摘要:

JOURNAL O F ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 41 Figures of Merit for Two-step Furnace Atomization Plasma Emission Spectrometry K. E. Anders Ohlsson Department of Analytical Chemistry University of Umed S-901 87 Umed Sweden Ralph E. Sturgeon Scott N. Willie and Van T. Luong Institute of Environmental Chemistry National Research Council of Canada Ottawa Ontario Canada KIA OR9 A furnace atomization plasma emission spectrometry (FAPES) system was assembled using a two-step graphite furnace which consisted of a spatially isothermal tube positioned at the top of a cup. It was possible to ignite and stabilize an He 50 W r.f. plasma tuned for a reflected power of less than 5 W inside the tube at temperatures of 2500-2600 K and subsequently heat the cup to vaporize the sample.Detection limits for Cr and Al were 298 and 30 pg respectively. Sensitivities and detection limits for Pb Cd and Sn were comparable to previously published values using a Massmann-type FAPES system employing a platform and Pd modifier. Keywords Furnace atomization plasma emission spectrometry two-step graphite furnace Furnace atomization plasma emission spectrometry (FAPES) is an emergent analytical technique wherein an atmospheric pressure r.f. plasma is formed inside a graphite atomizer to excite the analyte atoms which are then quantified by One of the problems encountered with the current configuration used in this l a b o r a t ~ r y * ~ ~ ~ ~ is that reflected power increases as the furnace temperature rises above 2000 K5 when the plasma is not continuously retuned.This presumably diminishes the energy coupled into the system that is available to excite the analyte and is one reason why the technique has so far proved attractive only for those elements that are relatively easily volatilized. With automatic impedance matching circuitry results have only been reported for Ag3 and these have been obtained under conditions of low rates of heating (< 1000 K s-') insufficient to elicit the optimum analytical response from less volatile elements. This is because (automatic) mechani- cal matching networks do not possess the required speed of response to maintain tuned conditions during rapid heat- The solution to this problem may lie with the use of a free-running r.f. oscillator. Techniques that are dependent on the electrical impe- dance of the gas phase in the graphite atomizer are influenced at higher temperatures by the increased emission of thermionic electrons. In a low-pressure d.c.glow dis- charge with the furnace acting as a hollow cathode [hollow cathode furnace atomic non-thermal excitation spectrome- try (HC-FANES)] Falk et a[.' observed a voltage drop at 1800 K for He and a concurrent decrease in the He I line emission (318.77 nm). Riby et aL8 used a side-heated cuvette with integrated contacts (ICC)9 with a centrally positioned carbon rod and reversed the polarity to create a hollow anode FANES system. Although the lower atomiza- tion temperature of the ICC and the temperature lag of the carbon rod partially reduced the problems associated with thermionic electrons the discharge voltage still collapsed at high temperatures producing a concurrent decrease in the Ar I1 (434.8 nm) support-gas line intensity.Similarly Magnusson'O reported that low volatility elements such as A1 and Sr could not be determined by laser-enhanced ionization (LEI) in a graphite furnace owing to the release of thermionic electrons at about 2300 K. This reduced the resistance between the tube wall and the central electrode thereby making detection of the d.c. analytical signal impossible. MagnussonIo also suggested separation of NRCC No. 34242 analyte vaporization and ionization into two different compartments with the detection chamber at a lower temperature to allow LEI measurements. Frech and Jons- son'' had earlier constructed such a device a two-step (TS) furnace consisting of a graphite cup fastened to an aperture at the bottom of a graphite tube.The cup could be heated independently from the tube permitting vaporization of analyte from the cup into the tube which was held at a pre- selected temperature. In this study the FAPES technique is realized using an ICC equipped TS furnace (TS-FAPES). This configuration was investigated as it was expected to permit high tempera- ture stabilization of the plasma in the tube prior to introduction of the analyte vapour. By matching the r.f. source to the impedance of the high temperature graphite tube a plasma could possibly be maintained above 2300 K with a low reflected power i.e. less than 10% ofthe forward power. Limits of detection (LODs) for a number of elements were evaluated and compared with previous results obtained with FAPES in the Massmann-type fur- n a ~ e .~ ~ Experimental Instrumentation The 13.56 MHz r.f. generator with antenna tuner coaxial cable spectrometer and data aquisition system has been described The TS atomizer with an ICC identical to that described earlier," was fitted with a coaxial 1 mm 0.d. graphite centre electrode. This was supported by a hollow Ta pin placed on the end of a type N r.f. connector and fed through a gas-tight Macor end cap which replaced the left-hand window assembly of the furnace. One of the four contacting blocks for the tube and the cup was grounded directly to the coaxial cable via a 2 cm wide braided strap and the other three were r.f. grounded through capacitors ( 1 0 nF).For temperatures above 2600 K and at forward powers exceeding 50 W problems with the control of the heating were experienced which led to rapid increases in the furnace temperature. This was most probably due to stray r.f. power despite precautionary grounding. Temperatures above 1300 K were controlled using infrared optical emission (from the graphite) viewed and fed back by independent fibre-optics for the tube and the cup. These temperatures were calibrated without the centre electrode inserted using a Series 1100 automatic optical pyrometer (Ircon Niles IL USA) focused through42 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 the injection hole into the cup or at the outer tube surface. The temperature of the tube remained the same (within 100 K) with the electrode in place running the He plasma however viewing of the cup with the pyrometer in this case was occluded The graphite parts were purged from below with He gas at 750 ml min-l.In addition a flow of 150 ml min-' protected the right-hand quartz viewing window. For atomic absorption spectrometry (AAS) studies the same type of monochromator and detector were used together with a continuous background correction system (H2 lamp). Reagents Stock solutions (1000 mg 1-I) were prepared by dissolution of high-purity metals (Cd Pb Sn A1 and Cr). Working standards were obtained by dilution of the stock solution with high-purity distilled de-ionized water (DDW) acidi- fied to 1% v/v with sub-boiling quartz distilled HN03.A 3% and a 0.3% m/v solution of high-purity NaCl (Ventron) were prepared in DDW. A 2500 mg 1-1 stock solution of Pd chemical modifier was prepared by dissolution of high- purity metal (Spex Industries) in HN03. Procedure All wavelengths were set using hollow cathode lamps. A nominal spectral bandwidth of 0.08 nm was used for the FAPES measurements. A forward power of 50 W was used throughout. Samples were injected using a 10 p1 Hamilton syringe equipped with a short section of poly(tetrafluoroethy1ene) (PTFE) tubing. A 1% HN03 solution was used as a blank. When using several of the solutions in combination they were loaded successively into the syringe tubing and co- injected. For comparison with previous s t ~ d i e s ~ ~ ~ ~ the samples were charred at 500 "C.The char step lasted for 30 s the r.f. power being applied for the last 5 s. The tube was then heated to the atomization temperature at which point the plasma self-ignited and 3 s later the cup was heated. This 3 s delay allowed the He plasma to ignite and stabilize before initiation of the cup atomization step. The system was r.f. tuned to minimum reflected power at the pre-set tube Table 1 Furnace programme TemperaturePC Stage Step Cup Tube Time/s Plasma Dry 1 110 20 30 Off Ash 2 500 20 20 off 3 500 20 5 On Atomize 4 500 2000* 3 On 5 2000* 2000* 5 On Burnout 6 2600 2600 3 off *2000 "C Sn; 1300-1400 "C Cd and Pb; 2200-2300 "C Al and Cr. atomization temperatures (for 50 W forward power the reflected power was about 5 W at 2500-2600 K and 1-3 W at lower temperatures).Table 1 gives the complete tempera- ture programme. Background correction was performed by subtracting a sequential measurement of a blank solution from the signal. Note that any small blank peak obtained might not be due to contamination (although this seems probable for the relatively large Cd blank) but could result from (pseudo-) continuum emission at the moment of cup heating due to changed background radiation from molecular species (i.e. CO N2 and OH) or from the plasma itself. This was confirmed by a few off-line measurements for Pb where the blank peak persisted. Results and Discussion Although the reflected power of a 50 W plasma can be initially tuned to 1 W at room temperature this will increase to 35-40 W as the temperature is ramped to 2600 K if continuous impedance matching is not applied.6 Automatching circuitry although suited to inductively coupled plasma (ICP) discharges is not capable of respond- ing quickly enough to these temperature changes when the rapid heating (2000 K s-l) necessary for optimal response in the FAPES system is used. With the present TS-FAPES system the plasma could be tuned to less than 5 W reflected power when the tube temperature was 2500-2600 K.However the plasma no longer self-ignited with the tube at room temperature under these conditions but did so at about 2300 K. The TS furnace thus permitted the plasma to ignite and stabilize in the constant temperature tube before the cup was heated and the sample vapour introduced into the analytical volume of the plasma. With a blank sample reflected power remained unchanged during cup heating whereas when vaporizing either 5 pg of Pd or 9 pg of NaCl it increased to peaks of 14 and 35 W respectively.Plasma impedance may change when large amounts of relatively easily ionizable substances "a ionization potential (IP)= 5.16 eV and Pd IP=8.33 eV compared with He IP=24.59 eV] are intro- duced resulting in more reflected power and therefore less power available to the plasma. These observations contrast with those made earlier using a Massmann furnace based FAPES system6 in that the rise in reflected power during tube heating was not influenced by the presence of up to 60 pg of NaCl. Plasma Background Emission from the 50 W plasma in the range 200-400 nm at temperatures of 600 and 1300 K was found to be similar to that reported earlier for the Massmann-type f ~ r n a c e . ~ The CO+ N2 and OH bands were present with the CO+ emission increasing with temperature. The OH structure at 305-315 nm (background for the A1 line at 309.3 nm) disappeared when increasing the temperature from 1300 to 2500 K at which point the apparent intensity of the N2 (1,O) band of the C37d,-B3Zg system was reduced.Concur- Table 2 Figures of merit n = 8 Sensitivity*/nA ng-I RSD* Element Unm Mass/pg LOD*/pg BEC*/pg (nA s ng-I) (O/O) Cd 228.8 165 2 .O( 3.2) 40 (190) 203 (105) 2.9(4.1) Pb 283.3 575 15.0(35) 135 (770) 53 (13) 25 (22) Sn 284.0 250 6.1( 12) 125 (630) 112 (44) 3.0(3.5) Cr 357.9 500 17 (300) 1350 (3800) 242 (108) 16 (21) A1 309.3 500 5.5( 30) 155 (1070) 764 (168) 4.9(9.1) *Values in parentheses are integrated response.JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL.8 43 Table 3 Estimates of RSD (Oh) for integrated absorbance of lead RSD (Oh) Temperature/K Technique 1400 2500 AAS 10-15 1-6 TS-FAPES 5-20 20-40 rently emission from the (0,l) band of the same N2 system at 355-365 nm (background for the Cr 357.9 nm line) increased. At the Pb 283.3 nm line where structured background is minimal continuum emission from the incandescent tube wall accounted for about 30% of the total background intensity. Figures of Merit The LOD absolute sensitivity and precision [expressed as relative standard deviation (RSD)] are summarized in Table 2 for a suite of elements at a given mass each determined from a minimum of eight replicate measure- ments of both the analyte and the blank signal.The LOD is defined as the mass which gives a signal equal to three times the standard deviation of the blank. Also given is the background equivalent concentration (BEC) for both methods of quantification. The LODs and the sensitivities for Pb Cd and Sn compare well with previous determinations5 obtained using a Pd modifier in a Massman-type FAPES instrument equipped with a platform. The precision however is poorer in the case of Pb. It can be seen from the data in Table 3 that the precision of the FAPES measurements improves with a lower atomization temperature of 1400 K. It is evident from the RSD of the AAS signals at this temperature that a major part of the imprecision originates from processes not related to the presence of the plasma.However it may be possible to improve the RSD by optimizing the analytical procedure. For example the ashing temperature Tash was set to 500 "C at which temperature the integrated absorbance is sensitive to variations in Tash (cf the ashing curve in ref. 12). At 2500 K however impedance matching problems with the plasma may be responsible for a deteriorated RSD of the Pb signal. A full explanation for this observation cannot be offered. The high RSD for Cr is probably due to an unfortunate choice of sample mass close to the LOD (for integrated measurements) and elevated background levels at this spectral line (cf Table 2 BEC values) due to strong emission from the second positive band of N2 impurities. The effect of increasing the drying time from 30 to 50 s with ashing at 200 "C and atomization at 1400 K was that the integrated absorbance for Pb by FAPES increased 60% (although the RSD worsened considerably but remained unchanged in the AAS mode).It is tentatively assumed that the signal enhancement in the He plasma is caused by the more efficient removal of water vapour. In an r.f. atmo- spheric Ar plasma (ICP) water has the well known effect of enhancing or suppressing the analyte emission (cf ref. 13). Lundberg et al. l4 used thermally excited atomic emission spectrometry (AES) to measure 16 elements at temperatures between 2580 and 2800 K in a TS furnace similar to that used in the present study. The LOD using integrated absorbance for A1 was 1.0 pg at 2580 K whereas Cr and Pb required 2800 K for LODs of 1 .O and 1 10 pg respectively.Unfortunately the thermal excitation contribution to the atomic emission signals with FAPES for A1 and Cr was not measured. Conclusions The TS-FAPES technique permits a stable plasma with low reflected power levels to be achieved when the furnace is at high atomization temperatures (2600 K). This permits extension of the technique to the more involatile elements as demonstrated by the success of the Cr and A1 measure- ments. Further investigations are warranted with this system to determine the effect of matrix constituents on the reflected power characteristics and the extent of chemical interferences. Based on the favourable results drawn from AAS studies,15 it is likely that this system may offer some advantages over the Massmann-based approa~h.~ Figures of merit (LOD absolute sensitivity and RSD) are similar to those obtained in a Massman-type FAPES with atomization from a platform and chemical treatment of the sample with Pd.5 National Research Council of Canada and the Swedish Natural Science Research Council are gratefully acknow- ledged for financial support to A.O.during his trip to and stay in Ottawa. W. Frech (Umeii University) is thanked for acting as intermediary in this project. References 1 Liang D. C. and Blades M. W. Spectrochim. Acta Part B 1989,44 1059. 2 Sturgeon R. E. Willie S. N. Luong V. Berman S. S. and Dunn J. G. J. Anal. At. Spectrom. 1989 4 669. 3 Smith D. L. Liang D. C. Steel D. and Blades M. W. Spectrochim. Acta Part By 1990 45 493. 4 Sturgeon R. E. Willie S. N. Luong V. and Berman S. S. Anal. Chem. 1990 62 2370. 5 Sturgeon R. E. Willie S. N. Luong V. T. and Berman S. S. J. Anal. At. Spectrom. 1991 6 19. 6 Sturgeon R. E. Willie S. N. and Luong V. T. paper No. 199 presented at the 18th annual FACSS meeting October 6-1 1 199 1 Anaheim CAY USA. 7 Falk H. Hoffmann E. and Liidke Ch. Prog. Anal. Spectrosc. 1988 11 417. 8 Ballou N. E. Styris D. L. and Harnly J. M. J. Anal. At. Spectrom. 1988 3 1 14 1. 9 Frech W. Baxter D. C. and Hiitsch B. Anal. Chem. 1986 58 1973. 10 Magnusson I. Spectrochirn. Acta Part By 1988 43 727. 1 1 Frech W. and Jonsson S. Spectrochim. Acta Part B 1982 37 1021. 12 Welz B. Akman S. and Schlemmer G. J. Anal. At. Spectrom. 1987 2 793. 13 Nixon D. E. J. Anal. At. Spectrom. 1990 5 531. 14 Lundberg E. Baxter D. C. and Frech W. J. Anal. At. Spectrom. 1986 1 105. Paper 2 /02326A Received May 5 1992 Accepted September 4 1992

ISSN:0267-9477    

DOI:10.1039/JA9930800041

出版商:RSC    

年代:1993

数据来源: RSC

摘要:

