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The AnalystThe Analytical Journal of The Royal Society of ChemistryAdvisory Board"Chairman: J. D. R. Thomas (Cardiff, UK)D. Betteridge (Sunbury-on-Thames,E. Bishop (Exeter, UK)W. L. Budde (USA)*C. Burgess (Ware, UK)D. T. Burns (Belfast, UK)*M. S. Cresser (Aberdeen, UK)L. de Galan (The Netherlands)D. Dyrssen (Sweden)*A. G. Fogg (Loughborough, UK)*C. W. Fuller (Nottingham, UK)V. D. Goldberg (London, UK)J. Hoste (Belgium)A. Hulanicki (Poland)*C. J. Jackson (London, UK)W. S. Lyon (USA)*P. M. Maitlis (Sheffield, UK)H. V. Malmstadt (USA)E. J. Newman (Poole, UK)UK) "J. M. Ottaway (Glasgow, UK)T. B. Pierce (Hamell, UK)E. Pungor (Hungary)J. R8iiEka (Denmark)P. H. Scholes (Middlesbrough, UK)D. Simpson (Thorpe-le-Soken, UK)R. M.Smith (Loughborough, UK)W. I. Stephen (Birmingham, UK)M. Stoeppler (Federal Republic of Germany)K. C. Thompson (Sheffield, UK)*A. M. Ure (Aberdeen, UK)A. Walsh, K.B. (Australia)G. Werner (German Democratic Republic)T. S. West (Aberdeen, UK)*P. C. Weston (London, UK)J. D. Winefordner (USA)P. Zuman (USA)"Members of the Board serving on the Analytical Editorial BoardRegional Advisory EditorsFor adviceand help to authors outside the UKDr. J. Aggett, Department of Chemistry, University of Auckland, Private Bag, Auckland, NEWDot. Dr. sc. K. Dittrich, Analytisches Zentrum, Sektion Chemie, Karl-Marx-Universitat, Talstr.Professor L. Gierst, Universite Libre de Bruxelles, Faculte des Sciences, Avenue F.-D.Professor H. M. N. H. Irving, Department of Analytical Science, University of Cape Town,Dr.0. Osibanjo, Department of Chemistry, University of Ibadan, Ibadan, NIGERIA.Dr. G. Rossi, Chemistry Division, Spectroscopy Sector, CEC Joint Research Centre,Dr. 1. RubeSka, Geological Survey of Czechoslovakia, Malostranske 19, 118 21 Prague 1,Professor K. Saito, Coordination Chemistry Laboratories, Institute for Molecular Science,Professor M. Thompson, Department of Chemistry, University of Toronto, 80 St. GeorgeProfessor P. C. 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ISSN:0003-2654    

DOI:10.1039/AN98611FX037

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

ANALAO 111(10) 1113-1224 (1986) October 1986111311391143115311591163116711711175117911831189119712031207121 11215121912211223TheThe Analytical Journal ofAnalystThe Royal Society of ChemistryCONTENTSDirectly Coupled Chromatography - Atomic Spectroscopy. Part 1. Directly Coupled Gas Chromatography - AtomicUse of a Matrix Modifier and L'vov Platform in the Determination of Copper in Pooled Human Saliva by ElectrothermalSelective Reduction of Arsenic Species by Continuous Hydride Generation. Part 1. Reaction Media-Robert K.Selective Reduction of Arsenic Species by Continuous Hydride Generation. Part II. Validation of Methods forN-Oxalylamine(salicylaldehyde hydrazone) as an Analytical Fluorimetric Reagent for the Determination of NanogramSpectrophotometric Determination of Vanadium(V) with Desferrioxamine B-Svjetlana Luterotti, Vladmir GrdinicExtractive Spectrophotometric Determination of Chromium(lll) in Steels Using 4-(2-Pyridylazo)resorcinol andXylometazoline HydrochlorideY.Anjaneyulu, M. R. P. Reddy, C. S. KavipurapuSpectrophotometric Determination of Molybdenum After Separation by the Adsorption of its Trifluoroethylxanthateon Naphthalene-Md. Farid Hussain, Mohan Katyal, Bal Krishan Puri, Masatada SatakeDetermination of Trace Amounts of Formaldehyde by Ion-exchange Resin Thin-layer Spectrophotometry-KiichiMatsuhisa, Kunio OhzekiSpectrophotometric Determination of Benzyl Penicillin in Pharmaceutical Preparations Using Copper(l1) Acetate as aComplexing Agent-Utpal SahaDevelopment of a Multi-sensor System Using Coated Piezoelectric Crystal Detectors-Sheila M.Fraser, Tony E.Edmonds, Thomas S. WestComplexation Equilibria of Some Sulphoazoxines. Part VI. Protonation Constants of 7-(4-Carboxyphenylazo)-8-hydroxyquinoline-5-sulphonic Acid by Computer-assisted Multi-component Spectra Analysis-Milan Meloun,Jaromira Chylkova, Michal BartoSSpectroscopy. A Review-Les Ebdon, Steve Hill, Robert W. WardAtomic Absorption