange (94/969). Sagittal coma and astigmatism are simultaneously reduced and the spectral performance of the Rowland mount is thereby much enhanced.A ‘double-monochromatic line intensity method’ for estab- lishing the spectral bandwidth of an AA spectrometer has been suggested by Chinese workers (93/4008). 1.4.3. Detectors The use of spectrum-imaging detector arrays in conjunction with a graded transmittance filter requires maintenance of the precise alignment between the array and the filter (93/2876) otherwise the detectors can receive significant amounts of light of unwanted wavelengths. Any gap between these two compo- nents can result in cross-talk between adjacent columns of detectors. A method of depositing the filter directly on to the array patented by NASA (93/2876) prevents problems of misalignment caused by mechanical shock or thermal expansion.Another invention applies the time-delay mode of operation of a charge-coupled device (CCD) photodetector to scanning multi-channel spectrometry (94/1171). The image is scanned along the CCD array in the direction of the internal readout scan and at the same rate as the internal scan and so the image size can exceed the size of the array. This removes the restriction on the wavelength coverage/resolution product imposed by finite array sizes. The patent reviewer claimed this to be an elegant solution to a long standing problem and a ‘nifty idea’. 1.4.4. Continuum source and simultaneous multi-element AAS All aspects of continuum source multielement AAS continue to be vigorously researched by Hardy. The pulsed continuum240 R JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL.9 source was again put forward as the solution to the lack of intensity at wavelengths below 280 nm in AA (93/C3023). Also described (94/294) was a graphite furnace AA spectrometer with linear photodiode array and a 300 W X e arc lamp. The 256 pixel array and associated microcomputer allowed absorbance values to approach a maximum as more pixels were used to cover the absorption profile. Absorbance noise decreased with increasing entrance slit-width and with the number of pixels involved in the calculation. Detection limits for some elements were similar to those given by line source AAS. In another Harnly study (94/320) the effect of spectral bandpass on S/N in this same type of instrument was examined. Arrays with 25- and 50-pm pixel centres and high and low resolution monochromators were included.It was verified that the detection limit in detector noise-limited conditions improved with the square root of the spectral bandpass of the monochromator and with the square root of the pixel width. Fernando et al. (93/3120) described a continuum source spectrometer with flame atomization and photodiode array detection in which the total light throughput had been improved in order to increase the measured source signal. Detection limits similar to those observed with conventional line source systems were produced at wavelengths as low as 223 nm. A monochromator with sufficient resolving power for using first-order diffraction was incorporated thus the spectral bandpass was matched to the width of the absorption line profile.Up to 11 elements were measured in a single spectrum. 1.4.5. Background correction in AAS A 35-page review with many references came from Dulude of Thermo-Jarrell Ash (94/340). Sources of background inter- ference were discussed as were most current means of correction and a comparison between systems was presented. From Varian (94/820) came advice on performance issues which may influence one’s choice of a Zeeman graphite furnace AA spectrometer. An optimized transverse Zeeman design with high data collection rate and polynomial interpolation coupled with a constant temperature zone furnace (presumably the features of the Varian offering in this field) were claimed to provide superior performance. SpeciJic and non-specijc absorption in AAS can both be measured using the classical standard additions method (93/3215).The method was applied both to the initial solution and to a dilution thereof and equations were established for calculating the non-specific absorption and concentrations in the initial solution. The method was verified for measurement of Pb in the presence of NaCl and KI. Two papers on background correction originate from China. In one (94/722) a new device called a self-reversal lamp was used as well as a normal HCL. The former is probably a substitute for the deuterium lamp in the better known con- tinuum method. In the second (94/1065) ‘an arbitrary change in the shape of the Ni line at 231.6 nm’ allowed background- corrected measurement of a number of elements with a double- channel time-resolved circuit though exactly how this happens is not clear.Nevertheless an improvement over other estab- lished methods was claimed. It is a pity that the translations from the originals into the available abstracts seem to have missed the essential points of both of these papers. 1.5. Instrument Control and Data Processing 1.5.1. Instrument control An important aspect of ‘control’ in any analytical technology spectroscopy included is the role of good laboratory practice and methodology and also the reliability and consistency of primary reference materials. A number of relevant papers on these themes have appeared recently from various international sources. A comprehensive review of analytical quality assurance prepared by authors from the Laboratory of the Government Chemist UK (93/2118) covers methodology and reference materials quoting 179 references.Laboratory accreditation by the National Assays Organization in France was discussed (93/3217) and the relevant legislation in that country was described. It was stressed that there should be a fully docu- mented system and laboratory workers must be fully aware of the importance of their role in ensuring quality. A series of papers from the NIST described ‘definitive’ methods in the certification of reference materials (93/2104); the certification development and use of standard reference materials and their role in accurate analytical chemistry (93/2105); and the independent method concept for certifying analytical reference materials (93/2106).As part of this concept methods were compared in an attempt to define the degree of independence required for methods to qualify as being indepen- dent on the basis of such criteria as the measured physical phenomena sample transport preparation standards and calibration. The basic requirements of calibration and control materials in Germany were discussed by Stamm (93/2177) and a concept for quality control of clinical laboratory findings was described bearing in mind the reference methods and medical requirements. Control of trace element determinations in candidate biologi- cal reference materials using an existing CRM was carried out with ETAAS ICP-AES and square wave voltammetry (94/35). The samples were all pressure-digested with nitric acid at 180 “C and 290 “C.Excellent agreement was obtained between found and certified values. Because of its small sample-size requirements solid sampling Zeeman AAS was shown to be a suitable method for the detection of micro-heterogeneity in reference materials (94/647). Some examples of materials where a particular particle-size fraction contains a much higher concentration of a trace element than the rest (the ‘nugget’ effect) were given. The results were treated statistically and the probable origins of the nuggets indicated. The role of a quality coefJicient in assessing the correctness of calibration of ETAAS was discussed by Belgian workers (94/87). A calculation was proposed to determine the quality of fit of a linear calibration established by least-squares regression. The quality coefficient was compared with other models for assessing the acceptability of calibrations.Chinese workers (93/3139) described a new automated AA spectrometer controlled by a microcomputer with a Chinese processing system while Deng (94/139) reviewed many aspects of the application of computers in atomic spectroscopic analy- sis during the last ten years in China. 1.5.2. Data processing The application of electronics and computer techniques to atomic spectrometry were reviewed in a Japanese journal (93/3251) though only one reference was cited. Another review from Swiss workers (94/1113) covered the problems encoun- tered in the calculation of theoretical sensitivities of flame AAS measurements. Thirty four references were given and a simple sensitivity formula was presented and discussed.Shuttler (94/125) described automated quality control features available with Perkin Elmer AAS software. A laboratory information management system (LIMS) and automated data acquisition system (93/3457) was connected to a Zeeman AA spectrometer for the analysis of a complex matrix (human serum). Though presently used more particularly for student training purposes extension into an automated laboratory system is envisaged. In the modelling ofcalibration curves for ETAAS L‘vov et al. (93/3968) proposed the inclusion of parameters such as the fraction of non-absorbed radiation a in the total intensity of radiation in the light source and in Zeeman-effect ETAAS the Zeeman effect sensitivity ratio R. Use of these allowed theJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL.9 241 R derivation of reasonably simple relationships for the lineariz- ation of the working curves. Interpretation of other experimen- tal observations and the optimization of analytical working conditions are also facilitated. A different approach to the processing of the transient signals obtained in ETAAS measurements was described by Hsiech and Pardue (94/694). The transient signals are first integrated and then a pseudo-first-order model is fitted to the time- dependent integrals in order to predict the total signal that would be measured if the atomization process were monitored to completion. This procedure is claimed to reduce the effects of variables such as atomization temperature presumably on the precision of the signals obtained.The relative merits of peak height and peak area measure- ments are the subject of a continuing long term debate. Doidge (94/52) believes that both should be taken into account in atomization mechanism studies (see also Section 1.2 p. 222R). A non-linear robust regression procedure for calibration in flame AAS originated from Poland (94/708). Based on the single median and repeated median methods the procedure is particularly adapted to non-linear calibration cases occurring in FAAS. Advantages over the least-squares method were discussed in the light of results from real samples and appear to be a resistance to the effects of outliers. Two other methods for curve linearization were evaluated by Wang et al. (93/3976) one being based on a mathematical transformation of the absorbance and the other on a correction for stray light. The quality coefficient used as a criterion of linearity indicated that the stray light correction method gave better results.1.5.3. Chemometrics A system for multivariate correction of chemical interferences in hydride generation AAS for Se Sb and As has been described by Heurion et al. (94/229). A training data set of 64 samples constructed according to a factorial design established the effects of chemical interference which were dominated by the mutual interference of As and Se. Workers from the Danish National Institute of Occupational Health (94/650) presented a discussion on a new computer program for integrated quality control method evaluation and projiciency testing as involved in its assessment scheme.The use of the program was illustrated by consideration as an example of the determination of Pb in whole blood (0.3-1.3 pmol 1-l) for a group of 29 laboratories using Zeeman- effect ETAAS. The Kalman filter a mathematical procedure for the reduction of white noise has been further developed by Brindle and Zheng for use with transient signals. The first of two papers (93/2721) reported an investigation into the use of the Kalman filter to improve the accuracy of measurement of transient signals such as those generated by FI systems and in batch determinations of Hg and the hydride-forming elements. The essential features of the Kalman filter were described together with the method used for improving the accuracy of measurement for a one-component system.The second paper (94/291) illustrated the application of the method to the determination of Ge in a computer controlled batch- hydride generator (linked in this case to a d.c. plasma emission spectrometer) and shows how a signal buried in white noise at a ratio of about 1:4 can be successfully and reliably retrieved. The method was considered to be superior to Fourier- transform smoothing. 2. ATOMIC FLUORESCENCE SPECTROMETRY As an analytical method AFS is at its most practical if the analyte element is separated from its sample matrix e.g. by HG or CV or GC. Papers devoted primarily to the generation of the atomic vapour are presented elsewhere in this 'Update'; in this section attention will be directed at the fluorescence process its generation detection and the information it pro- vides.A number of reviews of developments in AFS have been published. One review was devoted to geological applications of AAS and AFS (Chinese) (93/3335) another to electrothermal sample atomization for AAS and AFS (Russian) (93/3269) while a third considered the applications of AFS in environ- mental monitoring (English) (94/342). Technical developments in photon correlation and scattering which could be of rel- evance to AFS in some circumstances have been described (94/963). 2.1. Discharge Lamp-excited Atomic Fluorescence Instruments dedicated to the AF determination of elements for which CV hydride or organometallic compound generation methods are appropriate are increasing in popularity.Such instruments are frequently based on FI vapour generation with metal vapour or HCLs as excitation sources and non- dispersive detection of fluorescence. Such an instrument for Hg determination had a detection limit of 10 pg ml-' (94/102). Boosted discharge HCLs were used in optimization studies for the determination of As and Se (93/3408). Four atom cell designs were investigated and the simplest comprising a 10 cm borosilicate glass tube (3 mm i.d.) supporting a small Ar-H diffusion flame gave the best results. The detection limits were 0.1 and 0.05 pg 1-1 for As and Se respectively. Other workers have used HG-non-dispersive AFS instruments with HCls to determine Ge in geological samples (94/1097) and Se binding in human erythrocyte membrane (94/1233).The operating conditions of an HG-non-dispersive AFS instrument using a microwave excitation source have been examined in depth (94/1095). The factors affecting the deter- mination of Hg and Sb that were examined included micro- wave power temperature location of the quartz furnace interferences elimination of external electromagnetic fields and environmental effects. Ghaffari and Ingle (93/3088 93/3458) have described a microcomputer-based time-multiplex multiple-slit spectrometer based on air-H separated flame atomization and pulsed HCL excitation for use in multi-element analysis. Wavelength selec- tion was by a spectrometer with an array of slits in its focal plane set to transmit radiation from the analyte elements. The transmitted radiation was passed to a single photomultiplier for measurement.Detection limits (pg ml- ') for single element determination were as follows Au 0.2; Cd 0.005; Co 0.03; Fe 0.05; Mg 0.0008; Mn 0.007; Ni 0.04; Pb 1.0; Zn 0.02. Multielement detection limits were up to 5 times worse. Other workers used atomization in an ICP for the AFS analysis of high temperature superconducting materials (94/1016). The operating conditions were optimized for the simultaneous determination of Ba Cu and Y and Cu for which the corre- sponding detection limits were 0.5 0.05 and 1.5 pgml-' respectively. 2.2. Laser-excited Atomic Fluorescence Lasers are used in atomic spectrometry not only as the excitation source in AFS but also to atomize and ionize the analyte and as a diagnostic tool to probe atom vapours. Three242 R JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 reviews have examined these broader aspects of laser usage (93/C3039 93/3779 94/687).Several reports have been concerned with the determination of atomic parameters by laser-induced fluorescence (LIF). When the hyperfine structure constants and isotope shift values for the Cu D1 and D2 line were determined by LIF they were in agreement with literature values (94/976). Strategies for the LIF detection of Na atoms and compounds in high pressure combustors and optically thick environs have been studied by Rosenburger Weiland et al. (94/965),. An excimer laser (248 nm) was used to photodissociate the salt molecules present (NaOH and NaCl) and fluorescence was excited at 330nm and observed at 818 nm; sensitivities at the ppb level were obtained.A theoretical model of the fluorescence dip spectroscopy of the Ag atom produced results which agreed with previous observations provided the laser pulses were sufficiently intense to cause near saturation (94/308). The detection of trace elements by intra-cavity frequency dispersion laser atomic spec- troscopy has been examined theoretically (94/749). The devi- ation of the mean frequency from the mode generated by the atomic vapour provides the analytical signal. A detection limit of 10 ngml-' for Na was established experimentally and it was estimated that the attainable limit may be 0.1-1.0 pg ml-'. A phenomenon originating in the non-linear interaction between atoms and a diode laser field containing wide band noise has been used in high resolution spectroscopy (94/503).The system operates in an absorption mode and by analysing the intensity fluctuations of the light transmitted by the atomic vapour many atomic spectra across a wide wavelength range were observed simultaneously with high resolution and sensitivity. This technique might also lend itself to fluorescence detection. Fluorescence (Raman) spectra of REEs in fluorite have been observed (93/3 100) using a laser microprobe instrument. Excitation was by the UV and visible lines from an argon ion laser. Narrow emission lines (< 1 nm) from the 4f-4f electron transition in individual trivalent REEs (Eu Dy Ho Nd Sm Pr Tb T m ) were observed in the wavelength range 400-900 nm. Detection limits as determined by ICP-MS analy- sis of the fluorite were of the order of 0.05 ppm.It was suggested however that competition between fluorescence emission and radiationless energy transfer processes in common rock-forming minerals may limit the practical appli- cations of this technique. There has been a substantial number of reports of analytical applications of AFS. Two methods of background correction have been described. In one (93/3121) correction was achieved by modulating the dye laser wavelength by means of a piezo- electric pusher driving the wavelength tuning mirror. The laser pulses were synchronized with the pusher movement so that alternate pulses measured the atomic fluorescence signal and the background at a nearby wavelength. The other approach (93/3 162) used the transverse Zeeman-eflect to modulate the absorption of the fluorescence-exciting radiation.The exci- tation source was a pulsed excimer-pumped frequency-doubled dye laser and the atomizer was a graphite furnace within the transverse magnetic field operated at 60Hz. The laser was triggered at 240Hz and synchronized with the field-on field- off conditions of the magnet. The difference between the output signals for those two conditions was the analytical signal. Detection limits were 500fg for Co and 4fg for Pb with a linear dynamic range over 6-7 orders of magnitude. In the determination of REEs by AFS using ICP atomization wave- length selection by monochromator and photomultiplier detec- tion (93/213 1 ) spectral interference i.e. background radiation was reduced by decreasing the laser intensity.Detection limits were comparable with those of ICP-AES. In the determination of Sn by LIF in an air-H flame (93/3317) interferences by organic solvents and acids both enhancement and suppression have been