45R JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 ATOMIC SPECTROMETRY UPDATE REFERENCES The address given in a reference is that of the first named author and is not necessarily the same for any co-author. Papers 93lC 1 -93lC 1 75 were presented at the Sixth Biennial National Atomic Spectroscopists Symposium University of Plym- outh Plymouth UK July 22-24 1992. 93lC 1. 93lC2. 93lC3. 93lC4. 93x5. 93lC6. 93lC7. 93lC8. 93lC9. 931C 10. 93lC11. 93lC12. 93lC 13. 93lC 1 4. L’vov B. V. Extension of the dynamic range and linearization of calibration graphs in Zeeman graphite furnace atomic absorption spectrometry (Dept. Anal. Chem. St. Petersburg Tech. Univ. St. Petersburg 19525 1 Russia). Blades M. W. Hetipathirana T. Gill C. LeBlanc C. Development and characterization of new optical and mass spectrometric methods for trace element analysis (Dept.Chem. Univ. British Columbia Vancouver British Columbia Canada V6T 1Z1). Sharp B. L. 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Elemental analysis of food contact paper and board materials by ICP-MS (MAFF Food Sci. Lab. Food Safety Directorate Norwich Res. Park Colney Nor- wich Norfolk UK NR4 7UQ). Chenery S. R. N. Cook J. M. Rapid determination of rare earth elements (REEs) in single mineral grains by laser ablation microprobe inductively coupled plasma mass spectrometry (Anal. Geochem. Group British Geol. SUIT. Keyworth Nottingham UK NG 12 5GG). Thomsen M. Extending the applications of trace element determination in organic matrices (Perkin- Elmer Maxwell Rd. Beaconsfield Buckinghamshire UK). Crust G. A. Ebdon L. C. Hill S. J. Determination of trimethyllead in natural waters using HPLC-ICP-MS (Environ. Sci. Univ. Plymouth Drake Circus Plym- outh Devon UK PL4 8AA). Foulkes M.E. Nugues S. Determination of total arsenic and its speciation in vegetarian food supple- ments by nitrogen addition and coupled HPLC- ICP-MS (Plymouth Anal. Chem. Res. Unit Environ. Sci. Polytech. South West Drake Circus Plymouth Devon UK PL4 8AA). Fisher A. Ebdon L. Vl'orsfold P. On-line matrix removal for the analysis of food and biological materials by ICP-MS (Dept. Environ. Sci. Polytech. South West Drake Circus Plymouth Devon UK PL4 8AA). Marshall J. Franks J. Spectral interference effects in ICP-MS caused by the introduction of organic solvents (ICI Materials Wilton Res. Centre P.O. Box 90 Wilton Middlesbrough Cleveland UK TS6 8JE). Marshall J. Franks J. Analysis of liquids using laser ablation ICP-MS (ICI Materials Wilton Res. Centre P.O. Box 90 Wilton Middlesbrough Cleveland UK TS6 8JE).JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 47R 93lC62.93lC63. 93lC64. 93lC65. 93lC66. 93lC67. * 93lC68. 93lC69. 93x70. 93x7 1. 93x72. 93lC7 3. 93x74. 93lC75. 93lC76. Stroh A. Vollkopf U. Denoyer E. Extended analytical capabilities using flow injection ICP-MS (Boden- 2Fewerk Perkin-Elmer GmbH Postfach 10 1 1 64 D-7770 Uberlingen Germany). Phillips C. J. Batho A. Simultaneous multi-element determination of elements by atomic absorption spec- trometry (Thermo Electron Ltd. 830 Birchwood Boule- vard Warrington Cheshire UK WA3 742). Tyson J. F. Hanna C. P. McIntosh S. Determination of total mercury in waters and urine by flow injection chemical vapour generation atomic absorption spectro- metry (Dept.Chem. Univ. Massachusetts Amherst MA 01003 USA). de la Calle-Guntiiias M. B. Torralba M. R. Madrid Y. Palacios M. A. Bonilla M. Camara C. Dimunition of Sb and Se interference in the determination of arsenic by HG-AAS adding a-hydroxyacids and KI (Dept. Quim. Anal. Fac. Cienc. Quim. Univ. Complutense Madrid 28040 Madrid Spain). Branch S. Cobby J. M. Mixing monitoring in the food industry using atomic spectrometry (Rank Hovis McDougall Research Lord Rank Res. Centre Lincoln Rd. High Wycombe London UK HP12 3QR). Mora J. Hernandis V. Canals A Behaviour of a thermospray nebulizer as an introduction system of aqueous samples in flame AAS (Univ. Alicante Div. Anal. Chem. Aptdo. 99 03071 Alicante Spain). Howarth H. Moffett J. Mullins C. B. Vanclay E. Optimization of a flame atomization system for AAS (Varian Australian Pty.Ltd. 679 Springvale Rd. Mulgrave 3 170 Victoria Australia). Corns W. T. Stockwell P. M. Determination of mercury in gaseous samples (P. S. Analytical Ltd. Arthur House B4 Chaucer Business Park Watery Lane Kemsing Sevenoaks Kent UK TN 15 6QY). Gardiner P. E. Littlejohn D. Halls D. J. Fell G. S. Determination of selenium and plasma by electrother- mal atomic absorption spectrometry with deuterium background correction and direct calibration (Dept. Pure Appl. Chem. Univ. Strathclyde 295 Cathedral St. Glasgow UK G1 1XL). Thomas R. P. Davidson C. M. Littlejohn D. Ure A. M. Development of methods for the analysis of ammonium acetate extracts of soil by electrothermal atomic absorption spectrometry (Dept. Pure Appl.Chem. Univ. Strathclyde 295 Cathedral St. Glasgow UKGl IXL). Holden A. J. Nichol R. Littlejohn D. Studies of silicon atomization in electrothermal atomic absorption spectrometry (Dept. Pure Appl. Chem. Univ. Strath- Clyde 295 Cathedral St. Glasgow UK G1 IXL). Anderson P. Davidson C. M. Littlejohn D. Ure A. M. Shand C. Development and application of a method for the determination of caesium in soil by electrothermal atomic absorption spectrometry (Dept. Pure Appl. Chem. Univ. Strathclyde Cathedral St. Glasgow UK G1 IXL). Marchante Gayon J. M. Sanz-Medel A. Interference free vapour-phase probe atomization analysis of cad- mium and lead in samples with high salt concentrations (Dept. Phys. Anal. Chem. Fac. Chem. Univ. Oviedo Julian Claveria 8 33006 Oviedo Spain).Laborda F. Viiiuales J. Mir J. M. Castillo J. R. Selenium determination by ETAAS. Modifier effect of nickel and palladium on different chemical species of selenium (Dept. Anal. Chem. Univ. Zaragoza SO009 Zaragoza Spain). Zhang P. Littlejohn D. Neal P. Chemometric predic- tion and correction of interferences in inductively coupled plasma optical emission spectrometry (Dept. Pure Appl. Chem. Univ. Strathclyde 295 Cathedral St. Glasgow UK GI IXL). 93x77. 93lC78. 93lC79. 93lC80. 93lC8 1. 93lC82. 93lC83. 93lC84. 93lC8 5. 9 3lC8 6. 93lC87. 93lC88. 93lC89. 93lC90. McNeill R. Barnard C. L. R. Marshall J. Signal modulation and noise in detection systems for atomic spectrometry (Dept. Phys. Sci. Glasgow Polytech. Cowcaddens Rd. Glasgow UK G4 OBA). Espinosa Almendro J. M.Bosch Ojeda C. Garcia de Torres A. Can0 Pavdn J. M. Determination of cadmium in biological samples by inductively coupled plasma atomic emission spectrometry after solvent extraction (Dept. Anal. Chem. Fac. Sci. Univ. MAlaga 2907 1 Spain). Todoli J. L. Hernandis V. Canals A. Characteriza- tion of a new nebulizer for use in inductively coupled plasma atomic emission spectrometry (ICP-AES) (Univ. Alicante Div. Anal. Chem. Aptdo. 99 03071 Alicante Spain). Ivaldi J. C. Barnard T. W. Multivariate methods for the interpretation of simultaneous spectra from the inductively coupled plasma (Perkin-Elmer 76 1 Main Avenue Norwalk CT 06859-0293 USA). Roberts M. S. Snook R. D. Analysis of organic materials by discrete sample introduction inductively coupled plasma atomic emission spectrometry (DIAS UMIST Manchester UK M60 1QD).Ziara K. Lythgoe D. Snook R. D. Studies of spatial and intensity stability of a d.c. arc for scrap metal analysis (DIAS UMIST PO Box 88 Manchester UK M60 1QD). O’Gram S. J. Dean J. R. Marshall J. Murphy J. Sputter rate normalization of a glow discharge plasma (Dept. Chem. Life Sci. Newcastle Polytech. Ellison Bldg. Ellison Place Newcastle upon Tyne UK NEI 8ST). Riimmeli M. Steers E. B. M. Relationship between the electrical and spectral characteristics of a boosted glow discharge source (SECEAP Polytech. North Lon- don London UK N7 8DB). Kim A. W. Ebdon L. Hill S . J. Rowland S. Analysis of organometallic compounds by capillary gas chro- matography inductively coupled plasma mass spectro- metry (GC-ICP-MS) (Dept. Environ.Sci. Polytech. South West Drake Circus Plymouth Devon UK PL4 8AA). Hartley J. Ebdon L. Hill S. J. Analysis of precious group metals (PGMs) by slurry atomization inductively coupled plasma mass spectrometry (Plymouth Anal. Chem. Res. Unit Polytech. South West Drakes Circus Plymouth Devon UK PL4 8AA). Ford M. Ebdon L. Hill S. J. Investigations into the use of nitrogen addiction to the nebulizer gas flow of an ICP-MS in conjunction with laser ablation sample introduction (Plymouth Anal. Chem. Res. Unit Poly- tech. South West Plymouth Devon UK PL4 8AA). Arowolo T. A. Cresser M. S. Automated determina- tion of some sulfur species by cool-flame emission spectrometry (Univ. Aberdeen Dept. Plant & Soil Sci. Old Aberdeen UK AB9 2UE). Jimenez M. S. Mir J. M.Castillo J. R. Gas phases in AAS with thermospray continuous volatilization (Dept. Anal. Chem. Fac. Sci. Univ. Zaragoza 50009 Zara- goza Spain). Savage I. Williams K. Haswell S. J. Determination of mercury in water samples by AAS incorporating on- line microwave sample preparation and cold-vapour generation (Univ. Hull Hull UK HU6 7RX). Papers 93lC9 1-93lCl75 were presented at the Second Rio Sympo- sium on Atomic Absorption Spectrometry Rio de Janeiro Brazil June 2 1-28 1992. 93lC9 1. Knapp G. High performance sample preparation tech- niques for trace element analysis by AAS (Graz Univ. Technol. Dept. Anal. Chem. Micro Radiochem. A- 80 10 Graz TechnikerstraBe 4 Austria).48R 93lC92. 93x93. 93x94. 93lC95. 93lC96. 9 3lC9 7. 93lC98. 93lC99. 93lC 100. 93lC 10 1.93lC 102. 93K103. 93lC 93lC 93lC 93lC JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 Batistoni D. A. Distribution of analytes in spectroche- mica1 flames (Dept. Quim. Anal. Comis. Nac. Energ. Atom. Avenida Libertador 8250 1429 Buenos Aires Argentina). Giinner C. Schlemmer G. Flame AAS; is there room for improvement (Bodenseewerk Perkin-Elmer GmbH P.O. Box 10 1 164 D-7770 Uberlingen Germany). Krug F. J. Flow injection flame atomic absorption spectrometry (Centro Energ. Nucl. Argic. USP Caixa Postal 96 13400 Piracicaba SP Brazil). Silva I. A. Sella S. M. Campos R. C. Curtius A. J. Direct determination of lead in kerosene by ETAAS the use of a three component solution to stabilize the metal (Dept. Quim. da PUC-Rio 22.453 Rio de Janeiro RJ Brazil).Sperling M. Koscielniak P. Welz B. Examination and correction of interferences in flame atomic absorption spectrometry by a flow injection gradient peak ratio method Dept. Appl. Res. Bodenseewerk Perkin-Elmer GmbH P.O. Box 101 164 D-7770 Uberlingen Ger- many). Fang Z. Current trends in flow injection atomic absorption spectrometry (Flow Injection Anal. Res. Center Inst. Appl. Ecol. Acad. Sin. Box 417 1 1001 5 Shenyang China). Brubn F. C. G. Rodriguez E. A. A. Barrios G. C. Becerra J. Gras R. N. Reyes M. O. Salud S. Determination of total mercury in scalp hair of humans by gold amalgamation cold vapor atomic absorption spectrometry (CVAAS) (Dept. Anal. Instrum. Univ. Concepcih Casilla 237 Concepcih Chile). Schlemmer G. Slavin W. McIntosh S. Hanna C. P. Tyson J. F.Determination of total mercury by flow injection chemical vapour generation atomic absorption spectrometry (Perkin-Elmer Corp. 50 Danbury Rd. Wilton CT 06897 USA). We15 B. Sperling M. Yin X. Xu S. Sun X. On-line preconcentration separation and speciation for atomic absorption spectrometry using flow injection tech- niques (Dept. Appl. Res. Bodenseewerk Perkin-Elmer GmbH P.O. Box 101 164 D-7770 Uberlingen Ger- many). Frech W. Baxter D. C. Emteborg H. Bulska E. Deterination of mercury species in biological and environmental samples (Dept. Anal. Chem. Univ. Umei S-901 87 Umei Sweden.). L’vov B. V. Extension of the dynamic range and linearization of calibration graphs in Zeeman graphite furnace atomic absorption spectrometry (Dept. Anal. Chem. St. Petersburg Tech.Univ. St. Petersburg 19525 1 Russia). de Loos-Vollebregt. M. T. C. Padmos J. van Oosten P. Analytical evaluation of 3-field Zeeman atomic absorption spectrometry (Delft Univ. Technol. Lab. Mater. Sci. Rotterdamseweg 137 2628 AL Delft The Netherlands). 04. Hermann G. Coherent forward scattering atomic spec- trometry-advantages and limitations (I. Physik. Inst. Justus-Liebig-Univ. Giessen Heinrich-Buff-Ring 16 D- 6300 Giessen Germany). 05. Resende M. C. R. Campos R. C. Mercury speciation by cold vapour AAS using solvent extraction and organomercury reduction in non-aqueous medium (Dept. Quim. Univ. Estadual Maringb 87020 Maringb PR Brazil). 06. de Loos-Vollebregt M. T. C. Koot J. Flow injection hydride generation atomic absorption spectrometry determination of arsenic in aqua regia decomposition solutions (Delft Univ.Technol. Lab. Mater. Sci. Rotterdamseweg 137 2628 AL Delft The Netherlands. 07. Azeredo L. C. Sturgeon R. E. On-line separation and preconcentration for electrothermal atomic absorption spectrometry (UFRRJ Dept. Quim. Km 47 Antiga Estr. Rio-SP. Rio de Janeiro Brazil). 93lC108. 93lC 109. 93lC 1 10. 93lC 1 1 1. 93K112. 93lC 1 13. 93lC 1 14. 93lCll5. 9 3lC 93lC 93lC 16. 17. 18. 93lC 1 19. 93lC 120. 93x1 2 1. 93lC122. 93/C 123. Coutinho G. Schlemmer G. Shuttler I. Determina- tion of trace elements in biological and food samples using a transverse heated graphite atomizer with longi- tudinal Zeeman-effect background correction (Esc. Sup. Biotecnol. Univ. Catolica Portugesa Rua Dr. Bernardino Almeida 4200 Porto Portugal).Bradshaw D. K. Selection of analytical parameters for achieving optimum conditions for accurate analyte determination (Perkin-Elmer Corp. 400 Technol. Park Suite 1 Lake Mary FL 32746 USA). Jackson K. W. Qiao H. Modification by palladium in slurry electrothermal atomic absorption spectrometry (Wadsworth Center Labs. Res.. Dept. Health P.O. Box 509 Albany NY 1220 1-0509 USA). Miller-Ihli N. J. Use of ultrasonic slurry ETAAS for the determination of lead in environmental samples (US Dept. Agric. ARS BHNRC Bldg. 16 1 BARC-East Beltsville MD 20705 USA). Dittrich K. Heiner J. Wennrich R. Solid sampling using graphite furnaces (Univ. Leipzig Inst. Anal. Chem. Linnestr. 3 D-0-7050 Leipzig Germany). Miiller-Vogt G. Korneck F. Send W. Wendl W. Sputtering-a new method of solid sampling in ETAAS (Kristall- Materiallabor Univ. Karlsruhe Kaiserstr.12 D-7500 Karlsruhe Germany). Hinds M. W. Novel approaches to trace element determination in metal samples by electrothermal atomic absorption spectrometry (Royal Canadian Mint 320 Sussex Dr. Ottawa Ontario Canada K 1 A OG8). Bradshaw D. K. Analysis of refractory materials by graphite furnace AAS with slurry sample introduction (Perkin-Elmer Corp. 400 Technology Park Suite 1 Lake Mary FL 32746 USA). Granadillo V. A. Navarro J. A. Romero R. A. Spectroscopic characteristics of lead in real matrices when atomized from a graphite surface (Lab. Instrum. Anal. Fac. Experiment. Cienc. Univ. Zulia Maracaibo Zulia 40 1 1 Venezuela). Chui Pressinotti Q. S. H. Confidence interval in regression analysis (Inst.Pesquisas Tecnol6g. Estado de SBo Paulo SA Brazil). Sanchez J. M. Cubillan H. S. Granadillo V. A. Tahan J. E. Romero R. A. Mineralization of biological materials for the subsequent evaluation of total mercury by the cold vapor technique (Lab. Instrum. Anal. Fac. Exp. Cienc. Univ. Zulia Maracaibo Zulia 40 1 1 Venez- uela). Lima R. de Silveira C. L. P. Campos R. C. Study of detection limits for mercury determination by CVAAS and ICP-AES (194.2 nm line) using the gold trap technique (Dept. Quim. PUC-Rio 22.453 Rio de Janeiro Brazil). Castro e Silva E. Oliveira L. J. Silva S. A. Kuntze E. K. Mercury in the Baixada Cuiabana preliminary evaluation of the efficiency of a hood for gold buyer’s houses (Dept. Quim. UFMT Av. Fernando Corriia Costa slno. 78.100 Cuiabh MT Brazil).Zenebon O. Scorsafava M. A. Sakuma A. M. Mer- cury level evaluation in fish products (Inst. Adolfo Lutz Av. Dr. Arnaldo 355 CEP:O1246 SBo Paulo SP Brazil). Santelli R. E. Santos Mendes P. C. Gallago M. Valcarcel M. Determination of nickel in rocks by an on-line continuous precipitation-dissolution system coupled with flame atomic absorption spectrometry (Geochem. Dept. Fed. Fluminense Univ. Niteroi Bra- zil 24020). Lichtig J. de Paula A. Alves J. C. Determination of Aum and Agl in galvanoplastic baths by atomic absorp- tion (Inst. Quim. USP CP 20780. CEP 01498. SBo Paulo SP Brazil).JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 49R 93x1 24. 93/C 1 25. 93/C126. 93lC 127. 93lC128. 93lC 129. 93/C 1 30. 93lC 13 1. 93lC132. 93lC 93/c 33.34. 93lC135. 93lCl36 93lC137. 93lC138. Lichtig J. Costa Oliveira P. C. da Silva JuliHo M. S. Alves J. C. Systematic study of the effect of C1-on the interference of Fem on Crm and Crm determination by atomic absorption spectrometry (Inst. Quim. USP CP 20780 CEP 0 1498 Silo Paulo SP Brazil). Guimaraes Amendola M. L. Determination of total chromium (Crm plus Cr‘) in industrial emuents with high amounts of dissolved salts by atomic absorption spectrometry (DOW Productos Quim. Dept. Anal. Franco da Rocha Brazil). Vaz de Melo Mattos S. Prado G. Bastos E. M. Determination of some metals in honeys of Minas Gerais (Fund. Ezequiel Dias Div. Bromatol. Toxicol. Rua Conde Pereira Carneiro 80-30550 Belo Horizonte MG Brazil). Vaitsman D. S. de S. Azevedo,-I. Vaitsman E.P. de Matos V. L. R. kite Z. T. C. Avila A. K. Determina- tion of metals in fruits by flame atomic absorption spectrometry (Dept. Quim. Anal. Inst. Quim. Univ. Fed. Rio de Janeiro Bloco A CT. Lab. 518 Ilha do Fundgo Rio de Janeiro Brazil). Yaman M. Giiqer S. Determination of cadmium and lead in foodstuffs by atomic absorption spectrometry (First Univ. Sci. Arts Fac. Dept. Chem. Elazig Turkey). Cubillah H. S. SBnchez J. M. Navarro J. A. Tahih J. E. Romero R. A. Metal content of the drinking water in Maracaibo City (Venezuela) assessed by atomic absorp- tion spectrometry (Lab. Instrum. Anal. Fac. Exp. Cienc. Univ. Zulia Maracaibo Zulia 40 1 1 Venezuela). Amazarray M. T. R. Mozeto A. A. Origin transport and distribution of trace elements in Emboaba Lake Rio Grande do sul Brazil (Centro Ecol.UFRGS Port0 Alegre Brazil). de Toledo Salgado P. E. Salvador Lepera J. Evaluation of environmental exposure of children by determination of metals in biological samples (Dept. Princ. At. Natur. Toxicol. Fac. CiCnc. Farm. Araquara-UNESP Rod0 Araraquara-Jau km 1 14.800 Araraquara SP Brazil). Martins A. F. Morsch V. M. Dressler V. L. Krelling J. A. Flores E. M. M. Use of S-electron donor reagents as chemical modifiers for the determination of mercury by ETAAS (Dept. Chem. Fed. Univ. Santa Maria RS Brazil). Navarro J. A. Granadillo V. A. Romero R. A. Effect of several analyte isoformers on the atomic spectro- scopic behaviour of vanadium in the graphite furnace (Lab. Instrum. Anal. Fac. Exp. Cienc. Univ. Zulia Maracaibo Zulia 40 1 1 Venezuela).Burguera M. Burguera J. L. Flow injection analysis graphite furnace atomic absorption spectrometry for arsenic speciation using the Fleitman reaction (Dept. Chem. Fac. Sci. Univ. Los Andes P.O. Box 542 Mtrida 5 10 1 -A Venezuela). Burguera J. L. Burguera M. Determination of lead in biological materials by microwave assisted digestion and flow injection graphite furnace atomic absorption spectrometry (Dept. Chem. Fac. Sci. Univ. Los Andes P.O. Box 542 Mtrida 5101-A Venezuela). Wang X. Wei J. Ma G. Zhang Z. He Y. Liu S. and Ma W. Study of the determination of Cu Mnn Fem Cd and C m by flow injection atomic absorption spectro- metry with on-line exchange preconcentration (Dept. Chem. Nankai Univ. Tianjin 30007 1 China). Laborda F. Mir J. M. Castillo J. R.HPLC-ETAAS discontinuous coupling for selenium speciation (Dept. Anal. Chem. Univ. Zaragoza 50009 Zaragoza Spain). Belarra M. A. Anzano J. M. Lavilla I. Castillo J. R. Determination of lead by direct analysis of poly(viny1 chloride) by graphite furnace atomic absorption spectro- metry (Dept. Anal. Chem. Univ. Zaragoza 50009 Zaragoza Spain). 93/C 139. 93lC 140. 93lC 14 1. 9 3/c 1 42. 93lC 93lC 93lC 93lC 43. 44. 45. 46. 93/C147. 93/c 93lC 48. 49. 93lC 1 50. 93x151. 93lC152. 93lC153. Hermann G. Kling B. Koch B. Lasnitschka G. Moder R. Szardening T. Graphite furnace atomiza- tion and multi-element analysis of laser ablated aero- sols (Physik. Inst. Justus-Liebig-Univ. Giessen Hein- rich-Buff-Ring 16 D-6300 Giessen Germany). Costa M. F. Moreira I. Determination of Mnn andMn” in natural water samples by ETAAS (Dept.Quim. PUC-RIO R. MarquCs de S5o Vicente 225 Rio de Janeiro RJ cep 22.453 Brazil). Simonin M. E. Temporale R. Villamor M. A. Cabello B. Heavy metal analysis in suspended matter of natural waters by graphite furnace atomic absorption spectro- metry (Obras Sanit. Nacidn Dept. Lab. Av. Figueroa Alcorta 608 1 CP 1426 Buenos Aires Argentina). Avila A. K. Curtius A. J. Determination of silver by ETAAS after complexation and sorption on carbon (Dept. Quim. Anal. UFRJ Bloco A 21.941 Ilha do Fundso Rio de Janeiro Brazil). de Silva C. S. de Oliveira E. Determination of Crm in air of chrome plating plants and in urine of the workers by graphite furnace atomic absorption spectrometry (Inst. Quim. USP CP 20780 CEP 01498 SP Brazil).Carneiro M. C. Campos R. C. Curtius A. J. Alterna- tive microdigestion procedure for Sb Ni and V deter- mination in airborne particulate material by ETAAS (Dept. Quim. Pontificia Univ. Cat6lica Rio de Janeiro 22453 Rio de Janeiro Brazil). Stripeikis J. d’Huicque L. Tudino M. Portal R. Troccoli O. ETAAS petroleum characterization in oiled birds from Ponta Tombo (Argentina) (Dept. Quim. Inorg. Anal. Quim. Fis. Fac. Cienc. Exact. Natur. UBA Ciudad Univ. Pab. IL(1428) Buenos Aires Argentina). Gomes H. F. Dias J. C. M. Determination of lead in turbine fuel by graphite furnace atomic absorption spectrometry (Petrobrds Petrdleo Brasileiro SA Refin. Duque Caxias Setor Controle Qual. Rod. Washington Luiz Km 11 3.7 Campos Eliseos Duque de Caxias RJ CEP 25000 Brazil).Cristiano A. R. Alvarado J. Determination of cad- mium cobalt iron nickel and lead in cigarettes by graphite furnace atomic absorption spectrometry (Dept. Quim. Univ. Sim6n Bolivar Apartado 89000 Caracas 1080-A Venezuela). Cristiano A. R. Alvarado J. Determination of lead and cadmium in propolis by means of graphite furnace atomic absorption spectrometry (Dept. Quim. Univ. Sim6n Bolivar Apartado 89000 Caracas 1080-A Ven- ezuela). Romero R. A Navarro J. A. Granadillo V. A. Graphite furnace determination of trace metals during the management of renal insufficiency (Lab. Instrum. Anal. Fac. Exper. Cienc. Univ. Zulia Maracaibo Zulia 40 1 1 Venezuela). Giiqer S. Ozdemir Y. Manganese speciation in tea samples by atomic absorption spectrometry (Inonii Univ. Fac. Sci. Arts Dept.Chem. 44069 Malatya Turkey). Giiqer S. Ozdemir Y. Determination of Cr and A1 in tea samples by graphite furnace AAS (Inonu Univ. Fac. Sci. Arts Dept. Chem. 44069 Malatya Turkey). Feuerstein M. Schlemmer G. Improving detection limits by an order of magnitude by coupling hydride generation flow injection techniques with electrother- mal atomization (Bodenseewerk Perkin-Elmer GmbH P.O. Box 101 164 D-7770 uberlingen Germany). Fang Z. Tao G. Efficient flow injection system for in situ concentration of hydride forming elements in a graphite furnace (Flow Injection Anal. Res. Center Inst. Appl. Ecol. Acad. Sinica Box 417 110015 Shenyang China).JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 50R 93lC 93lC 54. 55. 93lC156. 93lC 93lC 9 3lC 93lC 93lC 57.58. 59. 60. 61. 93lC 162 93lC163. 93lC 164. 93lC165. 93lC 166. 93lC167. 93lC168. 93K169. Welz B. Demeny D. Sperling M. Investigations on the efficiency of removing chloride in the presence of different chemical modifiers (Dept. Appl. Res. Boden- seewerk Perkin-Elmer GmbH P.O. Box 101 164 D- 7770 Uberlingen Germany). Carnrick G. R. L’vov B. V. Slavin W. Likelihood of absolute AAS instrumentation (Perkin-Elmer Corp. Norwalk CT 06859-0293 USA). Sperling M. Hertzberg J. Welz B. Temporally and spatially resolved gas phase temperature measurements in a graphite tube furnace by CARS thermometry influence of operating conditions dosing hole and presence of a platform on gas phase temperature evolution (Dept. Appl. Res. Bodenseewqrk Perkin- Elmer GmbH P.O. Box 101 164 D-7770 Uberlingen Germany).Sturgeon R. E. Willie S. N. Luong V. T. FAPES plasma diagnostics and analytical applications (Inst. Environ. Chem. Natl. Res. Council Canada Ottawa Ontario Canada K1 A OR9). Dittrich K. Franz T. Niebergall K. Graphite furnaces for sampling and detection in trace analysis of micro- samples (Univ. Leipzig Inst. Anal. Chem. Linnestr. 3 D-0-70 10 Lxipzig Germany). Hermann G. Kling B. Lasnitschka G. Moder R. Scharmann A. Szardening T. Graphite furnace determination of high element concentrations using continuum sources (I. Physik. Inst. Justus-Liebig- Univ. Giessen Heinrich-Buff-Ring 16 D-6300 Giessen Germany). Alvarado J. Probe atomization in graphite furnace atomic absorption spectrometry (Dept. Quim. Univ. Sim6n Bolivar Apartado 89000 Caracas 1080-A Ven- ezuela).Nbbrega J. A. Baccan N. Krug F. J. Gine M. F. Berndt H. Tungsten coil as an alternative ‘low-tec’ atomizer for cadmium and lead (Inst. Quim. USP CP 20780 0 1498 Siio Paulo SP Brazil). Nbbrega J. A. Krug F. J. Silva M. M. Baccan N. Berndt H. Electrothermal atomization on tungsten coil heating rate and signal resolution (Inst. Quim. USP CP 20780 01498 Sgo Paulo SP Brazil). Silva M. M. Silva R. B. Krug F. J. Ndbrega J. A. Electrothermal atomization of barium in tungsten coils (Cent. Energ. Nucl. Agric. USP CP 96 13400 Piraci- caba SP Brazil). Silva R. B. Krug F. J. Silva M. M. Ndbrega J. A. Chromium determination in waters by tungsten coil AAS (Centr. Energ. Nucl. Agric. USP Caixa Postal 96 13400 Piracicaba SP Brazil). Carlos G. Bruhn F.Fernando E. Ambiado V. Woer- ner R. V. Garcia L. R. Tapis S. J. Optimization and application of a ‘low-cost’ vaporizer-atomizer to the determination of Cd Ni and Pb by electrothermal atomic absorption spectrometry (Dept. Anal. Inst. Fac. Farm. Univ. Concepci6n Casilla 237 Concepcidn Chile). Majidi V. Robertson J. D. Eloi C. Probing chemical reactions on heated graphite surfaces (Dept. Chem. Univ. Kentucky Lexington KY 40506 USA). Frech W. Ohlsson A. Iwamoto E. Cedergren A. Spike atomization and transfer of aluminium in a spatially isothermal graphite atomizer (Dept. Anal. Chem. Univ. UmeA S-901 87 Umei Sweden). Miiller-Vogt G. Miiller H. Hahn L. Wendl W. Modification of the graphite surface by oxygen and its effect on the determination of oxide forming elements (Kristall- Materiallab.Univ. Karlsruhe Kaiserstr. 12 D-7500 Karlsruhe Germany). Rojas D. Effect of the heating rate on the electrother- mal atomization of Co Ni and Cu (Dept. Quim. Fac. Cienc. Univ. Los Andes Apart. 478 Merida 5251 Venezuela). 93lC 1 70. Gilmutdinov A. Kh. Mrasov R. Three-dimensional distribution of oxygen and nitrogen in electrothermal atomization atomic absorption spectrometry (Dept. Physics Univ. Kazan 18 Lenin Str. Kazan 420 008 Russia). 93lC 17 1. Gilmutdinov A. Kh. Mrasov R. Dynamics of forma- 9 3lC 93lC tion of atomic and molecular species- and their dissipa- tion in graphite furnace atomic absorption spectrome- try (Dept. Phys. Univ. Kazan 18 Lenin Str. Kazan 420 008 Russia). 72. Brown G. N. Styris D. L. Mass spectrometric elucida- tion of mechanisms that control electrothermal atomi- zation of tin (Pacific Northwest Lab.Box 999 Rich- land WA 99352 USA). 73. Holcombe J. A. Wang P. Low pressure atomization for ETAAS (Dept. Chem. Biochem. Univ. Texas Austin TX 787 12 USA). 93lC 1 74. Rosso A. Piccinna M. Valiente L. Determination of trace and ultratrace levels of metallic contaminants in milk powder (Inst. Nacl. Tecnol. Ind. Dept. Quim. Gral. Paz Albarellos Costituyentes Casilla Correo 157 (1 650) San Martin Prov. Buenos Aires Argentina). 93lC175. L’vov B. Frech W. Condensation of matrix vapour interference effects on ETAAS (Dept. Anal. Chem. St. Petersburg Tech. Univ. St. Petersburg 19525 1 Russia). Papers 93lC176-931C405 were presented at the 1991 VIII Federa- tion of Analytical Chemistry and Spectroscopy Societies and the 30th Pacijic Confirence on Chemistry and Spectroscopy Joint Meeting October 6-1 1 1991 Anaheim CA USA 93lC176.93lC 177. 93lCl78. 93lC179. 93lC 1 80. 93lC18 1. 93lC182. 93lCl83. 93lC 184. 93lC185. Lograsso L. M. Coleman D. M. Number density measurements of atomic species in the high voltage uni- directional spark by hook spectroscopy (1 7 1 Chemistry Bldg. Wayne State Univ. Detroit MI USA). Culp M. Naito M. Reisz R. Chen S. Ng K. Dual microwave induced plasmas for atomic emission and atomic absorption spectrometry (California State Univ. Fresno Fresno CA 93740-0070 USA). Pilon M. J. Moran P. M. Schleicher R. C. Charge injection device array detection for d.c. arc (Thermo Jarrell Ash Corp. 3E Forge Parkway P.O. Box 9101 Franklin MA 02038-9 10 1 USA).Olson L. K. Caruso J. A. SFC He MIP for analysis of pesticide mixtures (Dept. Chem. M.L. 172 Univ. Cincinnati Cincinnati OH 45221 USA). Zhu G. Zhang H. Ruiz A. Browner R. F. Aqueous sample introduction for a reduced-pressure microwave induced plasma (Sch. Chem. Biochem. Georgia Inst. Technol. Atlanta GA 30332-0400 USA). Weed K. M. Tong W. G. Trace concentration elemen- tal analysis by non-linear multiwave mixing spectros- copy in flame and discharge atomizers (Dept. Chem. San Diego State Univ. San Diego CA 92 182 USA). Liang D. C. Blades M. W. Le Blanc C. Plasmas in furnaces-a solution for graphite furnace analytical atomic spectroscopy (Aurora Instrum. 303 1 Main St. Vancouver British Columbia Canada V5T 3G6). Browner R. F. Tarr M. A. Pan C.Nwogu V. Zhu G. Sample introduction for plasma emission and mass spectrometry complex answers to simple problems (Sch. Chem. Biochem. Georgia Inst. Technol Atlanta Montaser A. New sources for atomic spectrometry what has happened in the last two years? (Dept. Chem. George Washington Univ. Washington DC 20052 USA). Bonner Denton M. Ongoing revolution in optical spectrometry with new array detectors (Dept. Chem. Univ. Arizona Tucson AZ 8572 1 USA). GA 30332-0400 USA).JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 51R 93lC 1 86. 93lC187. 93lC 1 88. 93lC189. 93lC 1 90. 93lC191. 93lC192. 93x1 93. 93lC 194. 93lC 195. 93lC 196. 93lC 197. 93lC 198. 93lC 199. 93lC200. 93lC20 1. Houk R. S. Recent advances in plasma source mass spectrometry (Ames Lab.US Dept. Energy Dept. Chem. Iowa State Univ. Ames IA 5001 1 USA). Chisum M. E. Certification of laboratory working standards with emphasis on traceability to NIST stan- dard reference materials (Mason Hanger Silas Mason Co. P.O. Box 30020 Amarillo TX 7901 5 USA). Karanassios V. Li F. H. Salin E. D. Environmental sample preparation by an interrupted flow microwave digestion system (Dept. Chem. McGill Univ. 80 1 Sherbrooke St. W. Montreal Quebec Canada H3A 2K6). Haswell S. J. Barclay D. A Development of a continuous flow microwave digestion method for on- line sample preparation with atomic spectrometric detection (Sch. Chem. Univ. Hull Hull UK HU6 7RX). Grillo A. C. Temperature controlled mirowave diges- tion for the new EPE SW-346 procedures (Questron Corp. Box 2387 Princeton NJ 08543-2387 USA).Oatts T. J. Harold N. B. Buddin N. P. Sheuer M. I. Sample preparation of oils and oily wastes for ICP and AA spectroscopy using a high pressure ashing digestion technique (Martin Marietta Energy Syst. Oak Ridge K- 25 P.O. Box 2003 Oak Ridge TN 37831-7446 USA). Chan D. W. Anti-cancer drug monitoring by atomic absorption and clinical considerations (Dept. Lab. Med. Path. Oncol. Johns Hopkins Medical Inst. Balti- more MD 21205 USA). Long G. L. Magaritz M. Konen D. Amiel A. J. Brenner I. B. Determination of trace metals in the suspended material and waters of an aquifer (Dept. Environ. Sci. Energy Res. Wizmann Inst. Sci. Israel). Hinderberger E. J. Jr. Robbins R. G. Hartman L. A. Determination of arsenic using the Perkin-Elmer Model 3 100 FIAS (Univ.Missouri Environ. Trace Substances Res. Center 5450 S. Sinclair Rd. Columbia MO 65203 USA). Shrader D. Beach C. Moffett J. Determination of ultra-low mercury levels by cold vapour amalgamation AAS (Varian Optical Spectrosc. Instrum. 201 Hansen Court Suite 108 Wood Dale IL 60191 USA). Robbins R. G. Hinderberger E. J. Jr. Hartman L. A. Peak height or peak area? Determination of selenium using the Perkin-Elmer Model 3100 FIAS (Univ. Missouri Environ. Trace Substances Res. Center 5450 S. Sinclair Rd. Columbia MO 65203 USA). Willie G. N. Fukushi K. Okumura W. Sturgeon R. E. Berman S. S. Evaluation of atomic fluorescence absorption and emission techniques for the determina- tion of inorganic mercury (Inst. Env. Chem. Natl. Res. Council Canada Ottawa Ontario Canada K14 ORG).Robbins R. G. Hinderberger E. J. Jr. Hartman L. A. Determination of mercury using the Perkin-Elmer Model 3 100 FIAS-200 (Missouri Environ. Trace Sub- stances Res. Center 5450 s. Sinclair Rd. Columbia MO 65203 USA). Ting K. C. Kho P. Evaluation of GC-MIP-AED for pesticide residue determination in fruits and vegetables (California Dept. Food Agric. Pesticide Residue Lab. 169 East Liberty Ave. Anaheim CA 9280 1 USA). Bushaw B. A. Rare isotope analysis with high-resolu- tion lasers (Pacific Northwest Lab. Richland WA 99352 USA). Shaw R. W. Whitten W. B. Ramsey J. M. Chemical vapour deposition diagnostics using resonance ioniza- tion mass spectrometry (Anal. Chem. Div. Oak Ridge Natl. Lab. Oak Ridge TN 37831-6142 USA). 93lC202. 93lC203. 93lC204.93lC205. 93lC206. 93x207. 93lC208. 9 3lC209. 93lC2 10. 93lC2 1 1. 93lC2 12. 93lC2 13. 93lC2 14. 93lC2 15. 93lC2 16. 93lC2 17. 93lC2 18. 93lC2 19. Wendt K. Laser resonance ionization spectroscopy for trace analysis (Inst. Phys. Univ. Mainz Postfach 3980 D-6500 Mainz Germany). Olesik J. W. Spectroscopic imaging in the inductively coupled plasma (Dept. Chem. Univ. North Carolina Chapel Hill NC 27599-3290 USA). Farnsworth P. B. Ogilvie C. Correlation spectroscopy as a probe of excitation mechanisms in the ICP (Dept. Chem. Brigham Young Univ. Provo UT 84602 USA). Miller G. P. Mechanism for observing radiative losses from low temperature argon plasmas (Chem. Dept. Univ. Alabama Huntsville Huntsville AL 35899 USA). Olesik J. W. Hobbs S. E. Further insight into processes controlling ICP emission intensities from time-resolved measurements (Dept. Chem.Univ. North Carolina Chapel Hill NC 27599-3290 USA). Mermet J. M. Atomization processes versus excitation or ionization processes in an inductively coupled plasma (Lab. Sci. Anal. Univ. Lyon 1 69622 Ville- urbanne Cedex France). Smith F. G. Niu H. S. Chen X. Houk R. S. Fundamental studies of ion extraction and chemically tailored plasmas for inductively coupled plasma mass spectrometry (Ames Lab. US Dept. Energy Dept. Chem. Iowa State Univ. Ames IA 5001 1 USA). Meeks F. R. Re-evaluation of transition probabilities for atomic spectroscopy (Univ. Cincinnati Cincinnati Cai M. Montaser A. Mostaghini J. Computer simulation of helium inductively coupled plasmas (Dept. Chem. George Washington Univ.Washington DC 20052 USA). Brown R. G. Hotham D. March D. Tandem a sample introduction system designed to double sample throughput in ICP spectrometry (Leeman Labs. 55 Technology Dr. Lowell MA 0 185 1 USA). Salin E. D. Blain L. Direct sample insertion ICP analysis of geological materials (Dept. Chem. McGill Univ. 801 Sherbrooke St. W. Montreal Quebec Canada H3A 2K6). Rayson G. D. Yang Shen D. Determination of rare earth elements using an inductively coupled argon plasma axial viewing absorption technique (Chem. Dept. P.O. Box 30001 New Mexico State Univ. Las Cruces NM 88003 USA). Ivaldi I. C. Tracy D. Slavin W. Multi-component spectral fitting algorithms for improved analytical deter- minations in ICP-AES (Perkin-Elmer Corporation 76 1 Main Avenue Norwalk CT 06859-0293 USA).Schleisman A. J. Sewall V. Ultratrace metal analysis of high purity acids (Texas Instrum. P.O. Box 655012 MS 301 Dallas TX 75265 USA). Nygaard D. Dewers D. Alavosus T. Bulman F. Re- examination of end-on viewing of the plasma discharge in ICP-AES (Baird Corp. 125 Middlesex Turnpike Bedford MA 0 1 730 USA). Welz B. Sperling M. Hertzberg J. Influence of operating conditions and instrument design on gas phase temperature in a graphite furnace (Dept. Appl. Res. Bodenseewerk Perkin-Elmer P.O. Box 10 1 164 D- 7770 Uberlingen Germany). Jackson K. W. Qiao H. Physical and chemical aspects of modification in ETAAS (Wadsworth Center Lab. Res. Sch. Public Health New York State Dept. Health P.O. Box 509 Albany NY 12202 USA). Majidi V. Ratliff J. Simultaneous molecular and atomic absorption measurements in electrothermal atomizers (Chem.Dept. Univ. Kentucky Lexington KY 40506 USA). OH 4522 1-0 1 72 USA).52R 93lC220. 93lC22 1. 93lC222. 9 3lC22 3. 93lC224. 9 3lC2 2 5. 9 3lC226. 9 3lC22 7. 9 3lC228. 93IC229. 93lC230. 93lC23 1. 93lC232. 93lC23 3. 93lC234. 93lC235. 93lC2 36. 93lC237. JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 Fonseca R. W. Holcombe J. A. Electrothermal atomi- zation of Au and Ag; microdroplets or absorbed atoms (Dept. Chem. Biochem. Univ. Texas Austin Austin TX 78712 USA). Redfield D. A. Harris J. D. Styris D. L. Influence of A1:C on the efficiency of electrothermal atomization of aluminium (Northwest Nazarene Coll. Pac. Northwest Lab. P.O. Box 999 Richland WA 99352 USA).Gilmutdinov A. Kh. Electrothermal atomization as a physico-chemical phenomenon A preliminary analysis (Dept. Physics. Univ. Kazan 18 Lenin Str. Kazan 420008 Russia). Styris D. Redfield R. A. Harris J. D. Investigating the mechanisms associated with Group 111 atomization (Pacific Northwest Lab. P.O. Box 999 Richland WA 99352 USA). Guell 0. A. Holcombe J. A. Fonseca R. W. Can we use graphite furnace as a surface science technique? (Dept. Chem. Biochem. Univ. Texas at Austin Austin TX 787 12 USA). Young C. E. Pellin M. J. Calaway W. F. Burnett J. W. Whitten J. E. Coon S. R. Gruen D. M. Spiegel D. R. Davis A. M. Clayton R. N. Surface analysis by resonance ionization of sputtered atoms (SARISA) (Argonne Natl. Lab. Argonne IL 60439 USA). Bickel C. A. Detection of impurities in Zr by post- ionization of laser ablated neutrals (AECL Res.Chalk River Labs. Chalk River Ontario Canada KOJ IJO). Slavin S. S. Twenty-five years of lubricating oil analysis-from AA to ICP (Perkin-Elmer Corp. 761 Main Ave. Norwalk CT 06859-0293 USA). Monte Evans F. Role of metal alkylaryl sulfonates as analytical calibration standards for the determination of metals in lubricating oils (Conoco Inc. P.O. Box 1267 Ponca City OK 74603 USA). Riby P. G. Hamly J. M. Styris D. Balou N. Effect of cathode temperatures and thermionic electrons on emission signals for HA-FANES (USDA NCL BHNRC Bld. 161 BARC East Beltsville MD 20705 USA). Marcus R. N. Hess K. R. Langmuir probe investiga- tions of the effect of discharge gas identity in diode geometry glow discharge devices (Dept.Chem. Frank- lin Marshall Coll. P.O. Box 3003 Lancaster PA 17604 USA). Marcus R. K. Theory and use of Langmuir probes for glow discharge plasma diagnostics (Dept. Chem. Clem- son Univ. Clemson SC 29634 USA). Sacks R. McCaig L. Shi Z. Brewer S. W. Jr. Holbrook T. Modelling the low pressure magnetron glow discharge (Dept. Chem. Univ. Michigan Ann Arbor MI 48 109 USA). Horlick G. Zhao Y. Schroeder S. G. Excitation and ionization characteristics of glow discharge devices (Dept. Chem. Univ. Alberta Edmonton Alberta Canada T6G 2G2). Uzelac N. I. Leis F. Niemax K. Measurement of gas temperatures and metastable state densities in a mi- crowave boosted glow discharge using a diode laser (Inst. Spektrosc. Ange. Spektrosc. (ISAS Bunsen-Kirch- hoff-Str 1 1 D-4600 Dortmund 1 Germany).Tyson J. F. Flow injection techniques for improving the accuracy and precision of analytical atomic spectro- metry (Dept. Chem. Univ. Massachusetts Amherst MA 01003 USA). Lancaster H. L. 111 Ruzicka J. Christian G. D. Applications of sequential injection and sinsusoidal flow in atomic spectroscopy (Univ. Washington Dept. Chem. Seattle WA 96 195 USA). Welz B. Sperling M. On-line preconcentration separ- ation and speciation for graphite furnace AAS using FI 93lC238. 93lC239. 93lC240. 93lC24 1. !J 3lC242. 133lC243. 93lC244. ‘33IC245. ‘93IC246. 93lC247. 93lC248. 93lC249. 9 3lC250. 93x25 1. 9 3lC252. 93lC2 5 3. techniques (Dept. Appl. Res. Bodenseewerk Perkin- Elmer GmbH P.O. Box 101 164 D-7770 Uberlingen Germany). Riviello J. M. Siriraks A. Manabe R.M. Perform- ance enhancement of simultaneous ICAP-AES by direct coupling to an ion chromatograph (Dionex Corp. 222E Titan Way Sunnyvale CA 94806 USA). Israel Y. Barnes R M. Some applications of the stopped flow injection technique (Dept. Chem. Lederle Graduate Res. Centre Univ. Massachusetts Amherst Li Z. McIntosh S. Slavin W. Hydride generation ICP-AES for the simultaneous determination of hydride and non-hydride-forming elements (Perkin-Elmer Corp. 76 1 Main Ave. Norwalk CT 06897-237 USA). Rettberg T. Hutton R. C. Comparison of ETV and FI for the direct analysis of high purity reagents by ICP- MS (Fisons Instruments 32 Commerce Center Dan- vers MA 01923 USA). Denoyer E. R. Design strategies for optimizing flow injection ICP-MS (Perkin-Elmer Corp 76 1 Main Av.Norwalk CT 06859-02 15 USA). Sturgeon R. E. Willie S. N. Luong V. T. FAPES diagnostic and analytical progress (Inst. Environ. Chem. Natl. Res. Council Canada Ottawa Ontario Canada X 1 A OR9). Falk H. Ultrasensitive detection of atoms and ions using electrothermal atomizers (Spectro. Anal. Instrum. Boschstr. 10 W-4 1 90 Kleve Germany). Littlejohn D. Chaudhry M. Whitley E. Multi-tech- nique approach to the investigation of chemical interfer- ences in ETAAS (Dept. Pure Appl. Chem. Univ. Strathclyde 295 Cathedral St. Glasgow UK G 1 1 XL). Riby P. G. Hamly J. M. Styris D. L. Ballou N. Advances in hollow anode FANES (USDA NCL BHNAC Bldg 161 BARC East Beltsville MD 20705 USA). Blades M. W. Hettipathirana T. Furnace atomization plasma excitation spectrometry (FAPES)-temporal emission behaviour (Dept.Chem. Univ. British Col- umbia 2036 Main Mall Vancouver British Columbia Canada V6T 1Y6). Byme J. P. Chakrabarti C. L. Gregoire D. C. Lamoureux M. Ly T. Study of chloride interference mechanisms in graphite furnace atomic absorption spectrometry by electrothermal vaporization induc- tively coupled plasma mass spectrometry (Dept. Appl. Chem. Univ. Technology Sydney Australia). Hamly J. M. Increasing the spectral bandpass to improve the signal-to-noise ratio for continuum source atomic absorption spectrometry with a photodiode array detector (USDA-BHNRC-NCL Bldg. 16 1 BARC East Beltsville MD 20705 USA). Hollberg L. Robinson H. Magyar J. Fox R. Walt- man S. Mackie N. Characteristics of diode lasers and their applications to spectroscopy (Natl.Inst. Standards Technol. 325 Broadway Boulder CO 30303 USA). Shieh C. Determination of major elements and trace metals in waste-to-energy residues by atomic absorption spectrometry (Dept. Oceanogr. Ocean Eng. Environ. Sci. Florida Inst. Technol. Melbourne Florida 32901 USA). Walker F. Wilson M. Huntsberger T. G. Foust R. D. Jr. Chemical differentiation of clay sources by electrothermal atomic absorption spectroscopy (Dept. Chem. Northern Arizona Univ. Flagstaff AZ USA). Cappel J. B. Johnson C M. Extraction of hafnium from a geologic matrix obtaining acceptable yields of an elusive and highly matrix sensitive element (Dept. Geol. Geophys. Univ. Wisconsin 121 5 W Dayton St. Madison WI 53706 USA). MA 0 1003-0035 USA).JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL.8 53R 93lC254. 93x2 5 5. 93lC256. 93lC257. 93lC258. 93lC259. 93lC260. 93lC26 I. 93lC262. 93lC263. 93lC264. 93lC265. 93lC266. 93lC267. 93lC268. 93lC269. 93X270. Young J. P. Shaw R. W. Ramsey J. M. Resonance ionization mass spectroscopy using multiple diode lasers (Anal. Chem. Div. Oak Ridge Natl. Lab. Box 2008 Oak Ridge TN 37831-6142 USA). Koretsky M. D. Reimer J. A. Gas phase magnetic resonance studies of plasma processes (Dept. Chem. Eng. Univ. California Berkeley Berkeley Thomas R. J. Anderau C. J. Automating quality control protocols for ICP emission and ICP mass spectrometry (Perkin-Elmer 76 1 Main Ave. Norwalk Shah N. K. Pospisil P. A. Van Kley H. Application of pattern recognition and X-ray fluorescence spectroscopy for metals screening and preprocessing decisions of hazardous waste (Chern.Waste Management 150 West 137th St. Riverdale IL 60627 USA). Wu M. Hieftje G. M. Novel technique to investigate vaporization mechanisms in inductively coupled plasma emission spectrometry (Dept. Chem. Indiana Univ. Bloomington IN 47405 USA). Browner R. F. Pan C. Ruiz A. Zhang H. Zhu G. Influence of solvent interactions on basic plasma pro- perties for conventional ICP atmospheric pressure MIP and low pressure MIP sources (Sch. Chem. Biochem. Georgia Inst. Technol. Atlanta GA 30332 USA). Blades M. W. Wier D. Effects of solvent and solvent loading on ICP fundamental properties (Dept. Chem. Univ. British Columbia 2036 Main Mall Vancouver British Columbia Canada V6T IY6). Galley P. J. Hieftje G. M. Evaluation of atomic and ionic distributions within an Ar ICP via computed tomography and Abel inversion (Dept.Chem. Indiana Univ. Bloomington IN 47405 USA). Long G. L. McCleary K. A. Influence of water on an Ar MIP (Dept. Chem. Virginia Polytech. Inst. State Univ. Blacksburg VA 2406 1-02 12 USA). Hubert J. Bordeleau S. St.