Spectrometry-lnes Game, Leonard0 Balabanoff, Rita Valdebenito, Luz VivaldiAnderson, Michael Thompson, Elisabeth CulbardApplication t o Natural Waters-Robert K. Anderson, Michael Thompson, Elisabeth CulbardAmounts of Aluminium-Fernando de Pablos, Jose Luis Gomez Ariza, Francisco PinoExperimental Artifacts and Determination of Accurate Py Values-Kenneth W.Street, Jr., William E. Acree, Jr.Large-scale Separation of Lipids From Organochlorine Pesticides and Polychlorinated Biphenyls Using a PolymericHigh-performance Liquid Chromatographic Column-Mark P. Seymour, Terry M. Jefferies, Lidia J. NotarianniPolarographic Determination of Conjugated Dienes in Hydrogenation Products of Pyrolysed Gasoline-Jaroslav Polak,Leo5 JanaEek, Jiii VolkeDirect Potentiometry of Residual Water in Sulpholane Using the Proton lsoconcentration TechniqueMohamedRashid Omar KarimAutomated Procedure for pH Measurement Using A Flow Cell-Mark R. Howson, William A. House, Alan D.PethybridgeSHORT PAPERSFlow Injection Determination of Nitrite by Amperometric Detection at a Modified ElectrodeJames A.Cox, Krishnaji R.Kul karniDetermination of Ethylene Dibromide in Aquatic Environments-Arthur J. Libbey, Jr.BOOK REVIEWSTypeset and printed by Heffers Printers Ltd, Cambridge, EnglanCLASSIFIED ADVERTISEMENTSRestrictions on the transfer of currency from some overseas countries to the United Kingdom are sometimes moresevere. Careful enquiries should be made about the detailed arrangements for returning money to Britain after it 1 has been earned and banked in another country.CLASSIFIEDADVERTISINGDISPLAY ANDSEM I-D I SPLAY€1 0.00per singlecol. cm.column width83mmSend youradvertisements:-ClassifiedAdvertisements,BurlingtonHousePiccadilly,LondonWIV OBN.Tel: 01 437 8656arwell, is thelargest researchestablishment of the UnitedKingdom Atomic EnergyAuthority.It derives overhalf its income fromcontract researchundertaken on behalf ofindustry and governmentdepartments.For further details and anapplication form please write toMiss C. E. 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This is anapproved Dosimetry Service under the lonising RadiationsRegulations responsible for the determination of a wide rangeof radionuclides in urine and other samples as part of thesurveillance of workers a t a number of nuclear establishments.It is also responsible for the analysis of a variety ofenvironmental samples from all regions of the UK as part of aprogramme to study the dispersal of natural and man-maderadioactivity.The successful candidate will be responsible forthe development and application of appropriate analyticalmethods and for aspects of quality control.Applicants should have experience in a radiometric laboratory;experience in the interpretation and application of radiometricdata in the environmental field will be an advantage.Set in pleasant countryside midway between Oxford andNewbury, Harwell offers an excellent recruitment packageincluding competitive salaries, generous leave arrangementsand contributory pension scheme and, where appropriate,relocation expenses.D34\RLWAEMIUNITED KINGDOM ATOMIC ENERGY AUTHORITYIt can be assumed that all vacancies advertised in The Analyst for employment in the United Kingdom are open tomale and female applicants equally and conform to relevant UK laws and the British Code of Advertising Practiceunless accompanied by a printed statement explaining why an individual advertisement is excepted from suchlaws and/or Code. While the Publishers of The Analyst take all reasonable care to ensure that advertisementstherein conform to UK laws and the British Code of Advertising Practice they are not responsible for any claimsmade by individual advertisers in published advertisements. Where an individual advertisement is thought to be inbreach of relevant laws or codes of practice readers are invited to communicate with the Advertisement Manager

ISSN:0003-2654    

DOI:10.1039/AN98611BX039

出版商:RSC    

年代:1986

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN98611BP041

出版商:RSC    

年代:1986

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN98611BP045