attributed to changes in the concentration of free hydrogen atoms. This effect has been recognized in AAS for at least 25 years (e.g. Harrison W. W. and Juliano P. O. Anal. Chem. 1969 41 1016). Graphite furnace atomization has been employed in the determination of several elements in a variety of matrices. Lead was determined using AF excited by a Cu vapour laser in lake water samples without any sample preparation other than filtration and acidification (93/3255). The detection limit was 0.4 ng 1- Using graphite furnace-LEAF (93/3366) detection limitsfor Sb and Te (10 and 20 fg respectively) were comparable with those obtained by ICP-MS and a thousand times lower than by ETAAS.The linear range was over 6-7 orders of magnitude. The technique was successfully applied to the analysis of Ni alloy SRMs by both direct analysis of the solid and dissolution. Two-step LEAF with graphite furnace atomiz- ation and a palladium chemical modifier has been applied to the determination of Hg to give a detection limit of 90 fg and a linear dynamic range over 5 orders of magnitude (94/750). Vanadium was detected at pg levels from a side-heated integrated contact furnace with LEAFs (94/555). Excitation was by double resonance using visible radiation followed by detection of fluorescence in the UV with a solar blind photomultiplier thus eliminating the effect of scattered exciting radiation.Bromide was determined as aluminium bromide by laser excited non- resonance molecular fluorescence spectrometry at 284.5 nm [with excitation at 278.85 nm (93/2102)]. Barium hydroxide was used as the chemical modifier in the graphite furnace and the detection limit was 45 pg. There are several alternative techniquesfor atomizing samples prior to LEAFs. A planar magnetron discharge has been used to atomize Si from matrices of high purity indium gallium and niobium (94/747). This atomizer generated a greater Si atom density than a previously used hollow cathode discharge. The detection limit was about 1 ng 8-l. Lead was the analyte element in studies of atomization by a planar cathode glow discharge (93/3352).Temporal and spatial profiles of atom distribution showed that rapid sputtering and diffusion distrib- uted Pb throughout the sputtering chamber with maximum fluorescence occurring 100 ms after initiation of the sputtering discharge. The best S/N was obtained from measurements just below the anode. The detection limit set by Pb impurities in the cathode was 2 pg with sample volumes from 0.1 to 1.0 p1. An atomizer consisting of a filament vaporizer and microwave plasma has been used for the LIF determination of trace elements in pure water (94/695). Excitation was with a newly developed pulsed dye laser covering the spectral range 220-740 nm. Sixteen elements were determined mostly with a detection limit below 1 pg 1-l.Laser ablation was used to atomize the sample prior to LIF determination of Pb in stainless steel (94/1144). The ablation crater was 50-300 pm in diameter and 10 pm deep measurements were made 3 mm above the surface. Under optimum conditions the detection limit was 0.05 ppm. 2.3. Studies of Flames Plasmas and Atomic Vapours Using Laser-induced Fluorescence In a review Omenetto (94/1244) has discussed the use of tunable dye lasers in atomic spectroscopy with particular reference to LIF and laser-enhanced ionization or photoioniz- ation in flames plasmas and electrothermal atomizers operated at atmospheric pressure. Detection limits below fg levels are predicted for LIF with furnace atomization. Optical techniques notably LIF used for the study of pro- cesses inflames are usually assumed not to interact significantly with the system being examined.However the LIF detection of atomic oxygen in flames by two-photon excitation is suscep- tible to error resulting from oxygen production by photolysis of N20 and 02. This effect has been overcome and one dimensional imaging of oxygen atoms achieved by replacing a focused beam of laser radiation with a collimated one (94/967). The concentrations of C02 02 N2 CH and H20 in air-CH,JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 243 R flames have been determined by UV Raman scattering of narrow band XeCl excimer laser 308 nm radiation (94/964). Raman cross-section and temperature were also determined simultaneously from the intensity of the Raman bands. Single line and two line techniques based on LIF imaging of NO have been proposed for the determination of temperature distribution in hot gas jets (94/1172).In addition energy transfer in NO LIF was modelled with multi-level rate equations. Plasma diagnostics are facilitated by the use of LIF. The determination of neutral hydrogen in fusion plasmas uses the technique but high levels of stray light from the laser and plasma render the measurement difficult. To overcome the problem harmonic saturated spectroscopy has been used (93/3331). The technique is based on the non-linear response of a saturated atomic system and its ability to discriminate against intrusive noise. The pump laser was modulated such that I = I,sin2wt by selective detection at 4w high rejection of plasma emission and also stray light at the modulation fre- quency of the laser was possible. The ICP has been studied by saturated fluorescence and absorption spectroscopy of the argon 4s3Pl- > 4p3D2 transition (842.5 nm) using a semiconductor (diode) laser (93/2883).Spatially resolved saturation intensities quench rates and fluorescence yields were derived from measurements of the variation in spectral profile characteristics with laser intensity. Measurements from fluorescence and absorption spectroscopy were mutually consistent in the ana- lytical region 10 mm above the load coil. Fluorescence-dip spectroscopy was used to measure the quantum efficiency of fluorescence in an ICP (93/4049). The test elements were Ag Cu Ir and Pb and a steady state model was used to interpret the observations.Measurements of temperature in a d.c. arc jet generated when an H2-CH mixture flowed through an orifice in the anode have been made using LIF of various molecular species and C2 Swan band emission (94/966). The former indicated a Boltzmann gas temperature of 2100&200 K and the latter 5000 K; the difference in temperatures indicates that chemiluminescent reactions are the dominant excitation mech- anisms in the optical emission of the gas jet. 2.4. Coherent Forward Scattering (Atomic Magneto-optical Rotation Spectrometry) No papers describing analytical applications of CFS have been received for review in this section of Update. One paper (93/2210) however described the application of CFS as the basis for a resonance monochromator.The device was essentially a hollow cathode discharge system with the cylindrical cathode fabricated from the analyte element and mounted between crossed polarizers in a transverse magnetic field. The principal of the non-dispersive CFS monochromator was applied to give multi-element capability by mounting several cathodes of different elements in the HCL (94/629). The system was demonstrated using hollow cathodes of stainless steel and Cu to analyse the radiation from a GDL with Fe-Cu alloy cathodes (0 2 5 10mg g-' Cu). A linear calibration curve was produced. Further work on the device (94/628) indicated that spectral interferences from close lying Fe emission lines were rejected more efficiently by the device than by a conven- tional grating monochromator.Line profiles in CFS are much more complicated than those in conventional AAS as they are a consequence of dichroism and birefrigence in addition to Zeeman hyperfine and isotopic structure. An attempt has therefore been made to determine both theoretically and experimentally the profile of the Na D line (94/627). It is apparent that for the time being at least CFS has little to offer the practising analyst. 3. LASER ENHANCED IONIZATION Laser induced ionization has been extensively reviewed by Green and Seltzer (94/339). The review provides an introduc- tion to LEI in flames and other atom reservoirs including the production of the analytical signal and its detection. Detection limits comparable to those of other methods of analytical atomic spectroscopy were reported.Data sheets of information necessary when using resonance ionization spectroscopy in analytical chemistry have been prepared at NIST USA (94/633). Laser-enhanced ionization has been applied to the determination of the lifetimes of atomic metastable states in flames (93/2879). The lifetime of the lowest metastable state of Au in an air-C,H2 flame was found to be between 0.6 and 8.8 ps depending upon the stoichiometric conditions in the probe volume. The resonant multiphoton ionization character- istics of Hg atoms at low pressure have been studied (94/919). Stark shifts linewidth changes non-linearity and autoioniz- ation were observed and the information used to derive the optimum conditions to ionize atoms efficiently. Sodium and Li were used as model species for determining ionization yield and collisional ionization in an air-C2H2 flame (94/1003).Measurements were made under optical saturation conditions and the yields were 0.35 and 0.78 for Na and Li respectively. The collisional ionization rate for the latter was 2 x lo8 s-l. A graphite furnace was used to vaporize samples into an Ar stream for ionization in a minijlame burner. Excitation was provided by dual Nd YAG pumped dye lasers operating at 30 Hz. Detection limits for In Mg and T1 ranged from 1 to 260fg. Using a new technique lithium isotopes have been determined by Doppler-free continuous-wave f e l d ionization spectroscopy (94/1OO2). Stepwise laser excitation was used to excite atoms into long-lived Rydberg states. The excited atoms were carried from the irradiation zone in a thermal atom beam into the region of the ionization field.The detection limit was 20fg for 7Li and isotope selectivity for 6Li:7Li was better than 4 x Single and double resonance LEI of phosphorus monoxide were compared for the determination ofP in an air-C,H2 flame (93/2209). Single resonance measurements were carried out at 320.24 nm and double resonance at 324.64 nm and 557.96 nm. The detection limit of the former was 200 ng and of the latter 20 ng. For the determination of K in water by LEI an air-Ar-C2H2 flame was reported to give a higher signal than the conventional air-C,H flame (94/415). The detection limit for K by flame LEI (94/522) was improved by an order of magnitude from 1.0 to 0.1 pg 1-' by using a transition from the first excited atomic state with 580.2 radiation in place of the resonance line at 766.5 nm and an air-C2H2 flame in place of air-H,. A new type of split-cathode was used for the measurements.Flame LEI was compared with graphite furnace LIF for the determination of Cr in water (93/2878). The detection limit by LEI was 2 pg 1-' and by LIF 0.5 pg 1-l. These values were limited by contamination from the burner head and the graphite furnace. Methods for improving sensi- tivity by a two-step LEI excitation scheme and by reducing the effect of fluctuations in black body radiation of LIF measurements were proposed.244 R JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 LOCATION OF REFERENCES The full list of references cited in this Update have been published as follows 93/2094-93/2710 J.Anal. At. Spectrom. 1993 8( 5) 239R-262R. 93/2711-93/3353 J. Anal. At. Spectrom. 1993 8(7) 313R-336R. 93/3354-93/413 1 J. Anal. At. Spectrom. 1993 8( 8) 377R-404R. 94/1-94/614 J. Anal. At. Spectrom. 1994 9( l) 1R-23R. 94/615-94/960 J. Anal. At. Spectrom. 1994 9(2) 73R-85R. 94/961-94/1264 J. Anal. At. Spectrom. 1994 9(4) 135-146R. References have been made in this Update to the following papers presented at the XXVIII Colloquium Spectroscopicurn Internationale (CSI) Post-Symposium on Graphite Atomizer Techniques York UK July 5-7 1993. 93/CSIGAT-A 1 93/CSIGAT-A2 93/CSIGAT-A3 93/CSIGAT-B 1 93/CSIGAT-B2 93/CSIGAT-B3 93/CSIGAT-B4 93/CSIGAT-C2 9 3/C SIGAT-C3 93/CSIGAT-D1 93/CSIGAT-D2 93/CSIGAT-D3 93/CSIGAT-E1 Holcombe J. A.Scheie A. ETA-MS can we conduct micro-ultratrace analysis without an ICP ionizer? (Univ. Texas Austin TX 78712 USA) Rojas D. Study of nickel electrothermal atomization. (Univ. Los Andes Merida Apartado 5 101 A Venezuela) Sturgeon R. E. Pavski V. Chakrabarti C. L. Imaging the FAPES source. (National Research Council of Canada Ottawa Ontario Canada K1A OR9) Styris D. L. Brown G. N. Harris J. A. Bulk diffusion and graphite atomizers. (Pacific Northwest Laboratory Richland WA 99352 USA) Schlemmer G. Lehmann R. Ortner H. M. Rohr U. Performance criteria and test pro- cedures for new components and materials in electrothermal AAS. (Bodenseewerk Perkin- Elmer GmbH D-88647 Uberlingen Germany) Torsi G. Fagioli F. Reschiglian P. Locatelli C. Absolute analysis in electrother- mal atomization atomic absorption spec- troscopy-recent results.(Univ. Bologna Bologna Italy) Doidge P. S. Fundamental optical spectro- scopic data for absolute analysis using graphite furnace atomic absorption methods. (Varian Optical Spectroscopy Instruments P.O. Box 222 Springvale Victoria 3 171 Australia) Thomassen Y. Martinsen I. Kleiner J. Radziuk B. Sinemus H. W. Stabel H. H. Combined hydride generation electrothermal atomic absorption spectrometry for determi- nation of antimony in body fluids. (National Inst. Occup. Health Oslo Norway) Nichol R. Littlejohn D. Chen T. Ludke C. Evaluation of hollow cathode FANES for multi-element analysis of biological samples. (Dept. Pure Appl. Chem. Univ. Strathclyde Glasgow UK G11XL) Miller-Ihli N. High accuracy ultrasonic slurry GFAAS determinations.(US Dept. Agric. Nutr. Comp. Lab. Beltsville MD 20705 USA) Kurfiirst U. Pauwels J. Spectral interferences on lead in Zeeman atomic absorption spec- trometry by S2 molecules. (Univ. Fulda D-6400 Fulda Germany) Bermejo-Barrera P. Barciela-Alonso M. C. Yebra-Biurrun M. C. Bermejo-Barrera A Slurry sampling for determination of lead in marine sediments by ETAAS. (Fac. Chem. Univ. Santiago de Compostela Santiago de Compostela Spain) Hinds M. W. Brown G. N. Styris D. L. 93/CSIGAT-E2 93/CSIGAT-E4 93/CSIGAT-F1 93/CSIGAT-F2 93/CSIGAT-F3 93/CSIGAT-PI-3 93/CSIGAT-PI-5 93/CSIGAT-PI- 10 93/CSIGAT-PI-11 Comparison of silicon determination in gold by solution and solid sample graphite furnace atomic absorption spectrometric methods. (Royal Canadian Mint Ottawa Ontario Canada KIA OG8) Heitmann U.Sy T. Hese A. Schoknecht G. High sensitive detection of selenium arsenic and antimony by laser-excited atomic fluor- escence spectroscopy using electrothermal atomization. (Tech. Univ. Berlin Inst. Stahlungs- und Kernphys. Berlin Germany) Smith C. M. M. Harnly J. M. Determination of elements in the far UV using continuum source atomic absorption spectrometry and a linear photodiode array detector. (US Dept. Agric. Nutr. Comp. Lab. Beltsville MD 20705 USA) L’vov B. V. Precision and detection limits in Zeeman GFAAS. (St. Petersburg Tech. Univ. St. Petersburg 195251 Russia) de Loos-Vollebregt M. T. C. de Koning M. J. Padmos J. Dynamic range of analytical curves in Zeeman graphite furnace AAS. (Delft Univ. Technol.Lab. Mat. Sci. Delft The Netherlands) Slavin W. L’vov B. V. Su E. Yuzefovsky A. I. McCaffrey J. T. Michel R. G. Linear working curves and stable calibration for furnace AAS. (Bonaire Technologies Ridgefield CT 06877 USA) Harnly J. M. True B. Denton M. B. Graphite furnace AAS using a continuum source with a charge injection device (CID) detector. (US Dept. Agric. Nutr. Comp. Lab. Beltsville MD 20705 USA) Ma Y. Li Z. Li Y. Wang J. Application of metallic platform to study the possibility of standardless and absolute analysis in GFAAS. (Inst. Anal. Meas. Chinese Research Acad. Environ. Sci. Beijing China) Cabon J. Y. Le Bihan A. Direct deter- mination of zinc in sea-water using electro- thermal atomization atomic absorption spectrometry with Zeeman-effect background correction.Chemical and spectral interference effects. (Unite Rech. Assoc. Au CNRS No. 322 Univ. Bretagne Occidentale Brest-Cedex France) Smith C. M. M. Harnly J. M. Evaluation of the CERMAX xenon arc lamp for pulsed continuum source atomic absorption spec- trometry. (US Dept. Agric. Nutr. Comp. Lab. Beltsville MD 20705 USA)JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 245 R 93/CSIGAT-P1-12 Pawlick H.,. Eichardt K. Streck S. Comparative investigations on platform vari- (Dept. Chem. Univ. Kentucky Lexington KY 40506 USA) ants for a new transverse heated AAS graphite D-6900 Jena Germany) furnace system. (Carl-Zeiss- Jena GmbH 93/CSIGAT-G2 Jackson K. W. Qiao H. Effects Of surface interaction and heating rate on atomization of comer. (Sch. Public Health.State Univ. 93/CSIGAT-P2-13 Yuan D. Shuttler I. L. Portala F. New york Albany NY 12201-0509 USA) Comparison of on-line preconcentration aluminium by directly coupled flow injection Zakharov Yu. A. Analytical measurement in ETAAS. (Dept. Chem. Xiamen Univ. GFAAS How much is it correct? (Dept. Phys. Xiamen China) Univ. Kazan Kazan 420008 Russia) column materials for the determination of 93/CSIGAT-G3 Gilmutdinov A. Kh. Nagulin K. Yu. 93/CSIGAT-P2-14 Bozsai G. Melegh M. Varga J. Interference- free determination of silver in water by transversely heated graphite furnace atomic absorption spectrometry. (Nat. Inst. Hyg. P.O. Box 64 Budapest Hungary) Majidi V. Xu N. Robertson J. D. Eloi C. Probing chemical reactions in electrothermal atomizers gas phase and surface chemistry.93/CSIGAT-G1 93/CSIGAT-H2 Tittarelli P. Biffi C. Formation and stability of molecular species in electrothermal atomiz- ers. (Stazione Sperimentale per i Combustibili San Donato Mil. Italy) McAllister T. Gaseous oxides from nitrate decomposition in graphite furnaces. (CSIRO Clayton Div. Mat. Sci. Technol. Victoria 3168 Australia) 93/CSIGAT-H3 Abbreviated forms of the literature references quoted (excluding those to Conference Proceedings) are given on the following pages for the convenience of the readers. The full references names and addresses of the authors and details of the Conference presentations can be found in the appropriate issues of JAAS cited above. Abbreviated List of References Cited in Update 931578 Anal. Sci. 1991 7 91. 9312080 J.Anal. At. Spectrom. 1992 7 1075. 9312101 Fresenius’ J. Anal. Chem. 1992 343 773. 9312102 Talanta 1991 38 1071. 9312104 Spectrochim. Acta Part B 1991 46 1571. 9312105 Spectrochim. Acta Part B 1991 46 1577. 9312106 Spectrochim. Acta Part B 1991 46 1583. 9312118 Analyst 1991 116 975. 9312131 Anal. Chim. Acta 1992 258 73. 9312148 Lihua Jianyan Huaxue Fence 1992 28 102 104. 9312150 Lihua Jianyan Huaxue Fence 1992,28 113.9312151 Lihua Jianyan Huaxue Fence 1992 28 116 118. 9312154 Anal. Chem. 1992 64 724. 9312171 Fenxi Shiyanshi 1992 11(3) 43. 9312172 Fenxi Shiyanshi 1992 11(3) 45. 9312177 Eur. J. Clin. Chem. Clin. Biochem. 1991 29 247.9312181 Fresenius’ J. Anal. Chem. 1991,341,586.9312183 Fresenius’ J. Anal. Chem. 1992 342 692. 9312186 Fresenius’ J. Anal. Chem. 1992 342 924.9312188 Fresenius’ J. Anal. Chem. 1992,342,936.9312189 Fresenius’ J. Anal. Chem. 1992 342 941. 9312195 Bunseki Kagaku 1992 41 T77. 9312196 Bunseki Kagaku 1992,41,263.93/2197 Bunseki Kagaku 1992 41 317. 9312199 Zh. Anal. Khim. 1992 47 271. 9312200 At. Spectrosc. 1992 13 1. 9312209 Anal. Chem. 1991 63 1607. 9312210 Anal. Chem. 1991 63 1747. 9312691 Magy. Kem. Foly. 1991 97 128. 9312692 Magy. Kem. Foly. 1991 97 241. 9312715 Analyst 1992 117 1599. 9312717 Analyst 1992 117 1729.9312718 Analyst 1992 117 1735.9312721 Analyst 1992 117 1925. 9312726 Analyst 1993 118 85. 9312727 Analyst 1993 118 189. 9312730 Anal. Proc. 1992 29 399. 9312731 Anal. Proc. 1992 29 436. 9312876 Appl. Opt. 1993 32 780. 9312878 Appl. Opt. 1993 32 867. 9312879 Appl. Opt. 1993 32 899. 9312880 Appl.Opt. 1993,32 907. 9312881 Appl. Opt. 1993,32,919. 9312883 Appl. Opt. 1993,32,948. 9312885 Anal. Chem. 1992 64 2596. 9312887 Anal. Chem. 1992 64 2743. 9312896 Anal. Chem. 1992 64 3101. 9312897 Anal. Chem. 1992 64 3197. 9313079 At. Spectrosc. 1992 13 178. 9313084 Talanta 1992 39,469. 9313086 Talanta 1992,39 581. 9313088 Talanta 1992 39 749. 9313090 Talanta 1992 39 1089. 9313091 Talanta 1992 39 1097. 9313092 Talanta 1992 39 1219. 9313093 Talanta 1992 39 1293. 9313100 Geochim. Cosmochim. Acta 1992,56,2713.93/3103 Anal. 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ISSN:0267-9477    