-Onge L. Moisan M. Studies on surface wave induced plasmas in He and mixed gases (Univ. Montreal Dept. Chem. P.O. Box 6 128 Station A. Montreal Quebec H3C 357 Canada). Carnahan J. W. Non-metal ion emission in helium plasmas the role of charge transfer (Dept. Chem. Northern Illinois Univ. DeKalb IL 501 15 USA). Littlejohn D. Mohammad B. Ure A. M. Investigation of the chemistry of on-line preconcentration procedures for flame AAS and ICP-AES (Dept.Pure Appl. Chem. Univ. Strathclyde 295 Cathedral Street Glasgow UK G1 1XL). Sharp B. L. Observations on the character and reduc- tion of noise in inductively coupled plasma spectrome- try (Univ. Technol. Loughborough Leicestershire UK LEI 1 3TU). Browner R. F. Tarr M. A. Msimanga N. Edman K. New understanding of aerosol generation and aerosol transport processes studies with laser fraunhofer sizing and laser doppler velocimetry measurements (Sch. Chem. Biochem. Georgia Institute of Technology Atlanta Georgia 30332-0400). Marshall J. Franks J. Analysis of advanced materials by laser ablation ICP-MS (ICI plc Wilton Mater. Res. Centre P.O. Box 90 Wilton Middlesbrough UK TS6 8JE). Haswell S. J. Environmental and clinical sample analysis by total reflectance X-ray fluorescence spectro- metry-advantages and disadvantages (Sch.Chem. Univ. Hull Hull UK HU6 7RX). Wang P. Holcombe J. A. Cd atomization and interfer- ence mechanisms in graphite furnace atomizers (Dept. CA 94720-9989 USA). CT 06859-02 1 5 USA). 93lC27 1. 93lC2 72. 93lC273. 93lC2 74. 93x27 5. 93lC276. 93lC277. 93lC278. 93lC2 79. 9 3lC280. 93lC28 1. 9 3lC28 2. 9 3lC283. 93lC284. 93lC285. 93lC286. Chem. Biochem. Univ. Texas Austin Austin TX 78712 USA). Giiell Q. A. Holcombe J. A. Monte Carlo study on gas phase interferences with platform atomization (Dept. Chem. Biochem. Univ. Texas Austin Austin TX 78712 USA). Rojas D. Olivares W. Determination of the kinetic order in electrothermal atomization mechanisms (Dept. Quim. Fac. Cienc. Univ. Los Andes Apartade 19 Le Hechicera Merida 525 1 Venezuela).Camrick G. R. Li Z. Slavin W. Graphite furnace technology-improving on a 20 year old design (Perkin- Elmer Corp. 50 Danbury Rd. Wilton CT 06897-02 19 USA). Harnly J. M. Continuum source AAS with detection limits comparable to conventional AAS at wavelengths below 280 nm (USDA BHNRC NCL Bldg. 161 BARC-East Beltsville MD 20705 USA). Scheie A. J. Holcombe J. A. Electrothermal atomiza- tion mass spectrometry using second surface trapping (Dept. Chem. Biochem. Univ. Texas Austin Austin TX 78712 USA). Shrader D. Beach C. Determination of tin in complex samples by hydride generation and graphite furnace AAS (Varian Optical Spectroscopy Instruments 20 1 Hansen Court Suite 108 Wood Dale IL 60191 USA). Bradshaw D. K. Slavin W. Analyses of refractory materials by slurry sample introduction into a transversely heated graphite furnace (Perkin-Elmer 76 1 Main Ave.Norwalk CT 06859-0293 USA). Dabeka R. W. Novel refractory lead behaviour in graphite furnace atomic absorption spectrometry using a palladium modifier (Food Res. Div. Bureau Chem. Safety Food Directorate Health Prot. Branch Health Welfare Canada Ottawa Ontario Canada KIA 012). Wu M. Farnsworth P. B. Lee M. L. Gas chromato- graphy radio frequency plasma system for selective detection of nitrogen oxygen and sulfur in the near infrared spectral region (Dept. Chem. Brigham Young Univ. Provo UT 84602 USA). Kuzuya M. Piepmeier E. H. Taming those frolicking oscillations in a glow discharge for use in detecting gas chromatography eluates (Dept. Chem. Gilbert Hall 153 Oregon State University Corvallis OR 9733 1- 4003 USA).McCleary K. A Hausler D. W. Long G. L. Sullivan J. J. Diagnostic studies of a helium plasma atomic emission detector for gas chromatography (266 PL Phillips Petroleum Comp. Bartlesville OK 74004 USA). Farnsworth P. S. Use of a diode laser for time resolved absorption measurements in the ICP on a nanosecond time scale (Dept. Chem. Brigham Young Univ. Provo UT 84602 USA). Niemax K. Franzke J. Schneil A. Spectroscopic properties of commercial diode lasers (Inst. Spectro- chem. ange. Spektrosk. (ISAS) Bunsen-Kirchhoff-str. 1 I 4600 Dortmund Germany). Barber T. E. Walters P. E. Omenetto N. Wineford- ner J. D. Evaluation of absolute number densities by diode laser atomic absorption spectroscopy (Dept.Chem. Univ. Florida Gainesville FL 326 1 1 USA). Hergenroder R. Groll H. Niemax K. Simultaneous multi-element measurements using diode lasers (Inst. Spektrochem. angew. Spektrosk Bunsen-Kirchhoff str. 11,4600 Dortmund Germany). Peru D. A. Press P. J. Collins R. J. Comparison of cold digestion methods for the elemental analysis of a Y- type zeolite by inductively coupled plasma atomic54R JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 9 3lC28 7. 93lC288. 93lC289. 93/C290. 93lC29 1. 93lC292. 93lC293. 93lC294. 93lC295. 9 3lC2 9 6. 93lC297. 93lC298. 9 3lC2 99. 9 3lC300. 93lC30 1. 93lC302. emission spectroscopy (W. R. Grace 7379 RT 32 Columbia MD 22044 USA). Howard R. Evens F. M. Good laboratory practices for the spectrometric determination of metals in lubricating oils Canada Inc.P.O. Box 1267 Ponca Cm OK 74603 USA). Shkolnik G. Johnson D. Nham T. Analysis of samples in organic solvents utilizing a new ICP with a direct serial coupled c.f. generator (Varian Opt. Spec- trosc. Instrum. 201 Hansen Court Suite 108 Wood Dale IL 60 19 1 USA). Shkolnik G. Johnson D. Finotella F. Automation of the USEPA’s contract laboratory program requirements with a high resolution ICP (Varian Optical Spectros- copy Instruments 201 Hansen Court Suite 108 Wood Dale IL 601 9 1 USA). Romero R. A. Granadillo V. A. Navarro J. A. Spectroscopic behaviour of lead in the graphite furnace using analyte isoformation (Labs. Instrum. Anal. Fac. Exper. Cienc. Univ. Zulia Maracairo Zulia 40 1 1 Venezuela). Brenner I. B. Le Marchand A. Optimization of intensity measurement and acquisition in multi-element sequential analysis by ICP-AES-variable resolution and mathematical uses of measurement improves SIB ratios and limits of detection (Geol.Survey Israel 30 Walkhe Israel St. Jerusalem 95501 Israel). Long S. E. Martin T. D. Riviello J. M. Determina- tion of uranium by on-line chelation pre-treatment and ICP-MS (CMSL USEPA 16 West Martin Luther King Drive Cincinnati OH 45268 USA). Dall’ava D. Fremy L. Nadisic M. Devillard D. Comparison of matrix effects in ICP-MS-optimization for semiquantitative trace analysis in various matrices (CEA Valduc 2 1 120 Is-sur-Lille France). Chambers W. B. Improved detection limits for ICP- AES determination of trace metals in HF and NH4F etchants Sandia Natl. Lab. Bldg. 1324 Albuquerque NM 37 185 USA).Fields R. E. Noms J. A Bonner Denton M. Qualitative and quantitative aspects of d.c. APC spec- troscopy using a solid-state CID array detector (Univ. Arizona Dept. Chem. Tucson AZ 35721 USA). Layman L. Using more of the spectrum for atomic emission spectroscopy (Lafayette Coll. Easton PA 18042 USA). Salin E. D. Webb D. P. Intelligent instrument first steps toward autonomy (Dept. Chem. McGill Univ. 801 Sherbrooke St. W. Montreal Quebec Canada H3A 2K6). Wangen L. Gallimore D. Miller B. Bentley C. Use of curvy fitting and residual analysis for quantitation with the inductively coupled plasma emission spectro- meter (CLS-1 Los Alamos Natl. Lab. Los Alamos NM 87545 USA). Foster R. W. Spectrograph-like elemental analysis utilizing a novel solid state detector (Thermo Jarrell Ash Corporation 8E Forge Parkway Franklin MA 02038 USA).Bonner Denton M. On the utilization of multiplex detection to implement expert systems for atomic emission spectrometry (Dept. Chem. Univ. Arizona Tucson AZ 3572 1 USA). Goudwaard M. P. de Loos-Vollebregt M. T. C. Characterization of noise in ICP-AES (Delft Univ. Technol. De Vriez van Heystplantsoen 2 2618 82 Delft The Netherlands). Caruso J. Hywel Evans E. Satzger R. D. Carey I. M. Electrothermal vaporization for sample introduction in ICP-MS (Dept. Chem. Univ. Cincinnati Cincinnati OH 4522 1 USA). 93lC303. 931c304. !2 3lC305. 03/C306. ‘33lC307. t93/C308. 93/C309. 93lC3 10. 9 3 x 3 1 1. 93lC3 12. 93lC3 13. 93/C3 14. 93lC3 15. 93lC3 9 3 x 3 93lC318. 93/C3 19. Beauchemin D.Yves Le Blanc J. C. Enhancement of the capabilities of ICP-MS using flow injection analysis with air as the carrier (Queen’s Univ. Dept. Chem. 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Alberta Edmonton Alberta T6G 2G2 Canada). Nam S. Tan H. Montaser A. Helium inductively coupled flame mass spectrometry (Dept. Chem. George Washington Univ. Washington DC 20052 USA). Chisum M. E. Application of negative ion analyses on the flan 250 ICP mass spectrometer (Mason Hanger Silas Mason Co. P.O. Box 30020 Amarillo TX 7901 5 USA). Bradshaw N. Walsh A. Hutton R. C. Practical aspects of the resolving power of a double focusing ICP mass spectrometer (VG Elemental Ltd. Ion Path Road Three Winsford Cheshire UK). Zhu G. Pan C. Tarr M. A. Browner R. F. Matrix effects from concomitant elements in inductively coup- led plasma mass spectrometry (Sch. Chem.Biochem. Georgia Inst. Technol. Atlanta GA 30332-0400 USA) Tanner S. D. Matrix effects in ICP-MS-observation and explanation (SCIEX 55 Giencameron Rd. Thorn- hill Ontario Canada L3T 1P2). Chambers D. M. Shepherd M. A. Kamla G. J. Design considerations for ion-beam optimization in an ICP-MS instrument (Shell Dev. Comp. Westhollow Res. 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British Columbia 2036 Main Mall Vancouver British Colum- bia Canada V6T 1Y6). Cable P. R. Lazik C. Marcus R. K. Plasma character- istics of radio frequency glow discharge devices (Clem- son Univ. Clemson SC 29634 USA).Sacks R. D. Shi Z. Brewer S. W. Jr. Holbrook T. Physical properties and analytical application of a planar magnetron glow discharge (Dept. Chem. Univ. Michigan Ann Arbor MI 48109 USA). 9 3 x 3 3 8. 93iC339. 93lC340. 93lC34 1. 93lC342. 9 3lC343. 93lC344. 9 3 x 3 4 5. 93lC346. 93lC347. 93lC348. 93lC349. 93lC350. 93lC35 1. 9 3lC3 52. 9 3 x 3 5 3. 93lC354. Webster G. H. Boss C. B. Electric field measurements of surface wave launched plasmas as a gas chromato- graphy detector (Dept. Chem. Box 8204 North Caro- lina State Univ. Raleigh NC 27695-8204 USA). Evans L. J. Nio W. Selected topics in the develop- ment of methods for a multi-element electrothermal atomic absorption spectrometer (Perkin-Elmer Corp. 2772 North Garey Ave. Pomona CA 91762 USA). Carney K. P. DeVasto J.K. 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Value of X-ray spectrometry to the atomic spectroscopist in an industrial analytical environment (Dow Chem. Comp. Midland MI 45607 USA). Barclay D. Haswell S. J. Effect of high salt concentra- tion in quantitative determinations by total reflectance X-ray fluorescence spectrometry (Dept. Chem. Univ. Hull Hull UK HU6 7RX). Lichte F. E. Ups and downs of laser ablation induc- tively coupled plasma mass spectrometry (US Geol. Survey Box 25046 MS 973 Denver Federal Center Denver CO 80225 USA). Fredeen K. J. Benefits of mixed-gas plasmas for laser sampling ICP-MS (Perkin-Elmer Corp. 76 1 Main Ave. Norwalk CT 06859-0293 USA). Rettberg T.M. Analysis of wood and cellulose ma- terials by laser ablation ICP-MS (Fisons Instruments 32 Commerce Center. Danvers MA 01 923 USA). Koopenaal D. W. Smith M. R. Shuttleworth S. Laser ablation using UV waveguide lasers-introduction of an ICP-MS technique for sensitive surface and spatial analysis (Pacific Northwest Lab. P.O. Box 999 MS P8-08 Richland WA 99352 USA). Arrowsmith P. Wade C. P. Quantitative analysis of ceramic materials by laser ablation ICP-MS (IBM Corp. Storage Syst. Products Div. 5600 Cottle Road San Jose CA 95 193 USA). Chan W. T. RUSSO R. E. Study of pico- and nano- second pulsed laser-material interactions using ICP- AES (Appl. Sci. Div. Lawrence Berkeiey Lab. Ber- keley CA 94720 USA). Hutton J. C. Chakrabarti C. L. Hendrick K. L. Bertels P. C.Back M. H. Direct analysis of solids by cathodic sputtering in a glow discharge for atomic absorption spectrometry (Centre Anal. Environ. Chem. Dept. Chem. Carleton Univ. Ottawa Ontario Canada K 1 S 5B6). Broekaert J. A. C. Bricker T. Hieftje G. M. Investi- gations of jet-assisted glow discharge sources for the atomic spectrometric analysis of solids (Univ. Dort- mund Dept. Chem. P.O. Box 500500 W-4600 Dort- mund 50 Germany).56R JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 93K355. Banks P. R. Blades M. W. Characteristics of glow discharge plasma jets (Dept. Chem. Univ. British Columbia 3036 Main Mall Vancouver British Colum- bia Canada V6T lY6). 93/C356. Sacks R. D. Shi Z. Brewer S. W. Jr. Direct analysis of metals and alloys with a low-pressure magnetron glow discharge (Dept.Chem. Univ. Michigan Ann Arbor MI 48109 USA). 93/C357. Lazik C. Harvilla T. Marcus R. K. Bulk solid analysis by radio frequency glow discharge emission spectrome- try (Dept. Chem. Clemson Univ. Clemson SC 29634 USA). 93X358. Hieftje G. M. Heintz M. J. Development of a magnetically active r.f. glow discharge source for atomic emission spectroscopy (Dept. Chem. Indiana Univ. Bloomington IN 47405-400 1 USA). 93K359. Harrison W. W. Klingler J. A. Ionization processes in pulsed glow discharges (Univ. Florida Dept. Chem. Gainesville FL 326 1 1-2046 USA). 93K360. Cable P. R. Duckworth D. C. Marcus R. K. Mass spectrometric sampling of radio frequency powered glow discharges (Clemson Univ. Clemson SC 29634 USA). 93/C36 1. Swenters K.Sikharulidze G. G. Gijbels R. Compari- son of SSMS and GDMS for the analysis of high-purity materials (Dept. Chem. Univ. Antwerp (UIA) B-26 10 Wilrijk Belgium). 93X362. Pella P. A. X-ray analysis with the NIST X-ray microfluorescence spectrometer (Natl. Inst. Standards Technol. Gaithersburg MD 20899 USA). 93K363. Smit H. H. A. Vrebos A. R. Kusperes G. T. J. Analysis of coated materials with X-ray fluorescence (Philips Anal. Alrelo The Netherlands). 93K364. Van Espen P. Janssens K. Swerts J. Vincze L. Chemometrics approach to EDXRF ‘towards the grand unified theory’ (Dept. Chem. Univ. Antwerp (UIA) B- 26 10 Wilrijk Belgium). 93K365. Pella P. A Micro-scale quantitative X-ray fluorescence analysis Natl. Inst. Standards Technol. Gaithersburg MD 20899 USA). 93K366.Wang J. Hu S. S. Tao G. Y. Zhou S. J. Study on the expert system for the qualitative interpretation of wavelength-dispersive X-ray fluorescence spectra (Dept. Chem. Eng. Zhejiang Univ. Hangzhou 3 10027 China). 93K367. Richner P. Wunderli S. Analysis of transformer oils for polychlorinated biphenyls (PCBs) by ICP-MS (Swiss Fed. Lab. Mater. Testing Res. CH-8600 Duben- dorf Switzerland). 93K368. Patterson K. Y. Moser-Veillon P. B. Wallace G. F. Veillon C. Determination of zinc stable isotopes in biological materials by isotope dilution ICP-MS after matrix separation (USDA Beltsville Human Nutr. Res. Center Beltsville MD 20705 USA). 93/C369. Wang J. Evans E. H. Caruso J. A. Addition of molecular gases to Ar gas flows for the resolution of polyatomic ion interferences on arsenic selenium and vanadium in inductively coupled plasma mass spectro- metry (Dept.Chem. M.L. 172 Univ. Cincinnati Cincinnati OH 4522 1 USA). 93K370. Pinkston T. L. Determination of boron and phospho- rus in borophosphosilicate glass films by laser ablation ICP-MS (Sematech 2706 Montopolis Dr. Austin TX 78741 USA). 93K371. Tan S. Fucsko J. Balazs M. K. Determination of trace metals on silicon wafer surface by flow injection ICP-MS (Balazs Anal. Lab. 1380 Borregas Ave. Sunnyvale CA 94089 USA). 93/C372. Pinkston T. L. Multi-element determination of metal- lic impurities in photoresist by ICP-MS (Sematech 2706 Montopolis Dr. Austin TX 7874 USA). 93/C373. Ivanovic K. Coleman D. M. Kunz F. W. Schuetzle D. Analysis of automotive catalysts by inductively coupled plasma mass spectrometry (1 7 1 Chem.Bldg. Wayne State Univ. Detroit MI 48202 USA). 93K374. Wang P. Holcombe J. A. Direct solid analysis using low pressure electrothermal atomization atomic absorp- tion spectrometry (Dept. Chem. Biochem. Univ. Texas Austin TX 787 12 USA). 93/C375. Miller-Ihli N. J. Multi-element slurry GFAAS of biological materials (US Dept. Agric. Nutr. Comp. Lab. Beltsville MD 20705 USA). 93/C376. Broekaert J. A. C. Lathen C. Tschopel P. Tiilg G. Evaluation of slurry nebulization ICP spectrometry for the analysis of ceramic powders (Univ. Dortmund Dept. Chem. 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Mu H. Luan J. Application of intermittent injection desolvation-electrothermal vaporization method in inductively coupled plasma atomic emission spectrometry Fenxi Huaxue 1992,20 1 14 (Hanzhong China 7230 14).Yang J. Piao Z. Zeng X. Zhang Z. Chen X. Guan Q. Numerical derivative method in inductively coupled plasma atomic emission spectrometry. 111. Signal-to- background ratio and detection limit Fenxi Huaxue 1992 20 153 Changchun Inst. Appl. Chem. Chin. Acad. Sci. Changchun China 130022). Zhang Z. Piao Z. Zag X. Yang J. Chen X. Guan Q. Corrections of severely overlapped spectral interfer- ence in inductively coupled plasma atomic emission spectrometry by self-modelling curve resolution Fenxi Huaxue 1992 20 180 (Changchun Inst. Appl. Chem. Chin. Acad. Sci. Changchun China 130022). Wu J. Cai Y. Rao Z. Simultaneous determination of phosphorus potassium and sodium in plant samples with series detectors by flow injection analysis Fenxi Huuxue 1992 20 196 (Dept. Soil Sci.Agric. Chem. Beijing Agric. Univ. Beijing China 100094). Sun J. Li G. Liao Z. Simultaneous determination of trace rare earth elements in tea leaves by solvent extraction inductively coupled plasma atomic emission spectrometry Fenxi Huaxue 1992 20 242 (Yichang Med. Spec. Coll. Y ichang China).68R 931702. 931703. 931704. 931705. 931706. 931707. 931708. 931709. 9317 10. 9317 1 1. 9317 12. 9317 13. 9317 14. 9317 15. 9317 16. JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 Suo Y. Yi F. Huang Y. Determination of trace mercury in hair urine and nail by flameless non- dispersive atomic fluorescence spectrometry Fenxi Hu- axue 1992 20 335 (Northwest Plateau Inst. Biol. Chin. Acad. Sci. Xining China 810001). Mei E. Jaing Z. Liao Z. Determination of trace copper in pure sodium chloride by direct current arc with tungsten-spiral electrothermal vaporization for sample introduction Fenxi Huuxue 1992 20 348 (Dept.Chem. Wuhan Univ. Wuhan China 430072). Horvat M. Byme A. R. Preliminary study of the effects of some physical parameters on the stability of methylmercury in biological samples Analyst 1992 117 665 (Dept. Nucl. Chem. Univ. Ljubljana Lju- bljana Yugoslavia). Hara H. Suzuki F. Sasayama R. Gohshi Y. Deter- mination of lanthanum and strontium in lanthanum fluoride(II1)-strontium fluoride solid electrolytes by ICP- AES Bunseki Kuguku 1991 40 T217 (Meidensha Corp. Tokyo Japan 141). Mochizuki T. Sakashita A. Iwata H. Ishibashi Y. Gunji N. Laser ablation-ICP-AES of some alloy samples using aqueous standard calibration Bunseki Kuguku 1992 41 49 (Adv.Technol. Res. Cent. NKK Corp. Kawasaki Japan 2 10). Kubota T. Okutani T. Inamoto I. Takimoto K. Mechanism for sensitivity improvement for phosphorus with a zirconium modifier in graphite furnace AAS Bunseki Kuguku 1992 41 57 (Coll. Sci. Technol. Nihon Univ. Funabashi Japan 274). Nakahara T. 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Reference materials for the determination of elements in Mediter- ranean marine ecosystems Acta Chim. Hung. 199 1 128 507 (1st. Sup. San. 00161 Rome Italy). Matusiewicz H. Suszka A. Ciszewski A. Efficiency of wet oxidation with pressurized sample digestion for trace analysis of human hair material Acta Chim. 1080-A).JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 73R 931842. 931843. 931844. 931845. 931846. 931847. 9 3/84 8. 931849. 931850. 93/85 1. 931852. 931853. 931854. 931855. Hung. 1991 128 849 (Dept. Anal. Chem. Politech. Poznanska 60-965 Poznan Poland). Sipos M. Adamis T. Determination of tin in organo- tin stabilized poly(viny1 chloride) by graphite furnace atomic absorption spectrometry Acta Chim. Hung. 1991 128 869 (Natl.Inst. Hosp. Med. Eng. H-1525 Budapest Hungary). Levine H. S. Higgins K. L. Phosphorus determination in borophosphosilicate or phosphosilicate glass films on a silicon wafer by wavelength dispersive X-ray spectros- copy A h . X-Ray Anal. 1991 34 299 (Sandia Natl. Lab. Albuquerque NM 87 185 USA). Almeida D. M. Obenauf R. H. Considerations in the selection of standards for ICP instruments Am. Lab. (Shelton Conn.) 1992 24 SOZ SOBB SOFF SOGGY (Spex Ind. Inc. Edison NJ USA). Mentasti E. Porta V. Abollino O. Sarzanini C. Metal trace determination in sea-water samples from Antarctica. 11 Ann. Chim. (Rome) 199 1,81,343 (Dipt. Chim. Anal. Univ. Torino 10125 Torino Italy). Standards Association Australia Certified reference materials-general guide to material selection prepara- tion testing and certification Australian Standard AS 3870- 199 1 28 Mar 199 1.Pp. 20 (Standards House 80 Arthur St. North Sydney New South Wales 2060 Australia). Smirnova L. Vackova M. Zemberyova M. Speciation of some metals in soil Chem. Listy 1991 85 1235 (Prirodoved. Fak. Univ. Komenskeho 842 15 Bratis- lava Czechoslovakia). Shaheb-ud-Dean Tschemonyi P. J. Riley W. J. Elimination of matrix effects in electrothermal atomic absorption spectrophotometric determinations of bis- muth in serum and urine Clin. Chem. (Winston-Salem N. C.) 1992 38 119 (Dept. Biochem. R. Pert.h Hosp. Perth 600 1 Australia). Stuzka V. Krejci J. Indirect determination of chloro- phenols by atomic absorption spectrometry (AAS) after extraction of their ionic associates involving the dipyri- dylocopper(I1) or phenanthrolinocopper(i1) complex Col- lect.Czech. Chem. Commun. 1991 56 2827 (Dept. Anal. Org. Chem. Palacky Univ. 771 46 Olomouc Czechoslovakia). Francek M. A. Soil lead levels in a small town environment case study from Mt. Pleasant Michigan Environ. Pollut. 1992,76,25 1 (Dept. Geogr. Earth Sci. Cent. Michigan Univ. Mt. Pleasant MI 48858 USA). Jones K. C. Jackson A. Johnston A. E. Evidence for an increase in the cadmium content of herbage since the 1860s Environ. Sci. Technol. 1992 26 834 (Inst. Environ. Biol. Sci. Lancaster Univ. Lancaster UK LA1 4YQ). Suzuki K. T. Detection of metallothioneins by high- performance liquid chromatography-inductively coup- led plasma emission spectrometry Methods Enzymol. 1991 205 (Metallobiochem.Pt. B) 198 (Environ. Health Sci. Div. Natl. Inst. Environ. Stud. Tsukuba Japan 305). Klaassen C. D. Lehman-McKeeman L. D. Separation and quantification of isometallothioneins by high-per- formance liquid chromatography-atomic absorption spectrometry Methods Enzymol. 199 1 205 (Metallobiochem. Pt. B) 190 (Med. Cent. Univ. Kansas Kansas City KS 66 103 USA). Kaushik V. S. Hance R. L. Tseng H. H. Tobin P. J. SIMS-TEM study of fluorine implants and anneals into silicon and polysilicon Microbeam Anal. 199 1,26 481 (MOS Surf. Anal. Lab. Motorla Inc. Austin TX 78721 USA). Rankin A. H. Ramsey M. H. Coles B. Van Lange- velde F. Thomas C. R. Composition of hypersaline iron-rich granitic fluids based on laser-ICP and synchro- 931856. 931857. 9318 5 8. 931359. 931860.93/86 1. 931862. 931863. 931864. 931865. 931866. 931867. 931868. 931869. ton-XRF microprobe analysis of individual fluid inclu- sions in topaz. Mole granite eastern Australia Geo- chim. Cosmochim. Acta 1992 56 67 (Dept. Geol. Imp. Coll. London UK SW7 2BP). Rechenberg W. Statistical comparison of calibration line and standard addition line GIT Fachz. Lab. 1 99 1 35 1333 (Forschungsinst. Zementind. W-4000 Dues- seldorf 30 Germany). Dagmar Kalavska Determination of manganesem in tap water Int. J. Environ. Anal. Chem. 1991 45 159 (Dept. Ecosozol. Physiotactics Comenius Univ. 842 1 5 Bratislava Czechoslovakia). McLean C. J. McCombes P. T. Jennings R. Ledin- gham K. W. D. Singhal R. P. Novel ion optics for secondary ion suppression in sputter initiated laser post- ionization Nucl.Instrum. Methods Phys. Res. Sect. B 1991 B62 285 (Dept. Electron. Electr. Eng. Univ. Glasgow Glasgow UK G 12 8QQ). Gokmen A. Yalcin S. Versatile microcomputer inter- face and peripheral devices an application in deuterium lamp background correction graphite furnace atomic absorption spectrometry Rev. Sci. Instrum. 1992 63 255 (Dept. Chem. Middle East Tech. Univ. Ankara Turkey 0653 1). Fang Z. Flow injection on-line column preconcentra- tion in atomic spectrometry Spectrochim. Acta Rev. 1991 14 235 (Inst. Appl. Ecol. Acad. Sin. Shenyang China). Tyson J. F. Flow injection atomic spectrometry Spectrochim. Acta Rev. 1991 14 169 (Dept. Chem. Univ. Massachusetts Amherst MA 0 1003 USA). Osborne S. P. Ultrasonic nebulization inductively coupled plasma spectroscopy. Optimization for various matrixes Spectroscopy (Eugene Oreg.) 1992 7 37 (Fisons Appl.Res. Lab. Valencia CA 19355 USA). Ramamurthy S. Walzak T. L. Lu S. F. Lipson T. C. McIntyre N. S. Study of tinplate structure using imaging secondary ion mass spectrometry Surj Inter- face Anal. 1991 17 834 (Univ. West. Ontario Lon- don Ontario Canada N6A 5B7). Vriezema C. J. Zalm P. C. Impurity migration during SIMS depth profiling Surj Interface Anal. 1 99 1 17 875 (Philips Res. Lab.) 5600 JA Eindhoven The Netherlands). Turner N. H. Estimates of peak areas and relative atomic amounts from wide-scan XPS spectra Sut$ Interface Anal. 1992 18 47 (Surf. Chem. Branch Nav. Res. Lab. Washington DC 20375-5000 USA). Yebra Biurmn M. C. Bermejo Barrera A. Mella Luzao M. L. Bermejo Barrera M. P.Determination of copper traces in water by atomic absorption spectrometry Quim. Anal. (Barcelona) 1991 10 59 (Fac. Quim. Univ. Santiago Compostela Santiago Compostela Spain 15706). Goergl R. Wobrauschek P. Kregsamer P. Streli C. Measurement of the spectral distribution of a diffrac- tion X-ray tube with a solid-state detector X-Ray Spectrom. 1992 21 37 (Atominst. Oesterr. Univ. A- 1020 Vienna Austria). Uden P. C. Element specific chromatographic detec- tion by atomic emission spectroscopy ACS Symposium Series 479 1992 (American Chemical Society Wash- ington DC USA). Haswell S. J. Theory Design and Applications Ana- lytical Spectrosc. Lib. Vol. 5 At. Absorp. Spectrom. (Elsevier Amsterdam The Netherlands). Papers 93lC870-93lC909 were presented at the Ninth Czechoslovak Spectroscopic Conference ceskh Budejovice Czechoslovakia June 93lC870.Adametkovai D. Gratzlovai J. Hegyi L. Selenium and 22-24 1992.74R JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 93lC87 1. 93lC8 72. 93lC8 73. 93lC874. 93lC875. 93lC876. 93lC877. 93lC878. 93lC879. 9 3lC8 80. 93lC88 1. 93lC882. 9 3lC8 8 3. 93lC8 84. 93lC88 5. 93lC886. 9 3lC887. 93lC888. cardiovascular disease in elderly people (Res. Inst. Gerontol. Malacky Czechoslovakia). Albayrak S. Giireli L. L. Uzmen R. Yildiz I. Effect of complexing agents on coprecipitation of uranium with impurities and their determination with ICP-AES (Cekmece Nucl. Res. Training Cent. P.O. Box 1 Havaalani Istanbul Turkey). Bastl J. hbal K. Heavy metals in peats (JahoEeski Univ.ZemEdblski Fak. Katedra Chem. Ceskt Bud& jovice Czecholslovakia). Cernohorskf T. Determination of aluminium in bever- ages by AAS (Univ. Chem. Technol. Dept. Environ. Protection Pardubice Czechoslovakia). Curdovai E. Mohl C. Ostapczuk P. Quality control with CRMs for trace element determination in candi- date reference materials (Natl. Inst. Public Health Srobirova 48 100 42 Prague Czechoslovakia). Fara M. Koieluh M. Cermakovai L. Determination of thallium in solid emission and emission samples using ETAAS (Power Res. Inst. Prague Czechoslovakia). Figera M. Hladkf Z. RiSovai J. Determination of vanadium in petroleum products by ETAAS and ICP- AES (Fac. Chem. Technol. STU Dept. Anal. Chem. Radlinskkho 9 8 12 37 Bratislava Czechoslovakia). Hamplovai V. Mgilvokai Z.Novak J. Pure boron-use of AAS for the determination of silicon (Inst. Phys. Czechoslovak Acad. Sci. Prague Czechoslovakia). Heltai Gy. Atomic spectroscopy detectors for chro- matography (Univ. Agric. Sci. Dept. Chem. H-2103 Godolld Hungary). Hezina F. Filipu P. Determination of germanium in polyester matrix by inductively coupled plasma atomic emission spectrometry (Inst. Landscape Ecol. Czecho- Slovak Acad. Sci. Ceskt BudEjovice Czechoslovakia). Hoenig M. Particular problems encountered in trace element analysis of environmental samples by electroth- ermal atomic absorption spectrometry (ETAAS) (Inst. Recher. Chim. Minist. l’Agric. Leuvensesteenweg 17 B- 3080 Tervuren Belgium). Hutton R. C. Kingston A. Freedman P. A. Walder A. J. Platzner I. ICP-MS instrumentation and applica- tions in elemental trace analysis and isotope ratio measurements (VG Elemental Fisons Instrum. Ion Path Road Three Winsford Cheshire UK CW7 3BX).Kanickf V. BudiS J. Soldan M. Koltava D. Toman J. Determination of inorganic pollutants in drainage areas of the BEli and SemiE streams (Fac. Educ. Masaryk Univ. Brno Dept. Chem. PofiEi 7 603 00 Bmo Czechoslovakia). Kliment V. Analysis of high-temperature supercon- ducting films by XRFA and ICP-AES (Inst. Phys. Dubravski Cesta 9 84228 Bratislava Czechoslovakia). Kliment V. Depth-profiling with glow discharge optical spectrometry (Inst. Phys. Dubravskd Cesta 9 84228 Bratislava Czechoslovakia). Kolihovai D. Vyshkotilovai O. Doleial J. svortfkovai J. Determination of trace levels of some toxic metals in bio-ceramic materials by ETAAS (Dept.Anal. Chem. Cent. Labs. Inst. Chem. Technol. Technicki 5 166 28 Prague 6 Czechoslovakia). Koller L. Determination of arsenic in water using continuous hydride generation and excitation in the plasma source by MarinkoviE (Dept. Chem. Tech. Univ. KoSice Czechoslovakia). Korpel L. Vozair J. Some specific problems in environ- mental analyses (GeoI. Ecol. Lab. (GEL) SpiSski Novi Ves Czechoslovakia). Krakovskai E. Determination of Cd Pb and Mn by WETA 88 and influence of chemical modifiers (Dept. Chem. Fac. Metall. Tech. Univ. KoSice PuliS Pavel Air Force Sch. KoSice Czechoslovakia). 93lC889. Kriitoufkovai S. Jehlitka J. KO& J. Desorption of zinc from soils by selected organic compounds (Univ. Agric. Prague Czechoslovakia).913lC890. Kroupa E. Bastl J. Heavy metals stratigraphy in vertical profile of fishpound Vajgar sediment (JihoEeskB Univ. ZembdElski Fak. Katedra Chem. 6eskC Bud& jovice Czechoslovakia). 913lS89 1. Kubiziiakovai J. Laiznitka P. First experiences and the erformance SH-AAS 4000 (Ustav KrajinnC Ekol. ESAV CeskC BudEjovice Czechoslovakia). 93lC892. Kubovai J. Polakovitovai J. Stregko V. Medved J. Determination of Ta and Nb at low levels in geological materials by ICP-AES (Geol. Inst. Fac. Natl. Sci. Comenius Univ. Bratislava Czechoslovakia). 4’3lC893. Laiznitka P. Hezina F. Kubiziiak J. Short study about influence of matrix constituents in analyses of animal teeth (Ustav KrajinnC Ekol. CSAV CeskC BudEjovice Czechoslovakia). 93/C894. Loskotovai I. Helan V. Phblovai D.Pixovh H. Determination of the low concentrations of aluminium in steel on optical emission and XRF spectrometers (TiineckC Zelezimy AS Chem. ZkuSebny ZVU Hradec KrilovC Czechoslovakia). 93lC895. Matougek T. Dgdina J. Quartz tube atomizers for hydride generation AAS interferences in the selenium hydride atomization (Inst. Nucl. Biol. Radiochem. Czechoslovak Acad. Sci. Videiiski 1083,142 20 Prague 4 Czechoslovakia). 93lC896. Miholovai D. Szaikovai J. Bellama J. M. Mader P. Cibulka J. Determination of lead in new Czechoslovak biological reference materials of animal origin (Univ. Agric. 165 2 I Prague Czechoslovakia). 93K897. Novotnf I. Mermet J. M. Analytical diagnostics in ICP-AES (PiirodovEdecka Fak. Masarykovy Univ. Bmo Czechoslovakia). 93lC898. Paukert T.Use of microwave radiation for surface waters analysis (Czech Geol. Surv. MalostranskC ndm. 1 9 1 1 8 2 1 Prague 1 Czechoslovakia). 93lC899. Pdcha S. Determination of silver gold and platinum metals in multi-component sweeps by ICP spectrome- try (Safina SP Vestec Jesenice Prahy Czechoslovakia). 93lC900. RiSovai J. Hladky Z. Figera M. Determination of beryllium in environment by ETAAS and ICP-AES methods (Fac. Chem. Technol. STU Dept. Anal. Chem. Radlinskkho 9 8 12 37 Bratislava Czecho- slovakia). 93lC901. Rohlik V. Kroupovai V. Klein Z. Bastl J. Content of Mn Fe Cu and Zn in the foodstuffs of plant origin in South Bohemia (Dept. Anat. Physiol. Agric. Fac. Univ. CeskC BudEjovice Czechoslovakia). !)3/C902. Rychlovskf P. Bflf J. Denkovai P. Dithizone- polyurethane foam system used as a preconcentration step for the determination of Pb by FAAS in soils and surface water (Dept.Anal. Chem. Charles Univ. Albertov 2030 CS-128 43 Prague 2 Czechoslovakia). !?3/C903. Sharp B. L. Samples signals and noise in inductively coupled plasma spectrometry (Dept. Chem. Lough- borough Univ. Technol. Loughborough Leicestershire UK LE11 3TU). !?3/C904. Spgvatkovai V. Kratzer K. Cejchanovai M. Problems of the soil extraction (Tech. Univ. Prague Dept. Nucl. Chem. Prague Czechoslovakia). !931C905. StreSko V. Medved J. Kubovai J. Polakovitovai J. Determination of elements for certification of reference solutions (Geol. Inst. Fac. Natl. Sci. Comenius Univ. Bratislava Czechoslovakia). !93/C906. SzBkova J. Mader P. Bellama J. M. Comparison of decomposition procedures for arsenic determination inJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL.8 75R biological materials by hydride generation AAS (Agric. Enterprise 503 03 Smifice Czechoslovakia). 93/C907. Solt& P. PlieSovskal N. Comparison of photographic and photoelectric detection for REE analysis by ICP- AES (Dept. Chem. Fac. Metal. Techn. Univ. KoSice Czechoslovakia). 93/C908. Umanec L. Determination of As Bi Sb Se Sn Te apd Hg by hydride generation and ICP-AES (I’W-VUK Panenskk Bfeeiany Czechoslovakia). 93/C909. VodiEkovsi A. Sfkorovsi I. Geochemistry of North Bohemian sulfurous coal vertical profile (UsXav Geo- tech. CSAV Prague Czechoslovakia). Papers 93lC9 10-93lC997 were presented at the Third International Symposium on Analytical Chemistry in the Exploration Mining and Processing of Materials Sandton South Africa August 2-7 1992.93/c9 93/c9 93/c9 93/c9 93/c9 93/c9 93/c9 93/c9 93/c9 0. Thomassen Y. Chemical characterization of workroom air contaminants (Natl. Inst. Occup. Health P.O. Box 8 149 Dep. N-0033 Oslo 1 Norway). 1. Slickers K. A. Spectrochemical analysis in the metallurgical industry (Spectro Anal. Instrum. W-4 190 Kleve Germany). 2. Cornell D. H. Rare earths from supernovae to super- conductors (Univ. Natal Durban South Africa). 3. Perry B. J. Van Loon J. C Barefoot R. R. Speller D. V. Dry-chlorination-ICP-MS analytical method for PGEs and gold in rocks (Dept. Geol. Univ. Toronto Toronto Ontario Canada MSS 3B 1). 4. We4 B. Sperling M. Flow injection-the ultimate approach to automation in analytical chemistry (Dept.Appl. Res. Bodenseewerk Perkin-Elmer Gmb H Post- fach 10 1 164 Uberlingen Germany). 5. Watling R. J. Use of laser ablation ICP-MS for fingerprinting gold (Min. Sci. Lab. Chem. Centre 125 Hay St. Perth Western Australia 6004). 6. Willis J. P. To ash or not to ash? A dilemma in the sample preparation of coal for elemental analysis Geochem. Dept. Univ. Cape Town Rondebosch 7700 South Africa. 7. Watson A. E. Determination of the rare earth elements in geological samples (Spectro Anal. Instrum. Groenk- loof Pretoria South Africa 0027). 8. Jarvis K. E. Role of inductively coupled plasma mass spectrometry in mining and mineral exploration (NERC ICP-MS Facility Dept. Geol. Royal Hdloway Bedford New College Egham Surrey UK TU20 OEX).93K919. L’vov B. V. Extension of the dynamic range and linearization of calibration graphs in Zeeman graphite furnace atomic absorption spectrometry (Dept. Anal. Chem. St. Petersburg Tech. Univ. St. Petersburg Russia). 93/C920. Holcombe J. A. Wang P. Graphite furnace atomiza- tion of solids at low pressures (Dept. Chem. Biochem. Univ. Texas Austin Austin TX USA). 93/C921. Mermet J. M. Ducreux M. Gagean M. Laser ablation of solids for elemental analysis by inductively coupled plasma atomic emission spectrometry (Lab. Sci. Anal. Univ. Lyon France). 93/C922. Nickel H. Characterization of metallic and t hermic high-temperature materials for energy systems by means of atomic spectroscopy (Res. Cent. Julich Inst. Reactor Mater. Techn. Univ. Aachen 5 170 Julich Germany).93/C923. Willis J. P. XRF spectrometry 1. Trends and develop- ments. 2. Trace element analysis-use of influence coefficients to correct for inter-element effects (Dept. Geochem. Univ. Cape Town Rondebosch 7700 South Africa). 93/C924. Human H. G. C. Rohwer E. R. Laser-induced ioniza- tion and time-of-flight mass spectrometry as diagnostic tool in the processing of materials (Atomic. Energy Corp. P.O. Box 582 Pretoria South Af- rica 000 1). 93/C925. Feather C. E. Application of analytical chemistry to exploration geochemistry (Anglo American Res. Labs. (Pty) Ltd. P.O. Box 106 Crown Mines South Af- rica 2025). 93/C926. Walters P. E. Visser K. Atomic vapour laser isotope separation (AVLIS) of zirconium by polarization spec- troscopy (Dept. Phys. Univ. Stellenbosch Stellen- bosch South Africa).93K927. Oshemkov S. V. Artmonova E. O. Ashihmina E. I. Hait 0. V. Petrov A. A. Spectral analysis of geological samples with their evaporation by scanning CW-laser irradiation (Inst. Phys. Sankt-Petersburg Univ. Ulya- novskaya 1 Petrovorets St. Petersburg Russia). 93/C928. Kovarskii N. Ya. Kalyagin A. N. Electrochemically deposited magnesium hydroxide as a collector of trace elements from sea-water and its application for marine geology (Inst. Chem. Far-Eastern Div. Acad. Sic. Vladivostok Russia). 93/C929. Altman E. L. Krcmar B. Use of a graphite atomizer with electrostatic precipitation in geochemical explora- tion (Geol. Dept. St. Petersburg Univ. St. Petersburg Russia). 93/C930. Borkhodoev V. Ya. Universal program for XRF analy- sis by fundamental parameter method on the basis of optimization of continuous spectrum numerical integra- tion (North-East Interdisciplinary Res.Inst. Russian Acad. Sci. Far East Branch Magadan CIS). 93/C93 1. Khozhainov Yu. Kagramanov G. G. Extraction and concentration of microelements from sea-water by coprecipitation (Mendeleev Inst. Chem. Eng. Miussk- sys Sq. 9 125 190 Moscow Russia). 93K932. Khozhainov Yu. Suppression of the influence of the sample matrix during silver microquantities analysis by atomic absorption (Mendeleev Inst. Chem. Eng. Mius- skaya Sq. 9 125 190 Moscow Russia). 93/C933. Torgov V. G. Demidova M. G. Extraction-instrumen- tal methods for the determination and analysis of selenium with the use hex-1-ene (Inst. Inorg. Chem. Novosibirsk Russia).93/C934. Uhlig S. Pre-calibrated quantitative programs for X- ray fluorescence analysis in the exploration mining and processing of materials (Siemens AG AUT V37 1 P.O. Box 2 1 1262 D-7500 Karlsruhe 2 1 Germany). 93/C935. LaBrecque J. J. Radioisotope X-ray fluorescence for mineral exploration and exploitation-the case of lateritic material from Cerro Impact0 (Venezuela) (Inst. Venezolano Investig. Cien. (IVIC) Apartado 2 1827 Caracas Venezuela). 93/C936. Klich H. ‘C0MAR’-database for certified reference materials (Bundesanstalt Materialforsch. prufung Un- ter den Eichen 87 Berlin Germany). 93/C937. Dale L. S. Lavrencic S. A. Application of ICP-MS to the determination of low abundant trace elements in coal and coal products (CSIRO Div. Coal Energy Technol.Lucas Heights New South Wales Australia). 93/C938. Ring E. J. Reference materials in South Africa (Anal. Sci. Div. Mintek Private Bag X3015 Randburg South Africa). 93/C939. Anderson S. T. G. Application of laser ablation to inductively coupled plasma mass spectrometry (ICP- MS) (Anal. Sci. Div. Mintek Private Bag X3015 Randburg South Africa 2 125). 93/C940. RobCrt R. V. D. Application of ICP-MS to the analysis of rare earth elements (Anal. Sci. Div. Mintek Private Bag X3015 Randburg South Africa 2 125). 93/C94 1. Pohlandt-Watson C. Environmental analysis in mining and metallurgy (Anal. Sci. Div. Mintek Private Bag X30 15 Randburg South Africa 2 125).76R 93lC942. 93lC943. 93lC944. 93lC945. 9 3lC946. 93lC947. 93lC948. 9 3lC949. 93lC950. 93lC95 1. 93lC952.93lC953. 93lC954. 93lC955. 93lC956. 93lC957. 93lC958. 9 3lC9 5 9. JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 Morgan P. M. TG-GC study of volatile species emitted during the calcining of various green cokes (Sastech Res. Dev. P.O. Box 1 Sasolburg South Africa). Costa J. F. C. L. Sampaio C. H. Vilhena M. T. Graphic computer application in geochemical data representation of a coal basin (Mining Eng. Dept. Osvaldo Aranha Porto Alegre Brazil). Barzev A. Improvement of the instrument sensitivity in graphite furnace atomic absorption spectrometry (Anglo American Res. Labs. (Pty) Crown Mines South Africa). Barzev A. Grigorova B. Graham I. Laser ablation inductively coupled plasma mass spectrometry for the analysis of mineral grains (Anglo American Res. Labs.(Pty) Crown Mines 2025 South Africa). Shannon J. Combined Philips PW1606 and LINK EDS system Anglo American Res. Labs. (Pty) P.O. Box 106 Johannesburg South Africa). Jackson J. A. New approaches in gold determinations by AAS (Anglo American Res. Labs. (Pty) Johannes- burg South Africa). Weichselbaum J. Automatic gold analysis over a wide concentration range (Anglo American Res. Labs. (Pty) Johannesburg South Africa). De Brujin J. D. New concept in the assay of gold silver and the platinum group metals (Anglo American Res. Labs. (Pty) Johannesburg South Africa). Hou Y. Atomic absorption spectrophotometry for the determination of Cr(w) and Cr(Iv) in surface waters (Med. Coll. Zhenjiang China). Nham T. T. Brodie K. G. Sub-ppb measurements using inductively coupled plasma atomic emission spectrometry with an ultrasonic nebulizer (Varian Australia Pty 679 Springvale Rd.Mulgrave Victoria Australia). Tyler G. Brodie K. G. Dynamic background correc- tion for low level analysis in geological samples by ICP- AES (Varian Australia Pty 679 Springvale Road Mulgrave Victoria Australia). Zacharia A. N. Chebotarev A. N. Bouktit M. C. 'Furnace-flame' atomizer and its utilization in atomic- absorption analysis of non-ferrous metals and alloys (Dept. Chem. Odessa State University Odessa CIS). Zacharia A. N. Chebotarev A. N. Bouktit M. C. Some question of the atomic absorption analysis of solid powdered materials (Dept. Chem. Odessa State Univ. Odessa CIS). Miloshew S. Nishkow I. Atanasow St. Monitoring of waste waters for metallic impurities using ICP optical emission spectrometry (ICP-AES) (Central Lab.Miner. Proc. Bulgarian Acad. Sci. Sofia 1126 I Anton Ivanow Str. Bulgaria). Koppe J. C. Lisboa P. F. C. Geochemical exploration of gold depsits in Silo Sepe southernmost Brazil (Mining Eng. Dept. Univ. Fed. Rio Grande Sul Av Osvaldo Aranha 99504 90.2 10 Porto Alegre Brazil). Vegter N. M. Botha A. J. Fouche F. J. Determina- tion of the distribution of gold and other metals in activated carbon during adsorption (Dept. Mater. Sci. Metall. Eng. Univ. Pretoria Pretoria 0002 South Africa). Zheleznova A. A. Kuzmenko N. E. Analytical possibil- ities of the spectral aerosol spark technique for the determination of metals and halogens in aqueous and organic solutions of different materials (Lomonosov Moscow State Univ. Chem.Dept. Div. Anal. Chem. Lenin Hills GSP-3 Moscow 1 19285 Russia). Filichkina V. A. Abroskin A. G. Proscurnin M. A. Savostina V. M. Determination of transition metals of thermal lens spectrometry (Lomonosov Moscow State Univ. Chem. Dept. Div. Anal. Chem. Lenin Hills GSP-3 Moscow 1 19285 Russia.). 93lC960. Metil N. I. Shevchuk I. A. Concentration and flame- less atomic absorption determination of mercury in waters (Dept. Chem. Donetsk State Univ. The Uk- raine). 93lC96 1. Van Dyk G. J. Sidiropoulos N. Application of flame and electrothermal AAS in the determination of minor and trace elements in the mining and exploration or iron ore (Anal. Chem. Res. Dev. ISCOR Headquarters Pretoria South Africa). 93K962. Baohang H. Baofeng T. Rapid determination of Cu Mn Cd V Zr Ti Cr Mg B and Fe in aluminium alloys by ICP photoelectric spectrometry (Gen. Res.Inst. Non-Ferrous Metals Beijing China 100088). 93lC963. Claos E. G. Odinets V. M. Kinetic atomic absorption spectrometry (KAAS) (VarTech International Co Sci- entific Research Centre Tallinn Estonia). 93lC964. Rogers D. E. C. 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Determination of cadmium and other metal concentrations in rat blood urine faeces and internal organs after chelation therapy AA. ICP and PIXR studies (Dept.Natl. Health Population Dev. Natl. Centre Occup. Health Johannesburg South Africa). Stux R. Use of the time resolve spark analysis to improve accuracy in metals analysis (Thermo Jarrell Ash 8E Forge Pkwy. Franklin MA 02038 USA). Stankiewicz W. Boblibrzuch B. Tarchalska T. Motel W. Conception of new series of jewellery gold certified reference materials for X-ray fluorescence analysis (Inst. Non-Ferrous Met. Anal. Chem. Dept. 44-101 Gliwice ul. Sowinskiego 5 Poland). Stankiewicz W. Mzyk Z. Matrix effects in the X-ray fluorescence analysis of copper ores and of their enrich- ment products (Inst. Non-Ferrous Met. Anal. Chem. Dept. 44- 10 1 Gliwice ul. Sowinskiego 5 Poland).