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

ANALYST OCTOBER 1986 VOL. 111 1113 Directly Coupled Chromatography - Atomic Spectroscopy Part 1 Directly Coupled Gas Chromatography = Atomic Spectroscopy A Review Les Ebdon Steve Hill and Robert W. Ward* Department of Environmental Sciences Plymouth Polytechnic Drake Circus Plymouth PL4 8AA UK Summary of Contents 1. introduction 2. Coupled gas chromatography - microwave induced plasma 3. Coupled gas chromatography - inductively coupled plasma 4. Coupled gas chromatography - direct current plasma 5. Coupled gas chromatography - atomic absorption spectrometry 6. Coupled gas chromatography - atomic fluorescence spectrometry 7. Conclusion 8. References Keywords Review; coupled techniques; gas chromatography; atomic spectroscopy; trace metal speciation 1. Introduction The various techniques of analytical atomic spectrometry1 have been widely used in recent years to obtain total element information particularly on trace metal composition.Where-as these techniques are both selective and sensitive offering detection limits in the ng ml-1 range they yield by themselves only information on total concentrations. Currently there is a much increased demand to quantitatively determine the form of trace metals in a wide variety of samples; this is often termed trace metal speciation. Such information may be of vital importance to the toxicologist to indicate likely sources and transport mechanisms of elements in the environment to the clinician and to indicate the history of a sample. Several approaches to trace metal speciation have been suggested,2-4 including electroanalytical techniques,5,6 but one of the more promising approaches is to couple the separatory power of chromatography with the selectivity and sensitivity of atomic spectroscopy.This area until now has only been partially reviewed’-12 and the purpose of this review is to critically appraise coupled gas chromatography (GC) - atomic spectro-scopic approaches. Part 2 will consider coupled liquid chro-matographic procedures. Atomic spectroscopy offer the possibility of selectively detecting a wide range of metals and non-metals. The use of detectors responsive only to selected elements in a multi-component mixture drastically reduces the constraints placed on the chromatography step as only those components in the mixture which contain the element of interest will be detected.Certain requirements for element-specific detectors may be identified. Atomic absorption spectrometry (AAS) is inher-ently the most selective of the atomic spectroscopic techniques due to the “lock and key” mechanism.1 The various plasma emission sources microwave induced plasma (MIP) direct current plasma (DCP) and inductively coupled plasma (ICP), owing to their very high excitation temperatures produce a wealth of emission lines. Thus although not possessing the inherent selectivity of AAS the use of a suitable high-resolution monochromator reduces the possibility of spectral * Present address Plasma-Therm Inc. Route 73 Kresson Industrial Park Kresson NJ 08053 USA. interference and enables inter-element selectivity.This wealth of emission lines produced also permits multi-element detec-tion which normal line source AAS does not offer. Atomic fluorescence spectrometry (AFS) using line source excita-tion in theory offers similar selectivity to AAS coupled with the multi-element capacity of AES but in practice is limited by the availability of suitable line sources. The second prerequisite is that of sensitive detection for a wide range of elements. The most popular methods of generating atoms for AAS are in flames and by electrother-mally heated furnaces. The former usually gives poorer detectability owing to the shorter atomic residence times in the flame and problems of sample introduction. Relatively short useful linear ranges of 1-2 orders of magnitude are typical of absorption techniques.The plasma emission techniques use high temperature excitation sources thus enabling low levels of detection metals and the favourable source geometry often