DOI:10.1039/JA994090213R

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

248 R JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 Glossary of Abbreviations Whenever suitable elements may be referred to by their chemical symbols and compounds by their formulae. The following abbreviations are used extensively in the Atomic Spectrometry Updates. a.c. AA AAS AE AES AF AFS AOAC APDC ASV BCR CCP CMP CRM cv cw d.c. DCP DDC DMF DNA ECD EDL EDTA EDXRF EIE EPMA ETA ETAAS ETV EXAFS FAAS FAB FAES FAFS FANES FAPES FI FPD FT FTMS GC GD GDL GDMS Ge ( Li) HCL h.f. HG HPGe HPLC IAEA IBMK ICP ICP-MS alternating current atomic absorption atomic absorption spectrometry atomic emission atomic emission spectrometry atomic fluorescence atomic fluorescence spectrometry Association of Official Analytical Chemists ammonium pyrrolidinedithiocarbamate anodic-stripping voltammetry Community Bureau of Reference capacitively coupled plasma capacitively coupled microwave plasma certified reference material cold vapour continuous wave direct current d.c.plasma diethyldithiocarbamate N N-dime th ylformamide deoxyribonucleic acid electron capture detection electrodeless discharge lamp ethylenediaminetetraacetic acid energy dispersive X-ray fluorescence easily ionizable element electron probe microanalysis electrothermal atomization electrothermal atomic absorption spectrometry electrothermal vaporization extended X-ray absorption fine structure flame AAS fast atom bombardment flame AES flame AFS furnace atomic non-thermal excitation furnace atomization plasma excitation flow injection flame photometric detector Fourier transform Fourier transform mass spectrometry gas chromatography glow discharge glow discharge lamp glow discharge mass spectrometry lithium-drifted germanium hollow cathode lamp high frequency hydride generation high-purity germanium high-performance liquid chromatography International Atomic Energy Agency isobutyl methyl ketone (4-methylpentan-2-one) inductively coupled plasma inductively coupled plasma mass spectrometry (ammonium pyrrolidin- 1-yl dithioformate) spectroscopy spectrometry spectrometry ID IR IUPAC LA LC LEAFS LEI LMMS LOD LTE MECA MIP MS NAA NaDDC NIES NIST NTA OES PIGE PIXE PMT PPb PPm PTFE QC r.f.REE(s) RIMS RM RSD SEC SEM SFC Si( Li) SIMAAC SIMS SR SRM SSMS STPF TCA TIMS TLC TMAH TOP0 TXRF u.h.f. uv VDU vuv WDXRF XRF S/B SIN isotope dilution infrared International Union of Pure and Applied Chemistry laser ablation liquid chromatography laser-excited atomic fluorescence spectrometry laser-enhanced ionization laser-microprobe mass spectrometry limit of detection local thermal equilibrium molecular emission cavity analysis microwave-induced plasma mass spectrometry neutron activation analysis sodium diethyldithiocarbamate National Institute for Environmental Studies National Institute of Standards and nitrilo triace tic acid optical emission spectrometry particle-induced gamma-ray emission particle-induced X-ray emission photomultiplier tube parts per billion parts per million pol ytetrafluoroethylene quality control radio frequency rare earth element(s) resonance ionization mass spectrometry reference material relative standard deviation signal to background ratio size-exclusion chromatography scanning electron microscopy supercritical fluid chromatography lithium-drifted silicon simultaneous multi-element analysis with a continuum source secondary ion mass spectrometry signal to noise ratio synchrotron radiation Standard Reference Material spark source mass spectrometry stabilized temperature platform furnace trichloroacetic acid thermal ionization mass spectrometry thin-layer chromatography tetramethylammonium hydroxide trioctylphosphine oxide total reflection X-ray fluorescence ultra-high frequency ultraviolet visual display unit vacuum ultraviolet wavelength dispersive X-ray fluorescence X-ray fluorescence Technology