ISSN:0267-9477    

DOI:10.1039/JA993080045R

出版商:RSC    

年代:1993

数据来源: RSC

摘要:

JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 51 Applications of Ultrasonic Nebulization in the Analysis of Petroleum and Petrochemicals by Inductively Coupled Plasma Atomic Emission Spectrometry* Robert 1. Botto Bayto wn Speciality Products Exxon Research and Engineering Company Bayto wn TX 77522-4255 USA The availability in recent years of stable reliable ultrasonic nebulizers (USN) for inductively coupled plasma atomic emission spectrometry (ICP-AES) has led to new applications of ICP-AES in the petroleum and petrochemical industries. These applications take advantage of the high efficiency and high sensitivity of the USN and/or its desolvation capability and include direct analysis of volatile hydrocarbons such as toluene naphtha isopropranol etc. for trace elements; direct determination of lead in aviation fuel; trace analysis of solvents distillate oils and low-ash polymers prepared by high temperature ashing; and rapid analysis of heavy oils and finished lubricating oils by microwave digestion of small (0.1 g) samples.This paper presents the status of development of each of the above applications contrasting the performance of the standard pneumatic-type nebulizer system (cross-flow) and the USN. The analysis of volatile hydrocarbons uses the desolvator to remove most of the organic vapour prior to introduction into the plasma. Although this may be accomplished using a cooled spray chamber attached to a pneumatic nebulizer the high efficiency of the USN provides additional sensitivity tending to off set degradation in performance due to residual solvent loading and organic spectral background effects.The injection of oxygen into the outer and aerosol carrier streams further decreases these effects and yields detection limits for toluene and other solvents that are comparable with the aqueous performance of the USN. Keywords Ultrasonic nebulization; inductively coupled plasma atomic emission spectrometry; organic solvents; petroleum; oxygen-argon mixed gas plasma Interest in ultrasonic nebulization (USN) for inductively coupled plasma atomic emission spectrometry (ICP-AES) and ICP mass spectrometry is enjoying a revival due to the recent availability of stable convenient commercial equip- ment.’ The USN offers a number of important advantages for ICP. The high efficiency of aerosol production results in improved sensitivity and lower detection limits provided that aerosol desolvation is used to reduce the solvent load reaching the ICP.The present generation of USNs is reliable and convenient to operate. There are no tiny orifices to plug. The liquid/transducer interface is easy to adjust and maintain. The aerosol transport path is easily cleaned and flushed permitting rapid changeover from aqueous to organic operation and back again. Gas and liquid flow rates can be precisely controlled using mass flow controllers and a peristaltic pump. Transducer output is stable and tuning is simple or automatic. The limitations of the USN for ICP spectrochemical analysis do not come close to outweighing the advantages but need to be considered in many applications.Long rinse- out times are experienced for several elements in aqueous solution particularly B Hg and Se. Boron is frequently added in sample preparations using HF and is present at high concentrations in these samples. After analysing preparations of B the time required for washout to blank levels for determination of trace amounts of B is several hours. Enhanced acidhalt matrix interference effects have been noted with the USN system. Avoidance of these effects requires more precise matrix matching of samples and standards as for pneumatic nebulizer systems. ‘Desolvation effects’ have long been documented for USN applications to ICPS.~’~ It is still not clear which matrix interference and memory effects are associated with the desolvation facility and which are due to the aerosol generation and transport function of the USN.It is hoped that the current revival of interest in USNs will result in studies clarifying these uncertainties. *Presented at the 1992 Winter Conference on Plasma Spectro- chemistry San Diego CA USA January 4- 1 1 1992. The Baytown Specialty Products unit of Exxon Research and Engineering Company purchased a Cetac Technologies U-5000 ultrasonic nebulizer early in 1991 to expand the capabilities of the recently renovated and upgraded ICP- AES ~ystem.~ Application of the USN-ICP-AES to difficult analytical problems particular to the petroleum and petro- chemical industries was investigated and these studies are ongoing. The applications reported in this study take advantage of the high efficiency and high sensitivity of the USN and/or its desolvation capability.The direct analysis of volatile hydrocarbon liquids for trace elements by ICP-AES is highly desirable if lengthy sample preparation and the possibility of contamination are to be avoided. The contamination problem is particu- larly important for commercial solvents as they typically contain sub-pg ml-I levels of metals and ‘heteroatom’ impurities. Analysis of volatile organics by ICP-AES using conventional pneumatic nebulizers is often difficult owing to the organic vapour loading of the pla~ma.~q~ Various methods have been employed to limit and control the solvent vapour load including the use of a cooled spray chamber,’ a thermostated condenser between the spray chamber and plasma torch,* a solvent permeable membrane interface between the sample introduction system and the ICP9 and the use of very low sample flow rates1° or microlitre-size sample injections. Aerosol desolvation is another method that can be used to reduce organic vapour loading of the ICP.The USN consists of a highly efficient aerosol generator coupled to a desolvation apparatus capable of removing the bulk of the organic solvent before injection into the ICP plasma. This combination is the source of the ‘ultrasonic advantage’ i.e. detection limits for aqueous solution up to a factor of ten lower than with pneumatic nebulization. The aim of this study was to investigate whether the ultrasonic advantage would be retained while introducing volatile organic sol- vents into the ICP.This was achieved by testing several solvents of importance to the petrochemical industry. Specific applications included the determination of trace metals in toluene naphtha C and C8 hydrocarbons alco-52 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 hols etc. and the direct determination of trace contami- nant or added tetraethyllead in naphtha and commercial aviation fuel. The sensitivity advantage of the USN can aid in the characterization of solvents naphtha distillate oils low ash polymers and other petroleum-derived materials containing low levels of metallic contaminants. Solvents and oils can be analysed as aqueous solutions using the technique of sulfated ashing to help retain potentially volatile elements such as Pb.12 Polymers can be reduced to aqueous solutions by sulfated ashing or simple dry ashing.Large sample sizes (up to 500 g) can be processed to yield concentration factors of up to 20 or more. The USN provides the additional sensitivity enhancement for ultra-trace determinations. Sometimes rapid turnaround is needed for trace element analysis of heavy oils or used motor oils and furnace ashing procedures usually require overnight time periods. Analysis of these materials by dilution and direct aspiration of organic solutions may not be convenient or advisable particularly for used motor oils where metals may be present in particulate form. Microwave digestion provides a rapid alternative to furnace ashing. However most com- mercially available equipment for microwave digestion is able to accommodate only very small samples of heavy oils (0.1-0.5 g).The USN system in this case provides sufficient sensitivity to match what would be obtained from a typical sulfated ashing preparation analysed using pneumatic nebulization. The experimental approach and status of the above applications of USN in petroleum and petrochemical analysis are described in this paper. Experimental Instrumentation The dual spectrometer ICP-AES system described in ref. 4 was used in this study. The basis of this system is a ‘vintage’ Jarrell Ash AtomComp 7 50 polychromator. Plasma power was supplied by a 2.5 kW crystal-controlled generator. The Ultrasonic nebulizer USN was a Model U-5000 purchased from Cetac Technolo- gies. The pneumatic nebulizer was a Thermo Jarrell Ash fixed cross-flow nebulizer.The plasma torch (standard Thermo Jarrell Ash Fassell type) was interfaced to the USN using a simple right angle elbow joint of glass. The sample was pumped to the USN and cross-flow nebulizer using a Rainin ‘Rabbit-Plus’ four channel peristaltic pump with Viton rubber pump tubing (black-black for sample flow black-purple for USN-pumped drain flow). The ICP-AES gas system was modified for Ar-02 mixed gas plasma operation as shown in Fig. 1. Calibrated micrometer valves were used to control the oxygen flow rates to the outer intermediate or aerosol carrier argon streams. A mass flow controller (FC) guaranteed a steady controllable flow of argon aerosol carrier. A Y connector was placed in the desolvated aerosol transfer line connect- ing the USN with the plasma torch.This permitted the withdrawal of small amounts of incidental hydrocarbon condensate from this line. The thermocouple permitting control of the USN desolvator heating circuit is mounted in a thermowell centered in the path of the aerosol exiting the heated zone. Reagents and Solutions Ultrapure quality reagents and 18 MR quality de-ionized water were used to prepare aqueous calibration standards samples and blanks. Toluene heptane and isooctane (2,2,4- trimethylpentane) calibration standards were prepared us- ing spectroscopic grade solvents. Conostan S-2 1 (Conoco Specialty Products) 100 ppm m/m was diluted by mass with the chosen solvent to a concentration of 1 pg g-’ (21 elements). Blanks consisted of 1% m/m Conostan 75 Base Oil in the appropriate solvent.Calibration standards and blanks for the hydrocarbon solvent analyses were prepared fresh for each run. Calibration standards for propan-2-01 (IPA) analysis were prepared by diluting semi-conductor grade IPA with 18 MR water to a concentration of 70% v/v IPA after spiking with aqueous calibration standards containing the analyte ele- Plasma Oxygen ’ I torch I I Coolant ToJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 53 Table 1 Experimental conditions for USN-ICP-AES analysis USN conditions- Heater temperature/"C Chiller temperature/"C Transducer output/A Ar outed1 min-l Ar intermediate/] min-' Ar aerosol/ml min-' O2 outer/ml rnin-l O2 intermediate/ml min-l O2 aerosol/ml min-l Sample feed/ml min-1 Forward power/kW Reflected power/W Power control Observation height*/mm Integration time/s Mn intensity Cu:Mn intensity ratio Solvent boiling-pointPC Flow rates- Generator- Spectrometer- Other- Water 70% IPA 140 140 5 - 18 4.5 4.5 22 25 0 1 679 700 0 0 0 0 0 0 1.4 1 .o 1.2 1.8 5-10 15-20 Automatic Manual 16 16 10 10 42 000 100 000 2.1 0.5 100 - 82 *Measured as height above the load coil.Isooctane 125 - 14 4.6 25 0 633 60 0 0 1.3 2.1 50-60 Manual 20 10 20 000 3.1 99.3 Heptane 125 - 14 4.6 25 0 633 60 0 0 1.5 2.1 50-60 Manual 20 10 32 000 3.2 98.4 Toluene- 1 Toluene-2 Toluene-3 140 - 14 4.7 25 0 630 60 0 0 1 .o 1.8 30-40 Manual 13 10 120 000 1.3 1 10.6 140 - 14 4.7 22 0 620 48 8.5 0 1 .o 1.8 30-40 Manual 13 10 57 000 3.1 110.6 140 - 14 4.7 22 0 620 48 0 42 1 .o 2.0 30-40 Manual 16 10 64 000 1.8 110.6 ments.Each standard or blank also contained 1% v/v concentrated HCl or HN03 for enhanced stability. A 1% m/m solution of elemental Br in chloroform (CHC13) was prepared for the determinations of tetraethyl- lead (TEL). Instrumental Conditions for ICP-AES Experimental conditions for the analysis of various organic solvents by USN-ICP-AES are shown in Table 1. The conditions were chosen for optimum operability and maximum sensitivity. The three experimental conditions for toluene represent three methods of introducing oxygen into the plasma. Stable plasma operation was achieved at relatively high levels of reflected r.f. power (20-60 W) by the use of manual power control. Switching over to automatic power control under these conditions caused an overload condition extinguishing the plasma by power interrupt.Instrumental conditions for the analysis of aqueous solutions by ICP-AES using the USN are included in Table 1. Very similar conditions were used for analysis by ICP- AES with the fixed cross-flow nebulizer. The complete protocol for the analysis of aqueous solutions has been p~b1ished.l~ Sample Preparation and Analysis Aviation fuel samples for the determination of lead (TEL) were diluted 1+99 by mass in toluene. A sample of National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 2715 Lead in Refer- ence Fuel (0.54 g 1-'=2.04 g per gallon of TEL) was similarly diluted to serve as a calibration reference. Dilu- tions were made to a consistent final mass.To each diluted sample and to the diluted calibration reference was added 1 ml of the 1% Br in CHC13 per 80 ml of toluene solution and the solutions were thoroughly mixed. After waiting approxi- mately 1 min for reaction of the Br2 with the TEL to produce inorganic lead bromide 0.5 g of Conostan stabil- izer per 80 ml of solution was added and the solutions were again mixed. The Conostan stabilizer discharges any excess Br2 remaining after reaction with TEL. A calibration blank was prepared by adding 1 ml of the Br solution and 0.5 g of the stabilizer to 80 ml of toluene. The determination of lead by ICP-AES was performed soon after sample preparation using the USN-ICP-AES conditions for toluene (toluene-3 proved best). Calibration was performed using NIST SRM 2715 Reference Fuel and the blank.Calibration linearity was checked using various dilutions of the standard. Analyses of samples were alter- 1 iZl 70% IPA 0 lsooctane W e p t a n 69 Toluene-I Toluene-2 m Al308.22 nm Ca 315.89 nm Fe 259.94 nm Fig. 2 Detection limits (30) for various solvents/conditions using USN-ICP-AES ~~ ~~~ ~~~ ed 70% IPA 0 lsooctane DHeptane 10 1 %ene-1 Toluene-2 -L Ag 338.29 nm Ba 455.40 nrn Mg 279.55 nm Fig. 3 Detection limits (30) for various solventskonditions using USN-ICP-AES54 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 nated with analyses of the calibration standard to allow for calibration drift correction. Each determination was an average of four 10 s exposures. Samples of poly(propy1ene) (5-10 g each) were com- busted over a gas burner flame in a quartz beaker and the residue was ashed at 750 "C overnight in a muMe furnace.The ash was taken up in dilute nitric acid for ICP-AES analysis which was performed using the USN and cross- flow nebulizers. Microwave digestion of NIST SRM Fuel Oil 1634b was performed using a CEM Corporation Model 2000 digestion oven and pressure-controlled digestion vessels. Samples of mass 0.1-0.2 g were digested with 10 ml of concentrated HN03 using a five-stage programme reaching a maximum pressure of 165 psig. Each digestion stage lasted 20-30 min. Following digestion the acid content of the samples was evaporated to approximately 4 ml on a hot-plate and the sample was diluted to a final mass of 100 g with de-ionized water.The analysis using ICP-AES was performed using the USN. Results and Discussion USN Detection Limits The detection limits (30) using USN-ICP-AES for various solvents and experimental conditions are shown in Figs. 2-8. It is clear that comparable detection limits for water and organic solvents have been achieved using the USN. Detection limits for 70% IPA and isooctane are generally poorer than for water heptane and toluene. Oxygen was not used for the determination of IPA as it was not required to achieve stable plasma operation. Lower detection limits might have been achieved for IPA if oxygen had been employed however. Isooctane was the most difficult sol- vent of those investigated to introduce into the plasma via the USN without extinguishing it. Without the admixture of oxygen in the outer Ar flow stable plasma operation for isooctane could not have been achieved.The intensity ratios of Cu I 324.75 nm:Mn I1 257.61 nm shown in Table 1 reflect variations in plasma excitation conditions in each experiment. The 'cooler' plasma conditions characterized by the higher Cu 1:Mn I1 ratios are also associated with the lower Mn I1 intensities for 1 pg g-l solution concentration. Plasma excitation conditions certainly influence detection limits. Comparing detection limits for toluene- 1 (hotter) and toluene-2 (cooler) one would expect toluene- 1 condi- tions to yield superior detection limits for the 'hard' ion lines. The data in Figs. 3 and 4 for Mg I1 versus Ag I and for Cd I1 and Mn I1 versus Cu I are in agreement with these expectations.The data for Cr I and Na I in Fig. 5 are not. Thus background noise or other influences on detection limit may be dominant for certain lines. Detection limits using USN-ICP-AES for Sn I 189.99 nm pa 70% IPA 0 lsooctane = Heptane 5l Toluene-1 =Toluene-2 Toluene-3 - i Cd 214.44 nm Cu 324.75 nm Mn 257.61 nm Fig 4 Detection limits (3 a) for various solvents/conditions using USN-ICP-AES 70% IPA Olsooctane m Heptane Ti 1 ~ ~ ~ ~ e n e - 1 =Toluene-2 0) 3. n n \ *n Cr 357.89 nm Mo 202.03 nm Na 5h.99 nm Fig. 5 Detection limits (30) for various solvents/conditions using USN-ICP-AES in organic solvents are inferior to aqueous detection limits owing to an elevated structured spectral background attributed to carbon in the plasma (Fig. 8). The determina- tion of B in aqueous solutions using the USN is difficult because long rinse-out times are required as already noted.Boron retained in the USN is not a problem with organic matrices however. Good washout performance and detec- tion limits for B were obtained while analysing isooctane heptane and toluene as shown in Fig. 8. Ultrasonic Advantage The 'ultrasonic advantage' is a reality for both aqueous and organic solvent systems. The detection limits in aqueous and toluene solutions (toluene-3) measured using pneuma- tic nebulization and with the USN are shown in Table 2. The left-hand portion of the table displays the measured detection limits the right-hand portion shows enhancement factors based on those detection limits. Sensitivity for aqueous solutions improved by a factor of five on the average for USN over pneumatic nebulization.Detection limits for toluene using the pneumatic nebulizer were measured using the maximum possible sample uptake rate of 0.4 ml min-l and with oxygen admixed in the argon outer gas flow. Sensitivity and operability for toluene were greatly enhanced with the USN. Operability was improved with the use of the Ar-02 mixed gas plasma. The best configuration in terms of both sensitivity and operability has oxygen injected into the sample aerosol carrier in addition to the outer gas streams (toluene-3). With this configuration sensitivity for some elements was improved by 2-3 orders of magnitude for USN over pneumatic nebulization. Trace analysis of toluene by USN-ICP-AES is both practical and efficient. Detection limits for water (Ar plasma) and toluene (Ar-02 plasma) using USN are comparable (Table 2).Similar Cu 1:Mn I1 intensity ratios for the aqueous/toluene plasmas reflect similar excitation conditions (Table 1 ). Short-term precision and instrumen- tal drift are acceptable for toluene analysis by USN-ICP- AES (Table 3). Most of the instrumental drift is due to r.f. generator power drift. This source of drift is greater without the use of the automatic power control circuits. Improved generator equipment that would permit the use of auto- matic power control at higher levels of reflected power would provide more stable operation. Role of Oxygen Molecular oxygen mixed with the argon outer nebulizer or aerosol carrier streams has an important role in the analysis of volatile organic solvents by USN-ICP-AES.Oxygen stabilizes the plasma by reducing the effects of organic solvent loading. With the desolvation facility of the USNJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 5 5 Table 2 Detection limits (pg g-I; 3a) for water and toluene and enhancement factors based on the detection limits Enhancement factor Detection limitlpg g-l H2O C7Hs C7HS:HzO C7Hs:H2O H20 (PN)* C7H3 (PN) H20 (USN) C7H8 (USN) (PN:USN) (PN:USN) (PN) (USN) Element Unm Ag A1 Ba Ca Cd Cr c u Fe Mg Mn Mo Na Ni P Pb Si Sn Ti V Zn 338.29 308.22 455.40 3 15.89 2 14.44 357.89 324.75 259.94 279.55 257.6 1 202.03 589.99 23 1.60 214.91 220.35 288.16 189.99 334.94 292.40 206.20 0.0048 0.022 0.0003 0.0096 0.00 12 0.0039 0.0006 0.0006 0.00 12 0.0006 0.002 1 0.00 12 0.0075 0.038 0.0099 0.027 0.0 1 0.00 12 0.0045 0.00 15 0.025 0.02 0.0023 0.072 0.189 0.043 0.00 1 3 0.0083 0.0 1 0.0043 0.6 1 0.08 1.3 2.3 0.0085 0.016 0.059 0.0027 0.015 1 0.0007 5 0.001 7 0.000 13 0.003 0.000 19 0.00 1 0.0008 0.00 1 0.00075 0.000 18 0.0009 0.002 1 0.0025 0.01 1 0.002 0.0028 0.001 1 0.0005 0.000 7 2 0.0004 0.001 8 0.0049 0.000 18 0.00 1 9 0.0008 1 0.0 14 0.00074 0.00 16 0.001 1 0.0003 9 0.0078 0.0029 0.01 1 0.01 1 0.01 1 0.0027 0.047 0.00029 0.00 19 0.001 1 6.4 12.9 2.3 3.2 6.3 3.9 0.7 0.6 1.6 3.3 2.3 0.6 3.0 3.5 5.0 9.6 9.1 2.4 6.2 3.8 13.9 4.1 12.8 37.9 233.3 3.1 1.8 5.2 9.1 11.0 78.2 27.6 118.2 209.1 0.8 5.9 1.3 9.3 7.9 909.1 5.2 0.9 7.7 7.5 157.5 11.0 2.2 13.8 8.3 7.2 290.5 66.7 173.3 60.5 0.9 0.6 5.9 2.3 3.3 666.7 2.4 2.9 1.4 0.6 4.3 14.0 0.9 1.6 1.5 2.2 8.7 1.4 4.4 1 .o 5.5 1 .o 42.7 0.6 2.6 2.8 *PN = pneumatic nebulizer removing most of the organic solvent vapour oxygen scavenges the remainder.The result is a stable plasma matching closely the appearance and operational character- istics of an aqueous plasma. The use of oxygen obviates the necessity of using a second stage of cryogenic desolvation with the USN,14 at least for the solvents in this study. Oxygen permits the fixed frequency r.f. generator to operate at higher levels of reflected power without extinguishing the plasma and permits higher excitation temperatures to be achieved at lower forward power settings. Indeed a USN interfaced to an air ICP was capable of aspirating xylenes without any desolvati~n.~~ Oxygen improves the spectral characteristics of the organic ICP by reducing molecular emission from C,; C2 Table 3 Toluene analysis by USN-ICP-AES; short-term precision and drift (toluene-3) Precision* Drift? Element (%RSD) (%I Ag A1 B Ba Ca Cd Cr c u Fe Mg Mn Mo Na Ni P Pb Si Sn Ti V Zn 1.9 2.0 2.2 2.0 2.0 2.1 2.6 2.1 1.9 1.9 1.9 1.8 2.1 2.1 2.1 2.1 1.9 1.5 1.8 1.8 2.1 * l a from ten consecutive 10 s exposures.t l h calibration drift (mainly power drift). +0.9 +1.1 0.0 + 0.4 -4.7 - 12.8 + 4.2 +3.1 - 6.4 - 5.7 - 5.8 - 7.9 $7.1 - 11.6 -6.4 - 11.7 - 1.6 - 4.0 -2.2 - 4.4 - 12.4 has been identified as the dominant molecular species influencing plasma properties in organic solvent analysis by ICP-AES.16-18 Use of the Ar-0 mixed gas plasma reduces C2 emission in the initial radiation zone (‘bullet’) normal analytical zone and margins of the plasma where organic vapour bypassing the central channel has been entrained.With the introduction of oxygen into the aerosol carrier stream it is possible to eliminate the visible C2 ‘bullet’. One of the effects of reduced C2 emission is increased excitation temperatures for a given r.f. power setting as already noted. The other beneficial effect is a ‘cleaner’ spectral background having reduced molecular band structure. Improved sensi- tivity for the analysis of organic solvents is a result of this double benefit. In addition oxygen virtually eliminates the formation of carbon deposits on plasma torch parts. The minimum flow rate of oxygen used in this study is more than sufficient for stoichiometric combustion of the resi- dual vapour from desolvation of aerosols of heptane isooctane or toluene assuming near equilibrium with the condenser coolant at - 10” to -20 “C has been attained. Injector tips partially fouled from the analysis of organics can actually be cleaned while operating them in Ar-0,.The Ar-02 mixed gas plasma is now employed whenever organics are analysed in this laboratory by ICP-AES. This includes the analysis of heavy oils as tetralin solutions using the cross-flow nebuli~er.~ rn 70% IPA 0 IsooctaneDHeptane ISlToluene-1 llpp Toluene-2 MB Toluene-3 ‘i- I -Hzo Ni 231.’60 nm P 214.91 nm Pb 220.35 nm Fig. 6 Detection limits (3u) for various solvents/conditions using USN-ICP-AES56 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL.8 Table 4 Lead in aviation fuel by USN-ICP-AES versus XRF TEL by Sample USN-ICP-AES/g I-' I 2 3 4 5 6 7 Mean *Four exposures per determination (n = 4). 0.622 0.559 0.61 1 0.588 0.625 0.614 0.5 13 0.590 (0/2)*/g 1-' 0.0053 0.0042 0.0037 0.0061 0.0056 0.0077 0.0034 0.005 1 RSD (O/O) 0.85 0.76 0.6 I 1.04 0.89 1.25 0.67 0.87 TEL by XRF/g I-' 0.61 1 0.572 0.610 0.543 0.633 0.598 0.508 0.582 Lead in Aviation Fuel Tetraethyllead is still used in commercial aviation fuel for octane enhancement. The conversion of TEL into inorganic lead bromide is required to prevent the very efficient condensation and removal of the analyte in the USN desolvator. Once this conversion has been performed the solutions to be analysed consist of very dilute colloidal lead bromide in a toluene matrix.Using the Conostan stabilizer these solutions are apparently stable for at least a few hours. The results of TEL analysis for seven samples of aviation fuel performed using the USN-ICP-AES and using X-ray fluorescence (XRF) are shown in Table 4. These results show excellent precision of ICP-AES and good agreement with XRF. The detection limit for TEL in aviation fuel by USN-ICP-AES was found to be 0.0008 g 1-'(3a) assuming a 1 +99 mass dilution. By comparison the detection limit using XRF is approximately three orders of magnitude poorer and samples must be analysed without significant dilution. The determination of TEL in aviation fuel demonstrates the practicality of toluene analysis by USN- ICP-AES. - H,O Dl 70% IPA 0 lsooctane mHeptane El Toluene-1 Toluene-2 c - 0 3 10 c I B .- E .- - C 0 .- c 0.1 Fig.7 USN-ICP-AES n Ti 334.94 nm V 292.41 nm Zn 206.20 nm Detection limits (30) for various solventskonditons usii 1 - H,O a 70% IPA 0 lsooctane W e p t a n CiPToluene-1 =Toluene-2 Toluene-3 0 J 500 n I .- E I- - .- 50 CI c $ 5 0.6 Si 288.16 nm Sn 189.99 nm 0 249.77 nrn Fig. 8 Detection limits (30) for various solventskonditions using USN-ICP-AES Polymer Analysis The USN can provide increased sensitivity for the analysis of petroleum derived materials (solvents distillate oils low- ash polymers etc.) prepared by ashing techniques. An analysis of poly(propy1ene) using the USN and the pneuma- tic cross-flow nebulizer is shown in Table 5. This analysis is typical of a low-ash polymer containing only traces of polymerization catalyst residues and miscellaneous con- stituents.As expected the results from analyses of the same solutions using the two sample introduction systems are in good agreement generally. The poor relative standard deviation (RSD) for the determinations of iron probably reflects inhomogeneity in the polymer sub-samples. Preci- sion for the determinations made by USN-ICP-AES is generally better than for those made using pneumatic nebulization. Note that the determinations were performed at concentrations that averaged 6.2 times lower owing to sample dilution. Two determinations performed at very low levels (Li and Zn) showed a marked improvement in precision using the USN. Microwave Digestion USN-ICP-AES The determination of trace metals in heavy fuel oil by microwave digestion of small (0.1 g) samples is possible but extreme care must be exercised to avoid contamination from the acid digestion vessels and other sources.The results shown in Table 6 illustrate the magnitude of the problem. Severe contamination is noted for Al Ca and Na with Fe and Zn being moderately contaminated. The digestion vessel liners had been cleaned prior to use by heating in the microwave oven with concentrated nitric acid. This single-step cleaning process was apparently insufficient to eliminate the contamination. Aluminium Ca and Zn were noted in blank acid digestions performed in new vessel liners. Therefore the liner material contains the contaminant elements from manufacturing. Present efforts Table 5 Analysis of poly(propy1ene); pneumatic nebulizer (PN) versus USN results from 16 preparations (average dilution = 6.2) RSD (%) Element PNlpg g-I USN/pg g-' A1 6.80 6.8 1 Ba 0.015 0.0 16 Ca 5.83 6.19 Fe 0.87 1 0.9 16 Li 0.036 0.043 Mg 0.218 0.2 1 5 Na 1.83 1.68 P 2.38 2.66 Ti 2.09 1.93 Zn 0.096 0.097 PN USN 2.8 1.9 40 37 3.5 I .6 30 29 72 47 3.6 5.0 8.7 6.6 5.6 3.0 14 13 25 10JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL.8 57 Table 6 Analysis of NIST SRM 1634b Fuel Oil by microwave digestion USN-ICP-AES Mean*/ NIST Element Pg g-’ RSD (Oh) certificate/pg 1-’ Comments A1 48 47 (16) Contamination Ca 156 52 (15) Contamination Fe 42 14 31.6+2 Contamination Contamination Na 240 37 (90) Ni 28.1 16 28+2 V 54.6 5.8 55.4+ 1.1 - Zn 4.8 15 3.0 k 0.2 Contamination - *Six separate digestions/determinations having a dilution factor of approximately 300.are directed towards identifying a better cleaning process for new and used vessel liners and increasing the sample size used in digestion to 0.5 g or more. The accurate results obtained for Ni and V (determined in solution at concentra- tions of approximately 0.1 and 0.2 pg ml-l respectively) using the USN encourage further development of the technique. Conclusions The USN is a valuable addition to an ICP-AES system in the petroleum/petrochemical analysis laboratory. The cur- rent USN apparatus is stable convenient to operate and can be employed for routine analysis or for specialized research. The ‘ultrasonic advantage’ seen in the analysis of aqueous solutions is also enjoyed in certain volatile hydrocarbon solvent systems particularly with the aid of an Ar-02 mixed-gas plasma.Toluene is a convenient solvent for hydrocarbon samples and the determination of lead in aviation fuel diluted in toluene demonstrates the practical- ity of toluene analysis by USN-ICP-AES. Aqueous applications of USN-ICP-AES for petroleum/ petrochemical analysis taking advantage of the high sensi- tivity of the USN will expand rapidly as an increasing number of laboratories acquire the device. The applications in this study represent a modest beginning. There is no doubt that the future holds many additional opportunities to improve an existing ICP-AES method or develop a new method which would not have been practical without the ‘ultrasonic advantage’. The author appreciates the experimental assistance pro- vided by C. P. Carter I11 and help in preparing the manuscript provided by M. C. Benham. References 1 Fredeen K. J. Am. Lab. December 1990 22. 2 Mermet J. M. ICP InJ Newsl. 1978 4 89. 3 Schramel P. and Ovcar-Pavlu J. Fresenius’ 2. Anal. Chem. 1979 298 28. 4 Botto R. I. Talanta 1990 37 157. 5 Botto R. I. Spectrochim. Acta Part B 1987 42 181. 6 Kreuning G. and Maessen F. J. M. J. Spectrochim. Acta Part B 1989 44 367. 7 Hausler D. W. and Taylor L. T. Anal Chem. 1981 53 1223. 8 Maessen F. J. M. J. Seeverens P. J. H. and Kreuning G. Spectrochim. Acta Part B 1984 39 1 17 1. 9 Backstrom K. and Gustavsson A. Spectrochim. Acta Part B 1989,44 1041. 10 Nygaard D. D. and Sotera J. J. Appl. Spectrosc. 1987 41 703. 1 1 Avery T. W. Chakrabarty C. and Thompson J. J. Appl. Spectrosc. 1990 44 1690. 12 Botto R. I. Spectrochim. Acta Part B 1991,46 141. 13 Botto R. I. Spectrochim. Acta Part B 1984 39 95. 14 Wiederin D. R. Houk R. S. Winge R. K. and DSilva A. P. Anal. Chem. 1990 62 1 156. 15 Meyer G. A. Spectrochim. Acta Part B 1987 42 201. 16 Blades M. W. and Caughlin B. L. Spectrochim. Acta Part B 1985 40 579. 17 Kreuning G. and Maessen F. J. M. J. Spectrochim. Acta Part B 1987 42 677. 18 Pan C. Zhu G. and Browner R. F. J. Anal. At. Spectrom. 1990 5 537. Paper 2/034 74C Received June 30 1992 Accepted October 2 1992

ISSN:0267-9477    

DOI:10.1039/JA9930800051

出版商:RSC    

年代:1993

数据来源: RSC

摘要:

JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 59 Evaluation of a Modified Electrothermal Vaporization Sample Introduction System for the Analysis of Liquids by Inductively Coupled Plasma Atomic Emission Spectrometry J. M. Ren and Eric D. Salin* Department of Chemistry McGill University 80 1 Sherbrooke Street West Montreal Quebec Canada H3A 2K6 A Perkin-Elmer electrothermal vaporization (ETV) furnace was modified for use as a sample introduction device for inductively coupled plasma atomic emission spectrometry (ICP-AES). The major modification made is the addition of sheath and cooling gas flows. The sheath gas provides a thin sheath layer between the analyte vapour and the wall of the transport tube to prevent vapour condensation and the cooling gas cools the analyte vapour to promote aggregate formation.Experiments with liquid samples showed that the addition of these gas flows increases the analyte transport efficiency and reduces matrix effects on the transport efficiency. The results also suggest that the carrier gas flow rate affects the peak shape and peak intensity of the copper signal probably by changing the vaporization rate. With 10 pl sample solution loadings the detection limits range from 1 to 6 ppb for Cd Pb Zn Mn and Cu and the precision (relative standard deviation) varies from 3 to 6%. The system is flexible and holds promises for direct solid sample analysis. Keywords Inductively coupled plasma atomic emission spectrometry; liquid analysis; electrothermal vaporiza- tion; solvent vapour condensation; transport efficiency The inductively coupled plasma (ICP) has become the dominant source for rapid spectrometric multi-element analysis as a result of a set of desirable attributes including low detection limits a wide linear dynamic range and relative freedom from interferences.* The most common sample introduction technique used in ICP atomic emission spectrometry (ICP-AES) is pneu- matic nebulization which converts the sample solution into a finely dispersed aerosol. The merits of the technique are its simplicity high sample throughput good stability and low cost. However the low sample transport efficiency (typically 1 -3%)*13 leaves room for improvement in analyte detection limits. Many variations of electrothermal vaporization (ETV) devices have been explored as alternatives for sample introduction to the ICP.4-7 In an ETV-ICP system a liquid sample ( 10-50 pl) is loaded into the furnace dried charred and vaporized. The analyte vapour generated in the vaporization stage is carried to the plasma for AES analysis.Two problems may arise before the analyte reaches the plasma. First the analyte vapour may condense on the wall of the transport tube resulting in a low transport efficiency that depends on analyte mass as observed by Millard et a1.6 Second in the presence of other major sample constituents the analyte vapour may condense on the aggregates formed from these elements leading to a higher but matrix- dependent transport efficiency.8 On cooling the analyte vapour itself may form aggregates that are less likely to absorb on the wall of the tube and can be transported more efficiently to the ICP.8 Speeding up the cooling enhances aggregate formation and reduces analyte losses. Shen et al.4 added a cooling gas flow through four 0.5 mm holes located immediately down- stream from the ETV furnace tube.The peak height of the lead signal was increased by about 72% as a result of this modification. In our modified ETV system a similar cooling gas flow was used to promote aggregate formation. In addi- tion an internal sheath gas was added to provide a thin gas layer between the analyte vapour and the wall of the transport tube to reduce analyte vapour condensation on the tube wall. Experimental data showed that these measures increase signal intensities and reduce matrix interferences.Experimental Instrumentation The instrumentation software and chemical suppliers are given in Table 1 and the ETV and ICP operating para- meters in Table 2. The multi-channel photomultiplier tube (PMT)-based direct-reading spectrometer (Table 1) used for this work was modified by Technical Services Laboratories in order to handle fast transient signal^.^ The system allows 50 chan- nels to be interrogated every 2 ms or one channel to be sampled with a minimum time interval of 50ps. Table 1 Instrumentation materials suppliers Instrument or material ICP Spectrometer Jarrell-Ash Model 90750 Readout electronics and data acquisition software Data processing software Lab Calc Microcomputer AST X-former AT 10 MHz 80286 CPU ETV Model HGA 2200 Reference standard solutions Nitric acid Supplier Plasma Therm Kresson NJ USA Thermo Jarrell-Ash Franklin MA USA Technical Services Laboratories Mississauga Ontario Galactic Industries Salem NH USA AST Research Irvine CA USA Perkin-Elmer Norwalk CT USA Fisher Scientific Fair Lawn NJ USA J.T. Baker Phillipsburg NJ USA Canada *To whom correspondence should be addressed.60 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 Table 2 Instrument operating parameters ICP Plasma Therm R.f. generator Frequency Maximum power output Torch Typical power Tuning Cooling gas Sheath gas Central gas Observation height Spectrometer Focal length Grating Slits Model 2500 27.12 MHz crystal controlled 2.0 kW Fassel-t ype 1 .O kW forward < 10 W reflected Automatic Ar 16 1 rnin-l Ar 0.8 1 min-l See text 15 mm above the load coil Jarrell-Ash Model 90750 0.75 m 2400 grooves mm-l 25 pm entrance 50 pm exit ETV device Perkin-Elmer HGA-2200 Stage Temperature/"C* Ramp/s Holds Drying Charring Vaporization 100 60 10 400 10 30 2400 0 7.0 *ETV temperatures are nominal values as shown on the instrument not measured values.The modified Perkin-Elmer graphite furnace is shown in Fig. 1 and an enlarged view of the sheath and cooling gas section can be seen in Fig. 2. In the modified ETV system (Fig. I) one of the original internal gas inlets was used as the inlet for the carrier gas and the other as the inlet for the sheath and cooling gas. As can be seen more clearly in Fig. 2 some of the sheath and cooling gas flowed through four holes (0.5 mm) drilled on one of the graphite contact rings and then merged directly into the carrier gas.This design was similar to one described by Shen et aL4 and allowed rapid cooling of the Sheath and cooling gas inlet 11/ Glass shield / gas Carrier inlet J,T'Eu/r\ Graphite Aluminium Fig. 1 Modified Perkin-Elmer graphite furnace Sheath and cooling Cooling gas - Carrier g m i S h e a t h gas + analyte 3 Cooling gas Fig. 2 Sheath and cooling gas flow analyte vapour and promoted aggregate formation. The rest of the sheath and cooling gas flowed through a narrow gap cut between the graphite contact ring and a laboratory- constructed aluminium tube (7 cm x 1 cm id.) (Fig. 2). This gas called the sheath gas provided a thin gas layer between the wall of the transport tube and the gas mixture inside so as to prevent the analyte vapour from contacting and condensing on the tube wall.Eventually the sheath gas mixed with the analyte (in vapour or aggregates) and cooled it further. Other modifications included blocking of the graphite tube sampling port and replacement of one of the quartz windows with a graphite plug (see the left-hand side of Fig. 1). The outlet of the aluminium tube was connected to the torch with a 15 cm length of in 0.d. Teflon tube and a cylindrical glass tube (approximately 7 cm) with a ball- joint. A glass shield around the graphite contact rings was used to reduce the oxidation of the graphite components by air (Fig. 1). Argon (approximately 1 1 min-l) fed through the external gas inlets in the original ETV unit purged the air from within the glass shield.The carrier gas (argon) plus the sheath and cooling gas (argon) constituted the plasma central gas. The sheath gas and the cooling gas shared one inlet so their flow rates could not be adjusted independently. The flow-rate ratio of the sheath gas to the cooling gas was 4 1 . Procedure After the removal of the left end-cap labelled 'End cap' in Fig. 1 a solution (5 or 10 pl) was injected into the graphite tube with a syringe. Care was necessary to make the sample volume and the sample position in the furnace repro- ducible. The solution used was either 0.1 pg ml-' of Cd Pb Zn Mn and Cu or 1 pg ml-l of Pb and Cu both in 2% nitric acid. They were prepared from reference standard solutions and nitric acid. Solutions containing analytes and 1000 pg ml-l of Na were prepared by adding very small volumes of analyte reference standard solutions directly to a 1000 pg ml-l Na reference standard solution.To overcome problems associated with solvent vapour conden~ation,~J~ the left end cap of the furnace was removed during the ETV drying and charring stages. The positive pressure of the plasma forced the sheath andJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 61 cooling gas to flow toward this open end. This gas flow carried the solvent vapour out of the open end and to a vent system. Just prior to the vaporization stage the end cap was replaced so that the analyte vapour generated could be swept toward the plasma by the carrier gas as under normal conditions. This process was similar to that used by Carey et al.' and is termed here solvent vapour ventilation.In experiments where the sheath and cooling gas flow was shut off a three-way valve was used to switch the carrier gas to flow through the inlet of the sheath and cooling gas during the drying and charring stages to ensure that the solvent vapour was vented properly. The data acquisition process was triggered before the start of the vaporization stage and the chosen data acquisition parameters gave a data collection rate of nine points per second. Results and Discussion ETV Parameters The ETV parameters play an important role in determining analyte peak shape and peak intensity. Low drying and charring temperatures may lead to incomplete desolvation and possible abrupt solvent release at the beginning of the vaporization stage.High drying and charring temperatures may remove solvent completely but without ramping these high temperatures themselves may cause abrupt solvent release. If the drying and charring temperatures are too high loss of volatile elements may occur. Various drying and charring temperatures and durations were tested to obtain smooth signal profiles for 1 ng loadings of Cu and Pb while the vaporization temperature was kept at 2400 "C. When a low charring temperature (200 "C) was used Cu showed a small irreproducible peak preceding the main peak [Fig. 3(a)]. This small peak was attributed to micro-particles produced on sudden release of some remaining water from the analyte residue. When a higher charring temperature (400 "C) and a temperature ramp were used the small peak disappeared [Fig.3(b)]. No peak shape change or analyte losses were observed for Pb under these conditions. 6x 1 O5 4x105 2x105 In c c c 6x 1 O5 0 0 4x105 2~ 1 o5 0 5 10 Time/s Fig. 3 Effect of charring temperature on Cu signal (a) 200 "C ramp 0 s hold 60 s; (b) 400 "C ramp 10 s hold 30 s for 10 p1 of 1 pg ml-1 Cu 2x10' 1x10' $ 0 S 0 0 3x10' 2x10' 1x10' 0 ~~ 5 10 Time/s Fig. 4 Effect of solvent vapour ventilation on Pb signal (a) without ventilation; (b) with ventilation for 10 p1 of 1 pg ml-1 Pb The ETV vaporization temperature was then varied between 1700 and 2400 "C. After several firings at 1700 and 2000 "C a blank firing at 2300 "C showed that the vaporiza- tion of the analytes was not complete at the lower temperatures. At 2400 "C complete vaporization of Pb and Cu was achieved.The optimum ETV parameters found are listed in Table 2. These parameters were used throughout the remaining experiments. Solvent Vapour Ventilation Normally during the drying and charring stages the vaporized solvent is carried to the plasma. In the process the solvent vapour may condense on the wall of the transport tube. This condensed solvent can adsorb analyte vapour generated in the vaporization stage and cause analyte loss and memory effects. A few researchers4J0 have reported the problem and their solutions but none showed signal shape or intensity changes due to the problem. With this system this problem was eliminated by using the solvent vapour ventilation procedure described under Experimental. Fig.4 shows the peak shape of Pb with and without the use of the procedure. When solvent vapour ventilation was not used Pb showed a second peak and long tailing [Fig. 4(a)]. This may be due to the adsorption of the Table 3 Effect of sheath and cooling gas flows on analyte signals for lop1 of 0.1 pg ml-1 Cd Pb Zn Mn and Cu solution. Comparison made between camer gas=0.2 1 min-* sheath and cooling gas=0.6 1 min-l and carrier gas=0.8 1 min-I sheath and cooling gas= 0 1 min-l Increase in Increase in integrated Element peak height (Yo) signal (Oh) Cd 200 126 Pb 93 68 Zn 85 57 Mn 23 22 c u 0 4062 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 0 0 1x106 5x105 0 analyte vapour on the condensed solvent and a subsequent re-evaporation.When solvent vapour ventilation was used Pb showed a typical peak with higher intensity [Fig. 4(b)]. Only slight changes were observed in the peak shape of Cu. The element is less volatile and presumably forms aggre- gates more rapidly. Aggregates are less likely to be adsorbed by the condensed solvent. (b) 1 - - Analyte Transport Efficiency Condensation of analyte vapour on the wall of the transport tube results in low transport efficiency. To reduce or eliminate this condensation one can separate the analyte vapour from the wall of the tube and at the same time cool the analyte vapour to force it to form aggregates. As theoretical considerations indicate,8 low temperatures encourage the vapour to solid conversion. Lower tempera- tures are needed for more volatile elements to form aggregates. In the present design sheath gas was added to separate the analyte vapour from the wall of the transport tube and cooling gas was added to cool the analyte vapour (Fig.2). To establish the effect of these gases experiments were run with and without them and the peak intensities and integrated signal values obtained were compared. The total gas flow rate was kept unchanged so that the plasma properties were constant. The results are given in Table 3. As can be seen from Table 3 the increases in peak height due to the use of the sheath and cooling gas range from 0% for Cu to 200% for Cd and are related to element volatility. More volatile elements form aggregates with greater diffi- culty and therefore travel longer distances in vapour form increasing their chance of condensing on the wall of the transport tube.Therefore without the sheath and cooling gas the loss of volatile elements should be more severe. The prevention of this loss leads to a greater increase in peak height for the volatile than for non-volatile elements. The increases in integrated signal are less than those in peak height for all the elements except Cu (Table 3). The integrated signal is proportional to the total amount of analyte or the true analyte transport efficiency so inte- grated signal (not peak height absorbance) should be used as an indicator of the changes in analyte transport efficiency. In summary the use of the sheath and cooling gas increased the analyte transport efficiency and the degree of the increase depended on element volatility. Matrix Effects In ETV-ICP ~ y s t e m s ~ J ~ the presence of major sample constituents ( i e .the matrix) can increase the analyte transport efficiency (carrier effect). In an ideal system the analyte transport efficiency could be very high and the presence of matrix constituents would not affect the analytical performance. In the present system the use of the sheath and cooling gas increased the analyte transport efficiency and this increase should lead to reduced matrix effects. The matrix effects of 1000 pg ml-1 of Na on analyte peak heights and integrated signal with and without the use of the sheath and cooling gas are compared in Table 4. Each value in Table 4 was calculated from the signals obtained in the absence and presence of 1000 ppm of Na.The use of the sheath and cooling gas reduces matrix interference by about 50% for most of the elements monitored as is clear from the results given in Table 4. The interference is more severe for peak height than for integrated signal. Carrier Gas Flow Rate Versus Copper Peak Shape Experiments indicated that the peak shape of the Cu signal depended on the carrier gas flow rate (Fig. 5). With a carrier gas flow rate of 0.31 1 min-I a broad tailed peak was observed [Fig. 5(a)]. When the carrier gas flow rate was increased to 0.75 1 min-l while the total gas flow rate was kept constant a sharp peak of much higher intensity resulted [Fig. 5(b)]. However it was interesting that the peak areas were essentially unchanged indicating that complete vaporization was achieved under both conditions. The above observations suggested that the carrier gas flow rate influenced the vaporization rate of Cu.An 0 5 10 Time/s Fig. 5 Effect of carrier gas flow rate on Cu signal profile. (a) 0.31 and (b) 0.75 1 min-' for 10 pl of 1 pg m1-l Cu solution Table 4 Effect of sheath and cooling gas on matrix interference for 10 pl of 0.1 pg ml-I Cd Pb Zn Mn and Cu solution. Each value was calculated from the signals obtained in the absence and presence of 1000 ppm of Na Without sheath and cooling gas With sheath and cooling gas Increase in Increase in Increase in Increase in Element peak height (O/o) integrated signal (Yo) peak height (O/O) integrated signal (%) Cd 62 Pb 134 Zn 4 Mn 67 c u 167 18 50 - 30 37 82 - 13 60 - 39 17 78 - 19 8 - 49 16 40JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL.8 63 Table 5 Comparison of detection limits (30). The same ICP system was used with both sample introduction devices Liquid ETV-ICP Wavelength1 nebulization Element nm (order) (PPb) PPb Pg Cd 228.8 (I) 26 1 10 Pb 220.3 (I) 28 5 50 Zn 213.8 (11) 82 3 30 Mn 293.9 (I) - 6 60 c u 324.7 (I) 8 I 10 equilibrium or quasi-equilibrium might exist between the Cu atoms in the vapour phase and those in the solid phase. This was observed in ETV atomic absorption work by McNally and Holcombe." In the present system it was possible that when the carrier gas flow rate was low the argon in the furnace was saturated with Cu vapour and the excess of Cu atoms condensed on the wall of the graphite tube.These condensed atoms were vaporized later and resulted in peak tailing. Similarly at higher carrier gas flow rates all the Cu atoms vaporized were carried away immediately and the equilibrium shifted to favour vapori- zation and a normal sharp peak was produced [Fig. 5(b)]. Calibration Precision and Detection Limits Calibration graphs were established by injecting 10 p1 of solutions containing 0.1 1.0 or 10 pg ml-I of Cd Pb Zn Mn and Cu. The log-log calibration graphs were linear with a slope of 1.0 for Mn and Pb using both peak height and peak area. A similar calibration graph with a slope of 0.93 was established for the Cu peak area. The graph for Cu peak height was not linear possibly owing to changes in vaporization rate at higher concentrations. For Cd the most volatile element used the correlation coefficient between the integrated signal and analyte con- centration was 0,999 but the log-log calibration graph for peak height was not linear.Table 3 indicates that the use of the sheath and cooling gas led to a larger increase in Cd peak height than peak area which suggested that without the sheath and cooling gas the loss of Cd (due to condensation) affected the peak height more than the peak area. Assuming that even with the sheath and cooling gas there was still Cd loss this loss would affect the peak height more than the peak area hence the linearity of the calibration graph for peak height was worse than that for peak area. Considered in a different way the Cd might have been temporarily held up on the tube surface and released later and the concentration dependence of this phenome- non led to the poor linearity of the calibration graph for peak height. The relative standard deviations (RSDs) for peak height and the integrated signal varied from 3 to 6% in the concentration range used.The 30 detection limits with lop1 sample injections are given in Table 5. With a larger sample injection volume (i.e. 50 pl) proportionally lower detection limits could be obtained. Also given in Table 5 are detection limits obtained with conventional pneumatic nebulization sample introduction using the same ICP and optical system. On average the ETV sample introduction system provided detection limits one order of magnitude lower than the conventional nebulizer.Conclusions The modifications to the commercial ETV furnace were simple yet effective. The use of the sheath and cooling gas increased the analyte transport efficiency and reduced matrix interferences. Although only data with liquid samples are presented in this paper the ETV system was actually designed to be used as a high-temperature reactor for direct solid sample analysis. A previous ETV-ICP system designed for solid sample analysis in our laboratory showed matrix interfer- ences when it was used in botanical sample analysis.I2 It is believed that chemical reactions and cooling of the analyte vapour are necessary for the elimination of matrix interfer- ences on analyte vaporization and transport efficiency. To facilitate vaporization Freon or another halogen-contain- ing reagent will be added to the furnace.Chlorine or fluorine radicals generated from the decomposition of the reagent should react with solid sample powder to produce chlorides or fluorides which vaporize easily. To increase that analyte transport efficiency these vaporized species will be converted into oxides by oxygen added to the sheath and cooling gas (i.e. using chemical conden~ationl~). The oxides normally have higher boiling-points and form aggregates more easily so they can be transported more efficiently to the ICP. 1 2 3 4 5 6 7 8 9 10 1 1 12 13 References Olesik J. W. Anal. Chem. 1991 63 12A. Browner R. F. and Boorn A. W. Anal. Chem. 1984 56 786A. Gustavsson A. Spectrochim. Acta Part B 1984 39 743. Shen W. L. Caruso J. A. Fricke F. L. and Satzger R. D. J. Anal. At. Spectrom. 1990 5 451. Matusiewicz H. Fricke F. L. and Barnes R. M . J. Anal. At. Spectrom. 1986 1 203. Millard D. L. Shan H. C. and Kirkbright G. F. Analyst 1980 105 502. Carey J. M. Evans E. H. Caruso J. A. and Shen W. L. Spectrochim. Acta Part B 199 1 46 I 7 1 1. Kantor T. Spectrochim. Acta Part B 1988 43 1299. Legere G. and Burgener P. ZCP Znf News!. 1982 13 521. Aziz A. Broekaert J. A. C. and Leis F. Spectrochim. Acta Part B 1982 37 369. McNally J. and Holcombe J. A. Anal. Chem. 1991 63 1918. Karanassios V. Ren J. M. and Salin E. D. J. Anal. At. Spectrom. I99 1 6 527. Fuchs N. A. and Sutugin A. G. Highly Dispersed Aerosols Ann Arbor Science Publishers Ann Arbor MI New York 1970 pp. 7-24. Paper 2/02003C Received April 16 1992 Accepted August 26 I992

ISSN:0267-9477    

DOI:10.1039/JA9930800059

出版商:RSC    

年代:1993

数据来源: RSC

摘要:

JOURNAL O F ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 65 Evaluation of a Linear-flow Torch for Inductively Coupled Plasma Atomic Emission Spectrometry Norman N. Sesi Paul J. Galley and Gary M. Hieftje* Department of Chemistry Indiana University Bloomington IN 47405 USA Simplex optimized operating conditions for a linear-flow torch (LiFT) were evaluated with respect to those for a conventional tangential-flow torch (TFT). The LiFT was shown to out-perform an 18 mm i.d. TFT in terms of gas consumption precision long-term stability noise amplitude and level of background molecular-band emission. However the two types of torches offered comparable detection limits and similar responses to the addition of an easily ionizable element. Keywords Inductively coupled plasma; tangential- linear- and laminar-flow torches; atomic emission spectrometry; noise amplitude spectra Methods of chemical analysis can be characterized by their accuracy precision and detection limits.One of the dominant factors that sets limits on these figures of merit is noise. Low noise levels increase precision and permit the measurement of smaller signals thereby improving limits of detection. In an attempt to minimize random fluctua- tions in inductively coupled plasma (ICP) emission spectro- metry several research groups have experimented with the use of linear-flow torches (LiFTs) to replace conventional tangential-flow devices.I-I0 The term ‘linear’ is used here to describe the axial flow of the outer gas in contrast to the more commonly used term ‘laminar’.1-8 Both axial and tangential flows can be classified as either ‘laminar’ or ‘turbulent’ based on the calculated Reynolds number.The value of the Reynolds number used to distinguish between the ‘turbulent’ and ‘laminar’ flow regimes is approximately 2000.Ll A value below 2000 would be classified as laminar flow and a value greater than 2000 as turbulent flow. However for the conditions used here the gas flow of the tangential-flow torch (TFT) would also be classified as laminar.12 It must be kept in mind that the Reynolds number calculation is valid strictly for flow patterns below the rim of the intermediate tube. Accurate con- clusions cannot be drawn about the type of flow above this rim.12 Previous linear-flow outer-gas introduction systems have employed circular tubes or orifices located in the outer channel around the base of the torch. An alternative designI3 uses a boron nitride insert with rectangularly machined channels placed around the ‘tulip’ of a conven- tional t o r ~ h .~ - l ~ The use of rectangular channels instead of circular ones enables the construction of smaller well- defined channel cross-sectional areas. This design can produce higher outer gas velocities to dissipate the heat generated by the hot gases quickly and enables the effective inter-tube spacing to be controlled readily. MerrnetI4 has calculated a value of 0.27 mm as being the optimal intermediate-to-outer tube separation for an ICP torch with an outer tube i.d. of 18 mm. This calculated value is difficult to achieve in the routine manufacture of TFTs owing to problems encountered in accurate tube centring.Optimized operating conditions for an LiFT are evalu- ated with respect to those for a conventional 18 mm i.d. TFT. Subsequent characterization of both torches includes the measurement of precision long-term stability noise amplitude spectra detection limits interference effects and molecular band emission. *To whom correspondence should be addressed. Table 1 Experimental apparatus R.f. generator Monochromator Focal length Grating Slits Reciprocal linear dispersion Quartz lens Diameter Focal length Magnification Photomultiplier tube Operating voltage High-speed current amplifier Filter Data acquisition board Roll-off Data acquisition software Concentric nebulizer Spray chamber Peristaltic pump 40.68 MHz PlasmaTherm HFL 2000D with impedance matcher (Model PT/AMN/RCM) GCNMcPherson Model EU-700 350 mm 50 mm 1180 lines mm-l 4 0 p m x 3 mm (blazed at 250 nm) 2 nm mm-’ 50 mm 175 mm I:1 RCA IP28 -800 v Keithley Model 427 Krohn-Hite Model 3342 -96 dB per octave National Instruments National Instruments JE Meinhard Associates Scott-type Gilson Minipuls 2 NB-MIO- 1 6XL- 1 8 LabVIEW 2 version 2.2 Model TR30-3C Experimental Instrumentation The experimental apparatus used for this study is listed in Table 1 and the LiFT is shown in Fig.1. The inter-tube insert in the LiFT contains 25 rectangularly machined channels which are 0.9 mm in width and 18 mm in length. The depth of each channel is 0.47 mm. The TFT used in the present study is commercially available from Leco.This particular TFT serves only as a reference by which to gauge the performance of the LiFT. Although there are several types of commercially available TFTs the Leco design was chosen because it possesses ‘conventional’ dimension~.l~-~~ A conventional torch is defined here as a tangential-flow unit that has an 18-mm i.d. outer tube no constriction of the inlet ports no outer-tube extension a 1 mm i.d. injector tube and a separation of 1 mm between the ‘tulip’66 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 Table 2 Torch dimensions Parameter Linear Tangential Inner diameter of outer tube/mm 18 18 Length of flared portion of intermediate tube/mm 1st 25 Annular spacing between intermediate and outer tubeslmm 0.47* 1 Length of outer tube extending beyond intermediate tube/mm 23 20 Outer-gas inlet port diameterlmm 1 4 Recession of aerosol injection tube below rim of intermediate tube/mm Inner diameter of aerosol injection tube/mm 1 1 2 2 *Spacing between the insert and the outer tube.?Length of insert rather than of flared portion. and the outer tube. The relevant dimensions of the two torches are listed in Table 2. Operating Parameters In order to make an unbiased comparison between the LilT and the TFT a simplex algorithm (InstrumenTune-Up Elsevier Scientific Software) was used to optimize the performance of both torches at the Ca I1 393.366 nm emission line. The following parameters were optimized based on the criterion of analyte signal-to-background noise ratio (S/Nb) central intermediate and outer flow-rates; incident r.f. power; and height above the load coil (ALC).The resulting optimal operating conditions are listed in Table 3. During all experiments the sample-solution uptake rate was held constant at 1.0 ml min-l. Data Collection A National Instruments NB-MIO- 16XL- 18 data acquisi- tion board operating under LabVIEW 2 software was used to digitize the analogue signal for processing on a Macin- tosh I1 series computer. The data acquisition board con- tains a 16-bit analogue-to-digital converter used in a differential-input configuration to accept input signals between - 10 and + 10 V. The use of a differential-signal input provides a reduction in recorded noise improves common-mode noise rejection and permits the input signal to float within the common-mode limits of the instrumenta- tion amplifier.'* Channels Fig.1 (a) Diagram of the LiFT used in this study. A quartz outer tube; B quartz 'tulip'; C boron nitride insert [see (b) and (c)]; D quartz intermediate tube; E quartz central tube; F outer-gas inlet port; and G intermediate-gas inlet port. (b) Top view of the boron nitride insert on an expanded dimensional scale. (c) Expanded- scaie side-view of the boron nitride insert showing the rectangularly machined channels. Dimensions of individual components are given in Table 2 Table 3 Operating parameters Parameter Central gas flow ratell min-I Intermediate gas flow rate/l min-l Outer gas flow rate/l min-' Incident r.f. power/W Reflected r.f. power/W Sample uptake rate/ml min-l Detection time constanth Height above load coil/mm Linear 0.65 2.0 9.7 1025 ( 5 1 .o 0.1 12.1 Tangential 1 .o 1 .o 14.0 1025 < 5 1 .o 0.1 16 A program written in LabVIEW 2 was used for data acquisition and calculation of the noise amplitude spectra.This program is fully described elsewhere,19 so only a brief overview of the procedure is given here. The signal is digitized at a rate equal to twice the Nyquist frequency.20-22 Afterwards the average d.c. component is subtracted from each point in the array the waveform is apodized using a Hanning filter and then Fourier transformed. The noise amplitude spectra are obtained by taking the sum of the squares of the real and imaginery components of the Fourier-transformed w a v e f ~ r m ~ ~ . ~ ~ and dividing each data set by the current-to-voltage gain of the current amplifier to produce values in units of current.After the transformed signals are averaged in the frequency domain the square root of the averaged spectrum is multiplied by an empiri- cally determined constant and divided by the average d.c. photocurrent to yield noise spectra which are normalized for differences in signal strength. These values are plotted as 'reduced units' in the noise spectra later. The empirically determined constant is used to calibrate the output ampli- tude of the program directly in terms of nanoamperes root- mean-square (rms). 30 - g? 20 n tn K 10 0 Time constant/ms Fig. 2 Effect of detection time constant on precision at 393.4 nm. A TFT background from 1% v/v HNO,; B LiFT background from 1% v/v HN03; C TFT signal from 1 ppm Ca; and D LIFT signal from 1 ppm Ca. Viewing height LIFT 12.1 mm ALC; TFT 16 mm ALCJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL.8 67 Fig. 3 Noise amplitude spectra of Ca ion emission (393.4 nm) as a function of height ALC for (a) LiFT and (b) TFT. Sample solution 1 ppm Ca in I I vfv HN03. Nyquist frequency 5000 Hz; RC filter 4000 Hz 1.9 I 1 A 1 .I I I 1 1 0 100 200 300 400 500 Timelmin 1.1 ' Fig. 4 Stability of emission from 1 ppm Ca ion (393.4 nm). Viewing heights A LiFT' 12.1 mm ALC; B TFT 16 mrn ALC Figures of merit such as S/Nb and signal-to-background ratios (S/B) were obtained with another LabVIEW program written in this 1aborato1-y.~~ Typically the signal was acquired for 100 times the instrumental time constant of 0.1 s.Reagents Stock solutions were prepared in 1% HNOJ from analytical- reagent grade nitrate salts except for magnesium which was prepared from the metal. Analyte solutions used for the imaging studies were also prepared from suitable nitrate salts but were dissolved in distilled deionized water. Results and Discussion Simplex Optimized Conditions As Table 3 shows both the LiFT and TFT produced the greatest S/Nb at the same power level (1025 w). However the LiFT operated best at a total argon flow rate approxi- mately 20% less than required by the TFT used in this study. Although the LiFT possesses a constricted outer-gas inlet tube which has been shown to increase the swirl velocity,26 this is not the reason for the improvement in gas consumption.A constricted inlet tube affects the r.f. power and the outer flow required to ignite the plasma but has little influence on the stability of the discharge.*' A more probable reason for this advantage lies in the ability to machine the channels of the insert in the LiFT to any desired depth thereby enabling a more nearly optimal separationl4 to be attained between the intermediate and outer tubes. Although the present LiFT does not possess the theoretically optimal14 separation value it has a smaller intermediate-to-outer tube separation than the TFT. This inter-tube separation allows the LiFT to operate with increased outer-gas velocities better cooling efficiency and lower argon consumption. Of course the use of a specifi- cally designed low-flow TFT would most likely offset this advantage.The optimal viewing height for calcium ion emission is approximately 4 mm lower in the plasma from the LiFT than in the plasma produced by the TFT. This difference is almost certainly due to the lower central-gas flow rate (0.65 1 min-l and hence lower central-gas velocity found to be optimal for the LiFT. Y . I - - . . i 3 = 0 2 4 6 8 10 FrequencyIHz 0 2 4 6 8 10 FrequencyfHz Fig. 5 Low-frequency noise amplitude spectra of Ca ion emission (393.4 nm) as a function of height ALC for (a) LiFT and (b) TFT. Sample solution 1 ppm Ca in 1% v/v HN03. Nyquist frequency 15 Hz; RC filter 10 Hz68 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 L.U 1.5 - a 2 2 3 1.0 - 8 c c r a 0.5 - 0 Height ALC/mm Fig. 6 Effect of K on 1 ppm Ca ion emission at 393.4 nm.TFT A 0; B 100; and C 1000 ppm K. LiFT D 0; E 100; and F 1000 ppm K ""I 250 1 a H 5 200 C 2 2 150 0 100 c 50 0 5 10 Height ALC/mm 15 Fig. 7 Effect of K on 1 ppm Ca atom emission at 422.7 nm. TFT A 0; B 10; C 100; and D 1000 ppm K. LiFT E 0; F 10; G 100; and H 1000 ppm K Precision The precision attainable with the two torches as a function of instrumental time constant for analyte (1 ppm Ca) and background (1 O/o v/v HN03) signals are compared in Fig. 2. Time constants greater than 2 s were not investigated because of instabilities in the active low-pass filter used for this study. For time constants greater than approximately 5 ms there are no significant differences in precision between the torches. However for time constants less than 5 ms the LiFT shows better precision.A look at plots of noise spectra at different heights ALC (Fig. 3) reveals lower noise amplitude levels for the LiFT by a factor of approximately five than for the TFT. The positions of the peak audio- frequency noise components were determined to be a function of the outer gas flow rate and have been shown previously to be caused by plasma pulsations and vortex formation.6 The smaller audio-frequency peaks could be one reason why the LiFT exhibits better precision at very short time constants (Fig. 2). This potential advantage of the LiFT would not be realized in the measurement of conventional d.c. levels where low-pass filtering and inte- gration methods are commonly employed (time constants in the range 0.01-1 s).However the lower noise could become significant if transient sample pulses were produced or if a Fourier-transform spectrometer were employed. For example sample introduction techniques such as flow injection laser ablation and electrothermal atomization would probably benefit by the use of an LiFT. These techniques produce transient samples where shorter time constants must be employed in order to detect the signal of interest. Long-term Stability The stability of a Ca ion signal measured over a period of about 8 h is shown in Fig. 4. After approximately a 1-1.5 h warm-up period the long-term stability over a 7 h time- span for the LiFT and TFT was found to be 1.4 and 2.3% respectively. As the 0-10 Hz noise spectra (Fig. 5 ) show the better long-term stability of the LiFT is due to lower 11'' noise. This increased stability could be due to a reduced disturbance of the injector gas and aerosol flows.Tangenti- ally flowing outer gases would be expected to exert a lateral force on the central channel; however this effect would not be expected to occur in the LiFT which produces axial- flowing outer gases with force components that are directed upwards. Interference Effects The effect of added potassium as an easily ionizable element (EIE) on calcium ion and atom emission is shown in Figs. 6 and 7 respectively. The results of these experi- ments are in agreement with previous studies of interfer- ences caused by EIE.28-31 The ion emission shows an enhancement low in the plasma and a depression high in the plasma. Both torches exhibit the familiar cross-over point but at different vertical locations.The atom emission increases monotonically as the concentration of added EIE is raised. Presumably emission intensities peak lower in the LiFT than in the TFT because of the lower central-gas velocity used with the LiFT. The effect of phosphate on calcium atom and ion emission was also investigated. However no significant vaporization interferences were detected with either torch. Molecular Bands Maps of molecular-band emission were acquired from each entire plasma at once using a charge coupled device (CCD) camera with an optical system as described previo~sly.~~ The plasmas in these experiments were sustained with a 40.68 MHz solid-state r.f. generator ( L e ~ o ) . ~ ~ Also because of an inadvertent melt-down of the original TFT a comparable unit (Precision Glassblowing of Colorado) was used for the imaging studies. Although comparable torches would be expected to differ somewhat in their quantitative aspects qualitatively they should be similar.Images taken at the 306.36 nm OH bandhead while distilled de-ionized water was nebulized are shown in Fig. 8. In general the image of the LiFT appears to be displaced downward caused no doubt by the lower central and outer gas flows that it employs. The result is overall lower OH emission especially in the normal analytical zone. Also the OH 'bullet' peaks higher in the plasma for the TFT while that from the LiFT is barely visible and peaks below the rim of the torch located at the bottom edge of Fig.8. A comparison of N2+ emission at 391.44 nm in a dry plasma (Fig. 9) shows the same behaviour a downward- displaced emission pattern and reduced emission levels for the LiFT. Similar trends are apparent in argon atom emission at 430.0 1 nm (Fig. 10) and in continuum emission at 393.4 nm (Fig. 1 1).5*34*35 The reasons for the weaker molecular-band emission and continuum levels with the LiFT are not fully understood at the present time but their practical significance is clear. Detection Limits The detection limits and other figures of merit are listed in Tables 4 and 5 respectively for several analyte emission68 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 L.U 1.5 - a 2 2 3 1.0 - 8 c c r a 0.5 - 0 Height ALC/mm Fig. 6 Effect of K on 1 ppm Ca ion emission at 393.4 nm.TFT A 0; B 100; and C 1000 ppm K. LiFT D 0; E 100; and F 1000 ppm K ""I 250 1 a H 5 200 C 2 2 150 0 100 c 50 0 5 10 Height ALC/mm 15 Fig. 7 Effect of K on 1 ppm Ca atom emission at 422.7 nm. TFT A 0; B 10; C 100; and D 1000 ppm K. LiFT E 0; F 10; G 100; and H 1000 ppm K Precision The precision attainable with the two torches as a function of instrumental time constant for analyte (1 ppm Ca) and background (1 O/o v/v HN03) signals are compared in Fig. 2. Time constants greater than 2 s were not investigated because of instabilities in the active low-pass filter used for this study. For time constants greater than approximately 5 ms there are no significant differences in precision between the torches. However for time constants less than 5 ms the LiFT shows better precision.A look at plots of noise spectra at different heights ALC (Fig. 3) reveals lower noise amplitude levels for the LiFT by a factor of approximately five than for the TFT. The positions of the peak audio- frequency noise components were determined to be a function of the outer gas flow rate and have been shown previously to be caused by plasma pulsations and vortex formation.6 The smaller audio-frequency peaks could be one reason why the LiFT exhibits better precision at very short time constants (Fig. 2). This potential advantage of the LiFT would not be realized in the measurement of conventional d.c. levels where low-pass filtering and inte- gration methods are commonly employed (time constants in the range 0.01-1 s).However the lower noise could become significant if transient sample pulses were produced or if a Fourier-transform spectrometer were employed. For example sample introduction techniques such as flow injection laser ablation and electrothermal atomization would probably benefit by the use of an LiFT. These techniques produce transient samples where shorter time constants must be employed in order to detect the signal of interest. Long-term Stability The stability of a Ca ion signal measured over a period of about 8 h is shown in Fig. 4. After approximately a 1-1.5 h warm-up period the long-term stability over a 7 h time- span for the LiFT and TFT was found to be 1.4 and 2.3% respectively. As the 0-10 Hz noise spectra (Fig. 5 ) show the better long-term stability of the LiFT is due to lower 11'' noise.This increased stability could be due to a reduced disturbance of the injector gas and aerosol flows. Tangenti- ally flowing outer gases would be expected to exert a lateral force on the central channel; however this effect would not be expected to occur in the LiFT which produces axial- flowing outer gases with force components that are directed upwards. Interference Effects The effect of added potassium as an easily ionizable element (EIE) on calcium ion and atom emission is shown in Figs. 6 and 7 respectively. The results of these experi- ments are in agreement with previous studies of interfer- ences caused by EIE.28-31 The ion emission shows an enhancement low in the plasma and a depression high in the plasma. Both torches exhibit the familiar cross-over point but at different vertical locations.The atom emission increases monotonically as the concentration of added EIE is raised. Presumably emission intensities peak lower in the LiFT than in the TFT because of the lower central-gas velocity used with the LiFT. The effect of phosphate on calcium atom and ion emission was also investigated. However no significant vaporization interferences were detected with either torch. Molecular Bands Maps of molecular-band emission were acquired from each entire plasma at once using a charge coupled device (CCD) camera with an optical system as described previo~sly.~~ The plasmas in these experiments were sustained with a 40.68 MHz solid-state r.f. generator ( L e ~ o ) . ~ ~ Also because of an inadvertent melt-down of the original TFT a comparable unit (Precision Glassblowing of Colorado) was used for the imaging studies.Although comparable torches would be expected to differ somewhat in their quantitative aspects qualitatively they should be similar. Images taken at the 306.36 nm OH bandhead while distilled de-ionized water was nebulized are shown in Fig. 8. In general the image of the LiFT appears to be displaced downward caused no doubt by the lower central and outer gas flows that it employs. The result is overall lower OH emission especially in the normal analytical zone. Also the OH 'bullet' peaks higher in the plasma for the TFT while that from the LiFT is barely visible and peaks below the rim of the torch located at the bottom edge of Fig.8. A comparison of N2+ emission at 391.44 nm in a dry plasma (Fig. 9) shows the same behaviour a downward- displaced emission pattern and reduced emission levels for the LiFT. Similar trends are apparent in argon atom emission at 430.0 1 nm (Fig. 10) and in continuum emission at 393.4 nm (Fig. 1 1).5*34*35 The reasons for the weaker molecular-band emission and continuum levels with the LiFT are not fully understood at the present time but their practical significance is clear. Detection Limits The detection limits and other figures of merit are listed in Tables 4 and 5 respectively for several analyte emission68 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 L.U 1.5 - a 2 2 3 1.0 - 8 c c r a 0.5 - 0 Height ALC/mm Fig. 6 Effect of K on 1 ppm Ca ion emission at 393.4 nm.TFT A 0; B 100; and C 1000 ppm K. LiFT D 0; E 100; and F 1000 ppm K ""I 250 1 a H 5 200 C 2 2 150 0 100 c 50 0 5 10 Height ALC/mm 15 Fig. 7 Effect of K on 1 ppm Ca atom emission at 422.7 nm. TFT A 0; B 10; C 100; and D 1000 ppm K. LiFT E 0; F 10; G 100; and H 1000 ppm K Precision The precision attainable with the two torches as a function of instrumental time constant for analyte (1 ppm Ca) and background (1 O/o v/v HN03) signals are compared in Fig. 2. Time constants greater than 2 s were not investigated because of instabilities in the active low-pass filter used for this study. For time constants greater than approximately 5 ms there are no significant differences in precision between the torches. However for time constants less than 5 ms the LiFT shows better precision. A look at plots of noise spectra at different heights ALC (Fig.3) reveals lower noise amplitude levels for the LiFT by a factor of approximately five than for the TFT. The positions of the peak audio- frequency noise components were determined to be a function of the outer gas flow rate and have been shown previously to be caused by plasma pulsations and vortex formation.6 The smaller audio-frequency peaks could be one reason why the LiFT exhibits better precision at very short time constants (Fig. 2). This potential advantage of the LiFT would not be realized in the measurement of conventional d.c. levels where low-pass filtering and inte- gration methods are commonly employed (time constants in the range 0.01-1 s).However the lower noise could become significant if transient sample pulses were produced or if a Fourier-transform spectrometer were employed. For example sample introduction techniques such as flow injection laser ablation and electrothermal atomization would probably benefit by the use of an LiFT. These techniques produce transient samples where shorter time constants must be employed in order to detect the signal of interest. Long-term Stability The stability of a Ca ion signal measured over a period of about 8 h is shown in Fig. 4. After approximately a 1-1.5 h warm-up period the long-term stability over a 7 h time- span for the LiFT and TFT was found to be 1.4 and 2.3% respectively. As the 0-10 Hz noise spectra (Fig. 5 ) show the better long-term stability of the LiFT is due to lower 11'' noise.This increased stability could be due to a reduced disturbance of the injector gas and aerosol flows. Tangenti- ally flowing outer gases would be expected to exert a lateral force on the central channel; however this effect would not be expected to occur in the LiFT which produces axial- flowing outer gases with force components that are directed upwards. Interference Effects The effect of added potassium as an easily ionizable element (EIE) on calcium ion and atom emission is shown in Figs. 6 and 7 respectively. The results of these experi- ments are in agreement with previous studies of interfer- ences caused by EIE.28-31 The ion emission shows an enhancement low in the plasma and a depression high in the plasma. Both torches exhibit the familiar cross-over point but at different vertical locations.The atom emission increases monotonically as the concentration of added EIE is raised. Presumably emission intensities peak lower in the LiFT than in the TFT because of the lower central-gas velocity used with the LiFT. The effect of phosphate on calcium atom and ion emission was also investigated. However no significant vaporization interferences were detected with either torch. Molecular Bands Maps of molecular-band emission were acquired from each entire plasma at once using a charge coupled device (CCD) camera with an optical system as described previo~sly.~~ The plasmas in these experiments were sustained with a 40.68 MHz solid-state r.f. generator ( L e ~ o ) . ~ ~ Also because of an inadvertent melt-down of the original TFT a comparable unit (Precision Glassblowing of Colorado) was used for the imaging studies.Although comparable torches would be expected to differ somewhat in their quantitative aspects qualitatively they should be similar. Images taken at the 306.36 nm OH bandhead while distilled de-ionized water was nebulized are shown in Fig. 8. In general the image of the LiFT appears to be displaced downward caused no doubt by the lower central and outer gas flows that it employs. The result is overall lower OH emission especially in the normal analytical zone. Also the OH 'bullet' peaks higher in the plasma for the TFT while that from the LiFT is barely visible and peaks below the rim of the torch located at the bottom edge of Fig. 8.A comparison of N2+ emission at 391.44 nm in a dry plasma (Fig. 9) shows the same behaviour a downward- displaced emission pattern and reduced emission levels for the LiFT. Similar trends are apparent in argon atom emission at 430.0 1 nm (Fig. 10) and in continuum emission at 393.4 nm (Fig. 1 1).5*34*35 The reasons for the weaker molecular-band emission and continuum levels with the LiFT are not fully understood at the present time but their practical significance is clear. Detection Limits The detection limits and other figures of merit are listed in Tables 4 and 5 respectively for several analyte emissionJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 69 Table 4 Detection limits in ng ml-' Normalized to a 15 pm bandwidth 80 pm bandwidth Element Wavelengthhm LiFT TFT LiFT TFT Ca I Ca I1 Cd I Cd I1 c u I c u I1 Fe I1 Mg I* Mg 11* Y I1 422.673 393.366 228.802 214.441 324.754 224.700 2 5 9.940 285.2 13 280.270 37 1.030 19 82 420 120 28 0.32 7.9 9.2 2.2 3.3 25 78 550 170 33 11 0.26 7.5 3.5 4.4 3.6 0.062 15 79 23 1.6 5.3 1.8 0.43 0.63 4.9 0.05 1 15 100 32 1.5 6.3 2.1 0.68 0.83 *These values for the TFT were obtained with a comparable TFT not the originally optimized version.Table 5 Figures of merit. All solution concentrations were 1 ppm except for Cd and Mg where a 100 ppm solution and a 10 ppm solution were used respectively. Viewing position; LiFT 12.5 mm ALC; TFT 16 mm ALC (5 mm slit-height) Analyte signal/nA RSDS* (Yo) Background signal/nA RSDB (Yo) S/B Wavelength/ Element nm LiFT TFT LiFT TFT LiFT TFT LiFT TFT LiFT TFT Ca I Ca I1 Cd I Cd I1 c u I c u I1 Fe I1 Mg I t Mg IIt Y I1 422.6 73 393.366 228.802 2 14.44 1 324.754 224.700 259.940 285.2 13 280.270 37 1.030 21 22 1700 1600 340 340 97 110 50 47 2.3 2.7 8.8 7.5 540 330 2000 890 110 99 1.8 1.2 1.4 2.0 2.2 5.8 2.1 1.1 1.1 1.4 1.7 1.1 1.6 2.1 1.4 5.6 2.4 1.3 2.2 1 .o 5.2 3.0 6.3 5.5 4.7 3.0 8.3 6.5 4.0 1 1 7.1 7.1 2.0 3.9 4.7 3.0 2.6 5.3 4.1 4.9 2.5 1.6 3.0 2.1 2.4 2.0 2.7 2.0 2.3 3.1 *RSDS= relative standard deviation of the signal.tThese values for the TFT were obtained with a comparable TFT not the originally optimized version. 2.6 2.0 4.4 5.1 2.5 5.0 3.2 2.3 2.6 2.9 4.0 150 110 15 9.1 0.50 2.9 65 310 28 3.1 230 170 28 10 0.90 2.9 62 220 20 lines. Detection limits were calculated using the equation from Boumans and Vrakki~~g:~~-~O cL=kxO.Ol x RSDBxc0I(SIB) where cL is the detection limit k is a statistical factor related to the significance level (the value of 3 recommended by the International Union of Pure and Applied Chemistry was used for the calculations here) RSDB is the relative standard deviation of the background signal expressed as a percentage co is the concentration at which the analytical signal was measured and SIB is the analyte signal-to-background ratio.These individual values along with the standard deviation of the signal are compiled in Table 5. Although the LiFT shows lower values for background precision (RSDB) and continuum levels (Fig. 11) than the TFT no significant differences are observed for the other figures of merit. The greater background signals listed for the LiFT in Table 5 do not contradict what has been claimed previously about the lower continuum level from the LiFT (cf.Fig. 11). The background level from the LiFT is higher at its optimal viewing position (12.1 mm ALC) than that at the optimal height in the TFT (1 6 mm). This point is even clearer in Fig. 12. This behaviour leads to detection limits that are comparable (within a factor of t~0).41$42 Detection limits obtained here for elements with emis- sion lines below 230 nm are rather disappointing for both torches. Below this wavelength the particular photomulti- plier tube (RCA 1P28) used for these studies has a low quantum efficiency and hence decreased ~ensitivity.~~ L 3 40 .c L 20 0 5 10 15 20 Height ALC/mm Fig.12 Background emission at 393.4 nm while a l0h v/v HN03 solution is nebulized for A TFT and B LiFT Conclusions This study has demonstrated several advantages of using an LiFT instead of a conventional TFT lower argon consump- tion better precision at short time constants due to decreased vortex instabilities better long-term stability because of lessened flicker noise and reduced continuum emission. These factors would at first be expected to improve the detection limits obtained with the LIFT. However both torches were shown to produce com- parable limits of detection (within a factor of two) for conventional d.c. measurements. Nevertheless there might70 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 be an advantage to the LiFT for the measurement of transient signals.The authors wish to thank the National Science Foundation (CHE 90-20631) the National Institutes of Health (R01 GM46853-01) and the Leco Corporation for their support and Dr. Gary Rayson for use of the LiFT. References 1 Wendt R. and Fassel V. A. Anal. Chem. 1965 7 920. 2 Davies J. and Snook R. D. Analyst 1985 110 887. 3 Davies J. and Snook R. D. J. Anal. At. Spectrom. 1986 1 195. 4 Davies J. and Snook R. D. J. Anal. At. Spectrom. 1987 2 27. 5 Davies J. and Du C. M. J. Anal. At. Spectrom. 1988,3,433. 6 Winge R. K. Eckels D. E. DeKalb E. L. and Fassel V. A. J. Anal. At. Spectrom. 1988 3 849. 7 Tan H. Chan S. and Montaser A. Anal. Chem. 1988 60 2542. 8 Montaser A. and Clifford R. H. J. Anal. At. Spectrom. 1989 4 499. 9 Rayson G. D. and Shen D.Y. Appl. Spectrosc. 1992 46 1245. 10 Shen D. Y. Ph.D. Thesis New Mexico State University 1991. 1 1 Prandtl L. Essentials of Fluid Dynamics Blackie London 1952. 12 Boumans P. W. J. M. and Hieftje G. M. Inductively Coupled Plasma Emission Spectroscopy Part I Wiley New York 1987 ch. 5. 13 US patent 5,012,065 April 2 I 199 1 . 14 Angleys G. and Mermet J.-M. Appl. Spectrosc. 1984 38 647. 15 Fassel V. A. and Kniseley R. N. Anal. Chem. 1974 46 1 155A. 16 Greenfield S. McGeachin H. McD. and Smith P. B. Talanta 1976 23 1 . 17 Reed T. B. J. Appl. Phys. 1961 32 821. 18 National Instruments NB-MIO-I 6X User Manual Austin Texas August 1989. 19 Sesi N. N. Borer M. W. Starn T. K. and Hieftje G. M. Spectrochim. Acta Elec. in preparation. 20 Malmstadt H. V. Enke C. G. and Crouch S.R. Electronics and Instrumentation for Scientists BenjaminKummings Pub- lishing Menlo Park CA I98 1 . 2 1 Diefenderfer A. J. Principles of Electronic Instrumentation 2nd ed. W. B. Saunders Philadelphia 1979. 22 Ramirez R. W. The FFT Fundamentals and Concepts Prentice-Hall New Jersey 1985. 23 Ng R. C. L. and Horlick G. Spectrochim. Acta Part B 1981 36 529. 24 Monnig C. A and Hieftje G. M. Appl. Spectrosc. 1989 43 742. 25 Borer M. W. Sesi N. N. Starn T. K. and Hieftje G. M. Spectrochim. Acta Elec. 1992 47B El 135. 26 Genna J. L. Barnes R. M. and Allemand C. D. Anal. Chem. 1977,49 1450. 27 Rezaaiyaan R. Hieftje G. M. Anderson H. Kaiser H. and Meddings B. Appl. Spectrosc. 1982 36 627. 28 Blades M. W. and Horlick G. Spectrochim. Acta Part B 1981 36 881. 29 Rezaaiyaan R. Olesik J. W. and Hieftje G. M. Spectrochim. Acta Part B 1985 40 73. 30 Gunter W. Visser K. and Zeeman P. B. Spectrochim. Acta Part B 1985 40 617. 31 Olesik J. W. and Williamsen E. J. Appl. Spectrosc. 1989,43 1223. 32 Monnig C. A. Gebhart B. D. Marshall K. A. and Hieftje G. M. Spectrochim. Acta Part B 1990 45 261. 33 Brushwyler K. R. and Hieftje G. M. Appl. Spectrosc. 1992 46 1098. 34 Truitt D. and Robinson J. W. Anal. Chim. Acta 1970 49 401. 35 Truitt D. and Robinson J. W. Anal. Chirn. Acta 1970 51 61. 36 Boumans P. W. J. M. and Vrakking J. J. A. M. Spectrochim. Acta Part B 1986 41 1235. 37 Boumans P. W. J. M. and Vrakking J. J. A. M. J. Anal. At. Spectrom. 1987 2 5 13. 38 Boumans P. W. J. M. Spectrochim. Acta Part B 1991 46 431. 39 Boumans P. W. J. M. Spectrochim. Acta Part B 1991 46 641. 40 Boumans P. W. J. M. Spectrochim. Acta. Part B 1991 46 917. 41 Williams R. R. Anal. Chem. 1991 63 1638. 42 Stevenson C. L. and Winefordner J. D. Appl. Spectrosc. 1991,45 1217. 43 Ingle J. D. Jr. and Crouch S. R. Spectrochemical Analysis Prentice Hall New Jersey 1988 p. 558. Paper 210263 1 G Received May 20 1992 Accepted September 15 1 992