provides long linear working ranges. In atomic fluorescence, provided a suitably intense line source is available low level detection and long linear ranges are available. Long linear working ranges are frequently cited as desirable characteris-tics of chromatographic detectors but the levels of analyte in real samples are often close to the detection limit and sensitivity may rightly be seen as the major problem. Flames or plasmas whether chemical in FAAS and FAFS, or electrical in the ICP DCP and MIP consist of flowing gas streams and are therefore well suited to accept a gaseous analyte.Their continuous mode of operation is also advan-tageous because although the analyte peak is transient it is introduced into a flowing gas stream. Electrothermal atomisers are typically not continuous in their mode of operation and are designed for use with discrete condensed phase samples and thus require modifications before they can accept a flowing gas stream. The relative merits of the various couplings are perhaps best considered together with a review of their various applica-tions. As there are well over 100 references reported much of the information in this review is classified according to the type of detection system used and is presented in tabular form. This review is confined to the area of directly coupled gas chromatography - analytical atomic spectrometry and hence mass spectrometric detection has not been included nor ha 1114 ANALYST OCTOBER 1986 VOL.111 the related methodology of trapping compounds on chromato-graphic material for later thermal release and atomic spectro-scopic detection of the evolved gases.ls-16 2. Coupled Gas Chromatography - Microwave Induced Plasma The microwave induced plasma (MIP) has two basic charac-teristics that can be utilised when coupling to a GC instru-ment. The low gas temperature of the MIP allows small amounts of sample compatible with those of GC solutes to be introduced without extinguishing the plasma. In addition, sample introduction is easily facilitated as the carrier and plasma gases are the same. These advantages have made coupled GC - MIP a popular technique and many applications have been reported (Table 1).The first use of the MIP as an element-selective detector for organic compounds was reported by McCormack et al. in 1965.17 The effluent from a GC was connected directly to the silica tube containing the plasma discharge. Both the more sensitive tapered cavity and the coaxial cavity intended for larger samples were used. Two plasma types were utilised, low-pressure helium and atmospheric argon the latter being favoured owing to the complexity of the associated vacuum systems required when using low-pressure helium plasmas. Bache and Lisk later used an atmospheric argon plasma to determine pesticides in various samples by the selective detection of phosphorus18 and iodine.l9 Using a low-pressure argon plasma the same authors later lowered the detection limit by a further order of magnitude.20 The more energetic reduced pressure helium plasma has been used for the determination of halogens phosphorus and sulphur using atomic lines.21-23 Moye22 found that if a tapered rectangular cavity with a mixed argon - helium carrier was used a lower background emission for chlorine iodine and phosphorus detection in pesticide residues could be obtained. Dagnall et al.24925 used a quarter-wave radial cavity with low-pressure argon or helium plasmas for the determination of sulphur in various compounds. It was found that the most sensitive and specific emission wavelength was not the same for all the compounds examined.In addition thioglycolic acid was found to be very difficult to fragment,24 although a platinum wire in the base of the detector was found to catalyse the fragmentation process.25 Bache and Lisk29 were the first to use the low-pressure helium plasma for the detection of organomercury compounds after extracting the compounds from salmon using the established procedures of We~tOO.27~28 A potential use of the MIP detector for obtaining inter-element ratios has been reported by Dagnall