ISSN:0267-9477    

DOI:10.1039/JA994090248R

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

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Croall N. Westacott M. Richards D. C. Depth profiling study of scale formed on high silicon content steels using GDMS Spec. Pub1.-R. SOC. Chem. 1993 124(Applications of Plasma Source Mass Spectrometry 11) 140. (Dept. Chem. Univ. Coll. Swansea Swansea UK SA28PP). van Straaten M. Gijbels R. Fundamental aspects of an analytical glow discharge Spec. Pub1.- R . SOC. Chem.1993 124(Applications of Plasma Source Mass Spectrometry 11) 130. (Dept. Chem. Univ. Antwerp B-2610 Wilrijk-Antwerp Belgium). Ekstroem H. Gustavsson I. Application of ICP-MS to steel other metals and metal alloys Spec. Pub1.- R. SOC. Chem. l993,124(Applications of Plasma Source Mass Spectrometry 11) 150. (Swed. Inst. Met. Res. S 114 28 Stockholm Sweden). 941285 8. 9412859. 9412860. 9412861. 9412862. 9412863. 9412864. 9412865. 9412866. 94/2 8 67. Angelini E. Rosalbino F. Atzeni C. Virdis P. F. Bianco P. Lead isotope analysis of Nuragic bronzes and copper ores by ICP-MS Spec. Pub1.-R. SOC. Chem. 1993 124(Applications of Plasma Source Mass Spectrometry 11) 165. (Politec. Torino Torino Italy). Betti M. Garcia Alonso J. I. Arbore P. Koch L. Sato T. Analysis of highly radioactive liquid samples by ICP-MS Spec.Pub1.-R. SOC. Chem. 1993 124(Applications of Plasma Source Mass Spectrometry IT) 205. (Inst. Transuranium Elem. Comm. Eur. Commun. 7500 Karlsruhe Germany). Koropchak J. A. Liquid sample introduction to ICP spectrometries Spectroscopy (Eugene Oreg.) 1993 8(8) 20. (Nutrient Compos. Lab. U.S. Dept. Agric. Beltsville MD 20705 USA). To H. Niino Y. Arita M. Analysis for trace elements in salt crystals by secondary ion mass spectrometry Symp. Salt [Proc.] 1993 7 555. (Sea Water Sci. Res. Lab. Japan Tobacco Inc. Odawarashi Japan). Meng X.-h. Dilution ratio in isotope dilution mass spectrometry analysis Tungweisu 1992 5 232. (Beijing Res. Inst. Chem. Eng. Metall. Nucl. Ind. Beijing China 101 149). Smirnov V. K. Simakin S. G. SIMS depth profiling of implanted layers in silicon under nitrogen ion (N,') bombardment Vucuum 1993 44 885.(Inst. Microelectron Yaroslavl Russia 150007). Huang R.-b. Su Z.-h. Zheng LA. Wang Y.-j. Qing Q.-z. Laser plasma mass spectrometry of YBa,Cu,O - x superconducting sample Wuli Huaxue Xuebao 1993,9 823. (Dept. Chem. Xiamen Univ. Xiamen China 361005). He H.4 Du A. Zou X.-q. Sun Y.-l. Yin N.-w. Study on rhenium-osmium isotope systematics by using inductively coupled plasma mass spectrometry [ICP-MS] and its application to molybdenite dating Yankuang Ceshi 1993 12 161. (Inst. Rock Miner. Anal. Minist. Geol. Miner. Resourc. Beijing China 100037). Magomevbekov E. P. Krupenchenko A. V. Laser mass spectrometry study of segregation processes in intermet- allic compounds of the type ZrB (B=V Cr Mn) Zh.Neorg. Khim. 1993 38 1732. (Mosk. Khim.-Tekhnol. Inst. Moscow Russia). Chang W. Z. Wittry D. B. Calculation of X-ray fluorescence intensities for convergent X-ray beams Microbeam Anal. 1994 3( l) 23. (Dept. Mater. Sci. Eng. Univ. Southern California Los Angeles CA 90089-024 1 USA).JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 265 R 9412850. 941285 1. 9412852. 9412853. 9412854. 94/28 5 5. 94f2856. 94/28 57. extracts Soil Sci. SOC. Am. J. 1993 57 410. (Europa Sci. CreweICheshire UK CW1 1ZA). Stevens R. J. Laughlin R. J. Atkins G. J. Prosser S. J. Automated determination of nitrogen-1 5-labelled dinitrogen and nitrous oxide by mass spectrometry Soil Sci. SOC. Am. J. 1993 57 981. (Dept. Agric. North. Ireland Belfast UK BT9 5PX).Probst T. Zeh P. Kim J. I. Comparison of ICP-MS with neutron activation analysis for multielement determination in groundwaters Spec. Pub1.- R. SOC. Chem. 1993 124(Applications of Plasma Source Mass Spectrometry 11) 29. (Inst. Radiochem. Tech. Univ. Munchen D-8046 Garching Germany). Vandecasteele C. Van den Broeck K. Dutre V. Cooreman H. Environmental applications of ICP-MS using a PQe spectrometer Spec. Pub1.-R. SOC. Chem. 1993 124(Applications of Plasma Source Mass Spectrometry 11) 48. (Dept. Chem. Eng. Kathol. Univ. Leuven 3001 Louvain Belgium). Fecher P. Leibenzeder M. Zizek C. Decomposition temperature and its influence on trace element determi- nation by ICP-MS and ICP-AES Spec. Pub1.-R. SOC. Chem. 1993 124(Applications of Plasma Source Mass Spectrometry 11) 83.(Landesuntersuchungsamt Das Gesundheitswesen Nordbayern D-8520 Erlangen Germany). Yin M. Yin N.-w. Determination of trace elements in 4 Chinese biogeochemical reference materials by ICP-MS Spec. Pub1.-R. SOC. Chem. 1993 124(Applications of Plasma Source Mass Spectrometry 11) 115. (Inst. Rock and Miner. Anal. Beijing China 1 00037). Pichilingi M. Mason R. S. Gilmour D. Croall N. Westacott M. Richards D. C. Depth profiling study of scale formed on high silicon content steels using GDMS Spec. Pub1.-R. SOC. Chem. 1993 124(Applications of Plasma Source Mass Spectrometry 11) 140. (Dept. Chem. Univ. Coll. Swansea Swansea UK SA28PP). van Straaten M. Gijbels R. Fundamental aspects of an analytical glow discharge Spec. Pub1.- R . SOC. Chem. 1993 124(Applications of Plasma Source Mass Spectrometry 11) 130.(Dept. Chem. Univ. Antwerp B-2610 Wilrijk-Antwerp Belgium). Ekstroem H. Gustavsson I. Application of ICP-MS to steel other metals and metal alloys Spec. Pub1.- R. SOC. Chem. l993,124(Applications of Plasma Source Mass Spectrometry 11) 150. (Swed. Inst. Met. Res. S 114 28 Stockholm Sweden). 941285 8. 9412859. 9412860. 9412861. 9412862. 9412863. 9412864. 9412865. 9412866. 94/2 8 67. Angelini E. Rosalbino F. Atzeni C. Virdis P. F. Bianco P. Lead isotope analysis of Nuragic bronzes and copper ores by ICP-MS Spec. Pub1.-R. SOC. Chem. 1993 124(Applications of Plasma Source Mass Spectrometry 11) 165. (Politec. Torino Torino Italy). Betti M. Garcia Alonso J. I. Arbore P. Koch L. Sato T. Analysis of highly radioactive liquid samples by ICP-MS Spec.Pub1.-R. SOC. Chem. 1993 124(Applications of Plasma Source Mass Spectrometry IT) 205. (Inst. Transuranium Elem. Comm. Eur. Commun. 7500 Karlsruhe Germany). Koropchak J. A. Liquid sample introduction to ICP spectrometries Spectroscopy (Eugene Oreg.) 1993 8(8) 20. (Nutrient Compos. Lab. U.S. Dept. Agric. Beltsville MD 20705 USA). To H. Niino Y. Arita M. Analysis for trace elements in salt crystals by secondary ion mass spectrometry Symp. Salt [Proc.] 1993 7 555. (Sea Water Sci. Res. Lab. Japan Tobacco Inc. Odawarashi Japan). Meng X.-h. Dilution ratio in isotope dilution mass spectrometry analysis Tungweisu 1992 5 232. (Beijing Res. Inst. Chem. Eng. Metall. Nucl. Ind. Beijing China 101 149). Smirnov V. K. Simakin S. G. SIMS depth profiling of implanted layers in silicon under nitrogen ion (N,') bombardment Vucuum 1993 44 885.(Inst. Microelectron Yaroslavl Russia 150007). Huang R.-b. Su Z.-h. Zheng LA. Wang Y.-j. Qing Q.-z. Laser plasma mass spectrometry of YBa,Cu,O - x superconducting sample Wuli Huaxue Xuebao 1993,9 823. (Dept. Chem. Xiamen Univ. Xiamen China 361005). He H.4 Du A. Zou X.-q. Sun Y.-l. Yin N.-w. Study on rhenium-osmium isotope systematics by using inductively coupled plasma mass spectrometry [ICP-MS] and its application to molybdenite dating Yankuang Ceshi 1993 12 161. (Inst. Rock Miner. Anal. Minist. Geol. Miner. Resourc. Beijing China 100037). Magomevbekov E. P. Krupenchenko A. V. Laser mass spectrometry study of segregation processes in intermet- allic compounds of the type ZrB (B=V Cr Mn) Zh. Neorg. Khim. 1993 38 1732. (Mosk. Khim.-Tekhnol.Inst. Moscow Russia). Chang W. Z. Wittry D. B. Calculation of X-ray fluorescence intensities for convergent X-ray beams Microbeam Anal. 1994 3( l) 23. (Dept. Mater. Sci. Eng. Univ. Southern California Los Angeles CA 90089-024 1 USA).

ISSN:0267-9477    

DOI:10.1039/JA994090249R

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 815 Thermospray Nebulization as Sample Introduction for Inductively Coupled Plasma Mass Spectrometry Hans Vanhoe Luc Moens and Richard Dams Laboratory of Analytical Chemistry University of Ghent Institute for Nuclear Sciences Proefiuinstraat 86 B-9000 Ghent Belgium A sample introduction system consisting of a thermospray nebulizer and a desolvating unit was coupled to an inductively coupled plasma mass spectrometer. Several parameters were optimized including the sample uptake rate the power delivered to the capillary tube the temperature of the aerosol and of the cooling-water the carrier gas flow rate and the r.f. power. Under optimized conditions the sensitivity obtained with the thermospray system is a factor of 10 higher than with a pneumatic nebulizer combined with a spray chamber. The increase was observed for the following elements over the whole mass range Be Al Sc Co In Gd TI Th and U.Since similar background levels 10-40 counts s-' were observed better detection limits could be achieved (from 0.19 ng I-' for U to 1.3 ng I-' for Be). The relative standard deviation (RSD) on analyte signals for a short-term stability test (10 min) is between 3 and 8%. These values can be improved to less than 4% by the use of internal standardization. No drift in analyte signal during several hours was observed. The levels of oxide (MO+:M+) and doubly charged (M2+:M+) ions obtained with the thermospray system are about a factor of 2.5 lower than those obtained with the pneumatic system. Consequently the oxide ion levels for elements with the highest MO bond strength and the doubly charged ion levels for elements with the lowest second ionization energy are not above 1%.Keywords Inductively coupled plasma mass spectrometry; sample introduction; thermospray nebulization The analytical performance of an inductively coupled plasma (ICP) mass spectrometer is strongly related to the sample introduction system. As expressed by Browner and Boorn,' sample introduction is the Achilles' heel of atomic spectroscopy. Most of the ICP mass spectrometers are equipped with a sample introduction system consisting of a nebulizer and a spray chamber. Most often pneumatic nebulizers are chosen because of their simple construction. The poor nebulization efficiency inherent in pneumatic nebulizers (typically 1-2%) is however a major drawback and restricts the sensitivity of ICP Mass Spectrometry (ICP-MS).Consequently alternative nebu- lizers with an improved nebulization efficiency have been evaluated for introduction of solutions into an ICP-MS system e.g. ultrasonic neb~lizer~.~ direct injection nebulizer4 and hydraulic high pressure nebulizer.' In the past few years the use of thermospray nebulization to increase the efficiency of the sample introduction system was investigated. Originally used as an interface between liquid chromatography and mass spectrometry,6 thermospray nebul- ization was introduced as a sample introduction system for ICP atomic emission spectrometry (ICP-AES) in 1985 by Meyer et aL7 The liquid sample is forced through an electro- thermally heated capillary resulting in partial vaporization of the solvent and production of a fine spray.The aerosol droplet size produced by the thermospray system is much lower than that of a pneumatic system; Koropchak and Winn' reported median diameters for primary thermospray aerosols of typically 2 pm compared with median diameters produced by pneumatic nebulizers of more than 10 pm. This diameter is further reduced as the aerosol moves away from the tip of the capillary because of the high temperature of the aerosol (self-desolvating effect). Small droplets are more efficiently transported to the ICP since they are less prone to impaction and other loss processes. Koropchak et d9 reported an analyte transport efficiency of 53% using a capillary tube with an internal diameter of 50 pm.In addition a more rapid and efficient ionization occurs; small droplets more easily undergo desolvation volatilization and atomization. These features lead to an improved performance. Several authors reported signal-to-noise ratio enhancements in ICP-AES9," resulting in lower detection limits. Vermeiren et a!." reported detection limits for Ag Al Cd Co Cu Pb and Zn that are 12-18 times lower compared with those for a pneumatic nebulizer whereas Peng et a1." observed an improvement of the detection limit for 19 elements by a factor of 3 compared with sample introduction with a V-groove nebulizer. The aim of this study was to optimize and to evaluate the coupling of a thermospray nebulization system with an ICP mass spectrometer. In a preliminary study Meyer et d7 reported the use of a thermospray nebulizer for ICP-MS.They observed 15 times more counts for Ce and Tb compared with a concentric nebulizer. More recently Montaser et aL3 studied several nebulization systems for ICP-MS including thermo- spray nebulizers. The thermospray system used in this work consisted of an LC pump and a stainless-steel capillary tube with an internal diameter of 180 pm. Because solvent transport efficiencies are also high (Schwartz and MeyerI2 measured efficiencies above 50%) a desolvating system must be applied. Therefore the capillary tube was followed by a heated spray chamber and a condenser. The optimization procedure included the power applied to the capillary the sample-uptake rate the temperature of the aerosol and of the cooling-water the carrier gas flow rate and the r.f. power.Important analytical features such as stability detection limits background level and sensitivity are discussed and compared with those obtained with a pneumatic system. Also the levels of oxide and doubly charged ions are given. Experimental ICP-MS Instrument A VG PlasmaQuad PQ1 (VG Elemental Ltd. a division of Fisons Instruments Winsford UK) has been used in all experiments. The original interface was replaced by a high performance interface in order to improve the sensitivity. Details of the operating conditions are given in Table 1. Pneumatic Nebulization System The pneumatic nebulization system with which the thermo- spray system is compared consists of a Meinhard (TR-30-A3) concentric glass nebulizer and a double pass Scott-type spray chamber with surrounding liquid jacket made of borosilicate glass.The water flowing through the spray chamber is supplied816 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 Table 1 ICP-MS operating conditions Stage Parameter Plasma Frequency Torch Pneumatic Sample uptake rate nebulization Gas flow system Plasma A u x i 1 i a r y Nebulizer Ion sampling Sampling cone Skimmer cone Sampling depth Vacuum Expansion stage Intermediate stage Analyser stage Conditions 27.12 MHz Fassel-type 0.9 ml min - 14 1 min-' 1 1 min-' 0.820 1 min - Nickel 1.0 mm orifice Nickel 0.75 mm orifice 10 mm (from load coil) 2.2 mbar 1.0 x mbar 2.0 x mbar by a recirculating cooling system (Barrington LT6 -20 to 100°C) and is thermostated to within 0.1 "C.The sample is delivered to the pneumatic nebulizer with a peristaltic pump (Gilson Minipuls-2). Under optimum conditions a sample uptake rate and a nebulizer gas flow rate of 0.9 ml min-' and 0.820 1 min- ' respectively are applied. Thermospray Nebulization System The thermospray nebulizer consists of an electrically heated stainless-steel capillary tube of length 30 cm and i.d. 180 pm. Direct electrical heating was used to heat the capillary. This implies that a current in this work an a.c. current (50 Hz) is passed through the capillary. The power delivered to the capillary could be varied continuously between 0 and 200 W (a voltage variable between 0 and 6V) by using a variable transformer in combination with a second main transformer. The aqueous solution is delivered to the thermospray nebulizer by a Varian 8500 LC pump which is a single-syringe pump (volume 250ml) with a pump piston which is moved with a stepping motor via a speed reducer and a sprocket-chain driver assembly.The sample uptake rate can be controlled within 0.017 ml min-' (range 0-16 ml min-'). To avoid solvent overloading of the plasma the thermospray nebulizer must be followed by a desolvating system. Peng et al." employed a conventional cooled spray chamber whereas Montaser et aL3 used a membrane separator. In this work a heated spray chamber followed by a condenser was chosen. This approach is similar to the one used by Koropchak et ~ l . ~ Schwartz and MeyerI2 andElgersma et ~ 1 .' ~ A schematic overview of the desolvating system is given in Fig. 1. It consists of a conical flask in which the thermospray nebulizer is mounted using a PTFE piece. Large droplets which impact on the surface of the flask are removed through a drain at this stage. The conical flask is followed by an L-shaped tube (length 25 cm and i.d. 3.5 cm) which is heated by a heating tape. The use of a variable transformer allows the power to be changed from 0 to 100 W. The temperature which can be raised to about 200"C could be maintained at a constant value (within 1 "C) by insulating the heated tube with asbestos tape. The temperature of the heated aerosol was controlled by a mercury thermometer which was mounted at the end of the heated tube. Finally a modified Friedrichs condenser was used to condense and remove most of the solvent leaving the heated tube.The cooling-water which is supplied by a recirculating cooling system (Barrington LT6) was thermostated to within 0.1 "C. An argon carrier gas stream entering the thermospray system at the stage of the conical flask and controlled by a mass flow controller is used to carry the secondary aerosol towards the ICP. An evaluation using ICP-AES of the stability Thermometer Carrier gas 0-220 v Conical flask Thermospray probe f/ Towards ICP Fig. 1 Schematic overview of the desolvating system and the mass transport efficiency of this thermospray nebul- ization system was described previously in Test Solutions and Optimization Procedure For the optimization procedure a 10 pg 1-' multi-element solution (Be Al Sc Co In Gd T1 Th and U) was used. This solution was prepared in 0.14 mol 1-1 nitric acid from commer- cially available AAS standard solutions.For the short- and long-term stability experiments Li B Cu Cd Cs and Bi (from AAS-standard solutions) were also added to the multi- element solution. To reduce the level of impurities both the water and the nitric acid (14 moll-') were purified respect- ively by a Millipore Milli-Q water purification system (resis- tivity of 18 MQcm) and by a sub-boiling distillation system. These purification procedures give the lowest levels of metal impurities as shown in a previous publication." All results described in this work were obtained using the scanning mode for data acquisition.Normally scan conditions were chosen so that one measurement lasted about 1 min. The following isotopes were selected 7Li 9Be "B 27Al 45Sc 63Cu "Co '14Cd "'In 133Cs ls8Gd 205Tl 209Bi 232Th and 238U. Results and Discussion Optimization of Instrumental Parameters Power applied to the capillary tube and sample uptake rate Since the power applied to the capillary tube determines the vaporized fraction and in this way the signal intensity it is important to optimize the applied power. For the capillary used in this study a thermospray could be produced applying a power between 20 and 90 W. The influence of the applied power and of the sample uptake rate on the analyte signal is illustrated in Fig. 2 for 238U. As can be seen the intensity of the analyte signal is initially proportional to the applied power reaches a maximum at a certain power and decreases at higher powers.The power at which a maximum analyte signal intensity is obtained depends on the sample uptake rate; 46 W for 1 mI min-l 54 W for 1.33 ml min-' and 76 W for 1.67 ml min-l. The sensitivity is only slightly dependent on the sample uptake rate with a higher sensitivity for higher rates. The power settings of 20 and 65 W (sample uptake rate of 1.3 ml min-l) correspond to tip temperatures of the vapor- izer of 55 and 113 "C re~pective1y.l~ The observations described for U were analogous to those obtained for the other elements investigated with masses over the whole mass range. The levels of oxide (MO+:M+) and doubly charged ions ( M2+:M+) are not significantly dependent on the applied power as can be seen in Fig.3 for Th U and Ba (for a sample817 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 ' \ 2 I 15 30 45 60 75 90 Applied power/W Fig. 2 Ion signal intensity for 238U as