ISSN:0267-9477    

DOI:10.1039/JA9930800065

出版商:RSC    

年代:1993

数据来源: RSC

摘要:

JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 71 Development of an Atomic Fluorescence Spectrometer for the Hydride- forming Elements Warren T. Corns and Peter B. Stockwell PS Analytical Ltd. Arthur House 8 4 Chaucer Business Park Watery Lane Kemsing Sevenoaks Kent UK TN15 60Y Les Ebdon and Steve J. Hill Plymouth Analytical Chemistry Research Unit Department of En viromental Sciences University of Plymouth Drake Circus Plymouth Devon UK PL4 8AA A novel atomic fluorescence spectrometer is reported for the determination of hydride-forming elements principally arsenic and selenium. A miniature argon-hydrogen diffusion flame was used as the atomizer and the analyte elements were introduced as their gaseous hydrides from a fully automated continuous hydride generator.The hydrogen for the flame was chemically generated as a by-product of the sodium tetrahydrobo- rate reduction. Excitation was achieved using a boosted-discharge hollow cathode lamp. Fluorescence wavelengths of interest were selected using an interference filter. A solar blind photomultiplier was used as the detector. The instrument is notably compact and capable of full automation by connection to a personal computer using a DIO card. Optimization of the instrumentation is described. Detection limits (30) of 0.10 and 0.05pg I-' for arsenic and selenium respectively are reported as are a number of analyses of certified reference water samples which confirm the excellent accuracy and precision of the new instrumentation. Keywords Hydride generation; atomic fluorescence spectrometry; arsenic and selenium determination Hydride generation coupled to atomic fluorescence spectro- metry (AFS) has proved to be a sensitive method for the determination of elements that form volatile hydrides.l-I9 Thompson' in 1975 was the first to describe a dispersive atomic fluorescence system for the determination of ar- senic selenium antimony and tellurium after hydride generation.An argon-hydrogen flame maintained on a Pyrex tube was utilized as an atom cell and modulated microwave-excited electrodeless discharge lamps (EDLs) as an excitation source for each element. Detection limits using this system ranged from 0.06 to 0.1 pg 1-I. A similar dispersive AFS system was described by Ebdon et aL2 for the determination of arsenic and selenium using a continu- ous flow hydride generation approach.Atomization was achieved using a miniature argon-air-hydrogen flame burning on a glass Y burner located at the focal point of the entrance-slit lens. Excitation of atomic species using EDLs was obtained with illumination at 45" in preference to the conventional 90" illumination as this reduced background radiation and scatter thereby allowing signal amplification with a minimal increase in noise. The limits of detection for arsenic and selenium were found to be 0.34 and 0.13 pg l-l respectively. This system was later utilized for the determi- nation of arsenic and selenium in coal.3 Brown et aL4 used an electrothermally heated argon- sheathed quartz atomizer for the atomization of hydrogen selenide.Maintaining the atomizer at 800 "C the hydride was carried to the atomizer by a stream of hydrogen evolved from the decomposition of sodium tetrahydroborate. A dramatic improvement in sensitivity was observed when the flow rate of the sheathing gas was decreased so that a small argon-hydrogen flame ignited. With the flame ig- nited a limit of detection of 1.4 ng of selenium was obtained from a 10 ml sample solution. The increase in sensitivity observed with flame ignition is in agreement with the research of Diidina and RubeSka20 and Welz and Schubert-Jacobs.21 They suggested that the atomization of gaseous hydrides is caused by collisions with free hydrogen oxygen and hydroxyl radicals within the flame. In the absence of these radicals atoms may condense to form polyatomic species.Most of the hydride-forming elements can be detected using AFS in the ultraviolet (UV) region below 250nm. This is a useful spectral region as very little background emission is seen even from the flame atom cells. More important the spectrum is no longer complex as the analyte has been separated from the matrix during the hydride generation stage. It therefore follows that non- dispersive AFS is feasible. Tsujii and KugaS in 1974 were the first to describe hydride generation coupled to non-dispersive AFS. They reported a detection limit of 2 ng for arsenic using a zinc reduction procedure. A comparative study between disper- sive and non-dispersive systems for the determination of arsenic using pre-mixed argon-hydrogen and nitrogen- hydrogen flames was undertaken by Nakahara et aL6 The best limit of detection (0.12 pg 1-l) was obtained using a non-dispersive system with an argon-hydrogen flame atom cell.This system had the advantage of higher light through- put (large solid angle input and exit apertures and higher transmission) and simultaneous measurement of all fluores- cence lines. Nakahara and co-workers have subsequently published a series of papers on non-dispersive AFS for the determination of arsenic,6 bismuth,' lead,8 antim~ny,~ selenium,1° tin" and tellurium. l2 Azad et al. determined selenium13 and arsenic14 in soil digests by non-dispersive AFS using a hydride generation technique. The results obtained with this system were compared with those obtained using inductively coupled plasma atomic emission spectrometry and good agreement was obtained.Kuga and Tsuj iil developed an argon-sheathed pyrolytic graphite coated graphite furnace atomizer used in a vertical position for the atomization of arsenic. No atomic fluores- cence was observed when the atomization temperature was below 1 100 "C and therefore the furnace was maintained at a constant temperature of 1200 "C. A detection limit of 0.01 ng of arsenic was obtained for a 100 pl sample solution using non-dispersive AFS detection. D'Ulivo and co-workers used a non-dispersive AFS system coupled with hydride generation for the determina- tion of lead16 and dialkyl- and trialk~1lead.l~ The same groupla developed a multi-element system based on an argon-hydrogen miniature flame irradiated by four r.f.- excited EDLs each being modulated at a set frequency.The emitted fluorescence radiation was detected by one photo- multiplier tube (PMT) connected to four lock-in amplifiers72 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 tuned to the frequency of the relevant EDL. More recently the same group19 designed an electrothermally heated quartz tube flame atomizer for the determination of selenium. Using the batch approach evolved hydrides were swept into the atomizer by a stream of argon. A small argon-hydrogen flame then self-ignited at the hot tube outlet owing to the excess of hydrogen evolved during the decomposition of sodium tetrahydroborate. This flame was sufficient to achieve atomization indicating that atomiza- tion is probably via a free radical mechanism within the flame.The system was used to determine selenium in a range of certified reference materials (CRMs) such as coal fly ash sea-water fish muscle and fish tissues and the results obtained were in good agreement with the certified values. To date there are surprisingly no commercially avail- able atomic fluorescence detectors for the volatile hydride- forming elements. This is largely due to the lack of reliable high-intensity excitation sources. Recently boosted-dis- charge hollow cathode lamps (BDHCLs) have become commercially available22 and it would seem that these might offer a promising source for AFS. The development of an atomic fluorescence spectrometer and its suitability for coupling to continuous flow hydride generation is described in this paper.Preliminary work concentrated on the determination of arsenic utilizing a BDHCL as an excitation source. The instrumentation concepts were focused on three main areas the excitation source the atom cell and the optical configuration for the instrumentation. A detection system was developed that utilized an interference filter for wavelength isolation and reduction of flame emission. A solar blind PMT was used to detect fluorescence emission. The analytical performance of the system is described in detail for the determination of arsenic and selenium. Experimental Reagents Unless specified otherwise all reagents were of AnalaR or Aristar grade (Merck Poole Dorset UK). De-ionized water obtained with a Milli-R04 system (Millipore Bedford MA USA) was used throughout.Sodium tetrahydroborate in 0.1 moll-' sodium hydroxide solution was used as a reductant. Fresh solutions were prepared daily. Standard solutions were prepared by appropriate dilution of stock 1000 mg 1 - I arsenic(n1) and selenium(1v) standard solutions using hydrochloric acid. Fresh solutions were prepared daily. Potassium iodide (1% m/v in 4 mol 1-' hydrochloric acid) was used to reduce arsenate to arsenite. All glassware was soaked in 10% v/v nitric acid for 24 h prior to use and then rinsed five times with distilled water. NaBH 3.5 ml min-' Blank 7.5 mI min-' Sample 7.5 ml min-' Instrumentation The instrumental components of the atomic fluorescence spectrometer consist of a BDHCL with power supply an atom reservoir a collection of lenses to focus and collect useful radiation a UV filter a solar blind PMT and an electronic pre-amplifier readout system.The individual constituent units are discussed in more detail below. Continuous Flow Hydride Generation An automated continuous flow hydride generation system (PSA 10.003 PS Analytical Sevenoaks Kent UK) was used to generate covalent gaseous hydrides. A schematic diagram is shown in Fig. 1. The instrument consists of a constant-speed peristaltic pump to deliver reductant and acidified sample solutions an electronically controlled switching valve to alternate between blank and sample solutions and a gas-liquid separator which separates and delivers the gaseous products to an atom reservoir where subsequent determination can take place. Moisture carry- over from the separator was removed using a hygroscopic membrane dryer tube (Perma Pure Products Monmouth Airport Farmingdale NJ USA).This device consists of two concentric tubes 24cm in length connected with variable-bore T-piece connectors. The outer tube is made from poly(tetrafluoroethy1ene) (PTFE) and has dimensions 4 mm i.d. x 6 mm 0.d. The inner tube is a Nafion hygro- scopic membrane with dimensions of 2 mm i.d. x 3 mm 0.d. As the wet gas from the separator passes through the membrane the moisture is removed and transferred to the outer tube. Meanwhile a dryer gas flows in the opposite direction to that of the wet gas removing moisture on the outer surface of the membrane. The dryer can be any gas such as air nitrogen or argon provided that it is relatively dry.This device is described in more detail e1sewhe1-e~~ for the removal of moisture in the determination of mercury. The operating conditions for the hydride generator are given in Table 1. Table 1 Hydride generator conditions Parameter Value NaBH concentration 1.5% m/v in 0.1 mol 1-I NaOH NaBH flow rate 3.5 ml min-I HC1 concentration 3.0 mol 1 - I HCl flow rate 7.5 ml min-I Argon carrier gas flow rate 0.3 1 min-l Dryer gas flow rate 2.6 1 min-' - - - carrier Gas Dryer gas in Dryer gas out I - - - - - ) - - - J L 1 Hygroscopic membrane rotameter Gas-liquid separator - To detector Fig. 1 Schematic diagram of the continuous flow hydride generation system shown in the sampling position. The broken line represents the flow of the blank solutionJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL.8 73 1.0 $ 0.8 0.6 0.4 Excitation Source Fluorescence intensity is directly proportional to the inten- sity of the excitation radiation. Consequently a high radiance excitation source with a steady uniform level of radiance is required for atomic fluorescence in order to obtain good limits of detection. Most papers published on hydride generation AFS have utilized EDLs. When excited these lamps are very intense (typically 200-2000 times more intense than a conventional hollow cathode lamp) and emit narrow lines. Unfortunately they are often unpredic- table in use and require careful temperature control to achieve good stability.22 Radiofrequency-excited EDLs have also been utilized for hydride generation AFV but they are only 5-100 times more intense than HCLs.The r.f.-excited EDLs are more stable than microwave-excited EDLs but are usually less stable than HCLs. Although conventional HCLs may be utilized for atomic fluorescence they do not provide the intensity required for adequate excitation. Increasing the intensity by increasing the current leads to broadening and later self-reversal of the resonant lines by self-absorption. In AFS this phenomenon is not a problem provided the intensity of the central wavelength can be increased. Increases in the non-absorb- ing intensity cause only a small increase of scattered light. The intensity of the HCL may be increased without self- absorption broadening by superimposing a boosted positive column discharge across the hollow cathode discharge.22 This type of lamp is now commercially available (Super- lamp Photron Victoria Australia) and was thought to be a suitable high-intensity source for AFS. The boosted dis- charge HCL was optimized for boost discharge at primary currents of 25.0 27.5 and 30.0 mA in order to obtain the ' 0.70 I 1 I C I 0.55 / 0.45 1 /Y 0.40 1 d_l/ 0.35 1 C / 20 25 30 35 Boost current/mA Fig.2 Effect of boost current on SIB for arsenic at primary currents of A 25.0 B 27.5; and C 30.0 mA 15 20 25 30 Boost cur rent/ mA Fig. 3 Effect of boost current on SIB for selenium at currents of A 20.0 B 22.5; and C 25.0 mA primary maximum fluorescence the criterion of merit being the signal-to-background ratio (S/B). The effect of boost current on S/B for arsenic and selenium is shown in Figs.2 and 3 respectively. The maximum fluorescence for arsenic oc- curred when the primary and boost currents were set to 30 and 35 mA respectively. For selenium the primary and boost currents were both set to 25 mA to obtain maximum fluorescence. Exceeding the boost current optimum will reduce the intensity of the lamp in severe cases to zero. This is caused by electrons from the boost discharge sweeping through the cathode preventing electrons from hitting the cathode and thus reducing sputtering. The arsenic BDHCL was found to be approximately ten times more intense than a conventional HCL with a lamp current of 8 mA. The warm-up time for the BDHCL was found to be 30 min and the lifetime of the lamp was in excess of 5000 mA h. Atom Reservoirs The basic requirements of an atomic reservoir for AFS are an efficient and rapid production of free atoms with the minimum background and noise a high degree of reprodu- cibility with minimim memory effects low quenching properties and minimum dilution of the atoms. Most papers published on hydride generation AFS have utilized argon-hydrogen-air flames.This is because the flame emits very low background radiation over the wavelength region of interest the hydride compounds are easily decomposed in such a low-temperature flame and the quenching effect is relatively low in argon-supported flames and hydrogen. Four atom cell designs were investigated as illustrated in Fig. 4(a)-(d). Initial studies involved the use of the atomization cell shown in Fig.4(a). This consisted of a borosilicate glass tube (8.5 mm i.d. x 100 mm high) with inverted Y side-arms to act as gas inlets. Gases of the hydride generation process (argon hydrogen and hydrides) were passed into one arm of the burner whilst the other had a low flow of hydrogen obtained from a gas cylinder. The result was an argon-hydrogen diffussion flame upon ignition. Argon-hydrogen diffusion flames are normally transparent but in this instance a characteristic orange coloration was observed owing to the emission of sodium (a) 8.5 mm H H Ar H ASH 8.5 rnrn H Ar H ASH Capillaries Borosilicate glass tube - Argon sheath Electrically t-4 Ar Hi ASH Ar H,; ASH Fig. 4 Atom cell designs for hydride generation atomic fluores- cence spectrometry (a) inverted Y burner atom cell; (b) electrically heated glass tube atom cell; (c) argon sheathed electrically heated atom cell; and (d) chemically generated hydrogen diffusion flame atom cell74 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL.8 atoms. The sodium in the form of NaCl arises as a by- product of the hydride generation reaction (i.e. NaBH,+ HCl) and is delivered to the flame in the form of a fine aerosol. The optimum gas flow rates for the atomizer shown in Fig. 4(a) were found to be 0.4 and 0.3 1 min-l for hydrogen and argon respectively. At lower gas flow rates the flame was unstable owing to pulsations from the peristaltic pump of the hydride generation system. Further at low gas flow rates the base of the flame tended to sit inside the tube orifice because of insufficient gas velocities.At higher gas flow rates a decrease in fluorescence intensity was observed owing to analyte dilution and a shorter residence time of the atoms in the optical path. This atom cell design proved to be an effective means of atomizing gaseous hydrides and a limit of detection based on 3 0 of 1.5 pg 1-I of arsenic was obtained. The upper limit of the linear calibration range was found to be about 100 pg 1-L of arsenic. Concentrations exceeding this value were suscep- tible to self-absorption. The linear calibration range there- fore extended only over two orders of magnitude which is comparatively short for AFS. In view of the safety regulations associated with the use of hydrogen gas cylinders it was envisaged that a non-flame atom cell might be more suitable for a commercial instrument.The first flameless design investigated is shown in Fig. 4(b). This was a silica tube (8.5 mm 0.d. x 150 mm long) with one gas inlet for hydride generation products (hydrogen hydrides) and the carrier gas argon. The silica tube was evenly wound with Nichrome wire (2 m length 6.5 !2 m-I) and heated resistively via a Variac (0-240 V) transformer. With this arrangement temperatures of up to 850 "C were achieved. These were measured using a thermocouple device. Using a 1% m/v sodium tetrahydro- borate solution at a flow rate of 3.5 ml min-l hydrogen was generated at approximately 0.07 1 min-l. At tube tempera- tures above 750 "C the excess of hydrogen ignited at the top of the burner producing a mini argon-hydrogen diffusion flame.Attempts to extinguish this flame were unsuccessful. Further once the flame had been produced decreasing the temperature of the silica tube had no effect on the fluorescence intensity. This indicates that the atomization process was not via thermal decomposition but was due to free radicals in the flame. Several workers have discussed this theory in detail and proposed various mechanisms.20-21 This atom cell design produced a limit of detection of 6.7pg 1-I of arsenic and the upper limit of the linear calibration range was found to be about 1OOpg 1-I of arsenic. The inability to extinguish the flame led to the design of the atom cell shown in Fig. 4(c). This is similar to the previous design except that a series of capillaries were positioned around the outside of the inner electrically heated silica tube.A supply of argon was then introduced as a sheath gas to prevent flame ignition. Sheath gas flow rates of at least 1.5 1 min-l were required to extinguish the flame. At an atom cell temperature of approximately 850 "C in the absence of a flame no fluorescence was observed. However if the sheath gas was lowered sufficiently enough to allow diffusion of oxygen from the surrounding atmosphere to penetrate the sheath gas a mini argon-hydrogen diffusion flame was produced. This was found to be an effective means of atomizing the gaseous hydrides. Kuga and TsujiiIS developed an argon-sheathed pyrolytic graphite coated graphite furnace atomizer for the atomization of arsine. No atomic fluorescence was observed at furnace temperatures below 1 100 "C and therefore the furnace was maintained at a constant temperature of 1200 "C.Brown et al. and D'Ulivo et a1.19 both observed an increase in sensitivity for selenium when they allowed the ignition to a mini hydrogen diffusion flame produced from the chemical reagents. As mentioned previously this increase in sensitivity favours the suggestion that atomization of gaseous hydrides is caused by collision with free radicals within the flame. Although the atomization mechanisms for the gaseous hydrides are not fully understood there are clearly distinct advantages in using argon-supported flames in AFS. On the basis of the above considerations the atom call in Fig. 4(4 was investigated. This is an extremely simple design which consists of a 10 ern long borosilicate glass tube.Gases leaving the separator (argon hydrogen and hydrides) were passed through the centre of the tube and on ignition a small argon-hydrogen diffusion flame was pro- duced. The advantage here of using a continuous flow rather than the batch hydride generation process was that hydrogen was produced continuously thereby permitting a permanent flame. Other workers have only used this approach for the batch hydride techniq~e,~J~ but this only allows flame ignition for several seconds thereby giving an erratic baseline. Various tube diameters were investigated ranging from 11 mm 0.d. x 9 mm i.d. to 5 mm 0.d. x 3 mm i.d. The optimum arrangement for each tube diameter was determined and the analytical performance assessed.These findings are reported in Table 2. The optimum carrier gas flow rate was 0.50 1 min-' for the largest tube size and 0.28 1 min-' for the other tube sizes. Larger tube diameters require higher gas flow rates because at low flow rates the flame was found to sit inside the glass tube. However higher gas flow rates cause an increase in the limit of detection owing to atom dilution and a decrease in the residence time of the atoms in the optical path. In terms of analytical performance the most striking feature with varying tube diameters was the limit of detection. The values in Table 2 show that an improvement was observed with decreasing tube diameter. This is mainly due to two factors. The first is that the flame becomes more stable with decreasing tube diameter.Large tube diameters were more susceptible to the pulsation from the peristaltic pump of the hydride generation system an effect which was less prominent with smaller tube diameters. The second is that excitation was more efficient with a smaller flame 'Tube diameters of less than 3 mm i.d. were investigated but in these instances the flame actually lifted off the top of the burner because the gas velocity exceeded the burning velocity. The upper concentration limits of the linear calibration range for each atom cell are also given in Table 2. Concentrations exceeding the values shown are susceptible to self-ab~orption.~~ With an excitation beam of 6 mm at the centre of the atom cell tube ground-state atoms in the outer portion of the flame are less likely to be excited and Table 2 Analytical performance using various atom cell dimensions for arsenic Atom cell Width of Carrier Limit of Upper limit of tube dimensiodmm incident beamlmm gas flow rate/ 1 min-l detection (3a)/pg 1-' linear calibrationlpg 1 - I 1 1 0.d.x 9 i.d. 9 0.d. x 7 i.d. 7 0.d. x 5 i.d. 5 0.d. x 3 i.d. 7 6 6 6 0.50 0.28 0.28 0.28 6.7 0.9 0.6 0.3 100 70 80 100JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 75 may re-absorb fluorescence emission. This effect will be greater with larger tube sizes and therefore one would expect self-absorption to be more prominent. The linear calibration range in each instance spans only 2-3 orders of magnitude which is poor for AFS. The upper limit of the concentration range cannot be increased because of the self- absorption process but it is envisaged that improvements can be made at the lower concentration side of the calibration.The major advantage of this atom cell design was that no additional supply of hydrogen was required which is important in view of the present safety regulations associ- ated with the use of hydrogen cylinders. Because the hydrogen was generated chemically from the reagents of the hydride generation system the concentration of the reagents was extremely important and this is therefore discussed later. Interference Filter There are two instrumental approaches for AFS which can be classified into dispersive and non-dispersive measure- ment systems. Dispersive systems are normally based on modified atomic absorption or emission spectrometers and wavelength isolation is achieved using a monochromator.Atomic absorption apparatus usually has low light-gather- ing characteristics especially in the far-UV wavelength region. Atomic fluorescence however to be used to the best advantage requires a high light-gathering power. In fact no monochromation is required for atomic fluorescence be- cause it can be arranged so that only one fluorescent species is excited by an element-specific excitation source. This is different to the situation in atomic emission where the flame may excite all elements in the analytical solution simultaneously requiring single lines to be resolved. In contrast in atomic fluorescence it is possible to use all the lines of the element if a line source is used for excitation.Summation of these fluorescence lines is possible and therefore non-dispersive systems are usually more sensitive than dispersive systems. They are also less complex and do not require the use of an atomic absorption or emission spectrometer. On some occasions it may be advantageous when there is strong emission from the flame to use a filter between the atom reservoir and the detector or to modulate the light source and thus the fluorescence signal. Most papers on hydride generation AFS have utilized non- dispersive measurement systems and modulation for the reasons discussed above. In this study it was found that the introduction of an interference filter was required in order to reduce flame background and emissions from the excitation source that do not produce intense fluorescence lines.Interference filters are miniature interferometers and therefore in the strictest sense they may be classified as a single dispersive device. This approach proved to be more effective than modulation. The interference filter investigated (Envin Scientific Aylburton Gloucestershire UK) has a peak wavelength of 200 nm and a bandpass of f 10 nm at half-width. The transmission spectrum of this filter is shown in Fig. 5. This was obtained using a scanning UV-visible spectrometer (Perkin-Elmer Lambda 7) by mounting the filter in the optical beam. For arsenic the majority of the fluorescence signal is obtained at the three resonance lines 189.04 193.76 and 197.26 nm. The filter has relatively low transmission at these wavelengths and this affected the performance of the system.This filter is more suitable however for selenium as the most intense selenium fluorescence lines are at 196.09 203.99 and 206.28 nm where the filter has higher transmis- sion. The sensitivity of the AFS system can therefore be improved by an appropriate choice of filter. This is A v) U .- 5 12 t E $ - 3 8 U C v) .- .- E L ! E l- 0 Wavelengthlnm Fig. 5 Transmission spectrum of the interference filter from 190 to 600 nm t .- E v) 9) U - I 1 I 1 I 1 L I 330 325 320 315 310 305 300 295 Wavelengthlnm Fig. 6 Emission spectrum of the hydrogen diffusion flame between 295 and 330 nm Hydrogen diffusion flame Interference filter Solar blind PMT Amplifier readout and Fig. 7 Schematic diagram of the optical layout for the atomic fluorescence spectrometer illustrated by the limits of detection (30) of 0.10 and 0.05 pg I-* obtained for arsenic and selenium respectively.The purpose of the filter was to reduce background emission from the flame and lamp scatter from wavelengths that do not produce intense fluorescence. The hydrogen diffusion flame is of low energy and therefore has virtually no emission below 300 nm. There are however strong OH emissions emitting in the region between 306 and 320 nm that unfortunately are detected by the solar blind PMT. An emission spectrum of the flame is shown in Fig. 6. Unfortunately the interference filter had a small transmis- sion band in this wavelength region.76 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 Table 3 Background equivalent concentrations of the compo- nents that constitute the total background radiation for arsenic and selenium Background equivalent concentration/pg 1-I Background component Arsenic Selenium Ambient light 0.39 0.04 Flame emission 2.78 0.39 Lamp scatter 4.26 0.53 Fluorescence Total background 9.36 1.18 from reagents 1.93 0.22 Optical Configuration A schematic diagram of the optical system is shown in Fig.7. This was designed in such a way as to maximize the efficiency of the entrance and collection optics consistent with the minimum amount of background scatter. The components that constituted the total background signal were ambient light emission from the flame fluorescence from the reagents and lamp scatter. The most useful method to ascertain the various background contributions is by using background equivalent concentrations and typical values for arsenic and selenium are given in Table 3.Chemical Optimization of Continuous Flow Hydride Genera- tion for Arsenic and Selenium With any hydride generation system whether it be batch or continuous flow the concentration of the reagents and the chemical nature of the samples have a profound effect on the analytical performance of the instrument. This was especially true for this system as the function of the reagents was two-fold. Firstly they must generate a suffici- ent amount of hydrogen so that a flame could be main- tained and secondly also generate the hydride species. The effect of sodium tetrahydroborate and hydrochloric acid concentrations was investigated with respect to signal- to-noise ratio (S/N).Figs. 8 and 9 show the effect of hydrochloric acid concentration on the S/N at sodium tetrahydroborate concentrations ranging from 1 to 2.5 hydrochloric acid m/v in 0.1 mol 1 - I NaOH for arsenic and selenium respectively. The results show that the optimum S/N occurred at a reductant concentration of 1.5% m/v and hydrochloric acid concentrations between 3 and 5 moll-'. Sodium tetrahydroborate concentrations below 1 .O% m/v did not produce a usable hydrogen flame and concentra- tions above 2.5% m/v produced a large flame that was characterized by a small S/B. It is recommended for certain sample types to use acid concentrations above 3 mol l-l because at lower concentrations interference from transi- tion metals (e.g.Ni) may become prominent. Analytical Performance for Arsenic and Selenium The analytical performance of the hydride generation atomic fluorescence spectrometer can be characterized by the limit of detection linear dynamic range and precision and accuracy of measurements. The limits of detection (3a) as indicated earlier were 0.10 and 0.05 pg 1-* for arsenic and selenium respectively. They were dependent on a variety of parameters such as reagent purity transmission characteristics of the filter intensity of the source optical design and the chemistry of the system. Of these the main factor influencing the sensitivity was the transmission of the filter. The upper limit of the linear calibration range was 50 I - /- /-A- lo t c 7 \ D I 1 I 1 I 2 3 4 5 6 Hydrochloric acid concentration/mol I-' Fig. 8 Effect of hydrochloric acid concentration on S/N for arsenic at various concentrations of sodium tetrahydroborate A 2.0; B 1.5; C 2.5; and D 1.0% m/v 35 I 30 25 5 20 0) 15 10 I I I I I 2 3 4 5 6 Hydrochloric acid concentration/mol I-' Fig.9 Effect of hydrochloric acid concentration on S/N for selenium at various concentrations of sodium tetrahydroborate A 1.0; B 1.5; and C 2.5% m/v 100 pg 1-1 using the continuous flow approach for both arsenic and selenium. Concentrations exceeding this value were susceptible to self-ab~orption.~~ Carryover between samples with high concentrations was negligible as the atom cell has a small volume and the analyte was rapidly removed. The linear calibration range therefore spanned over three orders of magnitude which was better than for atomic absorption spectrometry.The upper concentration limit of the calibration range may be extended with the use of flow injection analysis and this procedure is described elsewhere for the determination of mercury.24 In order to assess the accuracy of the technique a range of certified water reference materials were analysed for arsenic and selenium. Prior to analysis arsenic(v) was reduced to arsenic(rI1) using acidified potassium iodide (1% m/v). The reduction process was found to take approximately 35 min at room temperature. Selenium(v1) was reduced to selenium(1v) using 4 mol 1-1 hydrochloric acid at 70 "C for 10 min. The certified values and values obtained in the present study are given in Table 4. The results obtained show that the technique is both accurate and precise for both arsenic and selenium.Conclusions A4 simple yet sensitive atomic fluorescence instrument has been developed for the determination of the hydride- forming elements. Boosted-discharge HCLs have been shown to be suitable excitation sources possessing good long- and short-term stability in comparison with other sources e.g. microwave-excited EDLs. Fluorescence signals were only obtained using a flame asJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 77 Table 4 Determination of arsenic and selenium in certified water reference materials; n= 5 Certified reference Analyte Certified value/ Value obtained/ material* PI3 1-' Pg I-' CASS-2 (Coastal Sea-water) As 1.01 k0.07 1.08 f 0.18 SLEW-1 (Estuarine Water) As 0.765 ? 0.093 0.697 f 0.020 IAENW-4 (Simulated River Water) Se 10.0 k 0.5 10.0 f 0.4 *CASS-2 and SLEW-1 were obtained from the National Research Council of Canada Nova Scotia Canada and IAENW-4 from the International Atomic Energy Agency Austria.the atomizer. Collisions with free radicals in the flame (He 0' and OH') appear to lower the required atomization temperature in contrast to an electrothermal atomizer design. A suitable flame was generated using the hydrogen liberated from the reagents (sodium tetrahydroborate and hydrochloric acid) used to generate the hydrides. Not only was the flame an effective atomizer obviating the need for an external hydrogen cylinder but an argon-hydrogen diffu- sion flame offered excellent low-quenching characteristics for AFS.Optimization of the atom cell identified sensitivity improvements with smaller burner diameters (3 mm id.). The presence of significant background emission from the flame required the use of some form of wavelength isolation. The best results were obtained by using a narrow bandwidth interference filter. The choice of filter can be varied for the different hydride-forming elements. The sensitivity of the detector for arsenic and selenium is excellent with limits of detection (30) of 0.10 and 0.05 pg l-l respectively using the 200 nm k 10 nm half- width filter. Greater sensitivity can be obtained by using a filter of specific wavelength. The accuracy and precision of the technique were examined for certified reference water materials and good agreement was obtained with the certified values.The system was totally automated in terms of operation and data collection when the different units were connected to an IBM AT compatible computer through a DIO card. The system described has recently been commercialized by PS Analytical. Future work will involve the development of specific applications for other hydride-forming elements. W.T.C. acknowledges an award under the Science and Engineering Research Council-Cooperative Award in Sci- ence and Engineering (CASE) scheme supported by PS Analytical. References 1 Thompson K. C. Analyst 1975 100 307. 2 Ebdon L. Wilkinson J. R. and Jackson K. W. Anal. Chim. Acta 1982 136 191. 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Ebdon L. and Wilkinson J. R. Anal. Chim. Acta 1987 194 177. Brown A. A. Ottaway J. M. and Fell G. S. Anal. Chim. Acta 1985 172 329. Tsujii K. and Kuga K. Anal. Chim. Acta 1974 72 85. Nakahara T. Kobayashi S. and Musha S. Anal. Chim. Acta 1979 104 173. Kobayashi S. Nakahara. and Musha S. Talanta 1979 26 951. Nakahara T. Kobayashi S. and Musha S. Anal. Chim. Acta 1978 101 375. Nakahara T. and Wasa T. Anal. Sci. 1985 1 291. Nakahara T. Wakisaka T. and Musha S. Anal. Chim. Acta 1980 118 159. Nakahara T. and Wasa T. J. Anal. At. Spectrom. 1986 1 473. Nakahara T. Wakisaka T. and Musha S. Spectrochim. Acta Part B 1981 36 661. Azad J. Kirkbright G. F. and Snook R.D. Analyst 1979 104 232. Azad J. Kirkbright G. F. and Snook R.D. Analyst 1980 105 79. Kuga K. and Tsujii K. Anal. Lett. 1982 15 47. DUlivo A. and Papoff P. Talanta 1985 32 383. DUlivo A. Fuoco R. and Papoff P. Talanta 1986,33,401. D'Ulivo A. Papoff P. and Festa D. Talanta 1983,30,907. D'Ulivo A. Lampugnani L. and Zamboni R. J. Anal. At. Spectrom. 1990 5 225. DEdina J. and RubeSka I. Spectrochim. Acta Part B 1980 35 119. Welz B. and Schubert-Jacobs M. Fresenius' 2. Anal. Chem. 1986,324 832. Watson C. A. J. Anal. At. Spectrom. 1988 3 407. Corns W. T. Ebdon L. Hill S. J. and Stockwell P. B. Analyst 1992 117 717. Corns W. T. Ebdon L. Hill S. J. and Stockwell P. B. J. Autorn. Chem. 1991 13 267. Paper 2/030140 Received June 8 I992 Accepted August 18 I992