et al. ,31 using two monochromators one set at a carbon line and the other set to monitor a he teroat om. 0 t her workers37,54,59791-93,95 have also used the MIP detector to determine inter-element ratios in an attempt to establish empirical formulae. The commercially available MPD 850 (Applied Chromatography Systems) low-pressure helium plasma system has also been used in this r01e.53,5~791,92 However Dingjan and De Jong76 found that it was necessary to use a reference compound if accurate ratio formulae were to be obtained.If unequivocal inter-element ratios could be determined independent of the sample type, GC - MIP systems would be capable of much identification work currently performed on more expensive GC - mass spectrometers. An oscillating slit mechanism for the deter-mination of hydrogen isotope ratios has been used by Schwarz et al. ,58 but the poor signal to noise ratios obtained gave poor precisions. More recent publications85791-94 have suggested that the use of capillary gas chromatographic columns, computerised data acquisition and peak-area measurements may improve the precision and accuracy attained.The passage of an organic compound through a plasma may result in the formation of carbon deposits on the walls of the quartz capillary absorbing part of the radiation and increasing the background emission.17 This can be prevented by either initiating the plasma after the solvent has passed through the detector,l8 or by adding traces of a scavenging gas. This gas may be either nitrogen,43 0xygen,3~-39 hydrogen39 or air17 added to the plasma gas; however as a result of this the spectral background is considerably increased. The MIP has proved to be popular as a detector for various metal chelates732J6J8>46 and also as a detector for various Hydride-forming elernents.45.52fj3@ Talmi and Bostick45 have determined alkylarsenical acid compounds in pesticides by generating their hydrides prior to GC - MIP analysis.The separation and sequential detection of As Ge Se Sn and Sb hydrides has also been demonstrated using a mixed argon -helium pla~ma.55~63~64. Little difference in detection levels have been found using various forms of microwave plasma by Mulligan et al.,(jl although the Beenakker TMolo cavity was found to be the easiest to operate. This method was used to determine the above hydride-forming elements in whole blood and enriched flour63 and in NBS orchard leaves.63.64 Coupled GC - MIP has also been used for the detection of various metals in volatile organometallic compounds. Lead has been determined as the tetraalkyl species15356 in petrol80JQ and in the atmosphere,74 and as trialkyllead chloride in water samples.77 Mercury as the diphenyl,56 dimethyl and diethyl derivatives74 has been detected using the TMOl0 cavity.Quimby et al.56 used the same cavity to determine manganese as the methylcyclopentadienyltricarbonyl derivative in petrol and as a silicon-specific detector for tetravinylsilane. The coupling of capillary columns with the TMolo cavity has also been demonstrated with great success for metal-specific detection of volatile organometallics.66~77~80~9~~92 This cavity is increasingly being seen as the optimum for GC - MIP studies as it is capable of operating a He plasma at atmospheric pressure. In a study of the pyrolysis of carborane silicone p0lymers,~8 the group at Amherst found that doping the plasma gas with hydrogen inhibited oxide or silicate formation by promoting borohydride formation which increased the populations of atomic boron rather than the ionic states.Hanie et al.70 have also used capillary columns for the determination of halides in pesticides using a helium plasma and a Surfatron cavity.