a function of the power applied to the capillary for three sample uptake rates A 1; B 1.33; and C. 1.67 ml min-' 2.5 1 3.0 0.5 t 4 0.5 0 ' I I I I 10 15 30 45 60 75 90 Applied powerw Fig.3 The ratios of MO+:M+ for A Th; and B U and C of M2+:M+ for Ba as a function of the power applied to the capillary for a sample uptake rate of 1.33 ml min-' uptake rate of 1.33 ml min-I). Only at high powers (above 70 W) can a small increase be observed owing to the fact that at these powers the signal of M + decreases more rapidly compared with that of MO+ and M2+.The ratios of YO+:Y+ GdO+:Gd+ Th2+:Thf and U2+:U+ (not given in Fig. 3) behave in the same way. Since at very low applied powers (< 35 W) the spray obtained was visibly unstable and at high powers (>80 W) a lot of turbulences in the spray could be observed the sample uptake rate and the applied power were maintained at 1.33 ml min-' and 55 W respectively. Aerosol temperature Heating the produced aerosol will decrease the droplet size and improve the analyte transport. Therefore the influence of the aerosol temperature on the intensity of the analyte signal was studied. The thermospray nebulizer itself produces a warm aerosol; an aerosol temperature of 68°C is obtained at a sample uptake rate of 1.33 ml min-'. The aerosol leaving the spray chamber can be further heated in the L-shaped tube (see Fig.1). As can be seen in Fig. 4 for 59C0 "'In and 238U the analyte signal intensity is strongly dependent on the aerosol temperature measured at the end of the heating system (Fig. 1). The sensitivity at a temperature of 118 "C is a factor of 60 higher than that without external heating. Further heating of the aerosol is not advantageous because the signal intensity decreases slightly. In addition a relatively unstable analyte signal is observed at high aerosol temperatures (above 130 "C). Since by heating the aerosol the amount of solvent reaching the plasma is reduced the levels of oxide and doubly charged ions were studied in detail (Fig. 5). Both levels are only moderately influenced by the aerosol temperature.The ratio of MO+:M+ for Th and U [also for Y and Gd (not given in Fig. 5)] is a factor of 1.6 lower than when no external heating 1200 r 1 I A I 60 90 120 150 180 Temperature (aerosolV'C Fig. 4 Ion signal intensities for C 59C0; B 1'51n; and A 238U as a function of the aerosol temperature (applied power 55 W; sample uptake rate 1.33 ml min-') 2.0 I 1 1.5 I x I 0 ' I I I I ' 0 60 90 120 150 180 Temperature (aerosol)/"C Fig.5 Ratios of MO+:Mf for A Th; and B U and C of M2+:M+ for Ba as a function of the aerosol temperature (applied power 55 W; sample uptake rate 1.33 ml min-') is applied owing to a lower solvent content of the plasma when the aerosol is heated. These observations indicate that most of the solvent is already removed without additional heating of the aerosol.The ratio of M2+:M+ for Ba [also for Th and U (not given in Fig. 5)] increases by about 50% with higher aerosol temperatures probably owing to a higher plasma potential as suggested by Gray et a1.I6 who found that increas- ing the water loading in the plasma induces an increase in the plasma potential. Therefore an aerosol temperature of 120°C was chosen because it combines a high sensitivity with low oxide and doubly charged ion levels. Cooling-water temperature Since the temperature of the cooling-water affects the water- loading of the plasma the influence of the cooling-water temperature on the analyte signal intensity and on the oxide and doubly charged ion levels was investigated. The results are summarized in Fig. 6 and 7. As can be seen the analyte signal intensity is strongly dependent on the temperature of the cooling-water; the sensitivity at a temperature of 1 "C is a factor of 7 higher than that at ambient temperature.These observations are similar to those of Jakubowski et who realized an intensity gain by a factor of 2-5 using a GMK nebulizer in combination with a desolvating system consisting of a heating and cooling unit. Higher levels of oxide (MO+:M+) and doubly charged ( M2+:M +) ions were observed when increasing the temperature of the cooling-water (Fig. 7). By varying the cooling-water temperature from 1 to 30"C the ratios of MO+:M+ for Th and U [also for Y and Gd (not given in Fig. 7)] and M2+:M+ for Ba [also for Th and U (not given in Fig. 7)] are increased by a factor of 2 and 1.4 respectively.Similar results were also found by Tsukahara and Kubota" for a concentric nebulizer818 1200 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 C /"\ - ?? 900- 2 e "I 600 t. .- m C - $ 300 n 0 10 20 30 Temperature (cooling water)/"(= B' \ I 3 I +\+ I - A - - Fig.6 Ion signal intensities for A 59C0; B '"In; and C 238U as a function of the cooling-water temperature (applied power 55 W; sample uptake rate 1.33 ml min-l; aerosol temperature 120 "C) 2.5 I I + 1.0 0 2 0.5 0 0 10 20 30 Temperature (cooling water)/"C + 0.5 % 0 Fig.7 Ratios of MO+:M+ for A Th; and B U and C of MZ+:M+ for Ba as a function of the cooling-water temperature (applied power 55 W; sample uptake rate 1.33 ml min-'; aerosol temperature 120 "C) combined with a heated glass tube and a modified Liebig condenser.They observed a relation between the increase of the oxide and doubly charged ion levels and the increase of the amount of water vapour reaching the plasma. Vermeiren et al." demonstrated that with the desolvating system described in this work the water-loading increases from 8.8 to 15.0 mg min-' by increasing the cooling-water temperature from 5 to 20°C. In order to get a maximum sensitivity and the lowest oxide and doubly charged ion levels a cooling-water temperature of 1 "C was used. Experiments are now underway using cooling- water temperatures below 0°C in order to improve the sensi- tivity and the oxide and doubly charged ion levels further. Results will be reported in the near future. Carrier gasjow rate In contrast with pneumatic nebulizers thermospray nebulizers have the advantage that the primary aerosol production is independent of the gas flow rate used.In this way the argon flow can be optimized without affecting the aerosol production. The signal response behaviour as a function of the carrier gas flow rate is similar to that obtained with pneumatic nebulizers." Fig. 8 shows that for 9Be '151n and 238U the carrier gas flow rate at which a maximum signal for M+ is obtained is nearly the same namely around 0.820 1 min-'. In this way one particular flow rate can be used for all the elements. The cooling-water and the aerosol temperatures have a great influence on the value of the flow rate at which a maximum signal intensity is obtained (Fig. 9 and 10).These maxima shift towards a lower carrier flow rate with increasing temperature of the cooling-water and with decreasing temperature of the aerosol. These observations can be explained by assuming that both temperatures influence the position of the zone in the plasma where a maximum density of singly charged ions M+ 580 680 780 880 980 Carrier gas flow rate/ml min ' Fig. 8 Ion signal intensities for A 9Be(x5); B "'In; and C 238U as a function of the carrier gas flow rate (under optimized conditions see Table 2) 1200 I I 580 700 820 9 40 Carrier gas flow rate/ml min ' Fig.9 Ion signal intensity for "'In as a function of the carrier gas flow rate for four cooling water temperatures A 1; B 10; C 20; and D 30 "C (under optimized conditions see Table 2) 600 I 580 700 820 940 ' Carrier gas flow rate/ml min Fig.10 Ion signal intensity for "'In as a function of the carrier gas flow rate for three aerosol temperatures A 68; B 120; and C 200°C (under optimized conditions see Table 2) O C C U ~ S . ~ ~ * ~ ~ A decrease of the solvent-loading of the plasma resulting from lowering the cooling-water temperature and increasing the aerosol temperature will move this zone towards the induction coil so that a higher carrier flow rate must be used to make sure that this zone is present in the sampling region of the sampling cone. The absolute signal intensities are also affected they decrease with higher cooling-water temperatures and with lower aerosol temperatures. R f . power The analyte signal intensity is moderately influenced by the r.f.power (between 1200 and 1500 W) as illustrated in Fig. 11 for 59C0 '151n and 238U. A maximum signal intensity is reached819 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 S I I 0 1150 1250 1350 1450 1550 Ref. powerw Fig. 11 Ion signal intensities for A 59C0; B "'In; and C 238U as a function of the r.f. power (under optimized conditions see Table 2) at an r.f. power of about 1400 W. Higher r.f. powers result in a slight decrease of the signal intensity. The optimum operating conditions of the thermospray nebu- lization system are summarized in Table 2. It can be mentioned that the auxiliary and the plasma gas flow rates did not significantly influence the sensitivity and were set at 1 and 14 1 min-' respectively. Sensitivity Since a thermospray nebulizer produces an aerosol with smaller droplet diameter as compared with the pneumatic nebulizer and therefore more particles are transported to the ICP a higher sensitivity should be obtained.The analyte signal inten- sities for a number of elements using the optimum operating conditions given in Table 2 were compared with those obtained with a concentric nebulizer combined with a spray chamber. A summary of the results obtained for a multi-element solution (each element present at a concentration of 10 pg 1-') is given in Fig. 12. As can be seen the sensitivity obtained with thermospray nebulization is on average a factor of 10 higher compared with that obtained with pneumatic nebuliz- ation. The increase is similar for all elements studied (Be Al Sc Co In Gd TI Th and U) over the whole mass range.The signal intensities obtained with a concentric nebul- izer combined with a spray chamber and with the same Table 2 Optimum operating conditions for the thermospray nebul- ization system Sample uptake rate Power applied to the capillary Temperature of the aerosol Temperature of the cooling-water Carrier gas flow rate Auxiliary gas flow rate Plasma gas flow rate R.f. power 1.33 ml min-' 55 w 120 "C 1 "C 0.820 1 min - ' 11 min-' 14 1 min-' 1350 W 1 XIO" I v) v) C 3 0 > c -. .= 1 x 105 .- CI .- v) c 0) v) I i n 4 I h I" Be A1 Sc Co In Gd TI Th U Element Fig. 12 Comparison of the sensitivity for a number of elements (at a concentration of 10 pg 1-I) obtained with the thermospray system and with the pneumatic system nebulizer combined with the desolvating system used for the thermospray nebulizer did not differ strongly from each other.There was a slight increase in intensity (10%) using the desolvating system probably owing to a more efficient sol- vent removal. Background and Blank Level The background level was constant over the whole mass range and varied between 10 and 40 counts s-' as illustrated in Fig. 13 showing the mass spectrum between 202 and 239 m/z of a solution containing 1Opg I-' of T1 Th and U. These count rates are similar to those obtained with a concentric nebulizer combined with a spray chamber. Experiments have however shown that the blank level is elevated for some elements owing to contamination from the stainless-steel capil- lary tube and/or other components of the thermospray system.Trace amounts of Cr Mn Fe Ni Zn Mo Pb (see Fig. 13) and Bi (see Fig. 13) could be noticed in a mass spectrum of a blank solution containing 0.14 moll-' nitric acid. Further studies will be carried out to reduce or eliminate this blank problem by using a fused silica capillary positioned inside a stainless-steel capillary. Such a capillary was successfully employed by Peng et al.." Detection Limits Table 3 lists the detection limits for Be Al Sc Co In Gd T1 Th and U obtained with the thermospray nebulization system and with the pneumatic nebulizer combined with a spray chamber. These detection limits (3s definition) were obtained by measuring ten times a blank solution (0.14moll-' nitric acid). For each element a small mass range (z 10 m/z) was scanned for about 1 min yielding an integration time of 6 s (m/z)-'.From Table3 it can be concluded that for the 9 elements studied the detection limits measured with the thermo- spray nebulizer are on the average a factor of 10 lower than the corresponding data measured with a pneumatic nebulizer. The reduction of detection limits can be attributed to the 1 o5 10' lo3 - m 1 al Q c 3 v) 102 10 w 0 204 208 212 216 220 224 228 232 236 m/z Fig.13 Mass spectrum between 202 and 239m/z of a solution containing 10 pg 1-' of T1 Th and U Table 3 Detection limits (ng 1-') obtained with the thermospray system and with the pneumatic nebulizer combined with a spray chamber Element Be A1 sc c o In Gd T1 Th U Isotope 9 27 45 59 115 158 205 232 238 Thermos pray nebulization 1.3 0.35 0.29 0.34 0.24 0.83 0.3 1 0.19 0.19 Pneumatic nebulization 12 3.9 2.1 3.7 1.3 9.1 3.9 2.1 1.2820 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL.improved sensitivity which results from the higher nebulization efficiency of the thermospray system. Montaser et a1.,3 who used a thermospray nebulizer combined with a membrane separator reported detection limits that were improved by a factor of up to 20 (an average of 4.6) for 15 elements. The values reported range from 0.5 ng 1-' for Pb up to 8 ng 1- for Cd using an integration time of 3 s (m/z)-'. Stability The stability of the thermospray nebulization system combined with the desolvating system was studied both on short- and long-term basis. The percentage relative standard deviation (Yo RSD) obtained for the short-term stability was calculated for 10 successive scans recorded in 10 min for a 10 pg l-' multi-element solution containing Li B Al Sc Cu Cd Cs Gd Bi Th and U.As can be deduced from the results presented in Table4 the RSDs vary between 3 and 8%. These values are significantly higher than those obtained with a pneumatic nebulizer combined with a spray chamber. The latter values are not above 3%. These observations are similar to those reported by Montaser et aL3 using a thermospray nebulizer with a membrane separator. They measured RSDs which were roughly twice the values measured with a pneumatic system. These short-term fluctuations can however be compensated for by the use of internal standardization. As shown in Table 4 the RSD obtained is less than 4% by the use of a suitable internal standard.The choice of the internal standard depends on the element to be determined.2' No drift in the ion signal intensity during several hours could be observed if the thermo- spray system was first stabilized for about 30 min. Oxide and Doubly Charged Ion Levels A comparison of the MO+:M+ and M2+:M+ ratios of various elements for thermospray and pneumatic nebulization was made. The results are given in Fig. 14 and 15. For both systems they were obtained under optimized conditions (with a maxi- mum ion signal intensity). As can be seen the levels of oxide (MO+:M+) and doubly charged (M2+:M+) ions obtained with the thermospray system are lower than those obtained with the pneumatic system; both are improved with a factor of about 2.5.The ratios (YO) of MO+:Mf range from 0.1 (0.32) for Y to 1.1 (2.5) for U whereas those of M2+:M+ range from 0.3 (0.6) for U to 1.0 (3.0) for Ba (the values given in parentheses are those obtained for pneumatic nebulization). The levels of oxide ions are similar to those obtained with a thermospray-membrane separator system by Montaser et aL3 They reported MOf:Mf values (YO) for Y and Ce of 0.1 and 1.3 respectively. The levels of doubly charged ions reported Table 4 Percentage relative standard deviations (O/O RSD) for a short- term stability experiment (ten successive measurements of a 10 pg I - ' multi-element solution recorded in 10 min) obtained with thermospray nebulization (TN) system and with the pneumatic nebulizer (PN) combined with a spray chamber TN without internal standard 5.3 4.7 6.7 4.1 5.7 7.9 3.1 5.9 3.9 4.2 4.6 PN 2.9 2.1 2.9 1.5 2.9 2.9 2.1 2.9 I .9 2.2 2.1 3.0 Thermospray nebulizer 0.5 Y Gd Th U Element Fig.14 Comparison of the MO+:M+-ratios for Y Gd Th and U obtained with the thermospray system and with the pneumatic system 3'5 I 3.0 t " I I Ba Thermospray nebulizer 0 Pneumatic nebulizer n Th U Element Fig. 15 with the thermospray system and with the pneumatic system Comparison of the M2+:M+-ratios for.Ba Th and U obtained by Montaser et aL3 are higher than those obtained in this work; the Ce2+:Ce+ measured was 6.0%. They attributed these higher values to the use of a 40.68 MHz ICP (instead of a 27.1 MHz plasma). Although the thermospray system gives higher solvent transport efficiencies the levels of oxide (MO +:M+) and doubly charged ( M2+:M +) ions are still lower compared with those obtained with a pneumatic system owing to the more efficient solvent removal by the desolvating system described in this work than in a conventional spray chamber.Studies are underway to improve the desolvating unit further. Conclusion It was demonstrated that under optimized conditions the thermospray nebulizer with a desolvating system gives a better performance in comparison with the pneumatic nebulizer. Sensitivity and detection limits are on average a factor of 10 improved when thermospray nebulization is employed because of the higher nebulization efficiency of the thermospray nebulizer. Also the levels of oxide and doubly charged ions relative to the levels of the singly charged ions are reduced by a factor of 2.5 so that the oxide ion levels even for elements with the highest MO bond strength and the doubly charged ion levels for elements with the lowest second ionization energy do not exceed 1 YO.Although thermospray nebulization is more susceptible to short-term fluctuations than pneumatic nebuliz- ation it was demonstrated that internal standardization could compensate for these variations. In this way on a short-term basis RSDs of less than 4% could be obtained. The stability on a long-term basis was similar for both systems if a warming- up period of 30 min was employed for the thermospray nebulizer. The performance of thermospray nebulization for the analy-JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL.9 82 1 sis of solutions with a high salt content (serum sea-water) and the alleviation of memory effects by flow injection will be studied. Future work will also involve the use of other non- metallic capillary tubes to avoid blank problems when samples in acid medium are analysed. Studies will be undertaken to improve the desolvating system in order to reduce spectral interferences caused by oxide and doubly charged ions further. 1 2 3 4 5 6 7 8 9 10 References Browner R. F. and Boom A. W. Anal. Chem. 1984 56 786A. Thompson J. J. and Houk R. S. Anal. Chem. 1986 58 2541. Montaser A Tan H. Ishii I. Nam S.-H. and Cai M. Anal. Chem. 1991 63 2660. Wiederin D. R. Smith F. G. Houk R. S. Anal. Chem. 1991 63 219. Jakubowski N. Feldmann I. Stuewer D. and Berndt H. Spectrochim. Acta Part B 1992 47 119. Blakely C. R. and Vestal M. L. Anal. Chem. 1983 55 750. Meyer G. A. Roeck J. S. and Vestal M. L. XCP Inf. Newsl. 1985 10 955. Koropchak J. A. and Winn D. H. Appl. Spectrosc. 1987,41,1311. Koropchak J. A. Aryamanya-Mugisha H. and Winn D. H. J. Anal. At. Spectrom. 1988 3 799. Peng R. Tiggelman J. J. de Loos-Vollebregt M. T. C. Spectrochim. Acta Part B 1990 45 189. 11 12 13 14 15 16 17 18 19 20 21 Vermeiren K. A. Taylor P. D. P. and Dams R. J. Anal. At. Spectrom. 1988 3 571. Schwartz S. A. and Meyer G. A. Spectrochim. Acta Part B 1986 41 1287. Elgersma J. W. Balke J. and Maessen F. J. M. J. Spectrochim. Acta Part B 1991 46 1973. Vermeiren K. A. Taylor P. D. P. and Dams R. J. Anal. At. Spectrom. 1987 2 383. Vanhoe H. Dams R. and Versieck J. J. Anal. At. Spectrom. 1994 9 23. Gray A. L. Houk R. S. and Williams J. G. J. Anal. At. Spectrom. 1987 2 13. Jakubowski N. Feldmann T. Stuewer D. Spectrochim. Acta Part B 1992,47 107. Tsukahara R. and Kubota M. Spectrochim. Acta Part B 1990 45 581. Vanhaecke F. Vandecasteele C. Vanhoe H. and Dams R. Mikrochim. Acta 1992 108 41. Vanhaecke F. Dams R. and Vandecasteele C. J. Anal. At. Spectrom. 1993 8 433. Vanhaecke F. Vanhoe H. Dams R. Vandecasteele C. Talanta 1992 39 737. Paper 4100873A Received February 2 1994 Accepted April 13 1994