ISSN:0267-9477    

DOI:10.1039/JA9930800071

出版商:RSC    

年代:1993

数据来源: RSC

摘要:

78R JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 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 CCP CMP CRM cw d.c. DCP DDDC DMF DNA EDL EDTA EDXRF EIE EPMA ETA ETAAS ETV EXAFS FAAS FAB FAES FAFS FI FPD FI- FTMS GC GD GDL GDMS Ge(Li) HCL h.f. HG HPGe HPLC IAEA IBMK ICP ICP-MS IR 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 capacitively coupled plasma capacitively coupled microwave plasma certified reference material continuous wave direct current d.c.plasma diammonium diethyldithiocarbamate N N-dimethylformamide deoxyribonucleic acid electrodeless discharge lamp ethylenediaminetetraacetic acid energy dispersive X-ray fluorescence easily ionizable element electron probe microanalysis electrothermal atomization electrothermal atomic absorption electrothermal vaporization extended X-ray absorption fine structure flame AAS fast atom bombardment flame AES flame AFS 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-methylopentan-2- inductively coupled plasma inductively coupled plasma mass infrared (ammonium pyrrolidin-1-yl dithioformate) spectrometry spectroscopy one) spectrometry IUPAC I A 1,C LEAFS LEI LMMS LOD LTE PvlECA PvlIP PvlS IVAA IVaDDC IVIES NIST IVTA OES I’IGE I’IXE I’MT PPb PPm PTFE (2C r.f.lXEE(s) RIMS RM IRSD !SIB !SEC !$EM !3FC !Si( Li) !SIMAAC SIMS !SIN 13R ISRM SSMS !STPF ‘TCA ‘TIMS ‘r L c ProPo ’TXRF 1u.h.f. uv VDU vuv WDXRF XRF 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 National Institute of Standards and nitrilotriacetic acid optical emission spectrometry particle-induced gamma-ray emission particle-induced X-ray emission photomultiplier tube parts per billion parts per million polytetrafluoroethylene 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 trioctylphosphine oxide total reflection X-ray fluorescence ultra-high frequency ultraviolet visual display unit vacuum ultraviolet wavelength dispersive X-ray fluorescence X-ray fluorescence Studies Technology

ISSN:0267-9477    

DOI:10.1039/JA993080078R

出版商:RSC    

年代:1993

数据来源: RSC

摘要:

JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 79 Simple Nitric Acid Dissolution Method for Electrothermal Atomic Absorption Spectrometric Analysis of Atmospheric Aerosol Samples Collected by a Berner-type Low-pressure Impactor Tuomo A. Pakkanen and Risto E. Hillamo Finnish Meteorological Institute Air Quality Department Sahaajankatu 22 E SF-008 10 Helsinki Finland Willy Maenhaut University of Ghent Institute of Nuclear Sciences Proe ftuinstraat 86 B-9000 Ghent Belgium The aim of this study was to develop a simple dissolution method for atmospheric aerosol samples collected using a Berner impactor. Particular care was taken to ensure that the procedural blank contributions were as low as possible for the elements investigated. The impactor samples were treated for two or three 20 min periods with 0.2 mol I-' nitric acid in polystyrene test-tubes in an ultrasonic bath at 50 "C.Electrothermal atomic absorption spectrometry (ETAAS) with a graphite furnace was used to determine 14 elements Al Ca Cd Cr Cu Fe K Mg Mn Na Ni Pb V and Zn. With the exception of Zn for which a platform was used all analytes were atomized off the wall of the graphite tube. The blank values for Al Cd Cu Mn Ni Pb and V were found to be at or below the detection limits of the method. The blank values for Ca Fe K Mg Na and Zn varied between 0.5 and 3 pg I-' but Cr showed an unsuitably high blank of 8 pg I-'. The dissolution method was tested on the National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 1648 Urban Particulate and the recoveries were found to be 80-93'/0 for Pb Zn Cd and Cu.The least recoverable elements in this matrix were Al Cr Fe K and Na with recoveries between 20 and 44%. A prolonged dissolution time had only a minor effect on the recoveries. Additional tests involved the analysis of ambient aerosol samples collected with a cascade impactor by both ETAAS and instrumental neutron activation analysis (INAA) with the latter technique providing the reference values. Six elements (Al Cu Mg Mn Na and V) were measured by both techniques. Compared with the NIST material the fine particle (equivalent aerodynamic cut-off diametert2 pm) impactor samples clearly showed better recoveries for Cu (91 "/O) Mn (go%) Na (1 02%) and V (96%). Similar or even better recoveries are also expected for fine particle Cd Zn and Pb which were not measured in our INAA procedure but exhibited the highest recoveries for the NET material.For At on the other hand the results from the impactor samples were similar to those for the NET material and there was a trend that the recoveries were decreasing with increasing particle size because of incomplete dissolution of the soil dust particles and a lower ability of the coarser particles to form a suspension. Moreover coarse particle Al was recovered mostly as particulate material. It is assumed that our dissolution method is valid for measuring fine particle Cd Cu Mg Mn Na Pb V and Zn in ambient aerosol samples collected on polycarbonate film by various types of impactors. Keywords Atmospheric aerosols; dissolution; nitric acid; electrothermal atomic absorption Spectrometry; cascade impactor Mass size distributions for atmospheric trace elements are generally determined by collecting atmospheric aerosol samples with cascade impactors and subsequently analysing the impaction foils by a sensitive analytical technique. As discussed by Maenhaut several techniques including neutron activation analysis X-ray techniques optical atomic spectrometric techniques and mass spectrometry may be used for analysing aerosol samples.When one resorts to atomic absorption spectrometry (AAS) or to techniques that utilize an inductively coupled plasma (ICP) for sample excitation the aerosol samples generally have to be subjected to an extraction dissolution or decomposition procedure prior to the analysis.Solubilization studies have been performed for bulk (total) aerosol samples and for non-size segregated reference materials. Nadkarni,z La- mothe et al.,3 Broekaert et aI.* and Wang et aLS used mixtures of strong acids at elevated temperatures and pressures. Comparisons of various dissolution methods have been carried out using digestion on a hot-plate6q7 and high-pressure digestion in a closed Teflon bomb.s However the results or conclusions from these studies on bulk samples may not necessarily apply to aerosol samples that are collected with a cascade impactor where the particles are separated into several size fractions. The fine particle fractions [equivalent aerodynamic cut-off diameter (EAD)<2bm] of such samples contain much less crustal rock material than bulk aerosol samples and various elements may be present in forms that are much more easily solubilized.Further even elements that are predominantly associated with insoluble particles in those fine-size frac- tions may be accurately determined if the fine particles can form a suspension in the solvent medium. The aim of this work was to establish a suitable dissolution method for atmospheric aerosol samples col- lected with a Berner-type low-pressure impactor so that several elements could be accurately measured by electroth- ermal atomic absorption spectrometry (ETAAS) using a graphite furnace. Also as typically only very small amounts of the analyte elements are collected in the finest particle stages of the Berner impactor the dissolution method had to be set up so that the blank values of the dissolution procedure were minimal.Experimental Aerosol Sampling and Sample Handling Aerosol samples were collected at two different locations viz. in Helsinki in June 1987 and in Utsjoki Finnish Lappland in February 1988,* and thus represent urban summer air and Arctic winter air respectively. During the Utsjoki sampling the whole country was covered by snow. To give some idea of the amounts of metals in the atmosphere concentrations in different particle sizes (Table 1) of the Helsinki sample are 0.3-1 30 ng m-3 for A1 and 0.08-3.4 ng m'3 for V. The concentration in the liquid depends on the sampled air volume and the number of spots analysed and varied between 1 and 17 and between 180 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL.8 by INAA and the results for Al Cu Mg Mn Na and V were Table 1 50% cut-off diameters (EAD) (um) for the various impaction stages of Berner impactor samples collected at Helsinki and Utsioki with those obtained by ETAAS. Stage No. Helsinki Utsjoki Pre-stage 15.7 14.0 10 7.5 6.7 9 3.7 3.3 8 1.92 1.72 7 0.93 0.84 6 0.5 1 0.46 5 0.34 0.30 4 0.176 0.162 3 0.108 0.103 2 0.062 0.064 1 0.03 1 0.034 and 175 pg 1-l for V and Al respectively for the Helsinki sample. The sampling device was a Berner-type low-pressure impactorQ with one pre-stage and ten regular impaction stages. The stage jet orifices of the Berner impactor used in this study were foundt0 to be of the same size which makes the aerosol collection symmetrical and on each substrate all the impaction deposits (spots) should have the same concentration of a certain element. Air was drawn through the device at a flow rate of about 25 1 min-' and the total air volume was 142.4 and 68.8 m3 for the Helsinki and the Utsjoki samples respectively.The 50% EADs for the various stages at the experimental sampling conditions were calculated as described by Hillamo and KauppinenlO and are presented in Table 1. The collection substrates in the impaction stages con- sisted of poreless Nuclepore polycarbonate films of 10 pm thickness. For the pre-stage and the coarse particle stages 10-7 these films were coated with Apiezon L vacuum greaselo to give adhesive properties to the substrates and to minimize particle bounce-off.As indicated below this coating did not contribute significantly to the blank levels of the analyte elements. Before use the impactor was washed with distilled de-ionized water obtained with a Milli-Q system (Millipore) and propan-2-01 (Merck analytical- reagent grade). All the accessories needed for handling the substrates and the samples were washed with 0.2 moll-' nitric acid (Suprapur) and/or Milli-Q-purified water and/or propan-2-01. Whenever possible the impactors were loaded and unloaded on a clean bench otherwise the handling of the samples was performed in the field or in a normal laboratory. Contamination from the laboratory air is expected to be minimal however as the analysis of blank impaction substrates that were handled in the same way as the real samples resulted in low blank values as will be indicated below. Nevertheless the use of a clean bench or a clean room is strongly recommended.lI The samples were stored in tightly closed plastic boxes in a dark storage room.The ETAAS analyses were performed within 1 month after the collection but the instrumental neutron activation analysis (INAA) was carried out in September 1989. Instrumental Neutron Activation Analysis One quarter sections of the impaction films of the various stages of the Berner impactor samples and of blank impaction films were subjected to INAA. The INAA involved a 5 min irradiation of each quarter section at a flux of about 3 x 10l2 n cm-2 s-l in the Thetis reactor of the University of Ghent and two y-spectrometric measure- ments with a high-resolution Ge detector.Full details of the INAA procedure were given by Maenhaut and Zoller12 and Schutyser et al. l 3 The short-lived isotopes were determined Dissolution Method for AAS For the Berner impactor samples one sixth to one half section of each impaction film was used for the dissolution experiment and subsequent AAS analysis. Each section was placed in an acid-washed 10 ml polystyrene test-tube 5 ml of 0.2 moll-' nitric acid (Suprapur) were added and the tube was immediately closed off with a stopper. The test- tubes were transparent so that the aerosol deposits (spots) on the impaction film could be visually inspected. To ensure good contact of the deposits with the solution the tubes were shaken by hand then placed in an ultrasonic bath at 50 "C for 20 min.Subsequently the tubes were again hand-shaken and a visual examination determined whether the aerosol spots were removed from the surface of the impaction substrates. This dissolution procedure (shak- ing by hand +ultrasonic bath) was repeated until there were no visible spots left on the substrates. Usually the proce- dure had to be carried out two or three times. The nitric acid was left in contact with the impaction film and with any remaining insoluble particulate residue until the ETAAS analysis was done. To establish how much a pro- longed dissolution time enhanced the recoveries this time period was varied from 1 d to a few weeks. For certain impaction stages (particle size fractions) the spots some- times remained slightly visible after the repeated dissolution treatment possibly because of staining due to soot carbon. No attempt was made to determine whether volatilization losses occurred during the dissolution procedure.In addition to the Berner impactor samples the National Institute of Standards and Technology (NIST) standard reference material (SRM) 1648 Urban Particulate Matter was subjected to the dissolution treatment. These experi- ments were carried out with subsamples of about 100 mg of NIST material. In order to examine whether some elements such as A1 were in suspension rather than truly in solution after the dissolution procedure the final liquid was filtered for some impactor samples and in two experiments with the NIST SRM. In this filtration use was made of Millipore Millex- HV4 filters (pore size 0.45 pm).However the filtration had the effect that the blank values for A1 became higher and unstable and this increased the uncertainty in the results of this examination. ETAAS Analysis The ETAAS analyses were performed at the Finnish Meteorological Institute Helsinki within 1 month after the sampling. The spectrometer was a Perkin-Elmer Model 3030 equipped with an HGA-600 graphite furnace and an AS-60 autosampler. For background correction a deuterium lamp was utilized. The graphite tubes and platforms were coated with pyrolytic graphite. To be able to dilute samples several times by a factor of 2 the sample injection volume (5-99 pl are possible) used in the analysis was 96 pl except for Zn for which it was 4Opl. The experimental conditions used for the various elements are given in Table 2.Each sample was analysed only once and quantification was effected via a calibration line that was established from three standard solutions and a zero standard as described by Barnett.14 Because the total sample volume was only 5 ml Na K Mg and Ca normally determined by flame AAS also had to be measured by ETAAS. Quantification was based on the peak area of the absorption line which made it possible to use lower atomization temperatures and flatter absorption signals. This made the detection limits poorer but allowed the determination of higher concentra-JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 81 Table 2 Analytical conditions for ETAAS. Most of these methods are sensitive t o interferences and are valid only if the total mass of the sample is low Aluminium Cadmium Calcium* Wavelength 309.3 nm Slit 0.7 nm Tube Pyrolytic graphite coated Temperature programme- temperaturePC Ramp Hold Time/s Furnace 90 2 2 140 2 30 1100 6 15 2500 1 5 2650 1 5 Chromium Wavelength 228.8 nm Slit 0.7 nm Tube Pyrolytic graphite coated Temperature programme- temperature/"(= Ramp Hold Time/s Furnace 90 2 2 140 2 30 250 6 15 1800 1 5 2650 1 5 Copper Wavelength 357.9 nm Slit 0.7 nm Tube Pyrolytic graphite coated Temperature programme- temperature/"C Ramp Hold Time/s Furnace 90 2 2 140 2 30 900 6 15 2100 0 3 2650 1 5 Potassium Wavelength 324.8 nm Slit 0.7 nm Tube Pyrolytic graphite coated Temperature programme- temperature/"C Ramp Hold Time/s Furnace 90 2 2 140 2 30 800 6 15 2100 0 3 2650 1 5 Magnesium Wavelength 422.7 nm 0.7 nm Slit Tube Pyrolytic graphite coated Temperature programme- temperature/"C Ramp Hold Time/s Furnace 90 2 2 140 2 30 900 6 15 2400 1 6 2650 1 5 Iron Wavelength 248.3 nm 0.2 nm Slit Tube Pyrolytic graphite coated Temperature programme- temperature/"C Ramp Hold Time/s Furnace 90 2 2 140 2 30 1000 6 15 2300 1 5 2650 1 5 Manganese Wavelength 766.5 nm Slit 0.7 nm Tube Pyrolytic graphite coated Temperature programme- temperature/"C Ramp Hold Time/s Furnace 90 2 2 140 2 30 800 6 15 2400 1 1st 2650 1 5 Sodium Wavelength 285.2 nm Slit 0.7 nm Tube Pyrolytic graphite coated Temperature programme- temperaturePC Ramp Hold Time/s Furnace 90 2 2 140 2 30 800 6 15 2200 1 3 2650 1 5 Nickel Wavelength 279.5 nm 0.2 nm Slit Tube Pyrolytic graphite coated Temperature programme- temperature/"C Ramp Hold Time/s Furnace 90 2 2 140 2 30 900 6 15 1900 0 2 2650 1 5 Lead Wavelength 589.0 nm Slit 0.7 nm Tube Pyrolytic graphite coated Temperature programme- temperature/"C Ramp Hold Time/s Furnace 90 2 2 140 2 30 800 6 15 2300 1 2 2650 1 5 Vanadium Wavelength 232.0 nm Slit 0.2 nm Tube Pyrolytic graphite coated Temperature programme- temperat ure/"C Ramp Hold Time/s Furnace 90 2 2 140 2 30 900 6 15 50 1 15 2400 0 4 2650 1 5 Zinc Wavelength 283.3 nm Slit 0.7 nm Tube Pyrolytic graphite coated Temperature programme- temperature/"C Ramp Hold Time/s Furnace 90 2 2 140 2 30 450 6 15 2200 1 4 2650 1 5 Wavelength 3 18.4 nm Slit 0.7 nm Tube Pyrolytic graphite coated Temperature programme- temperaturePC Ramp Hold Time/s Furnace 90 2 2 140 2 30 1200 6 15 50 1 15 2600 0 6 2650 1 5 Wavelength 2 1 3.9 nm Slit 0.7 nm Tube Pyrolytic graphite coated Chemical Temperature programme- temperaturePC Ramp Hold with platform modifier 6 Pg Mg(N03)* Time/s Furnace 90 2 2 140 2 30 700 6 15 1700 0 3 2650 1 5 *Graphite tubes give a signal at the wavelength of calcium and before analysis the tubes should be heated 10-20 times a t 2650 "C.tAtomization time should be kept short because the signal from the clean graphite tube increases with time.82 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 tions. Thus a whole set of impactor samples could be analysed with a single calibration graph by using the dilution possibilities of the autosampler only. Usually the best results for ETAAS analysis are ob- tained using stabilized temperature platform furnace (STPF) conditions,15 which minimize interferences during analysis.However Berner impactor samples are normally very lightly loaded the total mass per substrate typically being below 400 pg and severe interferences are rare during such analyses (for the NIST material this argument is not valid). In this work the atomization of the analyte was performed off the wall of a pyrolytic graphite coated graphite tube and only Zn was atomized using the STPF method. Several Berner impactor aerosol samples were analysed by both methods and excellent agreement was generally observed. Also the reference material NIST SRM 1648 was analysed by both techniques and again the results were found to agree well although the STPF method yielded slightly higher values i.e.by 5 3 9 and 9Oh for Cd Pb Mn and Fe respectively. The differences may result from the fact that the nitric acid was in contact with the sample 1 week longer in the STPF method. The use of off-the-wall methods has some advantages over STPF methods. When a sample is atomized off the wall a greater sample volume can be used for analysis and lower concentrations can be detected. If STPF methods are employed a chemical modifier is often required and the analyses last longer because additional autosampler steps are needed. However when a Berner impactor sample is abnormally heavily loaded it is recommended that the analysis of those stages with highest loadings be checked by flame AAS or an STPF method at least for those elements (e.g.Na K Cd Mn and Pb) that are sensitive to interferences in ETAAS. Results and Discussion Blank Values and Detection Limits Several unexposed (blank) polycarbonate impaction films were subjected to the dissolution procedure described above. In these experiments half of a film was placed in the polystyrene test-tube and the volume of 0.2 moll-' nitric ~~ Table 3 Detection limits and blank values (pg 1-I 1). The blank values and associated standard deviations are based on 5 samples (dissolution experiments) Detection Blank 1 Blank 2 Element limit* (PC+HNO,)T (PC+ApL+HNO,)t A1 Ca Cd Cr c u Fe K Mg Mn Na Ni Pb V Zn 1 .o 0.30 0.020 0.25 0.40 0.30 0.070 0.020 0.20 0.030 1 .o 0.60 1 .o 0.020 1 k0.5 1 20.5 0.01 kO.01 1024 0.1 20.1 1.5 k 1 1 20.5 0.5 2 0.2 0.1 k 0.05 1 kO.5 (0.5 <0.3 <0.5 0.5 k0.2 1.5 f 1 3.5 f 1.5 0.02 k 0.01 1024 0.2 f O .1 2.5 f 1 1 20.5 0.8 f 0.4 0.1 kO.05 1.5 f 1 (0.5 (0.3 co.5 0.7 f 0.4 * Quantitative detection limit of ETAAS (injection volume 96 pl). The values were determined by diluting a standard solution (injection volume 96 pl) to the point where the consistency of ten replicate analyses from one sample was no longer in the limits of 2 10%. tPC = polycarbonate film ( 1 5 cm3); ApL= Apiezon L vacuum grease (0.1-0.3 mg). acid was always 5 ml. The blank levels of various elements (in pg l-ll) for both ungreased and greased films are given in Table 3. A comparison was also made with the quantitative detection limits (DLs) of the ETAAS procedure.These DLs were determined by diluting a standard solution to the point where the repeatability of ten replicate ETAAS analyses (injection volume 96 pl) from one sample was no longer within the limits of f looh. The blank values of Al Cd Cu Mn Ni Pb and V are at or below the quantitative DLs of the technique and Ca Fe K Mg Na and Zn have reasonably low blanks in the range 0.5-3pg 1-l. Further the blank values for the greased polycarbonate film are very similar to those for the ungreased film and only Ca seems to be liberated from the grease. Also in previous work it was found that the Apiezon L vacuum grease released only negligible amounts of the various elements.I6 The polycarbonate film gives rise to substantial blank values for Cr but is otherwise a suitable material for aerosol collection with subsequent ETAAS analysis.Despite these low blank values it was observed that the analyte amounts on the two last impac- tion stages (Nos. 2 and I ) of our Berner impactor samples were very close to the blank values. It is therefore strongly recommended that the blank values be examined before any actual aerosol sampling andor ETAAS analyses are carried out when different batches of Nuclepore polycarbo- nate film test-tubes or nitric acid are used. Examination of Aluminium Concentration in Solution The low recoveries of Al Cr and Fe (Table 5 ) indicate that aluminosilicates and crustal rock particles are definitely not completely dissolved by the dissolution procedure pre- sented here. In order to examine how far the A1 measured by ETAAS is truly in solution rather than in suspension quarter sections of the various impaction films from one impactor sample (collected during summer at Helsinki) were subjected to the dissolution procedure and subsequent filtration.The same was also done with various subsamples of NIST SRM 1648 Urban Particulate Matter. The results of these experiments are presented in Table 4. With the impactor sample about half of the recovered coarse particle A1 is in suspended particulate form and there is a tendency for that fraction to increase with increasing particle Al. The result for stage 6 is an exception possibly because Table 4 Ratio of unfiltered to filtered A1 for the various stages of a Berner impactor sample and for NIST SRM 1648 Urban Particu- late Matter Impactor stage Ratio unfiltered to filtered A1 10 9 8 7 6 5 4 3 2 1 NIST SRM 1648t A B 2.4 1.8 1.7 1.7 3.0 1.3 - * - * - * - * 3.2 2.5 *The A1 concentration was close to the blank value.?Two slightly different dissolution-ETAAS schemes were used (A) test-tube in ultrasonic bath at 50 "C for 20 min ETAAS after 1 d; (B) test-tube in ultrasonic bath at 50 "C for 60 min ETAAS after 9 d. In each scheme two different subsamples were examined.JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 83 of an analytical error due to the variable A1 blank value in the filtration procedure. For NIST SRM 1648 A1 is mostly recovered in particulate form. Recoveries for NIST SRM 1648 Table 5 gives the recoveries for various elements as obtained by applying the dissolution procedure without filtration to NIST SRM 1648 (about 100 mg samples) and analysis by ETAAS.Because the mass of the NIST samples is high compared with that of impactor samples a larger sample volume of 10 ml was used. Two slightly different dissolution-ETAAS schemes (A and B) were used the difference being that the ultrasonic bath treatment lasted 60 min in scheme B compared with only 20 min in scheme A and there was a 9 d period between the dissolution step and the ETAAS in scheme B compared with only 1 d in scheme A. This arrangement was made to see how much a prolonged dissolution time enhances the recoveries. In each scheme two different subsamples were examined. The data for Ni and V are based on only one subsample however. The results in Table 5 are similar to those that were obtained by Infante and Acosta' with a mixture of HCl and HN03.It was observed that a large fraction of the reference material did not go into solution in our procedure and that most of the insoluble material sedimented to the bottom of the test-tubes in 5-10 min after shaking. Despite the large fraction of insoluble material reasonable recoveries were obtained for some elements e.g. for Cd (85%) Cu (80%) Mg (77%) Pb (99%) and Zn (86%). A prolonged ultrasonic bath treatment and longer standing time (scheme B) enhanced the solubilization for Al K Mn Na and Ni but had no effect on the recovery of the important pollutant elements Cd Cu Pb V and Zn. Recoveries for the Berner Cascade Impactor Samples For the Berner cascade impactor samples the recoveries were determined by comparing the ETAAS and INAA results the latter serving as reference.Exceptionally the Helsinki aerosol samples used in this comparison were dissolved in more dilute nitric acid i e . 0.01 moll-' (pH 2). However if the acid strength is less than 0.1 moll-' the risk of ion adsorption on the walls of the sample container (test-tube and/or ETAAS cup) is increa~ed.'~J* The ultra- sonic bath treatment for the Helsinki samples lasted 30 min Table 5 Recoveries (%) of elements after applying the dissolution procedure to NIST SRM 1648 Urban Particulate Matter. Two slightly different dissolution-ETAAS schemes (A and B) were used (see footnote of Table 3 for details). Data are averages for each based on two sub-samples (except for Ni and V dissolution experiments).Agreement between the two sub-samples was usually within +5% and in only two instances Mg(A) and Cr(B) was agreement worse than -e 10% Element A B A1 Cd Cr c u Fe K Mg Mn Na Ni Pb V Zn 38 85 20 80 42 34 77 66 44 40 99 61 86 48 84 20 82 45 45 80 75 54 72 93 63 86 Table 6 Recoveries (%) for the Helsinki aerosol samples as derived from comparing the ETAAS results with the INAA data (dissolution of the ETAAS samples in 0.01 mol 1-1 nitric acid) Stage No. A1 Cu Mg Mn Na V 10 9 8 7 6 5 4 3 2 1 28 118 80 78 91 35 91 114 78 87 47 90 107 89 136 51 89 -* 84 (168)t * - * 84 102 39 - 45 - 4 - * 99 112 -* - * -* 99 (260)t -* -* -* 86 108 -* -* -* -4 -* -* - * -* -* -* 105 94 101 101 102 97 109 94 -* -* Average 7-1 45 - * - 90 107 101 *The concentration was close to the detection limit(s) of ETAAS ?Data in parentheses were not retained when calculating the or INAA.averages. Table 7 Recoveries (96) for the Utsjoki aerosol samples as derived from comparing the ETAAS results with the INAA data (dissolu- tion of the ETAAS samples in 0.2 mol 1-1 nitric acid) Stage No.* A1 c u Mn Na v 10 -t -t 46 -t -t 7 57 79 (162)$ 107 93 9 43 55 91 80 -f 8 45 70 (211)$ 102 68 6 61 97 88 (161)$ 96 5 67 100 (150)$ 101 88 4 44 -t 91 83 83 Average 7-4 57 92 -o 97 90 *Films from stages 3-1 were not analysed by INAA. ?The concentration was close to the detection limit(s) of ETAAS $Data in parentheses were not retained when calculating the §Contamination (or other) problems. or INAA. averages. and the ETAAS analyses were performed after 2 weeks.For the Utsjoki aerosol samples 0.2 moll-' (pH 0.7) nitric acid and a 60 min ultrasonic bath treatment was used and the ETAAS measurements were carried out after 2 d. The recoveries for the Helsinki samples are presented in Table 6 and those for the Utsjoki samples in Table 7. The recoveries for Cu Mn Na and V from the fine particle impactor stages (7-1) of the Berner impactor samples are clearly better than those obtained from the NIST reference material although there appear to be some contamination or other problems with Mn and Na. Simi- larly better recoveries from the fine particles can be expected for most of the other elements that were measured in the NIST material but not determined by INAA in the impactor samples. However for a crustal element such as Al the NIST material and impactor samples yield similar recoveries although there is a trend for the recovery to decrease with increasing particle size.This can be explained by the limited solubility of the soil dust particles in the aerosol and the reduced ability of the coarser particles to go into suspension. For the Utsjoki samples all five elements listed in Table 7 seem to have worse recoveries with increasing particle size but it should be mentioned that the analytical errors for the large particle stages were greater here because of the low winter concentrations. Aluminium on the other hand is more completely dissolved from the Utsjoki samples than from the Helsinki samples. This may be a consequence of the fact that some snow was collected on the coarse particle stage impaction films.Possibly the84 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 snow had scavenged some fine particles. However a more likely explanation is that the higher A1 recoveries for the Utsjoki samples are the result of the stronger nitric acid used. Also differences in particle origin and nature may influence the solubilities and the ability to form a suspen- sion. The different particulate mass-to-solution volume ratios of the impactor samples and the NIST samples may have some influence when the solubilities of these different samples are compared. However we believe that this is not a problem as it could be seen that a large part of the NIST sample was insoluble. In any event if lower masses of the NIST sample were used it should have resulted in similar or higher recoveries in Table 5. More work is needed to verify the recoveries of Ca Cr Fe K and Ni from impactor samples.Conclusions From experiments with NIST SRM 1648 Urban Particulate Matter it can be concluded that a simple 20 min treatment with 0.2 mol 1-1 nitric acid in an ultrasonic bath is able to yield high recoveries for several metals from a total aerosol (non-size segregated) sample. The recoveries were higher than 80% for Cd Cu Pb and Zn. For most metals a prolonged dissolution time did not enhance the recovery except for Al K Mn and Ni recoveries of which became slightly higher and probably the same is true for impactor samples also. By comparing the ETAAS with the INAA results the elemental recoveries of Al Cu Mg Mn Na and V from the impactor samples could be calculated.These recoveries were compared with the corresponding recoveries from the NIST samples; values for Cu Mg Mn Na and V were clearly better from the impactor samples especially for the fine particles. For the fine particle Berner impactor samples it can be concluded that the recoveries are higher than 85% for Cd Cu Mg Mn Na Pb V and Zn even though there seemed to be some contamination or other problems with Mn and Na. Dissolution with 0.2 mol 1-l nitric acid in an ultrasonic bath at 50 "C may provide a routine method in the analysis of fine particle Berner impactor samples for Cd Cu Mg Pb V and Zn and probably also for Mn and Na. However in Table 2 only the ETAAS methods for Cu V and Zn are suitable for routine analysis.The methods for the other elements in Table 2 even though fast and practical are easily affected by various interferences. In this work the NIST SRMs and the Berner impactor aerosol samples were analysed both by STPF methods and off-the-wall of the graphite tube and very similar results were obtained. However if the impactor samples are abnormally heavily loaded it may be necessary to check the correctness of the off-the-wall results for a few heavily loaded stages by flame or STPF methods. From the experiments with the Berner impactor samples it appeared that there is a tendency for A1 to be less effectively solubilized and recovered with increasing parti- cle size. This can be explained by the limited solubility and the reduced ability to form a suspension for the coarser mineral particles.For Cu Mg Mn Na and V this phenomenon is not so pronounced. Furthermore coarse particle A1 was mainly recovered in suspended form. A drawback of the proposed dissolution method is that mineral soil dust particles are incompletely solubilized. The authors thank Art0 Jappinen for his assistance with the collection of the Utsjoki samples. T. A. P. and R. E. H. thank the Maj and Tor Nessling Foundation and the Academy of Finland for funding this work. W. M. acknowledges support from the Belgian Nationaal Fonds voor Wetenschappelijk Onderzoek the Interuniversitair Instituut voor Kernwetenschappen and the Impulse Pro- gramme 'Global Change,' supported by the Belgian State- Prime Minister's Service-Science Policy Office.1 2 3 4 5 6 7 8 9 10 1 1 12 13 14 15 16 17 18 References Maenhaut W. Control and Fate of Atmospheric Trace Metals ed. Pacyna J. M. and Ottar B. NATO AS1 Series Kluwer Dordrecht 1989 pp. 259-301. Nadkami R. A. Anal. Chem. 1984,56 2233. Lamothe P. J. Fries T. L. and Consul J. J. Anal. Chern. 1986,58 188 1. Broekaert J. A. C. Wopenka B. and Puxbaum H. Anal. Chem. 1982 54 2 174. Wang C.-F. Miau T. T. Perng J. Y. Yeh S. J. Chiang P. C. Tsai H. T. and Yang M.H. Analyst 1989 114 1067. Yamashige T. Yamamoto M. and Sunahara H. Analyst 1989 114 1071. Infante R. N. and Acosta I. L. At. Spectrosc. 1988 9 191. Jappinen A. Pakkanen T. Keronen P. Kulmala M. Hillamo R. and Viisanen Y. J. Aerosol Sci. 1988,19 1243. Berner A. Lurzer C. H. Pohl L. Preining O. and Wagner P. Sci. Total Environ. 1979 13 245. Hillamo R. E. and Kauppinen E. I. Aerosol Sci. Technol. 1991 14 33. Ross H. B. Methodology for the Collection and Analysis of Trace Metals in Atmospheric Precipitation Report CM-67 Department of Meteorology University of Stockholm 1984. Maenhaut W. and ZoIler W. H. J. Radioanal. Chem. 1977 37 637. Schutyser P. Maenhaut W. and Dams R. Anal. Chim. Acta 1978 100 75. Barnett W. B. Spectrochim. Acta Part B 1984 39 829. Slavin W. Manning D. L. and Carnrick G. R. At. Spectrosc. 1981 2 137. Pakkanen T. A. and Hillamo R. E. J. AerosolSci. 1988 19 1303. Sekerka I. and Lechner J. Influence of Container Material on the Loss of Silver Mercuric and Cupric Ions From Water Solutions Technical Bulletin 69 Inland Waters Directorate Water Quality Branch Ottawa Canada 1972. Haraldsson C. and Magnusson B. paper presented at Heavy Metals in the Environment Conference Heidelberg 1983. Paper 2/022 90G Received May 5 1992 Accepted August 20 1992