@ Recent developments of coupled GC - MIP systems have largely been based on the development of software for both system control and data handling. One such system described by Eckhoff et al.83 uses a polychromator - microcomputer system to monitor simultaneously four atomic emission wavelengths throughout an entire chromatographic run. The same system has also been used by Hass and Carus094 as an element-specific detector for the gas chromatography of halogenated compounds.Delaney and Warren85 have used a minicomputer to- modify the interface described by Estes et al. ,77 so that in addition to controlling the switching valves it also controls the monochromator wavelength setting and acquires the analytical data that the MPD and FID monitor. The above and other work in coupled GC - MIP systems are summarised in Table 1. 3. Coupled Gas Chromatography - Inductively Coupled Plasma The high capital cost of inductively coupled plasma (ICP) instrumentation together with the high running costs have resulted in its use mainly as a multi-element exictation source for routine analysis. Consequently use of the ICP as a detector for GC has been limited.However it does offer the advantage of withstanding organic solvents more readily than the MIP owing to the higher gas temperature and so may possibly be further utilised in this role in the future. To obtain a sufficient flow-rate to puncture the fire-ball and produce an annular plasma may mean augmenting the eluent flow from the GC column with an auxiliary Ar flow. This may reduce the sensitivity by dilution but failure to form an annular plasma will be more deleterious ANALYST OCTOBER 1986 VOL. 111 1115 Table 1. Coupled gas chromatography - microwave induced plasma optical emission spectrometry Elements and wavelength/ nm Reference c 17 388.3 F, 516.6 251.6 a , 278.8 Br, 298.5 Detector Tapered and co-axial cavities used the former more sensitive, the latter accepted larger samples.10 mm i.d. discharge tube at low pressure Chromatography Sample Comments Solutions of simple and heteroatom- the preferred carrier containing organic gas. At atmospheric compounds pressure Ar was used At low pressure He was as it gave a stable discharge. Dynamic range four orders of magnitude. Detection limits 2 x 10-16-2 x 10-7 s-l 206.2 s, 257.5 Atmospheric pressure Ar 2 ft glass U column Organophosphorus 1 mm i.d. quartz 5mmi.d.,5% SE30 insecticide residues discharge tube in a tapered cavity on 80-100 Chromosorb W. in pure form agricultural Ar = 20-115 ml min- l , T = 160-200 "C and food samples Diazinon Dimethoate, Ethion Parathion and Ronnel determined. Detection limit: 1.4-9.2 pg s-1 p, 253.565 18 Detection of Ionynil and metabolites.Recoveries from 66-108°/0 achieved. Detection limit: 4 x 10-"'gs-'of12 I, 206.2 I2 band 19 As in ref. 18 See ref. 18 Iodinated herbicide residues and metabolites in wheat oats and soil As in ref. 18 except reduced pressure Ar plasma See ref. 18 p, 253.565 20 Diazinon in grapes; see ref. 18 See ref. 18. Achieved increased sensitivity with low pressure discharge. Detection limit 6 x lo-13gs-* of P Detection limits: 9 x 10-12 6 x 10-"gs-1 Br, 478.55 c1, 479.45 I, 533.82 p, 253.57 s, 545.38 21 Reduced pressure helium plasma using tapered cavity. 5-10 mm Hg pressure 6 ft glass column 10% DC-200 on 80-100-mesh pesticides Gas-Chrom Q.Isothermal set at various T = 130-210°C Organic compounds and Ar - He (15 + 85) mixed plasma tapered cavity as longer lifetimes and less background emission obtained 4 ft x 4 in i.d. glass column 5% SE-30 on Gas-Chrom Q. Flow-rate = 27 ml min-l, T = 180"C, TI = 215 "C Pesticide residues of various P- C1- and I-containing compounds Detection limits: 0.07-1 1.5 ng p, 253.57 a , 221.00 I, 206.20 22 Monitored atomic S and C1 lines a , 479 * 45 s, 545.38 Reduced pressure helium plasma 6 ft x 4 in i.d. glass column 10% DC-200 on 100- 120-mesh Gas-Chrom Q Phenol-substituted insecticides in agricultural samples 23 24 Thioglycolic acid difficult to fragment. Detection limit 0.2 ng for CS2 at C=S band head t h radial line cavity Ar or He low-pressure (13-40 mbar) plasma 2.7 m x 6.5 mm i.d.Cu tubing packed with dinonyl phthalate. 