ISSN:0267-9477    

DOI:10.1039/JA9940900815

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

JOURNAL O F ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 823 Analysis of Aluminium Alloys Using Inductively Coupled Plasma and Glow Discharge Mass Spectrometry Xinbang Feng and Gary Horlick Department of Chemistry University of Alberta Edmonton Alberta Canada T6G 2G2 The application of inductively coupled plasma mass spectrometry (ICP-MS) and glow discharge mass spectrometry (GD-MS) to the analysis of aluminium alloys is presented. The spectral characteristics of these two techniques are compared and contrasted. For the most part GD mass spectra are simpler than ICP mass spectra in that species originating from the components of air water and solution solutes are essentially absent in GD spectra. However GD spectra show the presence of multiply charged Ar species and matrix and analyte based argide species are more prevalent than oxide species the opposite being the case with the ICP.For both techniques potential spectral interferences are evaluated and matrix effects are illustrated. For ICP-based analyses it is shown that matrix effects can be minimized by adjustment of the nebulizer gas flow rate and by the use of an internal standard which is easy to add to the dissolved samples. For GD-based analyses a matrix effect exists between low and high alloy aluminium samples and it is shown that the signal from AlAr can be used as an internal standard to minimize this matrix effect. Finally both techniques were applied to the analysis of a range of Alcan and Alcoa aluminium standards. Keywords lnductively coupled plasma mass spectrometry; glow discharge mass spectrometry; alu- minium analyses In the last decade mass spectrometry has emerged as a major technique in the area of elemental analysis.The two main systems that have seen major development in this decade are inductively coupled plasma mass spectrometry (ICP-MS)' and glow discharge mass spectrometry (GD-MS).' Both systems are applicable to the determination of trace amounts of elements in a wide variety of sample type^.^?^ The ability to directly analyse solid materials is a major asset of the GD and this ability complements the solution sample handling capa- bility of the ICP. In addition it is not necessary to have separate mass spectrometric instrumentation for each tech- nique as ICP and GD ion sources can be interfaced to the same mass ~ p e c t r o m e t e r ~ ~ ~ ~ ~ and at least one company (Finnigan MAT) is marketing a combination instrument.In this report the application of both techniques to the analysis of aluminium alloys is presented. This study was not approached as a head-to-head competition but is simply meant to provide in a single paper a presentation of these two techniques applied to the analysis of the same samples. In this way the two methodologies can be compared and con- trasted. For the most part the important areas to address during the development of a quantitative analytical method are similar for both techniques. They include semiquantitative analysis assessment of spectral overlaps assessment of matrix effects instrumental settings and choice of an internal standard.However details of each step for the two methods do differ and in particular spectral characteristics matrix effects and internal standardization have considerations unique to each technique. Other workers have used these techniques for the analysis of aluminium samples. Takeda et a1.8 have discussed the determination of ultra-trace amounts of U and Th in high- purity aluminium by the use of ICP-MS GD-MS has been used for the analysis of aluminium alloy^^*'^ and GD-MS has also been used for the routine quality control of high-purity aluminium'l and has been compared with SIMS for the determination of U and Th in aluminium.'2 Experimental ICP-MS System All measurements were carried out using a SCIEX (Perkin Elmer-SCIEX) Elan Model 250 ICP quadrupole mass spec- trometer.For the ICP-MS studies a standard MAK ICP torch was used with a Meinhard nebulizer and a Scott-type spray chamber. A sampling depth of 15mm from the load coil was used and the plasma forward power was 1.3 kW. The outer gas and intermediate gas flow rates were 12 and 11 min-'. Central (nebulizer) gas flow rates of both 1.1 and 0.9 1 min-' were used. Matrix effects were reduced at the lower central gas flow rate setting but with some sacrifice in signal inten- ~ i t y . ' ~ ' ~ The ion lens voltages selected were a compromise chosen to cover a large mass range.15 The settings used were 5 V for the Bessel box barrel (B) - 18 V for the Bessel box plates (P) - 16 V for the einzel lens ( E l ) and - 10 V for the photon stop (S2). GD-MS System A pin sample GD ion source described by Shao and Horlick6 was used for this work.This ion source was bolted directly onto the external interface plate of the mass spectrometer (SCIEX-Perkin-Elmer Elan Model 250) in place of the normal sampling cone (full details can be found in ref. 6 ) . Typical operating pressures were 2.5 Torr (1 Torr = 133.322 Pa) for the GD device 0.1-0.2 Torr for the region between the sampling plate and the skimmer and 10-7-10-6 Torr for the mass spectrometer. These pressures were lower than the typical operating pressures for this system used for ICP-MS where the pressure is about 1-4 Torr between the sampling cone and the skimmer and the mass spectrometer operates at about Torr. The current-voltage operating values for the GD ranged from 7.5 to 9.5 mA and 800-1200 V and the fill gas was argon.The anode of the GD was biased slightly positive (+7 V) and the shadow stop" of the Elan was biased slightly negative (- 13 V). This stop is normally at ground potential when the system is used for ICP-MS. The biasing arrangement and the dependence of the ion signal intensity on these bias voltages is illustrated in ref. 6. The Elan ion lens voltage settings for the GD-MS measure- ments were 6.5 V for the Bessel box barrel (B) -30.9 V for the Bessel box plates (P) - 22.4 V for the einzel lens (El) and - 8.6 V for the photon stop (S2). Samples The aluminium samples studied were all solid metal standards obtained from Alcan and Alcoa. The five reference materials824 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL.9 obtained from Alcan (lSCXG lSWL lSWM 1SXD and 2SDZ) were all low alloy aluminium where aluminium made up over 99% of the sample. These samples were all certified for Bi Cr Cu Fe Mg Mn Ni Pb Si Sn Ti and Zn and three of the samples were also certified for Be Ca Cd Co Ga Li Na Sr V and Zr. The amount of these elements present in the samples ranged from a high of 0.5% for some elements to low values in the region of 0.005%. Eight Alcoa standards were available SA-909 SA-1170 SA-1169 SS-356-B SS-A 132AA SS-D132-A SS-319E and SS-360-C. The first three standards are low alloy aluminium standards. Aluminium made up over 99% of the sample and they were certified for Si Fe Cu Mn Mg Ti and Zn with one sample also certified for Cr Ni Pb and Sn. The amount of these elements present ranged from 0.5 to 0.001%. The last five of the Alcoa standards listed above are high alloy alu- minium materials where aluminium represents from 82 to 92% of the composition.The Si content ranges from 6 to 12% Cu from 0.03 to 4% and then at levels below 1'340 Fe Mn Mg Ni Ti and Zn round out the certified elements. For the ICP measurements these materials had to be put into solution. They were dissolved using a method described by Ward and Marciello.16 With this method 100 mg of sample were dissolved using 10 ml of 6 mol I-' HC1. After dissolution which required heating and took about 5-10 min the solution was cooled and then diluted to 100 ml providing a solution that was about 0.1% Al. For some measurements a 0.01% A1 solution was also prepared.This dissolution method was effective only for the low alloy aluminium mate- rials and therefore the high alloy aluminium samples were not analysed using ICP-MS in this study. The high alloy aluminium samples are difficult to dissolve because of their high content of Si. Aqueous standard solutions for the ICP measurements were prepared from ICP-grade standard solutions obtained from Leco Corporation. For the GD work the aluminium standards had to be machined into sample pins which were used as the cathode in the GD. These pins were about 3 mm in diameter and about 15 mm in length. Both low and high alloy aluminium standards were studied with the GD-MS system. Results and Discussion Spectral Characteristics One of the more interesting aspects of this study has been the ability to directly inter-compare some of the spectral character- istics of ICP-MS and GD-MS.The ICP and GD mass spectra are shown in Fig. 1 for an Alcan low alloy aluminium sample (1SCXG) over the m/z range 1-45. The ICP sample was a 0.01% solution and the composition of the sample is shown in Table 1. The basic background species in ICP-MS have been established for some time and they were summarized several years ago by Tan and Hor1i~k.l~ As can be seen in Fig. 1 the GD has a considerably simpler spectrum compared with that of the ICP in this m/z range. To a great extent this results from the fact that solvent (H20 HCl) and atmospheric (02 N2) based species are generally absent in the GD spectrum. Note however the strong signal from Ar2+ in the GD spectrum [Fig.l(b)] which is absent in the ICP spectrum [Fig. l(u)]. Some spectra of this region with the vertical scale expanded are shown in Fig. 2. In the GD spectra [Fig. 2(b) and (c)] multiply ionized Ar species (Ar3+ Ar4+ Ar5+ and even Ar6+) are observed. There is certainly the possibility that A12+ could occur in the GD and at an m/z of 13.5 it could not be distinguished from Ar3+ which occurs at an m/z of 13.3. Likewise A13+ would overlap with Be at m/z 9. Finally Ar6+ constitutes a spectral interference for 7Li. The multiply charged argon and aluminium species do not appear in the ICP spectrum [Fig. 2(a)]. Finally the signals from Na and B 3.0 2.5 2.0 1.5 1 .I F I v) v) 0.5 .I- 3 0 0 0 .- c 3.0 v) a 4- 5 2.5 2.0 1.5 1 .o 0.5 5 10 15 20 25 30 35 40 45 0 m/z Fig.1 Mass spectra for (a) ICP-MS and (h) GD-MS of Alcan aluminium alloy (1SCXG) Table 1 Composition of Alcan lSCXG low alloy aluminium Composition Element (mass-%) Be Ca c o Cu Ga Mg Na Pb Sn v Zr 0.007 0.0058 0.02 0.022 0.015 0.25 0.0026 0.019 0.024 0.008 0.034 Composition Element (mass- %) Bi Cd Cr Fe Li Mn Ni Si Ti Zn 0.022 0.018 0.01 8 0.33 0.002 1 0.026 0.023 0.2 0.02 0.027 observed in the ICP spectrum and not in the GD spectrum are probably a result of contamination introduced at the dissolution step. The ICP and GD mass spectra for this sample are also presented in Fig. 3 for the m/z range 40-85. Important differ- ences exist in this spectral region. As a consequence of the HCl-based dissolution step chlorine-based species such as C10+ ClOH' and ArC1' are observed in the ICP spectrum [Fig.3(a)]. As is well known these species present spectral interference problems for the determination of V Cr and As. These chlorine-based species are not present in the GD spec- trum [Fig. 3(b)] which allows for the determination of these elements in aluminium samples by GD-MS. An important difference in spectral features between ICP-MS and GD-MS is the existence of metal argides in GD-MS? 27A140Ar+ is clearly present in the GD spectrum [Fig. 3(b)] and is not observed in the ICP spectrum [Fig. 3(a)]. The level of this argide (27A140Ar+) is about 0.06% relative to the aluminium signal. While this species does coincide with aJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 825 1 .o 0.5 0 5 10 15 20 25 30 35 40 45 m/z Fig.2 aluminium alloy ( 1SCXG) (scale expanded) Mass spectra for (a) ICP-MS (b) and (c) GD-MS of Alcan minor isotope of Zn (67Zn) its presence is actually an asset. As will be seen later AlAr+ can be used as an internal standard for GD analyses of A1 alloys. It is difficult to confirm the presence of other aluminium- based spectral features in these spectra. The small peak at m/z 43 in the ICP spectrum [Fig. 3(a)] could be AIOf as oxides are more prevalent in ICP-MS than in GD-MS but it also could arise from 43Ca+. Also AlOH+ and A12+ at m/z 44 and 54 coincide with COz+ and 40Ar14N+. Since nitrogen- based species are also absent in GD-MS spectra and since dimers are more prevalent than in ICP-MS the peak at m/z 54 in the GD spectrum is likely to be A12+.The ICP and GD mass spectra for the 80-125m/z range are shown in Fig. 4. Niobium (m/z 93) is present in the ICP spectrum but is absent in the GD spectrum. It seems that it must have entered the sample solution as a contaminant during dissolution. Also both ZrO + and NbO' species are observed in the ICP spectrum but are absent in the GD spectrum. Note that the spectra shown in Fig. 4 are for sample 1SWL and not lSCXG which was used to generate the spectra for Figs. 1-3. Although sample 1SCXG was not certified for Ag it was found to contain Ag and the lo9Agf peak obscured the 93Nb160+ signal the existence of which we wanted to illustrate. Finally the ICP and GD mass spectra for the m/z range from 190 to 220 are shown in Fig. 5. It is interesting to note the difference in relative intensities of the '08Pb and '09Bi peaks in these spectra.Two explanations are possible. Lead could have been added as a contaminant during dissolution or the differences in intensities could reflect differences in the degree of ionization between the ICP and the GD ion sources. It should be noted that relative intensity differences between the ICP and GD spectra can also be seen for other elements such as for 12'Sn and '"Sb (Fig. 4) and for Cu Zn and Ga (Fig. 3). Ti+ Mn' I j Ar,H + A 40 45 50 55 60 65 70 75 80 85 m/z Fig.3 aluminium alloy (1SCXG) Mass spectra for (a) ICP-MS and (b) GD-MS of Alcan 150 100 50 c I v) v) +d 5 . 0 0 > -. Y Sn + I Zr+ Nb' I I (a' I I I (b) Zr' I 7 - + Sb' 100 - 50 - m/z Fig.4 Mass spectra for (a) ICP-MS and (b) GD-MS of Alcan aluminium alloy (1SWL)JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL.9 826 800 600 400 200 I v) v) 4- 5 0 + Pb' Pb' 1 190 195 200 205 210 215 220 m/z Fig.5 aluminium alloy (1SWL) Mass spectra for (a) ICP-MS and (6) GD-MS of Alcan ICP-MS Analyses Many analysts who utilize ICP-MS are initially only experi- enced in ICP atomic emission spectrometry (ICP-AES) and some time is required to develop the proper analytical intuition for the development of quantitative analytical methods for ICP-MS. For the most part the important areas to address during the development of an ICP-MS method have been delineated and include semi-quantitative analysis assessment of spectral overlaps assessment of matrix effects instrument settings and choice of internal standard.A discussion of the consideration of these areas for the analysis of steels using ICP-MS has been presented by Vaughan and Horlick14 and an analogous approach is taken here for the analysis of aluminium alloys. Because of the similarity to the methodology presented in ref. 14 the discussion of each area is brief. The samples studied in this section include all the low alloy aluminium standards from both Alcan and Alcoa. Qualitative spectral scans In the last section spectral scans of the Alcan low alloy aluminium standard 1SCXG were presented. The presence of all the certified elements could be verified and in addition Sr Ag and Sb were observed in some samples. Because of the possibility of contamination during dissolution and also because of the existence of certain spectral interferences unique to ICP-MS the GD-MS results are a significant help in verifying the presence and/or absence of some elements (i.e.V and Cr are present Nb is probably not present). Evaluation of potential spectral interferences The basic isobaric and background spectral interferences in ICP-MS have been well d o c ~ m e n t e d . ' ~ . ~ ~ Some of the major problem species are summarized in Table2 for the common elements determined in aluminium alloys. Only the major background species are listed for water and dilute nitric acid sulfuric acid and hydrochloric acid solutions and the tables of Tan and Horlick17 should be consulted for more details. Some of the elements of interest in aluminium metallurgy (such as Si and P) cannot be easily identified because of spectral overlaps with species basic to the ICP discharge.These molecular background ions include 14N2' and 14N160H+ which affect the major isotopes of Si and P. Iron and Ca are also problems. For iron its major isotope (56Fe) is affected by ArO' its next two most abundant isotopes 54Fe and 57Fe are affected by ArN+ and ArOH' respectively and the least abundant isotope 58Fe has an isobaric overlap with the major isotope of Ni. The most serious problem concerns Ca where all of its six isotopes are affected. With its major isotope (40Ca) affected by 40Ar and its third most abundant isotope (42Ca) affected by ArH,' both isotopes of 46Ca (0.004) and 48Ca (0.187) suffer from the interference of NO2+ and isobaric overlap from 46Ti and 48Ti.Even the next least abundant isotope 43Ca (0.14) and the next most abundant isotope 44Ca (2.09) are affected by the oxide A10' and the hydroxide AlOH' as well as the background species CO,'. Molecular background species can also be formed from the components of the overall sample solution matrix. Sulfur and chlorine containing components can be particularly trouble- some. For example the use of HCl in the dissolution step presents some major potential problems. Two key elements that can be affected are V and Cr. A chloride containing matrix results in the formation of 35C10+ 35C10H+ and 37C10+ which interfere with both "V and ',Cr as well as with 53Cr. These are serious problems because 'OV is the only other naturally occurring isotope of V with a natural abundance of only 0.25% and "Cr is the only remaining isotope of Cr with a natural abundance of 4.34% and both 'OV and "Cr suffer from isobaric overlaps from 50Ti 36ArN 35C115N and 34S160 background species.In addition to N C Ar C1 and Al other sample components can also cause MO and MOH spectral interference problems. For example it can be seen from the spectra shown in Fig. 6(a) that some isotopes of Cd suffer spectral overlap from ZrO' species. This problem is illustrated in detail by the bar graph simulated spectrum shown in Fig. 6(b). Overall however for low alloy aluminium samples and for 0.01% solutions the analytes are normally at concentrations of less than 0.03 yg ml-' and thus MO and MOH spectral interference problems among analytes are minimal. Finally as mentioned above and in the last section alu- minium itself does not contribute in a major way to spectral interference problems for ICP-based determinations.It is a monoisotopic element and species such as A10+ AlOH' and Al,' are relatively minor or coincide with minor isotopes (A10' with 43Ca') or other plasma species (AlOH' with COz' Al,' with ArN'). Matrix efects and internal standardization In ICP-MS a high concentration of a matrix element is known to affect analyte sensitivity and analyte signal suppression is most commonly ~ b s e r v e d . ' ~ ~ ~ A set of data illustrating the matrix effect of excess aluminium (1000 pg ml-l) on the signal for Ni (0.1 yg ml-l) as a function of central gas flow rate is presented in Fig. 7(a). As shown by the plot in Fig.7(b) the Ni signal is seriously suppressed by aluminium if the central gas flow rate is set to the value that yields the maximum Ni signal. The matrix effect can be minimized [Fig. 7(c)] by a reduction in the central gas flow rate. All analytes exhibited behaviour similar to that shown for Ni in Fig. 7 . This approach to reducing matrix effects does result in a reduction of sensi- tivity. At the flow rate required for a reduced matrix effect (0.9 1 min-l) signal sensitivity was typically down 30-45%.JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 827 Table 2 Basic spectral interferences for elements of major interest in aluminium alloys [natural abundances (YO) in parentheses] Background species Element 7Li (92.5) 'Be (100) 23Na (100) 24Mg(78.8) 25Mg (10.15) 28Si (92.21) 32S (95.02) 40Ca (96.94) 46Ti (8.01) 48Ti (73.98) "V (99.76) "Cr (83.76) 53Cr (9.51) 54Fe (5.82) "Mn (100) 56Fe (91.66) 57Fe (2.19) 58Ni (67.77) 60Ni (26.16) 62Ni (3.66) 63Cu (69.1) 64Zn (48.89) 65Cu (30.9) 69Ga (60.16) 71Ga (39.84) "Sr (82.58) "Zr (51.45) '"Sn (32.59) "*Pb (52.35) '09Bi (100) 2 7 ~ 1 ( i o o ) 31P (100) 5 9 ~ ~ (100) Isobaric overlap H20 HNO H2S04 H Cl - 40Ar (99.60) 46Ca (0.004) 48Ca (0.19) - - 54Cr (2.38) - - 58Fe (0.33) - - 64Ni (1.16) - - lZ0Te (0.1) - Internal standardization is used in almost all quantitative ICP-MS determinations.Not only does it compensate for multiplicative noises but because of the generally similar nature of matrix effects among the elements it also compen- sates for matrix effects.17 In this work Co Y and Rh were found to be effective as internal standard elements.during dissolution. The GD samples could of course be contaminated during the fabrication step. It is felt that the pre-sputtering step that is common in GD methodology would remove any surface transferred contamination. Internal stan- dards however cannot be added to solid samples and one must rely on sample components to provide an internal standard. In the analysis of steels a minor isotope of Fe (57Fe) can be used.6 This is not possible for aluminium analyses as aluminium is monoisotopic. An important aspect of the GD-MS analysis of aluminium samples presented here is the use of AlAr to function both as an internal standard and to compensate for matrix effects. Analytical results Aqueous calibration curves for both internal standard and matrix-matching methods were employed. For matrix match- ing standard solutions were prepared with the addition of aluminium at a concentration of 100 pg ml-' in order to match the 0.01% A1 sample solutions.In order to determine some of the lower level analytes 0.1% solutions of sample were also measured with matrix matched (1000 pg ml-' Al) standards. Results are shown for one of the Alcoa standards in Table 3 and for one of the Alcan samples in Table4. These results were obtained with the use of matrix-matched standard solu- tions but did not involve the use of an internal standard. Evaluation of background spectral interferences The spectral characteristics of GD-MS and ICP-MS with respect to the analysis of aluminium samples were presented earlier in this paper.It was seen that although the two sources do share some spectral features many differences exist both with respect to the nature and level of certain background species. Thus spectral interference problems must be specifi- cally evaluated for the GD source. In short for GD-MS in contrast to ICP-MS multiply-charged Ar species are present (Ar2+ Ar3+ Ar4+ etc.) background species originating from the components of air water and solution solutes are minimal or completely absent and matrix and analyte-based argide species are more prevalent than oxide species. Many specific examples were presented earlier during the discussion of Figs. The argide problem is further illustrated in Fig. 8. In the high alloy Alcoa aluminium standard SS-319E Cu is 3.83% and CuAr can be seen in the spectrum shown in Fig.8. The 63Cu argide presents a spectral overlap problem for the mono- isotopic element Rh and the 65Cu argide overlaps with one of 1-6. GD-MS Analyses For conductive metal alloys the d.c. GD can be used for the direct analysis of a sample although some sample fabrication (ie. machining) is often required. All samples in this study were formed into pins 3 mm in diameter and 15 mm in length. In the ICP-MS work difficulty was experienced in achieving complete dissolution of the high alloy aluminium samples probably because of their high Si content and they were not analysed by ICP-MS in this study. In contrast both the high and low alloy aluminium samples could be analysed by GD-MS.Also because the solid sample can be analysed directly GD-MS is not prone to contamination that can occur828 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 I 800 ( a ) Zr+,Nb+ - 600 v) v) C 3 .I- 8 400 \ c > v) Q .- c 5 200 0 80 85 90 95 100 105 110 115 120 125 105 110 115 120 125 4 ( C) I NbO r 3 v) C a 13 .- .I- .- c 2 l a > .- .I- - a 0 106 108 110 112 114 116 118 120 122 124 107 109 1 1 1 113 115 117 119 121 123 125 m/z Fig. 6 ICP mass spectra of an aluminium alloy sample (Alcan 1SWM) illustrating the overlap of elemental isotopes and metal monooxides. (a) Actual spectra; (b) enlargement of (a) m/z 105-125; and (c) simu- lated spectrum the isotopes of Pd. Manganese Fe Ni and Zn are present at 0.58 0.68 0.20 and 0.35'/0 respectively and low signal levels of their argides are also present.Matrix ejfects and internal standardization Two types of aluminium alloys were analysed by GD-MS low alloy aluminium and high alloy aluminium. The signal levels for several elements (normalized to the 1 % concentration level) in one alloy from each sample type are listed in Table 5. The normalized signal levels are 45-50% lower for the low alloy aluminium compared with the high alloy aluminium. This indicates that a matrix effect is present in that the low and high alloy aluminium samples could not be used to establish a single calibration curve for elements common to both alloy types. However it was noticed that the signal for AlAr' was affected in approximately the same way. Thus it appears that the AlAr signal can be used in the manner of an internal standard to compensate for this matrix effect.One should be U 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 Central gas flow rate/l min-' (6) 50 25 t -25 t - 50 0.1 10 100 1000 50 25 51 0 1 -25 1 - 50 0.1 1 10 100 1000 IAll/pg m l ~ ' Fig. 7 Effect of A1 concentration on the Ni signal as a function of (a) central gas flow rate for 0 pg ml-' of A1 (solid line) and 1000 pg ml-' of A1 (broken line) showing A flow rate for maximum signal and B flow rate for reduced matrix effects; (b) A1 concentration at the central gas flow rate yielding maximum signal intensity; and (c) at a reduced central gas flow rate Table 3 Results of the analysis of Alcoa standard SA-909 Element 24Mg 55Mn 58Ni 60Ni 63cu 65cu (j4Zn 66Zn Certified value( O/O) 0.030 0.03 1 0.034 0.034 0.03 1 0.03 1 0.030 0.030 Result(%) 0.0316 0.03 19 0.0353 0.0296 0.03 16 0.0302 0.0321 0.03 15 RSD(%) (n=4) 4 2 3 5 4 5 3 5 cautioned however that an argide may not under all GD operating conditions mimic analyte signal behavi0~r.l~ The difference in signal intensities between the low and high alloy aluminium samples can in part be accounted for by differences in sputtering rate.Each sample was sputtered twice for a 1 h period for the first time and a 2 h period for the second time. The difference in mass lost between these two sputtering periods was obtained and the sputtering rate calcu- lated. This gave a sputtering rate for the second hour. ThisJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 829 Table 4 Results for the analysis of Alcan standard 1SWL by ICP-MS Element 24Mg 48Ti "Mn 60Ni (j3CU W U 64Zn 66Zn 69Ga "Zr "Sn Certified value(%) 0.01 5 0.025 0.023 0.023 0.03 0.03 0.023 0.023 0.012 0.013 0.024 Result ( YO) 0.0142 0.0243 0.0229 0.0225 0.0340 0.0335 0.0260 0.0243 0.01 11 0.01 30 0.0173 RSD(Yo) (n=4) 3 2 2 2 2 2 2 2 3 2 2 CuAr' 800 11 '''Nb+ I 1 ZnAr' r I 600 c C 3 8 \ 2 400 .- tn al 4- - 201r 0 85 90 95 100 105 110 115 120 125 m/z Fig.8 Glow discharge mass spectrum of a high alloy aluminium sample (Alcoa SS-319E) approach was used as these aluminium samples required significant pre-sputtering time ( 15-20 min) before stable signals could be obtained.In this experiment the sputtering rate for the low alloy aluminium (SA-909) was about 40+ 3 pg min-' while the sputtering rate for the high alloy aluminium (SS-319E) was about 57 & 3 pg min-'.This is a 30% difference and partially explains the signal differences shown in Table 5. Further explanation may lie in differences in the degree of ionization in the GD for these two sample types but this is just speculation. Whatever the complete explanation may be for the signal differences observed for these two alloy types use of AlAr as an internal standard does compensate for this matrix effect. The AlAr+ also functions as a classic internal standard to compensate for signal changes as a function of time. These samples required a considerable pre-sputtering time in the range of 15-20 min. This is illustrated in Fig. 9(a) for the Cu signal. The AlAr' signal [Fig.9(b)] follows the analyte signal over this time and the ratio (Cu:AIAr) stabilized (zl-2% relative standard deviation) in about 20 min [Fig. 9(c)]. This 8000 (a) 6000 4000 2000 0 0 10 20 30 40 50 Ti me/m in Signal intensity (GD-MS) as a function of time for (a) Cu; and (b) AlAr; and (c) the signal intensity ratio of Cu to AlAr pre-sputtering time is probably required to remove an oxide coat from the aluminium samples. An attempt was made to shorten this pre-sputtering time by operating the GD device at higher currents but sparking often ensued and this approach to shortening this time has not yet proved to be reliable. On the other hand Marcus and Duckworthg have shown that by the use of an r.f.-powered GD rapid analysis of aluminium samples should be possible.Analytical results A group of calibration curves was established by using the Alcan low alloy aluminium standards lSCXG lSWL lSWM Table 5 Comparison of relative signal intensities (GD-MS) of analytes (normalized to 1 YO level) between high.and low alloy aluminium samples Normalized intensity* Mass 24 48 55 58 63 64 67 Analyte Mg Ti Mn Ni c u Zn AlAr High alloy (90% Al) 2 10000 280000 290000 140000 110000 126000 8000t Low alloy (99yo Al) 120000 15oooO 150000 70000 60000 64000 4000 Loss in intensity for low alloy Al(%) 43 46 48 50 45 49 50 * Signals normalized to the 1% concentration level. t Normalized intensity of AlAr for the high alloy is 7200/0.90= 8000.830 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 Table 6 Detection limits of trace elements directly in Alcan aluminium solids by GD-MS Elements Ti V Mn Ni c o c u Zn Ga Zr Sn Pb Bi Mg Mass 24 48 51 55 58 59 63 64 69 90 120 208 209 Detection limits (ppb) 108 42 31 30 59 30 63 58 44 10 41 87 56 Table7 Results for the analysis of lSWL low alloy aluminium by GD-MS Element Mg Ti V Mn Ni c o c u Zn Ga Zr Sn Pb Bi Certified value( %) 0.015 0.025 0.019 0.023 0.022 0.00 1 0.030 0.023 0.012 0.0 13 0.024 0.018 0.018 Result (%) 0.0145 0.0230 0.0160 0.0202 0.0205 0.001 3 0.0278 0.0209 0.0107 0.0129 0.0225 0.0195 0.0193 RSD(%) 2 1 1 2 2 6 3 3 3 2 3 1 2 2.5 2.0 1.5 (a) - - -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0 0.5 1.0 - 2.5 2.0 1.5 1 .o 0.5 0 -2.5 -2.0 -1.5 -1.0 -0.5 0 0.5 1.0 Log [concentration (%)I Fig.10 Calibration curves for (a) 24Mg and (b) 63Cu in both high and low alloy aluminium standards with AIAr' (m/z 67) as the internal standard Table 8 Results for the analysis of SS-360-C high alloy aluminium by GD-MS Certified Element value( Yo) Result(%) R S D (Yo) Mg 0.52 0.503 4 Ti 0.079 0.076 1 Mn 0.22 0.224 4 c u 0.3 1 0.308 3 Zn 0.25 0.248 4 lSXD and 2SDZ for the determination of Mg Ti V Mn Ni Co Cu Zn Ga Zr Sn Pb and Bi; AlAr' was the internal standard.The concentrations for these components in the standards were in the range of 0.001-0.030% except for one of the standards which contained 0.25% Mg. The slopes of the log-log plots for the calibration curves were in the range of 0.95-1.06. Detection limits (3s) for these elements were evalu- ated. They were obtained based on the standard deviations (n= 16) of background noise and the sensitivity of analyte signals.The detection limits (mass-%) calculated are summar- ized in Table 6. The low alloy aluminium 1SWL was analysed for all the above components as an 'unknown'. The results are listed in Table 7 and the standard deviations for the results were calculated based on n=6. Another group of calibration curves was established by using both low and high alloy aluminium standards from Alcoa for the determination of Mg Ti Mn Ni Cu and Zn. The seven standards were SA-909 SA-1170 SA-1169 SS-356-B SS-A132AA SS-D132-A and SS-3 19E. The composition of the components for the Alcoa standards was in the range of 0.009-1.3% for Mg 0.03-2.5% for Ni and 0.03-3.8% for Cu and the slopes of the log-log plots for the standard curves were usually in the range 0.85-0.95.Calibration curves for 24Mg and 63Cu with AlAr+ as the internal standard are shown in Fig. 10. The slopes of the log-log plots in Fig. 10 are 0.90 (Mg) and 0.89 (Cu) and the correlation coefficients are 0.998 (Mg) and 0.996 (Cu). Note that with the use of AlAr' as the internal standard both low and high alloy aluminium standards can be used to establish a single calibration curve. An Alcoa high alloy aluminium sample (SS-36O-C) one not used to establish the calibration curves was analysed as an 'unknown' sample and the results are listed in Table 8. Conclusions Clearly both ICP-MS and GD-MS can be successfully applied to the analysis of aluminium alloys. The GD-MS technique has the advantage that sample dissolution is not required and that air solvent and solute do not contribute to the spectral background.However potential spectral interferences unique to each technique still abound and care is still required in assessing their presence or absence. It is also important to point out that even though dissolution involves dilution of the analyte 100-10 000-fold when 1-0.01 YO sample solutions are prepared ICP-MS still has comparable or superior detection limits when referenced back to the solid composition; a conse- quence of the 1-10pgml-' range of detection limits for ICP-MS uersus the 1-10 ng g-' detection limits currently typical for GD-MS. Finally ICP-MS analyses typically require dissolution of a sample. This step is prone to contamination and for many samples is difficult to quantitatively complete.In fact many new materials are simply difficult to dissolve. On the other hand GD-MS analyses do have time-consuming steps involving sample form fabrication and pre-sputtering and certainly some contamination is possible during fabrication although the pre-sputtering step should minimize surface trans- ferred contaminants. References Horlick G. and Shao Y. Inductively Coupled Plasma Mass Spectrometry for Elemental Analysis in Znductiuely Coupled Plasmas in Analytical Atomic Spectrometry ed. Montaser A. and Golightly D. W. VCH Publishers 2nd edn. 1992 pp. 551-612. Harrison W. W. J. Anal. At. Spectrom. 1992 7 75. McLaren J. W. At. Sectrosc. 1992 13 81. Koppenaal D. W. Anal. Chem. 1990,62 303R.JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 83 1 5 6 7 8 9 10 11 12 Kim H. J. Piepmeier E. H. Beck G. L. Brumbaugh G. G. and Farmer 0. T. Anal. Chem. 1990 62 639. Shao Y. and Horlick G. Spectrochim. Acta Part B 1991,46 165. Kawaguchi H. Paper presented at the 1992 Winter Conference on Plasma Spectrochemistry San Diego CA USA January 6-11 1992 (paper No. IL14). Takeda K. Yamaguchi T. Akiyama H. and Masuda T. Analyst 1991 116 501. Marcus R. K. and Duckworth D. C. Pittcon Atlanta GA USA 1989 (paper No. 657). Vieth W. and Huneke J. C. Spectrochim. Acta Part B 1991 46 137. Vassamillet L. F. J . Anal. At. Spectrom. 1989 4 451. Shilomatsu H. M. and Iyer S . S. Nucl. Instrum. Methods Phys. Res. Sect. A 1988 280 488. 13 Tan S. H. and Horlick G. J . Anal. At. Spectrom. 1987 2 745. 14 Vaughan M. A. and Horlick G. J. Anal. At. Spectrom. 1989,4,45. 15 Vaughan M. A. and Horlick G. Spectrochim. Acta Part B 1990 45 1301. 16 Ward A. F. and Marciello L. F. Anal. Chem. 1979 51 2264. 17 Tan S. H. and Horlick G. Appl. Spectrosc. 1986 40 445. 18 Vaughan M. A. and Horlick G. Appl. Spectrosc. 1986 40 434. 19 King F. L. McCormack A. L. and Harrison W. W. J. Anal. At. Spectrom. 1988 3 883. Paper 3/0665OI Received November 5 1993 Accepted March 22 1994