ISSN:0267-9477    

DOI:10.1039/JA9930800079

出版商:RSC    

年代:1993

数据来源: RSC

摘要:

JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 85 Behaviour of Cadmium Cobalt and Lead in Chlorine-containing Organic Solvents in Electrothermal Atomic Absorption Spectrometry Emil Tserovsky Sonja Arpadjan and lrina Karadjova Faculty of Chemistry University of Sofia 1126 Sofia Bulgaria The behaviour of Cd Co and Pb in chlorine-containing organic solvents (1,2-dichIoroethane chloroform and carbon tetrachloride) in electrothermal atomic absorption spectrometry was investigated. The influence of the chlorine content in the solvent the chemical form of the analyte the atomizer type and the chemical form of palladium used as a chemical modifier was evaluated. Loss-free atomization levelling of the absorbance signals for various solvents and lowering of the non-specific light absorbance were established using tungsten- impregnated tubes as atomizers.Key words Electrothermal atomic absorption spectrometry; chlorine-con taining organic solvents; cadmium cobalt and lead; tungsten-impregnated tubes The determination of elements by electrothermal atomic absorption spectrometry (ETAAS) in the presence of chlorine-containing solvents is hampered by the forma- tion of volatile organometallic compounds or of volatile thermally stable chlorides. The determination of trace amounts of lead in petrol4 and in reference fuelsS by ETAAS requires conversion of alkyllead compounds into inorganic species prior to measurement. The high vola- tility of the alkyllead compounds hinders the direct deter- mination of trace amounts of lead in the organic phase.The possibility of using tungsten-impregnated tubes as atomizers for the determination of trace amounts of elements in chlorine-containing organic solvents and of alkylleads in various organic liquids has not been investi- gated previously. Tungsten-impregnated tubes were introduced into analyt- ical ETAAS practice in order to achieve a higher degree of atomization and a higher sensitivity for elements that atomize only with great difficulty on carbon (e.g. silicon and titanium). The presence of a high concentration of tungsten on the graphite tube eliminates to a great extent the formation of stable carbide compounds. Useful results have also been obtained with tungsten-impregnated tubes in the investigation of the atomization of Cd Co Cu Fe Ni and Pb in isobutyl methyl ketone (IBMK) toluene and xylene.6 An improvement in the reproducibility an en- hancement of the sensitivity and also an increase in the maximum loss-free pyrolysis temperature were observed.In this work the influence of the type of atomizer and the chemical form of the analyte and the modifier on the behaviour of Cd Co and Pb dissolved in 1,Zdichloro- ethane (C2H4C12) chloroform (CHC13) and carbon tetra- chloride (CC14) was investigated. The possibility of over- coming the depressive effect of chlorine-containing solvents on the absorbance signals using tungsten-impregnated tubes as atomizers and an organic phase-soluble palladium chemical modifier was studied. The optimum conditions for loss-free atomization of lead when present as alkyl- lead compounds in various organic solvents were also established.Experimental Measurements were carried out on Perkin-Elmer 1 1 OOB and Zeeman 3030 atomic absorption spectrometers with HGA-700 and HGA-600 graphite furnaces respectively. The light sources used were an electrodeless discharge lamp for Cd and hollow cathode lamps for Co and Pb. The spectral bandpass and wavelengths used (228.8 nm for Cd 240.7 nm for Co and 283.3 nm for Pb) were as recom- mended by Perkin-Elmer. Standard uncoated graphite tubes pyrolytic graphite coated graphite tubes (PGT) tungsten-impregnated graphite tubes (W-impregnated GT) and tubes with a platforms were used. The W-impregnated GTs were prepared as described previ~usly.~ Solutions ( 10 pl) were introduced into the atomizer manually during the hold time of step 1 (Table 1) using micropipettes (Eppendorf).The atomic absorption signals were recorded on an Epson 800MX printer. The tempera- ture programmes used are summarized in Table 1. A stock standard solution of cadmium of concentration 1 g 1-l (Merck Darmstadt Germany) was used for the preparation of working standard solutions by appropriate dilution. An organic working standard solution of Cd was prepared by extraction of the cadmium-dithiocarbamate chelate from aqueous standard solution. A 1 ml volume of standard solution with a Cd concentration of 1 pg ml-l was mixed with 3 ml of 0.1 mol 1-' acetate buffer (pH 4.66) (Merck No. 7827) I ml of 1% ammonium pyrrolidin-1-yl dithioformate [ammonium pyrrolidinedithiocarbamate (APDC)] and 5.0 ml of IBMK and extracted for 1 min.Then 10 pl from the organic layer obtained were diluted with 1000 pl of the studied organic solvent. In this way standard solutions with concentrations of 2 pg 1-1 in IBMK C2H4C12 CHC13 and CC14 were obtained. Elemental standard solutions ( 1000 pg ml-l) of Co and Pb dissolved in oil (Merck No. 1506 1 and 15501) as cyclohexane butyrates (CHB) and an elemental standard solutions of Pb (300 pg ml-I) as tetramethyllead (TMPb) were also used. The working standard solutions were prepared by appropriate dilution with the various organic solvents. Organic solvents (analytic-reagent grade Merck) were used as received. Doubly distilled water was used through- out. Table 1 Temperature programme Step Parameter 1 2 3 4 5 TemperaturePC 50 120 Var.* Var.* 2650 Ramp time/s 2 10 10 0 1 Hold time/s 8 15 30 3 3 Read - - - On - Internal gas (Ar) flow rate ml/min-l 0 300 300 0 300 *Variable; see text and figures.86 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL.8 100 100 h Q g 80 5 80 4 60 n C 9) s 60 n Q 40 2 +? s1 .- cr" 20 40 Q .- c c - 5 20 K n n " Cd co Pb Fig. 1 Absorbance signals of the elements relative to that in IBMK depending on chlorine content of the solvent; atomizer PGT Preparation of Palladium Modifier A 6 ml volume of palladium atomic absorption standard solution (Aldrich) of concentration 1 g 1 - l was diluted in an extraction tube with 30 ml of 6 moll-' HCl then 3.0 ml of methyltrioctylammonium chloride (MTOACI) solution in IBMK were added and extracted for 5 min.Under these conditions palladium was extracted into IBMK as the ion association complex PdC14(MTOA)2. The concentration of Pd was further varied by dilution with IBMK. Appropriate volumes of the Pd solutions in IBMK thus obtained were mixed with the organic solution of the analytes prior to introduction into the graphite furnace. Results and Discussion Atomization from the Pyrolytic Graphite Coated Graphite Tube The behaviour of Cd Co and Pb during the atomization in C2H4C12 CHC13 and CC14 when the atomization was carried out from the PGT is illustrated in Figs. 1-3. The absor- bance signals for the analytes for C2H4C12 CHC1 and CC14 were compared with those for the same analytes with the same concentrations but dissolved in IBMK i.e. organic solvent without chlorine.Significant losses of the elements even at low pre-treatment temperatures were established. These losses are greater for the easily volatilized Cd and Pb than for Co (Fig. 1). Further the percentage losses increase with increase in the chlorine content in the organic solvent being highest in CCl,. The formation of volatile chlorides in the presence of high chlorine concentrations in the furnace may be a possible explanation for this behaviour. It can be assumed that the reaction of chloride formation is faster than the reduction of the analytes to their elemental states. With the chlorine-free solvent IBMK no significant losses of Cd Co and Pb were observed when the elements were present as dithiocarbamate complexes or as salts of organic acids (cyclohexane butyrates) (Fig.1 ). However the atomi- zation of lead in IBMK is connected with strong losses of the analyte when the element is present as an alkyllead compound probably owing to the high volatility of the tetramethyllead itself (Fig. 2). The stabilizing effect of palladium as a chemical modifier depends on the chemical form of the palladium on the mode of introduction of the modifier into the furnace on the chlorine content in the solvent and on the amount of the modifier. As can be seen from Fig. 3 the absorbance signals for all organic solvents are levelled when the solvents are previously mixed with the soluble PdC14(MTOA)2. The mixing of the solvents and palladium as the ion association complex PdC14(MTOA)2 in the furnace and the use of aqueous palladium solution (PdC12) does not eliminate the fincoated tube Uncoated tube without modifier with modifier W-impregnated tube Fig.2 Absorbance signals of Pb as tetramethyllead in IBMK and CC14 relative to that of Pb as Pb-CHB in IBMK depending on the atomizer type; modifier 7 pg m1-I of Pd as PdC14(MTOA)* losses of Cd and Pb. The pre-treatment and atomization curves (Figs. 4 and 5 ) show that in the presence of 2 pg ml-I of palladium in the solvents maximum loss-free pre- treatment temperatures of 800 "C for Cd and 1000 "C for Pb can be applied. An increase in the palladium concentra- tion in the solvent to 7 pg ml-l leads to stabilization of Pb up to 1200 "C in the pre-treatment step. The optimum Pb Pb Mixing in Preliminary Mixing in Preliminary furnace mixing furnace mixing Fig.3 Absorbance signals of Cd (as Cd-APDC) and Pb (as Pb-CHB) in different chlorine-containing organic solvents relative to that in IBMK depending on the mode of introduction of the modifier; atomizer PGT b D 0' 1 I I I 400 800 1200 1600 2000 Tf "C Fig. 4 Thermal pre-treatment and atomization curves for tetra- methyllead with modifier PdC14(MTOA)2 in an uncoated tube A in IBMK with 7 pg ml-I of Pb at 7',,=2300 "C; B in IBMK with 2 ,ug ml-1 of Pb at Tat= 1400 "C; C in CC14 with 7 pg ml-1 of Pd at Tat= 2300 "C; D in CC14 with 2 pg ml-1 of Pd at T' = 1400 "C; E in IBMK with 2 pg ml-I of Pd at Tpyr= 1300 "C; and F in CC14 with 2 pg ml-1 of Pd at Tpyr= 1000 "CJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 87 atomization temperatures are 1300 "C for Cd and 1600 "C for Pb.At higher atomization temperatures the integrated absorbance signals for Cd and Pb were lower regardless of the presence of the palladium modifier. The behaviour of Cd and Pb in C2H4C12 CHC13 and CC14 in ETAAS with a platform as atomizer does not differ substantially from the previously described behaviour of the analytes when the PGT were used. The palladium modifier in organic form [PdCl,(MTOA),] has to be mixed with the organic solvents prior to their introduction into the furnace. In the presence of 2 pg ml-1 of palladium in the solvent stabilization of Pb up to 1000 "C during the pre- treatment step can be achieved and higher atomization temperatures (1 700 "C and above) are necessary for atomi- zation from the platform (Fig. 6).A B C E ic " 300 700 1100 1500 1900 TI"C Fig. 5 Thermal pre-treatment and atomization curves for Cd as Cd-APDC in different solvents with modifier 2 pg ml-I of Pd as PdC14(MTOA)2 in a PGT A CHCI,; B IBMK; C CCI,; D C2H4C12; and E water 0.2 700 1000 1300 1600 1900 Tl°C Fig. 6 Thermal pre-treatment and atomization curves for Pb as tetramethyllead on the platform with 2 pg ml-l of Pd as PdCl,(MTOA), A in IBMK with Tat=2000 "C; B in CCI4 with Tat= 2000 "C; C in IBMK with Tpyr= 1000 "C; and D in CCl with Tpyr= 1000 "C Atomization from a Tungsten-impregnated Tube A satisfactory stabilization of Cd and Pb in chlorine- containing solvents was observed when tungsten-impreg- nated tubes were applied. As can be seen from Fig. 7 the use of tungsten-impregnated tubes eliminates to a large extent the losses due to the chlorine-containing organic solvents. These atomizers permit higher loss-free pyrolysis temperatures of up to 500 "C for Cd 800 "C for Pb and 1500 "C for Co (without modifier) and also diminish non- specific light absorption in comparison with PGTs.Prob- ably the tungsten impregnation of the tubes prevents the formation of volatile chlorides. The tungsten itself present as an impregnation medium in the furnace acts as a Table 2 Characteristic masses (m,) and pyrolysis ( Tpyr) and atomization (Tat) temperatures for different solvents PGT W-impregnated GT Analyte Cd-APDC Cd-APDC CO-CHB Pb-CHB Pb-CHB TMPb Solvent IBMK C2H4C12 CHCI3 CCl Aqueous IBMK C2H4C12 CHC13 CCl Aqueous IBMK CCl Aqueous IBMK C2H4C12 CHCl3 CCl Aqueous IBMK CCl Aqueous IBMK CCl IBMK CCl CHC13 C2H4C12 Pd concentration/ TPyJ 0 500 0 500 0 500 0 500 0 400 2 800 2 800 2 800 2 800 2 700 0 1200 0 1200 0 1200 0 1200 0 450 0 450 0 450 0 450 0 450 2 700 2 700 2 700 2 700 0 400 0 400 2 5 50 2 550 pg ml-' "C Tat/ "C 1000 1000 1000 1 000 1300 1300 1300 1300 1300 1400 2400 2400 2400 2400 1200 1200 1200 1200 1400 1600 1600 1600 1600 1200 1200 1300 1300 md Pd concentration/ Pg pg ml-I 0.5 1 0 0 0 0 0.58 0 0.50 2 0.55 2 0.65 2 0.75 2 0.55 2 14.7 0 30.0 0 41.9 0 8.25 0 21.1 0 0 0 0 8.80 0 17.1 2 17.2 2 16.9 2 15.2 2 0 0 17.3 2 17.5 2 * * * - - - * * * - - - * * - - TPYJ "C 600 600 600 600 600 800 800 800 800 800 1400 1400 1400 1400 600 600 600 600 5 50 800 800 800 800 700 700 800 800 Tat/ "C 1600 1600 1600 1600 1800 1800 1800 1800 1800 1800 2400 2400 2400 2400 1600 1600 1600 1600 1800 2200 2200 2200 2200 1600 1600 1900 1900 md Pg 0.4 1 0.43 0.45 0.48 0.52 0.44 0.45 0.47 0.64 0.57 13.5 13.5 15.3 10.1 22.8 28.1 30.0 31.3 11.1 14.0 14.1 13.9 14.5 47.1 43.0 17.2 16.6 *Characteristic mass could not be calculated because of significant losses of the analyte during the pyrolysis step.88 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL.8 100 I 80 C 4 60 n s 40 > .- c - 2 20 n " Cd co Pb Pb + modifier Fig. 7 Absorbance signals of the elements relative to that in IBMK depending on the chlorine content in the solvent and the presence of modifier; atomizer W-impregnated GT chemical modifier leading to quantitative retention of the analytes. The tungsten impregnation does not allow deep penetration of the organic solvents into the graphite leading to their more complete removal from the furnace at relatively low charring temperatures.The signals recorded for IBMK C2H4C12 and CC14 had almost the same charac- teristics of height area shape and appearance time (Fig. 8). Hence the tungsten-impregnated tubes have a levelling effect thus facilitating calibration by analyses of chlorine- containing organic solvents. The characteristic masses presented in Table 2 confirm the conclusions drawn above. Conclusion Tungsten-impregnated tubes may be preferred for atomiza- tion in ETAAS analyses of chlorine-containing organic solvents. These tubes lead to reduced losses to lower non- specific light absorption and to levelling of the absorbance signals for the various solvents. An additional stabilizing effect can be achieved by mixing the solvents with organic phase-soluble palladium chemical modifier in the form of the ion association complex PdC14( MTOA)2. 0 3.0 Time/s Fig. 8 Absorbance signals for Cd as Cd-APDC in (a) IBMK (b) C2H,Cl2 and (c) CCI,; atomizer W-impregnated GT References Karwoska R. Bulska E. and Hulanicki A. Talanta 1980 27 397. Volland G. Kolbin G. Tschopel P. and Tolg G. Fresenius' Z. Anal. Chem. 1977 284 1. Volynsky A. Spivakov B. and Zolotov Yu. Talanta 1984 31 449. Aneva Z. and Iancheva M. Anal. Chim. Acta 1985,167,37 1. Epstein M. S. At. Spectrosc. 1983 4 62. Tserovsky E. and Arpadjan S. J. Anal. At. Specfrom. 1991 6 487. Arpadjan S. Karadjova I. Tserovsky E. and Aneva Z. J. Anal. At. Spectrom. 1990 5 195. Paper 2/02971E Received June 5 1992 Accepted September 7 1992

ISSN:0267-9477    

DOI:10.1039/JA9930800085

出版商:RSC    

年代:1993

数据来源: RSC

摘要:

JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 89 Determination of Impurities in Germanium Tetrachloride Germanium Dioxide and High-purity Germanium by Zeeman-effect Electrothermal Atomic Absorption Spectrometry E. Sentimenti and G. Mazzetto Temav SPA Centro Ricerche Venezia Via delle lndustrie 39 30175 Venezia Port0 Marghera Italy E. Milella* CNRSM Centro Nazionale Ricerca e Sviluppo Materiali Via G. Marconi 147 72023 Mesagne Brindisi Italy A procedure is reported for the determination of intermediate and final products obtained during the multi-stage process of germanium purification. Zeeman-effect electrothermal atomic absorption spectrometry was used and the optimum operating conditions were found to be the same for germanium tetrachloride germanium dioxide and elemental germanium.The matrix was easily removed by evaporation e.g. as germanium chloride without loss of most of the impurities. Results are presented for 18 elements commonly present at trace levels. The detection limits are as low as 1 x 1014-1 x 10l6 atoms ~ m - ~ . Keywords Germanium tetrachloride; germanium dioxide; germanium; Zeeman-effect electrothermal atomic absorption spectrometry; impurities Germanium does not occur in the free state in nature but is found in low concentrations in some metallic ores such as argyrodite (Ag2S and GeS,) germanite (CuS FeS and GeS,) and blende (ZnS with 1% of GeS2). Germanium is fre- quently employed in thermal imaging lenses and windows in infrared systems because of its optical properties i.e. high refractive index which varies slowly with respect to the wavelength low absorption in the infrared range and low thermal expansion coefficient.In addition the small amount of energy (about 2.9 eV) necessary for the pro- duction of an electron pair and the low pray absorption coefficient make its use advantageous over other materials as a detector for ionizing radiation^.'-^ Single-crystal germanium employed in these applications must show a high crystal perfection lifetime characteristics of charge carriers and a content of electrically active impurities lower than 1 x loLo atoms ~ m - ~ . The flow chart of a standard procedure4 for the industrial production of single-crystal germanium is shown in Fig. 1. The processing of germanium is difficult with a long series of different operations and it is necessary to monitor and determine the most common impuritie~~-~ in each phase.Techniques such as gas chromatography-mass spectro- metrya and spark-source mass spectrometry9 have been applied to the characterization of germanium tetrachloride atomic emission spectrometryI0 to germanium dioxide and photoelectron spectroscopy,' neutron activation analy- sis,I2J3 spark-source mass spe~trometry,~~ atomic emission ~pectrometry~~ and atomic absorption ~pectrometry'~J~ to high-purity germanium. In this paper a procedure is described for the deter- mination of trace impurities in germanium tetrachloride germanium dioxide and elemental germanium via Zeeman- effect electrothermal atomic absorption spectrometry (Zee- man ETAAS) without any prior treatment of the sample or preconcentration or separation of the analytes of interest.Optimum operating conditions were investigated and the results show that the conditions are similar for all three species. This allows the rapid and accurate analysis of materials obtained by refining germanium with a well established and relatively inexpensive technique. *To whom correspondence should be addressed. I I Metallic ores or minerals Ge concentrate c ? GeCI Chlorination Ge polycrystal Ge single crystal Hydrolysis Reduction zone refining Horizontal-vertical monocrystallization casting Fig. 1 Germanium purification scheme Experimental Apparatus A Perkin-Elmer Model 5000 atomic absorption spectro- meter equipped with a Model 056 strip-chart recorder a Model HGA-500 thermal programmer pyrolytic graphite coated graphite tubes and a L'vov platform was used throughout.Zeeman-effect background correction was ap- plied. High-purity (~99.999%) argon was used as the purge gas. Reagents De-ionized water obtained with a Milli-Q water purifier (Millipore) was used throughout. The reagents used in- cluded HC1 (Ultrex 2 Baker) HN03 (Ultrex 2 Baker) HC104 (Carlo Erba) and H2S04 (Carlo Erba). Working standard solutions were prepared daily from 1 mg ml-1 stock standard solutions (Carlo Erba) of each element.90 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 Table 1 Blank levels of reagents Blank level/ Element pg g-' A1 As Bi Cd c o Cr c u Ga In 1.8 0.08 0.07 (0.02 0.09 0.01 0.03 0.2 0.09 Element Li Mn Ni Pb Sb Se Si Sn Te Blank level/ 0.01 0.01 (0.01 0.12 0.3 0.02 1.2 0.06 0.05 Crm g-' Germanium Tetrachloride Processing A 25 ml volume of GeC1 is heated gently to dryness in a platinum evaporating dish then 10 ml of 9 moll-' HCl are added and the procedure is repeated.Nitric acid (5 ml) is added and the solution is transferred into a 25 ml calibrated flask and diluted to volume with water. Determination of arsenic In order to avoid the loss of arsenic e.g. as volatile AsC13 oxidation is necessary. A 10 ml volume of GeCl and 10 ml of HN03 are mixed and heated gently to dryness then 10 ml of HCl are added and the same procedure is repeated. A 2 ml volume of HN03 is added and the solution is transferred into a 10 ml calibrated flask and diluted to volume with water. At present it is very difficult to determine antimony (see under Results and Discussion).All samples standards and blank solutions were sub- jected to the same procedure. Germanium and Germanium Dioxide Processing A 2 g sample of Ge is dissolved in 50 ml of HN0,-HCl (1 + 3) or 2 g of GeO in 50 ml of 9 moll-' HCl and 10 ml of HN03 in a 100 ml poly(tetrafluoroethy1ene) (PTFE) beaker (pre-cleaned with the same acids overnight and then rinsed with water). The solution is evaporated to dryness then 10 ml of HCl (1 + 1) are added and the same procedure is repeated. A 5ml volume of HN03 is added and the solution is transferred into a 50 ml calibrated flask and diluted to volume with water. The same procedure is used for a blank and for a standard solution with known amounts of each element.If a tetragonal structure is present in the GeO sample chemical etching must be applied by dissolving 0.5 g of sample in 20 ml of 9 moll-' HCl in a PTFE-lined bomb for 6 h at 200 "C. Determination of antimony A 2 g amount of Ge is dissolved in 2 ml of HC104 and 50 ml of HN03-HCl ( l + 3 ) . The solution is evaporated until white vapour is evolved then 15 ml of HCl are added and the same procedure is repeated at least twice. Finally 2 ml of H2S04 are added the solution is diluted to 50 ml with water and the analysis can be started. Operating Conditions The work was performed on a clean bench. Under the experimental conditions adopted the main contamination source is due to the reagents (Table 1). Table 2 Instrumental settings used in Zeeman ETAAS determinations Parameter Dry Char 1 Char 2 Atomize Purge Cool 1 Cool 2 * * * Temperature/"C 150 - - - 2750 500 20 Ramp/s 20 20 3 0 1 3 2 Holds 20 20 5 5 3 5 10 Gas flow rate/ml min-' 300 3000 ot ot 300 300 300 *Element-specific temperatures are given in Table 3.t50 ml mine' for aluminium. _____~ Table 3 Element-specific parameters in ETAAS determinations Element A1 As Bi Cd c o Cr c u Ga In Li Mn Ni Pb Sb Se Si Sn Tet Wavelength/ nm 309.3 193.7 223.1 228.8 242.5 357.9 324.8 287.4 303.9 670.8 279.5 232.0 283.3 2 17.6 196.0 25 1.6 286.3 214.3 Slit/ nm 0.7 0.7 0.2 0.7 0.2 0.7 0.7 0.7 0.7 0.4 0.2 0.2 0.7 0.2 2.0 0.2 0.7 0.7 Sample volume/pI 5 20 20 5 10 10 10 20 20 5 10 10 10 5 30 5 30 10 Location STPFC STPF STPF STPF Wall Wall STPF STPF STPF Wall STPF Wall STPF STPF STPF STPF STPF STPF Char I/ "C 1500 600 500 600 1400 1650 1000 800 800 800 1400 1400 5 50 800 300 1400 800 900 Char 2/ "C 1500 600 500 600 1400 1650 1000 800 800 800 1400 1400 550 800 300 1400 800 900 Atomize/ "C 2500 2600 2100 2000 2500 2500 2500 2650 1800 2500 2200 2500 2000 2300 2600 2650 2100 2200 *STPF= stabilized temperature platform furnace.?For Te nickel nitrate was used as a chemical modifier.JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 91 Table 4 Determination of impurities in elemental Ge by ETAAS and GDMS Concentrationhg g-' Element A1 As Bi Cd c o Cr c u Ga In Li Mn Ni Pb Sb Se Si Sn Te ETAAS 140 t 76 t 4 0 t 1 5 <35 21 <20 <74 98 t 1 2 t 4 (90 t 4 0 t 1 2 0 t 1 3 t 1 8 5 t 4 0 (90 GDMS 3 90 1 - - 19 3 3 80 0.7 0.4 3 1 7 8 21 10 3 Table 5 Detection limits and results of chemical analysis for impurities in GeCl Detection limit/ Concentration/ Element ng ml-1 ng ml-I A1 As Bi Cd c o Cr c u Ga In Li Mn Ni Pb Se Si Sn Te 3.0 1.4 1.6 0.6 1.4 0.5 0.8 3.0 2.3 0.5 0.2 3.6 1.6 0.5 7.4 1.6 3.6 58 80 5 10 3 2 7 <3 t 2 2 1 5 9 65 140 30 t 4 After obtaining test ashing and atomization curves the optimum operating parameters given in Tables 2 and 3 were established and applied for each type of material.The integration time for analysis was generally limited to 5 s and the calculations were based on integrated absorbance (peak area). Five measurements for each element were made. The standard deviation of the blank S is about 0.001 s. The standard additions procedure was used for each determination. The amounts added were in the range 10-100 PI taken from diluted 1 mg ml-l standard solu- tions.The standard solutions of Cu Pb Bi and Ni were in the form of nitrates those of Al Ga In Sn Se Te Li Cd Mn and Co as chlorides As as sulfate and Cr Si and Sb as aqueous solutions of their salts. Only for the determination of Te was nickel nitrate necessary as a chemical modifier in order to obtain higher sensitivity. Results and Discussion After sample dissolution Ge was removed as the chloride" without loss of most of the metal impurities hence the results do not show a matrix influence. During the vaporiza- tion of the samples a check of possible losses was performed by adding known amounts of each analyte Table 6 Detection limits in GeO and Ge metal Detection limit/atoms Concentration/ Element ng g-' Ge Ge02 A1 As Bi Cd c o Cr c u Ga In Li Mn Ni Pb Sb Se Si Sn Te 76 34 40 15 35 13 20 74 57 12 4 90 40 120 13 185 40 90 9.60 x 1015 1 .3 0 ~ 1015 6.20 x 1014 4.32 x 1014 1.92 x 1015 8 . 1 0 ~ 1014 1 . 0 2 ~ 1015 3 . 2 4 ~ 1015 1.69 x 1015 4.63 x 1015 2.36 x 1014 4.94 x 1015 6.26 x 1014 3 . 1 9 ~ 1015 4 . 1 0 ~ 1014 1 . 0 9 ~ 1015 2.28 x 1015 2.20 x 10'6 7.6 1 x 1015 1 . 0 3 ~ 1015 4.92 x 1 0 1 4 3.43 x 1014 1.52 x 1015 6.64 x 1014 8.09 x 1014 2.57 x 1015 1 . 3 4 ~ 1015 3.67 x 1015 1 . 8 7 ~ 1014 3.92 x 1015 4.97 x 1014 2.53 x 1015 3.25 x 1014 8.64 x 1014 1.81 x 1015 1 . 7 4 ~ 10l6 Table 7 Results of analysis of Johnson Matthey batch No. A75054 Ge02 Concentration/ Concentration/ Element ng g-l Element ng g-' A1 As Bi Cd c o Cr c u Ga In < 76 790 (40 90 t 3 5 (13 85 < 74 280 Li Mn Ni Pb Sb Se Si Sn Te < 12 <4 < 90 89 480 t 1 3 3000 < 40 < 90 before the treatment and verifying the concentrations afterwards.In Ge and GeO Sb was determined in an oxidizing medium of HClO,. It was not possible to test this condition in GeC1,. In fact it was very difficult to test possible losses of Sb in GeC1 and Ge0 precipitates because of the hydrolysis caused by the addition of an aqueous standard solution of Sb. No certified standard samples are available. Tests were made on a Ge02 sample grade A batch No. A75054 provided by Johnson Matthey in order to verify the procedure adopted for GeO,. For Ge metal the accuracy of the analysis was compared with the results given by glow discharge mass spectrometry (GDMS) (Table 4).Tables 5 and 6 give the detection limits (CL)18 calculated for the analysis of GeCl Ge0 and elemental Ge using the expression CL=4.604S,,/rn where 4.604 is the value of Student's t for four degrees of freedom and at the 99.5% confidence level S is the standard deviation of the blank and rn is the slope of the calibration graph. It should be stressed that the detection limits refer to 25 ml of GeCl 2 g of GeO and 2 g of Ge metal and that the sensitivity of the method was mainly determined by the purity and amounts of the reagents used for the sample dissolution and matrix elimination. It was observed that S did not change much; a value of about 0.00 1 s (integrated absorbance) was usually found. In addition the slope of the calibration graph for each element was the same for GeCl GeO and elemental Ge.For elements such as A1 and Si many difficulties in eliminating incidental contamination arise; this is also due to the presence of these elements in the materials com-92 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 monly used in the laboratory. Better results could be expected by avoiding contamination from the surroundings as much as possible. Typical results of analyses of elemental Ge GeCl and GeO are given in Tables 4 5 and 7 respectively. The C values obtained show that Zeeman-effect ETAAS gives excellent results for the analysis of both GeCl and GeO,. The sensitivity of the technique does not permit the detection of impurities at the concentration levels required for high-purity Ge single crystals.Nevertheless the method is useful in order to determine higher amounts of impurities such as dopants added to obtain n-type Ge crystals (dopant Sb) or p-type Ge crystals (dopant Ga or In) in the concentration range 1 x 10l6-1 x 1019 atoms ~ r n - ~ . The procedure reported here could provide useful infor- mation for inspecting and monitoring the over-all pro- duction cycle of Ge in a simple manner by a single technique. The authors thank Dr. L. Meregalli for collaboration and acknowledge financial support from the Fondo EN1 per la Ricerca of the Ente Nazionale Idrocarburi (ENI) Group. References Baertsch R. D. and Hall R. N. IEEE Trans. Nucl. Sci. 1971 17 235. Sakai E. McMath T. A. and Fowler I. L. IEEE Trans.Nucl. Sci. 1971 18 228. Drummond W. E. IEEE Trans. Nucl. Sci. 1971 18 91. 4 Guislain H. De Laet L. and Coursier A. Metallurgie 1982 22 125. 5 Haller E. E. Hansen W. L. Hubbard G. S. and Goulding F. S. IEEE Trans. Nucl. Sci. 1976 23 81. 6 Meszaros I. and Molnar I. Magy. Alum. 1982 19 46. 7 Devyatykh G. G. Andreev B. A. Balobonov V. V. Gawa V. Gusev A. V. Ikonnikov B. V. Maksimov G. A. Nechuneev Yu. A. and Pyatov M. Yu. Izv. Akad. Nauk SSSR Neorg. Mazer. 1986 22 1957. 8 Krylov V. A. Krasotskii S. G. Sokolova G. V. Stepanov A. I. and Suchinskaya V. E. Vysokochist. Veshchestva 1989 (6) 95. 9 Aggarval S. K. Adams F. and Adriasenssens E. Fresenius’ 2. Anal. Chem. 1984 318 402. 10 Pimenov V. G. Timonin D. A. and Shishov V. N. Zh. Anal. Khim. 1986 41 1173. 1 1 Bykova E. M. Iglytsin M. I. Kurkova E. A. Levinzov D. I. Sidorov V. I. and Shershel V. A. Zuvod. Lab. 1976,42,415. 12 Razumova G. N. Shuba I. D. and Vasiliev I. Radiokhi- miya 1970 12 133. 13 Ginzburg M. I. Marunina N. I. and Milenin E. S. Tsvetn. Metall. 1977 (l) 56. 14 Murugaiyan P. Pure Appl. Chem. 1982 54 835. 15 Pimenov V. G. Pronchatov A. N. Maksimov G. A. Shishov V. N. Shcheplyagin E. M. and Krasnova S. G. Zh. Anal. Khim. 1984 39 1636. 16 Pimenov V. G. and Timovin D. A. Vysokochist. Vesh- chestvu 1988 (l) 149. 17 Luke C. L. and Campbell M. E. Anal. Chem. 1953,25 1589. 18 Liteanu C. and Rica I. Statistical Theory and Methodology of Trace Analysis Ellis Horwood Chichester 1 980. Paper 2/03234A Received June 19 1992 Accepted August 21 1992

ISSN:0267-9477    

DOI:10.1039/JA9930800089

出版商:RSC    

年代:1993

数据来源: RSC