1 .O pl injections S compounds CS2, thiophene, thioglycolic acid, DMSO and SO2 s, S 190.0 S 191.5 C=S 257.6 common to all compounds C2,516 See ref. 24 6 x 0.6 mm i.d. Cu tubing packed with either Porapack P or Q S compounds CS2, thiophene dimethyl sulphide and thioglycolic acid Used Pt wire in base of detector to catalyse fragmentation process. Detection limits low ng range S c, Monitored C=S band head at 257.6 and atomic C line at 247.9 2 1116 ANALYST OCTOBER 1986 VOL. 111 Table l-continued Detector Chromatography Sample Low-pressure (5-10 Torr) See ref.20 S - halogen- and P-He plasma. See ref. 20 containing pesticide residues in a wide range of food products Reduced pressure He plasma in a tapered cavity; cf. ref. 21 Atmospheric pressure Ar plasma, 20 cm x 2 mm i d . quartz tube surrounded by 2 h cavity See ref. 30 2 ft X 5/32 in i.d. glass column 60-80-mesh Chromosorb 101. He = 80 cm3 min - 1, T = lOO"C, 6 ft X '/32 in i.d. glass column 20%,0V-17 and OV-1 (1 + 1 m/m) on 80-100-mesh Gas-Chrom Q. T = 152"C, 30 and 70 cm x 6 mm i.d. packed with Porapak S TI = 140 "C. TI = 208 "C 0.7 m x Q in stainless steel Chromosorb 101 Ar plasma. Essentially 10 f t x in i.d. the same as in ref. 17 stainless-steel column 20% Carbowax 20M on Chromosorb P, 60-80 mesh. Ar = 48 cm3 min-1, T = 75 "C Low-pressure He plasma using MPD 850 system, O2 and N2 used as scavengers to prevent C build-up Methylmercury dicyan-diamide phenyl-mercury(I1) acetate, methylmercury dithizonate MeHgCl in salmon Range of C- 0- N- and halogen-containing compounds Range of C- S- and halogen-containing compounds Various organic compounds Comments Westoo extraction procedure27.28 for MeHgCl in salmon.Linear range: 0.1-100 ng for MeHgCl Several cavities examined 2 h preferred because it produced a long (ca. 8 cm) stable discharge with little local overheating. Detection limits: 10-20 pg s-' Use of two monochromators one set to atomic C line the other set to the hetero-atom line. By monitoring emission from both inter-element ratios were obtained.Detection limits: 0.04-4.5 ng s-1 Found selectivity for Hg over various organic compounds, always >lO3. Detection limit 0.3 ng Detection limits: 0.03-3.0 ng s-1 Element and wavelength/ nm Reference Br 26 478.55 c1, 479 * 45 I, 533.82 p , 253.57 s, 545.38 253.7 Hg 7 29 c, Monitored atomic C line at 247.9 c2 band head at 516.5 and band head at C2/CN 385-389 30 c 31 247.9 1, 206.2 s, 182.0 p, 253.5 (21, 259 band Br, 292 band Hg 32 253.7 c , 247.8 H, 486.1 D, 656.2 0, 777.2 N, 746.9 F, 685.6 c1, 479.4 Br, 470.5 I, 516.1 s, 545.4 3 ANALYST OCTOBER 1986 VOL. 111 1117 Table l-continued Detector Chromatography Sample Similar system to ref.30 2 columns both except t h Evenson 0.6 m x 4.8 mm i.d., cavity 70 W forward power 1. Universal B coated with Ar plasma ignited after 10% Apiezon L. elution of solvent 2.0.5% Apiezon Lon glass beads (0.2 mm diameter). Both conditioned for 36 h at 200 "C Acac and tfa chelates of Al Cr Cu Ga Fe, Sc and V f h Evenson cavity used reduced pressure (10 Torr). He plasma generated in a 6cm x 8mmi.d. quartz tube Ar plasma generated in a quartz capillary, 1.6 mm i d . X 25 cm, placed in a tapered rectangular type cavity Reduced pressure He plasma 0.1-1 YO. O2 or N2 added as scavenger l o r 2 c m x l m m i.d. Cu tubing packed , with either Poropak Q or 5A molecular sieve. T = 125 "C, .- 5O-pl injections Stainless-steel tubing, 72cm x 4mmi.d., 0.5% SE-300n glass beads 60-80 mesh.Ar = 150cm3min-1, T = 160 "C, TI = 200-210 "C Comments MIP responded both non-specifically to C or specifically to the metal of interest. Detection limits: 2 x 10-12-2 x 10-11 g s-1 Element and wavelength/ nm Reference A1 34 396.2 0 , 357.9 c u , 324.7 Ga, 294.4 Fe 7 344.1 s c , 361.4 v, 318.4 CO C02 SO2 and N2 in Gas mixtures were c, known amounts of pure N, Detection limits s, air prepared by injecting 247.9 gas into an air-filled flask fitted with a septum. 20-50 p.p.m. 190.0 337.1 nm (N2 band head) Metal acac chelates A CN band was observed Al, chloroform probably due to N2 Be , Failed to chromatograph Cr, dissolved in for all complexes 396.2 impurity in the Ar.234.9 acac chelates of CuII 425.4 FeI" and VIv. Two orders of magnitude for Be and Cr. One order for Al. Detection limits: 0.01-100 ng 3 m X 2.5 mm i d . 