ISSN:0267-9477    

DOI:10.1039/JA9940900823

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

JOURNAL O F ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 833 Direct Analysis of Materials Using Direct Sample Insertion Devices and Mixed Gas lnductively Coupled Plasma Atomic Emission Spectrometry* X. R. Liu and Gary Horlickt Department of Chemistry University of Alberta Edmonton Alberta Canada T6G 2G2 It is shown that a direct sample insertion (DSI) device can be used in conjunction with inductively coupled plasma atomic emission spectrometry for the direct determination of trace elements in a variety of materials. The majority of analyses involving DSI devices have concerned samples in the form of small aqueous solution volumes or dried solution residues. Successful analyses have now been carried out for the direct insertion of AI,O3 Al metal oil and botanical samples.The key operational feature that has allowed the successful direct determination of trace elements in these materials with essentially no a prior; sample treatment is the utilization of an argon-oxygen mixed gas plasma. The calibration curves are linear over a dynamic range of 3-4 orders of magnitude and the detection limits are in the range of tens of picograms. Keywords lnductively coupled plasma atomic emission Spectrometry; direct sample insertion; trace elements; mixed gas plasma The direct analysis of materials and in particular solid mate- rials remains a problem and a challenge for inductively coupled plasma (ICP) spectrometry. A number of methods have been applied to introduce solids directly into plasmas including direct insertion of samples into the plasma electrical spark and arc ablation electrothermal vaporization laser ablation agitation vessels for powder introduction and slurry nebuliz- ation.These methods have recently been reviewed.' For a number of years in this laboratory we have been developing the technique known as direct sample insertion (DSI). In this system a sample is placed into or onto a probe and the probe is then inserted into the plasma. In most systems the probe is a graphite cup which is inserted axially into the central channel of the plasma from below the discharge. Some of the features of DSI include the direct analysis of various sample forms including solutions solution residues slurries powders and solids; high efficiency in that 100% of the sample enters the plasma; the ability to handle small amounts (a few p1 ormg) of sample; and the ability to process the sample through dry ash and vaporization cycles in situ.Limitations attributed to DSI include a low vaporization temperature (z 2000 "C) which results in selective volatilization an inability to vaporize refractory materials and carbide formation. Chemical modification has been used with some success to overcome these limitations. A wide range of halide salts have been used as chemical modifiers to enhance vaporization including NH,Cl AgC1 NaCl KCl CdCl BaF and NaF. Poly( tetrafluoroethylene) (PTFE) powder has also been mixed with solid samples to enhance vaporization and Freon has been used as a gaseous chemical modifier. These studies are summarized in Table 5 of ref. 2. However chemical modifiers can introduce contaminants and may interfere with the stable operation of the plasma because of vapour generation.In addition powdered chemical modifiers cannot be effectively added to chip form samples solid materials or oils. An alternative approach to enhance the volatilization of samples is to modify the plasma. Mixed-gas plasmas have been used to improve the performance of DSI system^.^,^ The use of mixed-gas plasmas (Ar-N and Ar-0,) to augment the performance of a DSI system coupled to an inductively coupled plasma (ICP) atomic emission spectrometer is further investi- gated in this study. Successful analyses can be carried out with * Presented in part as a Plenary Lecture at the European Winter Conference on Plasma Spectrochemistry Granada Spain January 10-15 1993.t To whom correspondence should be addressed. the direct insertion of a variety of inorganic powdered mater- ials metallic materials (A1 based alloys) botanical samples food samples and oil. Volatile refractory and carbide forming elements can all be determined. The key operational feature that has allowed the successful analysis of these materials is the utilization of an Ar-0 mixed-gas plasma. Experiment a1 System Description A schematic diagram of the DSI-ICP atomic emission spec- trometry (AES) system is shown in Fig. 1. This system is a combination of two systems previously constructed in this laboratory. The ICP and the spectrometer are those described by Karanassios and H ~ r l i c k ~ and the DSI sub-system and read-out electronics are those described by Chan and Horlick.6 The stepper motor driving the DSI probe is controlled by an IBM PC.The system computer is a 486 computer which controls the IBM PC sequences data acquisition and is used for all data processing. The hardware components and some system parameters are listed in Table 1. It should be noted that while a 5 kW plasma source was used for this work the normal powers utilized ranged from 1.5 to 2.0 kW. Mixed-gas plasmas are established by first lighting an all- Ar plasma and then slowly adding either N or 0 to the outer (coolant) and intermediate (auxiliary) gas flows.' The foreign gas is added to the Ar using a pair of rotameters and a mixing tube. The central gas (Ar only) is passed through a A Lens 2170 steps I llll \ I lP7 \ I Amplifiers I I) Stepper motor To Ar-H,O 1.0 I min IBM PC PCMotion I 486 I 33MHz stepper motor control board RS-232 Fig.1 coupled plasma atomic emission system Schematic diagram of the direct sample insertion-inductively834 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 Table 1 Hardware specifications and typical operating conditions for Ar-0 and Ar-N mixed gas ICP-DSI-AES system ICP ICP generator ICP typical operating conditions Oxygen mixed gas plasma Nitrogen mixed gas plasma Spectrometer DSI system DSI probe Stepper motor control board Data acquisition System computer Plasma Therm ICP 5000 HFS-5000D; 27.12 MHz; max power 5.5 kW Forward power 1.8 kW; reflected power < 30 W; observation height 14 mm above load coil Outer gas 18 1 min-' with 20% 0 in Ar; intermediate gas 1 1 min-' with 20% 0 in Ar; Outer gas 18 1 min-' with 2% N in Ar; intermediate gas 1 1 min-' with 2% N in Ar; central A 1 m Pachen-Runge mount 29 channel direct reader with a 1200 groove mm-' concave The DSI device is described in detail in refs.5 and 6. No major modifications were made Graphite electrodes. Spex Industries Edison NJ USA PCMotion (Rogers Labs Santa Ana CA USA) for IBM-PC DT2801-A (Data Translalion MA USA) with a 12-bit analogue-to-digital converter IBM compatible 486/33 MHz with 8 MB RAM. DOS 6.0 and Windows 3.1 central gas 1 1 min-' with water vapour gas 1 1 min-' with water vapour grating except that it is controlled by an IBM-PC computer instead of an Apple 11+ plastic bottle containing water in order to add water vapour to this Ar flow.For reasons unknown this prevented and/or quenched arcing of the plasma to the DSI probe during insertion and retraction. It is also possible to avoid arcing by adding a small amount of He to the central gas,6 but the water vapour proved to be a simple solution to this problem. Finally in order to successfully run a mixed-gas plasma it may be necessary to modify the capacitance in the ICP matching network in order to maintain a low value of reflected power. In the present case a 150 pF capacitor was added in parallel to the variable parallel tuning capacitor (C2 in the PlasmaTherm schematic) in the matching network; C2 is the variable air capacitor. The sample probes are standard d.c. arc graphite electrodes [see Table 1 and Fig.2(a)]. The only modification was to drill a hole in the bottom of the electrode so that it could be mounted on the quartz rod of the DSI assembly. Sample probes were pre-burned in the mixed-gas plasma for 30s in order to remove possible impurities and contaminants. In the case of the Ar-0 (20%) plasma the sample cup was partially consumed by this operation making the walls of the cup thinner but still intact. This was beneficial in that it made it easier to burn the cup off and consume the sample during a subsequent analysis using the pre-burned probe. During an actual run ( x 80 s) with the Ar-0 (20%) mixed- gas plasma the cup of the sample probe is normally totally consumed. The shape of the sample probe after a determination is shown in Fig. 2(b). In many ways for those readers familiar ( a ) 3 1.6 m m l .17 mm n b) H 4.57 mm Fig.2 Diagram of the graphite sample probes (a) before insertion and (b) after insertion into an Ar-0 (20%) mixed gas ICP with d.c.arc methodology some of the attributes of mixed gas DSI are analogous to those of the Stallwood jet.8 A variety of samples were studied in this work they ranged from simple aqueous solution residues to inorganic and organic powders metallurgical solids and oil. Details of the specific samples and amounts analysed are given under Results and Discussion. Software Three main programs have been written to support the oper- ation of the DSI system one for pre-burning sample probes one for data acquisition during an analysis and one for post- run data processing. The pre-burn program simply sequences an insertion and retraction for a pre-set time of insertion.The data acquisition program provides for complete control over the insertion and retraction sequence. Dry ash insertion and retraction times and positions can all be set. Signals from up to six channels of the polychromator can be simultaneously digitized at a rate of 177 points per second per channel. This allows the transient emission signals characteristic of DSI systems to be followed. The data processing program includes routines for data display and plotting peak height and peak area calculations background correction and calculation of limits of detection (LODs). Results and Discussion Mixed-gas DSI Preliminary Studies for Aqueous Solution Residues Initial studies were carried out with the addition of low levels ( M 2%) of the foreign gas to the outer gas.At this low level of mixed gas the N 0 and air mixed-gas plasmas all show similar effects. The effect of various mixed-gas plasmas on the emission signal for V from a DSI probe is shown in Fig. 3. The sample was an aqueous solution containing 1 pgml-' each of 10 elements. The sample size was lop1 and was run as a solution residue the water being evaporated off under a heat lamp prior to insertion. Vanadium has a high boiling-point and a tendency to form a carbide (see Table 2). As can be seen from the signal shown in Fig. 3(a) there is essentially no emission from V using a normal Ar plasma with the DSI system. However a substantial signal is seen for V when a mixed-gas plasma is utilized [Fig.3(b) (c) and (41. If the sample probe that was first inserted into the normal Ar plasma is subsequently inserted into an Ar-air mixed plasma a small signal is seen for V emission indicating that it is 'tied-up' in the graphite probe probably as a carbide [see Fig. 3(e)]. Similar results were observed for Cr and Co. They are somewhat more volatile than V and a small emission signal was observed for both these elements in the 100% Ar plasma. The signal in each case was enhanced about 5-6 times by useJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 835 9 - 300 (II C 0 v .- 200 100 10 20 (6) 30 0 10 20 30 40 0 40 0 10 I 1 I I 20 30 40 10 20 30 40 0 10 20 30 40 Time/s Fig. 3 (2%) plasma; and (e) insertion into an Ar-air (2%) plasma after insertion into an Ar plasma Signals for vanadium (10 ng aqueous sample solution residue) (a) Ar plasma; (b) Ar-0 (2%) plasma; (c) Ar-air (2%) plasma; ( d ) Ar-N Table 2 carbides' [(d) denotes decomposition] Boiling-point data for Zr Ti V and A1 and their oxides and Element 7&,/OC Oxide Gp/OC Carbide XJC Zr 4377 ZrO 5000 ZrC 5100 Ti 3287 T i 0 >3000 TIC 4820 A1 2467 A1203 2987 Al,C 2200(d) V 3380 V,O 1750(d) VC 3900 of the mixed-gas plasmas.Signals were also observed for each of these elements in the second insertion experiment. The signals for a relatively volatile element (Mn) are shown in Fig. 4. While a signal is observed for Mn using a normal Ar plasma the emission signal is enhanced by about a factor of three by use of a mixed-gas plasma.The second insertion experiment for Mn however shows no evidence of residual Mn in the sample probe after insertion into the 100% Ar plasma. These results indicate that the mixed-gas plasmas not only facilitate the release of non-volatile constituents from the probe but that they also increase the emission signal of volatile elements. For volatile elements this appears to be mainly an increase in the peak height of the emission signal as a conse- quence of vaporizing the analyte in a shorter time. Sharper signals in DSI generally translate to improved detection limits. The effect of plasma power and amount of mixed gas constitu- ent (N,) on the analyte signal is shown in Fig. 5 for V. These data were taken at an observation height of 12-15mm above the load coil.Although the most intense signals were obtained at a power of 2 kW a power of 1.75 kW is normally used. This tends to preserve the life of the torch. The data shown in Fig. 5 indicate that the added mixed-gas constituent should be about 1-2% for these aqueous solution residue samples. The quantitative performance of the DSI system for the analysis of aqueous solution sample residues is summarized in Table 3. These results are for the Ar-N mixed gas plasma at a power of 1.75 kW. Except for V all elements were tested over a dynamic range of four orders of magnitude (0.1-1000 ng) and excellent calibration curves were obtained in all cases. The calibration curve for Cr is shown in Fig. 6 as an example. The LODs are 3s limits with the standard deviation of the blank based on the measurement of 11 replicates.The precision values are for 1 ng signal levels and are again based on 11 replicates. Peak areas were measured in all cases. The poor LOD and more limited dynamic range for V were caused by the fact that with the Ar-N mixed gas plasma all the V is not released from the sample probe. This is shown by the data presented in Fig. 7. The signal for the first insertion of a 1 pg sample of V (100 pg ml-' x 10 pl) into an Ar-N plasma is shown in Fig. 7(a). The signal was monitored for 50 s. Even after five successive 50 s insertions [Fig. 7(b)] a substantial V signal can still be observed (vertical scale expanded 5x). The slope of the log-log calibration curve obtained for V (Table 3 slope= 1.15) suggests that the fraction of V vaporized is different for different concentrations.Thus it would be best to fully vaporize the V in order to increase the sensitivity and improve linearity. This can be done by use of the Ar-0 mixed-gas plasma with a 20% level of O as shown by the signal traces in Figs. 7(c) and ( d ) . With the Ar-0 plasma the V is completely vaporized in 80-120 s [Fig. 7(c)] and a second insertion shows no evidence of V emission [Fig. 7(d)]. This is no doubt related to the fact that the probe cup is completely consumed when it is inserted into this Ar-0 mixed gas plasma. It should be noted that the probe cup could not be vaporized by utilizing an Ar-0 (2%) plasma in a reasonable time (k several min). In addition for the direct analysis of solid samples the Ar-0 (20%) plasma proved to be superior to the 2% mixed-gas plasmas and results are presented in the next section illustrating the performance of this plasma for DSI.Ar-0 (20%) Plasma DSI The results shown in Fig. 7 indicate that the Ar-0 (20%) plasma is considerably more capable of vaporizing the elemen-836 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 1 140 ( a ) 120 100 80 60 - - - - - 140 cn i7 120 60 40 20 0 1 I I 1 I I I 1 I 30 40 0 10 20 30 40 L I I 0 10 20 30 40 0 10 20 30 40 0 10 20 30 40 Tiine/s Fig. 4 Signals for Mn (10 ng aqueous sample solution residue) (a) Ar plasma; (b) Ar-0 (2%) plasma; (c) Ar-air (2%) plasma; ( d ) Ar-N2 (2%) plasma; and (e) insertion into an Ar-air (2%) plasma after insertion into an Ar plasma 1 I I I I 0 1 2 3 4 5 N2 in Ar (%) Fig.5 Effect of plasma power and N1(%) on the vanadium signal (peak area) at A 2.0; B 1.75; C 1.5; and D 1.25 kW tal constituents in samples than is the Ar-N (2%) plasma.This is borne out by the signals shown in Fig. 8. In contrast to the aqueous solution residue samples run so far the samples utilized to obtain the signals shown in Fig. 8 were a variety of materials with complex matrices and were run directly. The A1203 samples were Spex TSAL-1 (Spex Industries Edison NJ USA) A1,0 five-step standards. About 0.2 mg of the powdered sample was added to the graphite probe followed by direct insertion of the probe into the plasma. Signals are shown for 0.033% Cu [Fig. 8(a)] 0.0033% Zr [Fig. 8 ( d ) ] and 0.033 YO Ti [Fig. 8 ( g ) ] . The A1 alloys were either Alcan (Alcan International Kingston Ontario Canada) or Alcoa (Aluminium Company of America PA USA) standard reference materials (Table 4). These materials were run as filings.About 0.2mg of sample was placed in the graphite probe followed by direct insertion into the plasma. For quantitative work A1 was used as the internal standard. Signals are shown in Fig. 8 for 0.03% Cu [Fig. 8(b)] 0.31 YO Cu [Fig. S(e)] and 0.025% Ti [Fig. 8(h)] in both low and high alloy Al. The rice sample was National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 1568a Rice Flour. The graphite probe was loaded with 5mg of sample taken directly from the bottle. The sample was then dried in the probe under an IR lamp and was ashed in situ just under the plasma by inserting the probe to a position 19mm below the top of the load coil for 30s before final insertion.Signals shown in Fig. 8 are for 2.4 ppm Cu [Fig. S(c)] and 4.4 ppm A1 [Fig. S(f)]. The oil samples were prepared from Conostan S21 (Conostan Division Conoco OK USA) a standard contain- ing 21 elements at the 500ppm level. Lower concentrations were prepared by dilution of this stock solution with Conostan base oil. For analysis 10 pl of oil were added to the graphite cup and it was placed under an IR lamp for 20min. The samples were then ashed in situ in the same manner as described for the rice sample. The signal for 1 ppm of Fe in oil is shown in Fig. 8(i). Overall the time behaviour of the signals (Fig. 8) is more complex than that observed for the solution residues shown earlier and they are also matrix dependent.In fact they are reminiscent of what would be observed in a d.c. arc moving plate time study. However quantitation is possible using integrated signal intensities (i.e. signal area) as is shown later.JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 837 Table 3 Summary of quantitative performance for solution residue samples with Ar-N mixed gas DSI-ICP-AES Element v Ni c o Ag Cr Cd c u Fe Zn Mn A/nm 292.4 231.6 228.61 328.07 205.55 226.5 324.75 259.94 2 13.86 257.61 Range/ng 1 .o- 1000 0.1 - 1 000 0.1-1000 0.1-lo00 0.1- 1000 0.1 - 1000 0.1-1000 0.1 - 1000 0.1 - 1000 0.1 - 1000 Slope of log-log plot 1.15 0.87 0.92 0.98 0.98 0.95 0.95 0.99 0.92 0.94 R 0.997 0.994 0.99% 0.999 0.999 0.999 0.999 0.998 0.999 0.999 LOD/pg* 3 80 420 60 40 30 3 15 11 5 3 R S D f( "/o) 55 7 7 8 12 5 14 5 10 4 * LOD = 3(SD),/S; ( SD)b =standard deviation of peak areas of eleven blank runs; S = sensitivity.t RSD calculated from peak areas of eleven 1 ng samples. 0 0.1 1.0 10.0 100.0 1000.0 Log (masdng) Fig.6 Log-log calibration curve for chromium run as aqueous solution ( 10 pl) sample residues in an Ar-N (2%) plasma. Each point is the average of three replicate determinations and the slope of the plot is 0.98 250 200 150 100 A v) c .- 5 50 2 I! e o 5 250 c .- - ro C 5 200 150 100 50 0 50 ( a ) I 40 10 20 30 40 50 0 10 20 30 40 50 30 20 20 40 60 80 0 20 40 60 80 Time/s Fig. 7 Comparison of vanadium signals for (a) and (b) Ar-N (2%) and (c) and ( d ) Ar-0 (20%) plasmas.Signals shown are for the first insertion [(a) and (c)] and for the fifth insertion (b) and for second insertion ( d ) of a sample probe. The sample was 10 pl of a 100 pg ml-' aqueous solution The signals shown in Fig. 8 for both Zr and Ti should be noted. These are both quite refractory elements (see Table2) and neither could be seen using a normal Ar plasma or an Ar-N mixed-gas plasma. With the Ar-0 mixed gas plasma the baseline of the signal tended to increase during an insertion run. This happens because the background emission from the plasma increases as the probe burns away. A blank trace representing this behaviour can be measured by running an empty sample probe and analyte traces can be corrected by subtraction. This type of correction has been applied to the Zr and Ti signal traces shown in Fig.8. Calibration curves for Si and Cu in A1 alloys are shown in Fig. 9. The alloys were standards obtained from Alcoa and Alcan and ranged from low to high alloy A1 samples (Tables 4 and 5). Signals from both the low and high alloy samples are plotted on the same calibration curve. The Si concen- trations ranged from 0.001 to 11.85% and the Cu con- centrations from 0.0013 to 3.83%. The samples were run directly as filings ( = 0.2 mg) with no other sample preparation. Aluminium was used as an internal standard. The plasma was an Ar-0 (20%) plasma run at 2 kW and the observation time was 120 s. In addition calibration curves (not presented) were established for Fe Ti and Mn in these A1 alloys and they were comparable in quality to those shown in Fig. 9.Calibration curves for Ti Zr and V in A1203 are shown in Fig. 10. Although not shown comparable data were also obtained for Mn and Cu. The samples are Spex A1203 Table 4 Sample information for Alcan A1 standards Concentration in sample (mass-%) Element c u Fe Mg Mn Ni Si Ti Zn Bi Cr Pb Sn Be Ca Cd c o Ga Li Na Sr v Zr 2s DZ 0.041 0.54 0.035 0.042 0.045 0.22 0.041 0.046 0.059 0.046 0.045 0.045 - - - - 0.022 - - - 0.007 - 1s WL 0.03 0.26 0.015 0.023 0.022 0.08 0.025 0.023 0.018 0.0 19 0.018 0.024 0.029 0.0005 0.006 0.001 3 0.012 0.0019 0.001 1 0.00 19 0.0 19 0.013 1s WM 0.006 0.082 0.005 0.005 0.006 0.072 0.005 0.0 16 0.007 0.006 0.006 0.006 0.0007 0.00 19 0.004 0.01 0.0022 0.001 2 0.004 0.018 - - 1s XD 0.013 0.09 0.006 0.005 0.005 0.06 0.013 0.005 0.006 0.006 0.006 0.006 - - - - 0.001 - - - 0.001 - 1s CXG 0.022 0.33 0.25 0.026 0.023 0.2 0.02 0.027 0.022 0.018 0.019 0.024 0.007 0.005% 0.018 0.02 0.015 0.002 1 0.0026 0.008 0.034 -838 ( d) v) + '2 250 - 3 $ 200 - - JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL.9 250 200 300 250 200 150 100 50 0 300 250 200 150 100 50 0 300 ( C) - 0 10 20 30 40 50 0 20 40 60 80 100 120 0 20 40 60 80 100 120 300 250 ; 1 200 150 0 20 40 60 80 100 120 0 20 40 60 80 100 120 0 10 20 30 40 50 200 250 t 150 - - 0 20 40 60 80 100 120 0 20 40 60 80 100 120 Timeis 0 20 40 60 80 Fig. 8 Examples of DSI signals using an Ar-02 (20%) plasma for (a) Clu (0.033%) in Al,O,; (b) Cu (0.03%) in A1 low alloy; (c) Cu (2.4 ppm) in rice; ( d ) Zr (0.0033%) in Al,O,; (e) Cu (0.31%) in A1 high alloy; (f) A1 (4.4 ppm) in rice; ( g ) Ti (0.033%) in A1,0,; (h) Ti (0.025%) in A1 low alloy and (i) Fe (1 ppm) in Conostan S21 oil Table 5 Sample information for Alcoa A1 standards Concentraition in sample (mass-%) Element SS3 19-E6 SSAl32-AA SS360-C SA 1 169-2 SA1170-6 SA909 SA1507-7 c u Fe Mg Mn Ni Si Ti Zn Cr Pb Sn Ga v 3.83 0.68 0.18 0.58 0.2 6.23 0.10 0.35 1.02 0.77 1.26 0.070 2.52 11.85 0.057 0.058 0.0005 0.3 1 0.8 0.52 0.22 0.26 9.17 0.079 0.25 0.057 0.16 0.062 0.21 0.26 0.038 0.076 0.1 0.02 1 0.021 - - 0.1 0.56 0.009 0.027 0.23 0.039 0.039 - 0.03 1 0.082 0.030 0.03 1 0.034 0.06 1 0.03 0.03 0.027 0.03 0.026 - 0.0013 0.00 1 < 0.0002 < 0.0002 < 0.0002 0.00 1 0.001 0.001 < 0.0002 0.001 0.001 0.001 -JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL.9 839 m m I 0 0.001 0.01 0.1 1 .o 10.0 k 3 Y m 0 Q. 0 2 L 1 1 0 -1 0 0.001 0.01 0.1 1 .o 10.0 Log [concentration (%)I Fig. 9 Calibration curves for (a) Si and (b) Cu in low and high allow aluminium. The slopes of the curves are 0.9 (Si) and 0.89 (Cu) 3.0 2.5 ( a ) - 2.0 1.5 1 .o 0.5 0 -1.5 -1 About 0.2mg of powder was added to the sample cup the signals were recorded for 120s and the plasma power was 2 kW. The results shown in Fig. 10 indicate that DSI-ICP- AES with an Ar-0 mixed-gas plasma is applicable to the determination of refractory elements in a difficult matrix. Detection limits were determined using 0.2 mg of the 0.001 % level samples. The 3s detection limits (n= 11) are 35 pg (Cu) 10 pg (Mn) 90 pg (V) 100 pg (Zr) and 80 pg (Ti).Calibration curves were also established for Mn Fe Cu Ni and V in oil using the DSI system with the Ar-0 mixed gas plasma. The only sample treatment was to pipette 10 pl of oil into the probe cup and dry it under a heat lamp for 20min. In addition an in situ ashing step was implemented for these samples by positioning the sample probe 19 mm below the top of the load coil for 30 s before insertion. The plasma was again an Ar-0 (20%) plasma run at 1.75 kW and the observation time was 70 s. The calibration curves (0.1 to 500 pg ml-l) for Ni and V are shown in Fig. 11. The samples were prepared from Conostan S21 engine oil standard with Conostan 75 base oil used as the diluent. The 3s detection limits (n = 11) for these oil samples were 350pg (V) 520pg (Ni) 25 pg (Cu) 60pg (Fe) and 25 pg (Mn).It should be noted that only about 0.2 mg of sample was run for the analysis of the solid and powdered materials. Larger sample loads took too long to burn off tended to spatter out of the cup or gave signals that saturated the photomultiplier tube. The low sample load that was used resulted in higher detection limits and can lead to large sampling errors for heterogenous samples. So far there has been no evidence of unusual scatter on the calibration curves that have been established which indicates that the samples are homogeneous. It would however be useful to have more flexible control over the gain on each channel of the direct reader and a system is being designed that incorporates a programmable gain option for each channel.Finally in a related study carried out in this laboratory Ying and Kratochvil" analysed a number of agriculture/food reference materials using DSI. These materials were analysed directly and included NIST SRM 1572 (Citrus Leaves) SRM 1568a (Rice Flour) SRM 1567a (Wheat Flour) RM 8413 (Corn Kernel) RM 8412 (Corn Stalk) and a variety of potential Canadian reference materials such as wheat gluten corn bran Durum soft winter and hard red spring wheat flours whole 0 0.001 0.01 0.1 Log [concentration (%)I Fig. 10 Calibration curves for (a) Ti; (b) Zr and (c) V in A1,0 base standards. The slopes of the curves are 1.15 (Ti) 1.03 (Zr) and 1.09 ( V ) standards originally used in d.c. arc analyses. Shao and Horlick" analysed these materials using DSI-ICP-AES but were unable to obtain quantitative results for refractory elements such as Ti Zr and V.For this work the samples were not weighed but A1 was used as an internal standard. 0 1.0 10 100 1000 Log (mass/ng) Fig. 11 the curves are 0.98 (Ni) and 0.99 (V) Calibration curves for (a) Ni and (b) V in oil. The slopes of840 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 milk powder whole egg powder cellulose starch and bovine muscle powder. The DSI-ICP-AES technique proved effective in determining the trace element composition of all these samples and the results will be presented in a separate report. Conclusions The utilization of mixed-gas plasmas clearly augments the performance of DSI-ICP-AES for the direct analysis of mate- rials. The trace element composition of a number of important types of samples can now be directly determined with a minimum level of sample preparation.The study by Ying and Kratochvil’* mentioned above focused in part on an assess- ment of the trace element homogeneity of agricultural/food reference materials a study that would have been difficult without DSI technology. Future studies will focus on the direct analysis of soil samples and on automation of the DSI system to allow computer controlled insertion of a series of DSI sample probes and computer controlled gain for each measure- ment channel of the direct reader. Financial support by the Natural Sciences and Engineering Research Council of Canada (NSERC) and the University of Alberta is gratefully acknowledged. 1 2 3 4 5 6 7 8 9 10 11 References McLeod C. W. Routh M. W. and Tikkanen M. W. ‘Introduction of Solids into Plasmas’ in Inductively Coupled Plasmas in Analytical Atomic Spectroscopy ed. Montaser A. and Golightly D. W. VCH Publishers New York 2nd edn. 1992 p. 721. Karanassois V. and Horlick G. Spectrochim. Acta Rev. 1990 13 89. Sommer D. and Ohls K. Fresenius’ 2. Anal. Chem. 1980,304,97. Pettit W. E. and Horlick G. Spectrochim. Acta Part B 1986 41 699. Karanassios V. and Horlick G. Spectrochim. Acta Part B 1990 45 85. Chan W. T. and Horlick G. Appl. Spectrosc. 1990 44 380. Choot E. H. and Horlick G. Spectrochirn. Acta Part B 1986 41 889. Stallwood B. J. J. Opt. SOC. Am. 1954 44 171. CRC Handbook of Chemistry and Physics ed. Weast C. R. CRC Press Boco Raton 59th edn. 1978-1979. Shao Y. and Horlick G. Appl. Spectrosc. 1986 40 386. Ying L. and Kratochvil B. in preparation. Paper 3106651 G Received November 5 1993 Accepted March 22 1994

ISSN:0267-9477    

DOI:10.1039/JA9940900833

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 84 1 Effect of Colloidal Stability of Ceramic Suspensions on Nebulization of Slurries for Inductively Coupled Plasma Atomic Emission Spectrometry* Juan C. Fariiias and Rodrigo Moreno lnstituto de Cerarnica y Vidrio (C. S. 1. C.) 28500 Arganda del Rey Madrid Spain Jean-Michel Mermet Laboratoire des Sciences Analytiques Universite de Lyon I 69622 Villeurbanne Cedex France The direct solid analysis of ceramic powders can be carried out by inductively coupled plasma atomic emission spectrometry (ICP-AES) using slurry sample introduction. However a highly stable suspension is needed in order to obtain a representative aerosol for introduction into the ICP. In this work the importance of the effect of the rheology and the stability of the ceramic suspensions on the analytical results provided by slurry nebulization ICP-AES is demonstrated.The basic concepts involved in the stabilization and homogenization of ceramic slurries are discussed. A general overview of the stabilizing mechanisms (electro- static steric and electrosteric) and the role of the different stabilizing additives and the most adequate use of them is described. Alumina (A1,03) slurries as a case study are discussed. The rheological parameters such as zeta potential viscosity and sedimentation have been studied by changing the pH of the slurry and by introducing different dispersing additives (Dolapix PC-33 Darvan-7 Darvan-C sodium hexametaphosph- ate glycerol plus Kodak photoflow Triton X-1 00 and Produkt PKV-5088). Their effect on stability is discussed as well as the relationship between the stability of the slurry and the intensity and precision of the measurements provided by ICP-AES.It is clearly demonstrated that higher intensities and lower relative standard deviation values are obtained for a well-dispersed stable slurry. Keywords Inductively coupled plasma atomic emission spectrometry; signal enhancement; slurry nebuliz- ation; ceramic suspension; colloidal stability Inductively coupled plasma atomic emission spectrometry (ICP-AES) is nowadays the most appropriate technique for the chemical analysis of ceramic materials.'-5 However this technique requires that the sample be in solution prior to the analysis. The process of dissolution can lead to problems including losses of volatile elements contamination increase in the analysis time dilution of the analyte etc.In order to avoid these problems direct solid analysis by ICP-AES using slurry sample introduction techniques has received increasing interest over the last few years. The technique has been applied to different inorganic and ceramic materials such as k a ~ l i n ~ . ~ soils,1o slags," geological materials,12-16 firebrick,l7 alumina (A1203),18-20 silica ( SiO,)," titania ( Ti02),21 zirconia (Zr02),22 silicon carbide ( SiC)'9,20 and silicon nitride (Si3N4).23 The two main factors determining the capability of the technique are the particle size of the starting p o ~ d e r s ~ * " * ' ~ ~ ~ and the stability and homogeneity of the s l ~ r r i e s . ~ ~ - ~ ~ The effect of particle size has been studied by different workers either by using several particle size fractions of one sample (e.g.k a ~ l i n ~ clays,' slags," whole or by using materials with different particle sizes (e.g. kaolin,6 A1203,18'19 Si3N4',). In these investigations a definite relationship between particle size and transport and atomization efficiencies is demonstrated. It has been proved that large particles are excluded by the spray chamber and do not reach the plasma,6~18.19*24 and that only small particles contribute sig- nificantly to the analyte atomic emission signal. Different workers recommend working with particle sizes lower than around 10,23,26 8' and 5 pm.I8 The effect of the stability and homogeneity of the slurries has not been studied thoroughly in the literature.However a highly stable and homogeneous slurry is required in order to achieve a homogeneous reliable aerosol for introduction into the plasma in order to provide precise and accurate analytical results. The literature reports only on the introduction of * Presented at the 1993 European Winter Conference on Plasma Spectrochemistry Granada Spain January 10-1 5 1993. different additives to assure these characteristics of the slurry. Table 1 shows the different stabilizing methods that have been used for several types of inorganic materials. The following key aspects can be noted in this table. ( i ) In samples of the same type a great variety of different additives has been employed. For silicate-based materials (soils clays kaolins etc.) the following additives have been used glycerol + Kodak photoflow tetrasodium pyrophosphate (Na,P207) Triton X-100 NH solution HCl and HN03.For advanced ceramic materials (A120 TiO ZrO Sic Si,N4) glycerol sodium hexametaphosphate (NaHMP so-called Calgon) alone or mixed with monoisopropanolamine and ethanol have been used. In some cases no additives were employed. (ii) The same additives have been used by several workers with large differ- ences in their concentration varying by up to a factor of 100 (e.g. Triton X-100 and NaHMP); and (iii) in many cases no additives have been used. In these cases a simple agitation either mechanical or ultrasonic was used to disperse the powders. In any instance it seems that all the additives and stabilizing procedures have been used empirically and without a real understanding of their role in the suspension and stability mechanisms. Most of them may not be the most suitable and can be modified in order to enhance the stability properties of the slurry.Nevertheless some workers have shown an interest in some of the parameters involved in the stability of the slurries to be analysed by ICP-AES. Ebdon and Collier6 have compared the effect of three dispersants Calgon Dispex (sodium polyacryl- ate) and NH solution for kaolin slurries showing that NH solution is the most adequate; they studied the influence of NH concentration on the atomization efficiency and the influence of the slurry viscosity on the nebulization efficiency. Fernandez et a/." have also studied the effect of three disper- sants (Triton X-100 Na4P,07 and NH solution) in slag slurries; they also found that the most effective was NH solution.Laird et al.' calculated the percentage recovery in slurries of clay minerals when different concentrations of HNO,Table 1 Additives used in the literature for stabilizing suspensions of inorganic materials Concentration (%) 40 40 40 0.01 0.04 0.1 0.5 1 0.05 0.1 1 0.006 0.01 0.02 0.1 0.5 0.1 10 10 90 0.35 0.35 3.1 1 mol I-' 2 moll-' - - - - - - - Main additive Glycerol Other additives HC1 (0.5 mol 1 - I ) Kodak photoflow (0.2%) Comments 90 rnin ultrasonic agitation As an antifoaming agent and a dispersant. 10 rnin ultrasonic agitation 5 min magnetic agitation and 30 min ultrasonic bath to complete the dispersion 10 s ultrasonic probe Protective colloid.2 10 min magnetic agitation - - Sample ZrO Geological materials Technique ICP-AES ICP-AES Ref. 22 12 14 13 16 27 28 29 30 24 17 15 10 31 21 32 i 8 23 33 34 31 35 1 1 6 7 36 16 9 8 37 38 39 40 19 41 Kodak photoflow (2%) - Geological materials Silicate materials ICP-AES ICP-AES Triton X-100 HN03 (5%) - Coal and coal fly ash Iron oxide pigments Bituminous and sub-bituminous coal Whole coal Firebrick ETAAS * ETAAS* ICP-AES Wetting and dispersing agent As a dispersant ICP-AES ICP-AES Tetrasodium p y rophosphate ( Na4Pz07 1 As a dispersing agent Dispersant solution Thixotropic slurry Geochemical materials Soils Whole coal ICP-AES FI-ICP-AESt ETAAS* - - H2 antifoam agent (0.2%) and Viscalex HV30 thixotropic thickening agent (2%) Monoisopropanolamine (0.020/,) pH = 10 70 "C - Sodium hexametaphosphate [(NaPO3)J Ti02 ICP-AES > 10 min magnetic agitation Iron oxide and titanium oxide Refractory materiais Si3N Coal Whole coal Whole coal pigments a-AI203 CV-AAS f ICP-AES ICP-AES ICP- MS§ ETAAS* ETAAS* ETAAS* Dispersing agent As a dispersant. 1 min ultrasonic agitation As a dispersant Wetting agent.5 min magnetic agitation Wetting agent. 5 min magnetic agitation As a dispersant. 8 rnin ultrasonic agitation and 2 3 rnin 15 min ultrasonic bath and magnetic agitation As a dispersant. 30 rnin ultrasonic bath6 and magnetic magnetic agitation agitation6s7 - 5 min magnetic agitation and 30 rnin ultrasonic bath 15 s ultrasonic probe Sonicated for 30 s at 40 W and magnetic agitation 5 min magnetic stirring 3 5 min magnetic stirring 3 min magnetic stirring Vortex mixing - Aerosol OT Ethanol - HNO (0.5%) HNO ( 5 % ) - NH solution Slags Kaolin ICP-AES ICP-AES Kaolin Silicate materials Clays Clay minerals A1203 Soils Soil River sediment Refractory oxide powders (Al,O SiO and Sic) Sic DCP-AESI ICP-AES ICP-AES ICP-AES ETAAS* ETAAS* ETAAS* ETAAS* ICP-AES HNO HC1 None ETAAS * 15 rnin ultrasonic bath and magnetic agitation * Electrothermal atomization atomic absorption spectrometry.t Flow injection inductively coupled plasma atomic emission spectrometry. 1 Cold vapour atomic absorption spectrometry. 3 Inductively coupled plasma mass spectrometry. 1 Direct current plasma atomic emission spectrometry.JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 843 were added.Lopez Garcia and Hernandez Cordoba2* studied the stabilization provided by Triton X-100 at different concen- trations on iron oxide pigments. Van Borm et aL2’ focused on the importance of pH adjustment in stabilizing A1203 and Sic slurries. In most instances however a lack of understanding about the processes involved in the colloid chemistry of the slurries can be observed. For this reason the aim of the present work deals with two main objectives (1) to clarify the most important funda- mentals on which the theory of slurry stabilization is based showing the different types of stabilizing adhtives and the most adequate use of them; and (2) to demonstrate the influence of the stability on the intensity and precision of the ICP-AES measurements and consequently on the analytical results.Alumina slurries under different pH conditions and with different stabilization agents are reported as a case study. Theoretical Considerations Stabilization of Ceramic Slurries The stability of a suspension depends on the interaction among the particles. There is an attractive interaction due to the London-Van der Waals forces which tend to link the particles to each other. On the other hand when the particles are immersed in a polar liquid they develop an electrical double layer around them. This double layer provides a repulsive force among the particles. The slurry stability is only achieved when the repulsive interaction dominates over the attractive London-Van der Waals forces. This constitutes the electrostatic stabilizing r n e ~ h a n i s m ~ ~ ’ ~ ~ which can be provided by the following agents pH electrolytes and surfactants.Another possible kind of stabilization is the polymeric mechanism in which the stability is provided by means of long-chain polymers adsorbed onto the surface of the particles preventing contact between them. This mechanism usually known as the steric stabilizing mechanism is preferred in the case of high solids loading suspensions in non-aqueous media. A third possible mechanism is the so-called electrosteric stabilizing mechanism which results from a combination of both electrostatic and steric mechanisms. Electrostatic stabilizing mechanism When a particle is immersed in a polar liquid a potential gradient is originated between the particle surface and the liquid medium which can be described by the Nernst equation RT ZF E =Eo + - In a where Eo is the standard potential when the activity of the potential determining ion (a) is unity Z is its valence F is the Faraday constant R is the gas constant and T is the absolute temperature.In ceramic suspensions the ions that determine the potential are H+ and OH-. For oxides like A1203 the surface charge is negative and the protons are attracted to the surface thus creating a gradient of concentration from the surface to the liquid (Fig. 1). On the other hand the OH- ion concentration decreases near the surface. These gradients of concentration give rise to a charged layer from the surface to the liquid the so-called electrical double layer. This follows the Stern model which supposes a mono- layer of counter-ions strongly adsorbed to the particle surface and a diffuse layer in which the concentration of counter-ions decreases as the distance increases (Fig.2). When the concentration of the potential determining ion is altered the relative adsorption of ions onto the surface and the surface potential change according to the Nernst equation. There is a certain concentration of potential determining ions Polar liquid Fig. 1 Concentration gradient of H+ and OH- ions for a ceramic oxide particle dispersed in a polar liquid Particle surface /- I- Stern plane d 1/K Distance + Fig.2 Stern model of the electrical double layer. The potential changes from t+ho (surface potential) to t+ha (Stern potential) in the Stern plane and decreases up to 0 in the diffuse double layer 6 is the distance from the particle surface to the Stern plane; 1 / ~ is the Debye length that is the double layer thickness; and z is the potential at the Stern plane at which the positive and the negative surface activities are equal and the net surface potential is zero.This concentration defines the so-called isoelectric point; at this point there is no double layer and the particles flocculate. When a particle surrounded by a double layer is moving through the liquid the Stern layer and part of the diffuse layer move also. The potential at the shear plane is called the zeta potential (4‘).44 The zeta potential value is zero at the isoelectric point. These concepts are schematically illustrated in Fig. 3. The surface potential and the isoelectric point are not affected by the potential determining ions that is the pH.However the counter-ions (those with opposite charge to that of the surface) have a strong effect on the diffuse double layer.844 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 1 Shear plane \ Extension of the diffuse layer of counter-ions Concentration of cations Stern layer Concentration of anions Fig. 3 Double layer model for an electronegative particle immersed in a polar liquid. The potential at the shear plane is the zeta potential An increasing concentration of counter-ions reduces the thick- ness of the double layer and thus the zeta potential because the distance between the surface and the shear plane does not change as plotted in Fig. 4.In practice a slurry becomes stable when the zeta potential value is high far away from the isoelectric point. This fact usually makes necessary the addition of one of the following dispersants (i) a potential determining ion (that is a pH modification); or (ii) a counter-ion. The effect of a counter-ion is given by the flocculation value (the concentration required to produce flocculation). This value decreases when the coun- ter-ion charge increases and for a series of ions of the same charge decreases when the relative atomic mass increases. For this reason monovalent ions (e.g. Na' NH4+) are preferred to disperse ceramic powders. The most usual dispersants for ceramic slurries are sodium orthophosphate (Na3P04) sodium acid pyrophosphate ( Na,H2P20,) Na4P,0 sodium tripoly- phosphate ( Na5P3OIo) and NaHMP (a cyclic structure with 6- 13 phosphate groups).In non-aqueous media the electrostatic repulsion is less Distance t Shear plane Fig. 4 Effect of concentration of counter-ions on the zeta potential. As the shear plane is located at a fixed distance the zeta potential I(/sl (ix. the potential energy at the shear plane) is higher for lower counter- ion concentration A. For higher concentrations B the zeta potential I(/s2 decreases effective due to the lower ionic concentration and the lower dielectric constant of organic liquids. However electrostatic stabilization can be achieved by means of surface active agents surfa act ant^).^' These agents have a hydrocarbon chain (lyo- phobic) and a polar group (lyophilic). The hydrocarbon part is soluble in oils while the head group is soluble in water.The surfactants may be non-ionic anionic or cationic depending on the charge of the head group. Usually the surfactants contain groups such as OH- -COOH -SO3- -NH2- -OS03- NH4+ etc. the most commonly employed being the following. Non-ionic Triton X (polyethyleneoxy- ethanol) and alkalonamides; anionic phosphate ester sulfosuc- cinate and sodium dodecylsulfate; and cationic quaternary ammonium. Steric stabilizing mechanism This mechanism is based on the adsorption of macromolecules onto the particle surface.46 Steric stabilization is preferred in organic media. However in order to provide the required stability the steric stabilizers must have relative molecular masses higher than 10000.On the other hand they must anchor strongly to the surface. The steric model is shown schematically in Fig. 5 (a). Poly(methy1 methacrylate) poly- acrylamide polystyrene poly(viny1 acetate) etc. are commonly used to provide steric stability which is advantageous for both aqueous and non-aqueous media since sterically stabilized particles can be thermodynamically stable whereas electro- statically stabilized particles are only metastable. The magni- tude of the steric repulsion depends on the surface coverage the configuration of the adsorbed polymers and the thickness of the adsorbed layer. Electrosteric stabilizing mechanism Under some conditions a combination of electrostatic and sferic mechanisms can be useful to enhance stability. This combination is referred to as the electrosteric mechanism which generally originates from charges associated with the anchored polymer that is a polyelectrolyte [Fig.5(b)].47 The use of polyelectrolytes is common practice in dispersing Fig.5 Stabilization of slurries by means of the adsorption of long- chain polymers onto the surface (a) steric mechanism in which the stability is achieved by steric hinderance and (b) electrosteric mechan- ism in which the steric effect is reinforced by the presence of charges along the chain providing an electrostatic repulsionJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 845 ceramics the most usually used being the salts of organic tannic acids humic acids and polycarbonic acids. Rheology of Ceramic Slurries As reported by other workers,6 the viscosity influences both the aspiration rate and the nebulization process.The basic concepts of rheology4* are discussed below. The viscosity of a suspension is a measure of the internal resistance of its parts to the relative movement. The viscosity is Newtonian when the shear force per unit of area z between two parallel planes of moving liquid is proportional to the rate gradient duldx T = ~ I du/dx where y~ is the viscosity whose units are Pa s. This is the ideal behaviour of liquids but usually ceramic slurries do not show this ideal behaviour and the viscosity value depends on the shear rate. Furthermore the rheological behaviour can show a time dependency. Steady-state behuviour When the particles tend to agglomerate an increasing shear rate breaks the contacts between particles and the viscosity decreases.This phenomenon is known as pseudoplasticity or shear-thinning. Plasticity is very similar but in this instance the suspension does not flow until a certain shear stress limit is achieved. This limit is known as the yield point. A third type of behaviour is the so-called dilatancy or shear-thickening in which the viscosity increases with the shear rate. These three types of behaviour are plotted in Fig. 6(u). Time-dependent behaviour Two general types of behaviour exist. Thyxotropic behaviour is similar to plastic or pseudoplastic behaviour but depends on time. When a thyxotropic slurry is sheared at a constant rate the viscosity decreases; when the shear stops the system acquires its starting structure thus giving rise to a thyxotropic cycle.This behaviour is shown in Fig. 6(b). Shear rate - Shear rate -+ Shear rate - Fig. 6 Non-Newtonian rheological behaviour of slips. There are two general kinds of behaviour those showing no time dependency (a) and those varying with time thyxotropy (b) and rheopexy (c) Fig. 7 Structure of slurries of plate-like particles and possible aggre- gation mechanisms. When the system is relaxed the plates are parallel (a); when a disturbing force is applied the plates become disorientated forming structure by means of face to face interactions (b) giving place to card-pack aggregation (c) or by means of edge to face interactions card-house aggregation ( d ) The time-dependent effect in which the viscosity increases with time at a constant shear rate is known as rheopexy [Fig.6(c)]. The rheology of a slurry is very dependent on the shape of the particles. In general spherical particles show no time dependency. But in the case of platelets or rod-like particles some aggregation exists especially for highly concentrated slurries. This case can be illustrated as in Fig. 7(a) and (b) for a mass of platelets suspended in a liquid.49 When there is no external disturbing force the platelets arrange themselves with their long axes horizontal and parallel to each other [Fig. 7(a)] when this suspension is disturbed the particles become dis- orientated since they have to re-disperse in a new plane [Fig. 7(b)]. This is the case with highly concentrated slips of clays in which the surface has a negative net charge while the edges have a positive net charge.When the solids content increases the platelet particles attract each other to form aggregates [Fig. 7(c) and (43. This fact is responsible for the time dependent behaviour of concentrated clay slurries. Experimental Instrumentation The pH measurements were performed by using a Metrohm Model 691 pH meter. The zeta potential and the viscosity were measured with a mass transport analyser (Micromeritics USA) and with a rotational viscometer (Haake Rotovisco RV20 Germany) respectively. The ICP-AES measurements were performed with a Spectroflame-ICP D system from Spectro Analytical Instruments (Germany). This system is equipped with a 27 MHz generator and a dual monochromator. A high power of 1600 W and a low carrier gas flow rate of 0.6 1 min-' were used in order to minimize the possible problems due to incomplete volatilization of the particles.The i.d. of the injector was 1.7 mm. A conespray nebulizer and a single-pass spray chamber were used. Measurements of the line intensities were carried out based on the use of the standard direct peaking mode procedure. Both this procedure and a long integration time 10 s resulted in a lowering of the observed fluctuations of the signal due to the random injection of the particles and consequently in a decrease of the relative standard deviation (RSD) values. The elements and lines studied were the follow- ing the macro-constituent (A1 308.215 nm) and three minor elements (Ca 393.366 nm Si 288.158 nm and Fe 238.204 nm).846 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL.9 .. Reagents The desired pH was attained by adding either HCl or NH40H (Merck Germany); NaHMP (Carlo Erba Italy) was used as the inorganic electrolyte. Different surfactants and polyelectro- lytes were used to stabilize the slurries Triton X-100 (Fisher USA) and glycerol (BDH UK) plus Kodak photoflow liquid (Eastman Kodak USA) were used as surfactants. The polyelec- trolytes were Dolapix PC-33 (Schimmer-Schwarz Germany) Darvan-7 and Darvan-C (Vanderbilt USA) and Produkt PKV-5088 (Schimmer-Schwarz Germany). Samples A commercial A1203 powder prepared in two different milling steps was used (Al,03 Alcoa CT-3000 and CT-3000 SG). The first has aggregates with a mean size above 20 pm. The superground (SG) powder is a milled powder with a mean particle size of 0.5 pm in which the presence of soft agglomer- ates (about 4 pm) can be observed.Procedure The coarse powder was studied by using sedimentation tests. The fine powder was studied by means of zeta potential viscosity and sedimentation tests. The zeta potential was measured for concentrated aqueous slips as a function of pH and viscosity measurements were performed for concentrated slurries as a function of both pH and NaHMP concentration. The sedimentation tests were performed in 25 ml graduated test tubes for different de-flocculation conditions. The slurries were prepared with a solids content of 1% m/m followed by 15 min of agitation in an ultrasonic bath prior to the test. In order to achieve the best stability and homogeneity of the slurries different kinds of dispersants were used (1) changes in pH by adding HC1 or NH40H; (2) inorganic dispersants such as NaHMP; and (3) organic dispersants either surfactants or polyelectrolytes at different concentrations.For ICP-AES 20 consecutive emission intensity measurements from 2% m/m slurries were performed for each slurry and for each element. Results and Discussion Influence of pH on the Slurry Stability The zeta potential versus pH of A1203 fine powder is plotted in Fig. 8. As can be seen the isoelectric point occurs at pH 9. At this point the slurry is not stable. According to this plot stability could be achieved at either acidic or basic pH values because in these pH zones maximum zeta potential values are obtained.However in the basic zone very high viscosities are obtained when the pH is increased with NH40H.” This can be seen in Fig. 9 which shows the viscosity of alumina slurries at different pH values where the basic zone is not included since the viscosity is very high (out of scale of the viscometer). 40 m 35 t C O I I I 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 PH Fig. 9 Apparent viscosity versus pH for concentrated A1,0 slurries (shear rate= 100 s - l ) . The minimum viscosity is achieved at pH 4-5 As expected the minimum viscosity occurs at those pH values where the zeta potential is at a maximum i.e. pH4. This result is in good agreement with the expected result as pointed out before. Therefore the most appropriate conditions for the preparation of a homogeneous slurry is pH 4-5.The measurements mentioned above can also be verified with sedimentation tests. Thus the sedimentation curve of alumina slurries at different pH values is plotted in Fig. 10. From this curve it can be seen again that the best stability is achieved in the acidic zone. The slurry at pH 9 exhibits a very high sedimentation rate as expected taking into account that this pH corresponds to the isoelectric point. At pH 10 par- tial sedimentation occurs as predicted by the viscosity measurements. On the other hand the behaviour of the coarser alumina powder is governed by the presence of large hard agglomerates. In this instance the mixing of the powder is very difficult as the agglomerates settle when agitation stops. The sedimen- tation curve for this powder is shown in Fig.10; the pH control is not sufficient itself to provide the required stability. This stability can only be achieved by milling the starting agglomer- ated powder in a ball mill. In this instance as the agglomerates may be broken down dispersion of the powder is most likely to occur. All these data clearly demonstrate the determining role of the pH as an electrostatic stabilizer. The H + or OH- ions known as potential determining ions act on the particle modifying the electrical double layer thickness as discussed under Theoretical Considerations. Some workers as can be seen in Table 1 have added acidsg.16 or b a ~ e ~ ~ ~ ~ ~ but 30 I 0 2 4 6 8 10 12 14 Ti m e/m i n 6 5 6 7 8 9 10 1 1 12 13 PH Fig. 8 Zeta potential oersus pH of alumina slurries showing that the isoelectric point occurs at pH x 9 Fig.10 Sedimentation behaviour of A1,0 slurries fine grained CT-3000 SG at A pH 2.3 4 and 5.9; B pH 10.9; and C pH 9 and coarse agglomerated CT-3000 at D pH 2.3 4 5.9 9 and 10.9. The sedimentation height was defined as the height of the sedimentation front in a graduated test tubeJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 847 160 2 E 120 8 80 v) -- c > v) v) .- 5 40 surprisingly they do not report the pH which is the parameter that actually controls the stability. - - - - Influence of Dispersants on Slurry Stability Different kinds of dispersants were studied by using sedimen- tation tests. In all cases the final pH values provided by the addition of these dispersants are between 8.8 and 9.2 (ie.the pH of minimum stability). The results are shown in Fig. 11. Firstly an inorganic dispersant usually employed in cer- amics such as NaHMP," is considered. Slips de-flocculated with this dispersant are stable with time and no sedimentation occurs as reported el~ewhere.~~ The use of NaHMP has also been reported for slurries of ceramic powders such as A1203,'* Ti0221 and Si3N4,23 at concentrations of 0.1 0.01 and 0.5% respectively using ICP-AES. However the effect of the disper- sant must also be controlled because an excess can be deletere- ous to the stability of the slurry. This fact is demonstrated in the present work for A1203 slurries. Fig. 12 shows the effect of the concentration of NaHMP on the viscosity of A1203 slurries. As can be seen the viscosity first decreases and then above a concentration of 0.1% m/m of NaHMP increases i.e.there is a concentration of NaHMP for which the viscosity is at a minimum. Thus in order to disperse a slurry properly adequate control of the additives is required; not only the kind of additive and its properties but also its most effective concentration. A typical surfactant such as Triton X-100 has also been studied. As can be seen from sedimentation behaviour this surfactant does not provide the expected stability in alumina slurries although it has been used for slurry ICP-AES. Other workers have used Kodak photoflow in glycerol to 30 I I A I Fig. 11 Effect of different dispersants on the sedimentation behaviour of the Al,03 slurry CT-3000 SG A Dolapix PC-33 Darvan-7 Darvan-C and NaHMP; B glycerol + Kodak photoflow; C Triton X-100 and D PKV-5088 2oo ; I I I I I I 0 0.2 0.4 0.6 0.8 1.0 [NaHMPl(% m/m) Fig.12 Viscosity of concentrated A1203 slurries as a function of NaH M P concentration disperse geological rnaterial~~'-'~ and ZrO powders.22 The results obtained in the present work indicate that no real dispersion is achieved. A few minutes are sufficient for the sedimentation. However the very high viscosity of glycerol makes sedimentation difficult. Lastly four common polyelectrolytes for dispersing alumina slurries were considered. PKV-5088 is a common dispersant for non-oxide ceramics but does not prevent the sedimentation of A1203. The other three dispersants (Dolapix PC-33 Darvan-C and Darvan-7) are generally used in ceramic slurries of oxides and are obviously able to keep the particles perfectly dispersed.52 As previously indicated all these dispersants modify the pH of the slurry to values of between 8.8 and 9.2.Although this pH corresponds to the isoelectric point the addition of these polyelectrolytes at concentrations of 0.5% m/m with respect to the solids is sufficient to provide the required stability. This fact can be explained by an electrosteric mechanism in which adsorption of the molecules onto the particle surface takes place. Influence of Fine and Coarse Powders on the Intensity and Precision of the ICP-AES Measurements Fig. 13 shows the values of the intensity and RSD for slurries prepared from both A1203 starting powders at the maximum stability pH of 4.The results for the macroconstituent (Al) and those obtained for the three minor components (Ca Fe and Si) are shown in the figure. As can be seen the finest powder gives the highest intensity values and the lowest RSD values. This is particularly important in the case of Al where the intensity increases in a 65 1 ratio although the RSD decreases by a factor of 20. For minor elements particularly Ca this variation is not so clear because the treatment of the slurries at acidic pH in an ultrasonic bath partially dissolves these elements. These differences are related to the stability of the slurry as slurries prepared from the coarse powder do not become stable as coarse agglomerates are present and tend to settle quickly as observed from the sedimentation curves.These agglomerates are rejected during transport and do not reach the plasma. Furthermore the atomization efficiency is lower. There is therefore a diminution of the homogeneity of the aerosol resulting in a lower precision in the measurements. Influence of pH on the Intensity and Precision of the ICP-AES Measurements The effect of the slurry pH on the analytical measurements can be seen in Fig. 14 where the values of intensity and RSD ta Intensity Al ' Ca I Fe I Si Al Ca ' Fe ' Si Element 18 16 14 12 10 * 5 a 6 4 2 0 Fig. 13 Intensity and RSD values of all the elements studied for the starting A1,0 powders at maximum stability conditions (pH = 4) (a) CT-3000; and (b) CT-3000 SGJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL. 9 14 El Intensity m RSD 12 10 8 - s n - 6 4 2 n 2.3 4.0 5.9 9.0 10.9 PH intensity and RSD values of A1 for CT-3000 SG under )H conditions nding to A1 from slurries of fine-grained A120 at pH values are plotted.The higher the stability of the t pH 4) the higher the intensity results and the lower values. Once again the worst results are obtained for st stability that is at the isoelectric point (pH 9). The btained at pH 11 are worse than those corresponding idic conditions which is consistent with the previously results. itensity and RSD values corresponding to the minor (Ca Fe and Si) are shown in Figs. 15 and 16 rely. The behaviour of these minor elements is quite o that of the macroconstituent. ! of the Dispersants on the Intensity and Precision of the S Measurements ct of the dispersant on the intensity and precision is related to the capability of the dispersant to provide ility to the system.urries prepared with the additives NaHMP Dolapix Darvan-7 and Darvan-C present a high stability as :d in Fig. 11. For these additives very high intensities r low RSD values are obtained for A1 as can be seen in These results are very similar to those obtained for prepared at pH 4 (Fig. 14). In contrast the Triton nd PKV-5088 additives do not provide the required A 1 a 2.3 4.0 5.9 9.0 10.9 PH Intensity values of Ca Fe (x40) and Si ( x 30) for CT-3000 r different pH conditions 16 14 12 10 a 6 4 2 n A I I I I I 2.3 4.0 5.9 9.0 10.9 PH Fig. 16 pH conditions RSD values of Ca Fe and Si for CT-3000 SG under different 550 16 I Intensity 14 A v) 4- .- 5 500 12 2 2 9 10 1 +-’ .- 450 8 n v) z CT X > 1 6 u .- 400 4 u - 2 350 0 A B C D E F G Additive Fig.17 Intensity and RSD values of A1 for CT-3000 SG with different dispersing additives A Triton X- 100; B PKV-5088; C glycerol + Kodak photoflow; D Dolapix PC-33; E Darvan-7; F Darvan-C and G NaHMP stability to the system. Consequently the slurries prepared with these additives show very low intensity and high RSD values similar to the case of slurries prepared at pH 9 where no stabilization occurs. The glycerol-Kodak photoflow mixture also presents low intensities and high RSD values which dem- onstrates the inability of this mixture to disperse the powder. In Figs. 18 and 19 intensity and RSD values respectively of the minor elements are plotted showing the same behaviour as A1 for both intensity and RSD.Conclusions Some efforts to facilitate the analysis of inorganic materials by using the slurry ICP-AES technique have been described in the literature. However the study of the stability of the slurries to be analysed has not been considered sufficiently. In this work the basic concepts involved in the stabilization of slurries are clarified. Besides transport and volatilization problems it has been demonstrated that the stability and the homogeneity of slurries play a significant role in the obtainment of adequate analytical performance. High emission intensity and high pre- cision are only achieved if the slurry is stable homogeneous and reliable as a more representative sample delivery to the plasma is achieved. The higher the stability of the slurry the higher the intensity and the lower RSD values obtained for both macroconstituents and minor elements.JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY AUGUST 1994 VOL.9 849 A B C D E F G Additive Ca Fig. 18 Intensity values of Ca Fe ( x 40) and Si ( x 30) for CT-3000 SG with different dispersing additives A Triton X-100; B PKV-5088; C glycerol+Kodak photoflow; D Dolapix PC-33; E Darvan-7; F Darvan-C; and G NaHMP 16 14 12 10 A 8 v) u 6 4 2 n 2 ; 8 Ca " A B C D E F G Additive Fig. 19 RSD values of Ca Fe and Si for CT-3000 SG with different dispersing additives A Triton X-100; B PKV-5088; C glycerol + Kodak photoflow; D Dolapix PC-33; E Darvan-7; F Darvan-C; and G NaHMP Different dispersant additives may be useful to provide the required stability to the slurry (1) potential determining ions (pH) (2) inorganic electrolytes or counter-ions (3) surfactants and (4) polyelectrolytes.The most usual methods of determin- ing the stability characteristics of the slurry are the zeta potential and the viscosity measurements. 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ISSN:0267-9477    

DOI:10.1039/JA9940900841

出版商:RSC    

年代:1994

数据来源: RSC