10% Apiezon L on 60-80-mesh solutions element detection used to DCMS-treated calculate empirical formula Chromosorb W. Effluent split 1 1 to FID and MIP of magnitude for F. Wide range of organic Multi-non-metallic of organic compounds. Linear range 4 orders Detection limits: 0.03-3.0 ng s-1 c , 247.8 H, 486.1 D, 656.2 F, 685.6 c1, 479.4 Br, 470.5 I, 516.1 s, 545.4 N, 746.9 0, 777.2 Reduced pressure He plasma doped with 1 % 02 4 h Evenson cavity U tube columns Chelates Cr(tfa), Use of MPD as a specific Cr , packed with Chromosorb Cr(acac), Cr(hfa) detector for Cr and as a 357.87 W-HP with 3% OV-101 non-specific detector by loading monitoring the atomic C line.Detection limit 1.5 X 10-11-8.0 x 10-10gs-lofCr 35 36 37 3 1118 ANALYST OCTOBER 1986 VOL. 111 Table l-continued Detector Chromatogaphy Sample Comments 4 h Evenson cavity DB-5 coated fused-silica Organomercury Interface consists of a maintained at 5 Torr. capillary column -selenium and -arsenic DB-5 coated fused-silica 0.75-m Roland Circle (30 m long 0.25 pm film compounds capillary column passed direct reader with thickness) througha 1.6mmi.d. 12 outputs nickel tube connected to the top of the plasma head Tapered cavity system essentially the same as ref. 17.Ar plasma, 35 W forward power Ar plasma (see ref. 4), atmospheric pressure Reduced pressure 1-10 Torr He plasma Atmospheric pressure Ar plasma 30 W forward power see ref. 40 See ref. 40 4 h Evenson cavity. Atmospheric pressure. Ar plasma 70 W forward power 4 ft x 0.5 mm i d . glass column packed with 4% SE-30 on 30-60-mesh Chromosorb G-HP 3 ft column 4% FFAP on 80-100-mesh Gas-Chrom Q. Ar = 90cm'min-1, T = 150"C, TI = 200 "C 3 ft column 1% FFAP on 80-100-mesh carbon beads. Ar = 95 cm3 min- 1, T = 135 "C, TI = 200 "C 2 ft column Chromosorb 101 He = 80cm3min-1, T = 115 "C, 3 ft column 4% FFAP on 80-100-mesh Gas-Chrom Q. Ar = 110-120 cm3 min- 1 , T = 220-240 "C, TI = 135 "C TI = 245-260 "C 6 f t column 5% Carbowax 20M on 80-100-mesh Chromosorb 101.Ar = 100cm3min-1, T = 175 "C, TI = 180 "C 0.9 m PTFE column 3 mm i.d. 10% SE-30 on 70-80-mesh Gas-Chrom Z . Ar = 30-150 ml min-1, T = 180-190°C, TI = 200 "C Se compounds in environmental samples, looked at various NBS materials with good agreement MeHgX in benzene extracts of biological samples and in air CH3HgX in water and air (CH3),Hg in water and air As and Sb in environmental samples Alkylarsenic acids in pesticide and environmental samples MMA and DMA Human blood serum SeIV complexed with Pd to form the volatile piaselenol complex followed by toluene extraction. Detection limit 40 pg of Se 0.1 pg 1-1 for water samples and 15 p.p.b. for solid samples or OH as all eluted simultaneously; see refs.41 and 42 for explanation. Detection limit: 0.5 pg g-1-1 ng g-l X designates C1 Br I Hg 9 253.7 ~ Element and wavelength/ nm Reference H 39 486.1 c, 247.8 N, 746.9 0, 777.2 F, 685.6 p, 253.6 s, 545.4 (21, 479.5 Br, 470.5 As 9 200.3 Se , 204.0 Hg, 365.0 Se , 204 40 As111 and SbIII As, converted into Ph3AsH 228.8 and Ph3 SbH extracted Sb, into diethyl ether 259.8 separated by GC. Detection limits: 20 pg of As 50 pg of Sb As compounds converted As, into hydrides. Detailed 228.8 study of hydride generation and trappings of the evolved arsines. Linear range 0.01-20 p.p.m Detection limit 20 pg as As in water samples Low-temperature ashing Cr , followed by chelation 357.9 with H(tfa) to form Cr(tfa)3 which is extracted into benzene.Linear range 1-10 pg of Cr. Detection limit: 9 x 1043g 41 42 43 44 45 4 ANALYST OCTOBER 1986 VOL. 111 1119 Table l-continued Detector Low-pressure (150 mbar) He plasma cavity type 214L. Inter-element selectivity improved by use of wavelength modulation Atmospheric pressure Ar plasma in quartz capillary, 25 cm X 1.6 mm i.d. Tapered rectangular cavity 50 W forward power Chromatography Sample Element and wavelength/ Comments nm Reference Organic compounds Demonstrated that at Hg 7 47 Hg( Me)CI low pressures 253.65 fragmentation occurs via collisions with atomic He, whereas at high pressures the collisions are with He2. Linear range: 0.02-0.5 ng.Detection limit 5 x lO-*4g Column 45 cm x 3 mm i.d. Trace levels of Cu and glass 0.5% SE-30 on Al in Zn metal 60-80-mesh glass beads. Ar = 80 cm3 min - 1, T = 14OoC, TI = 180°C Cu and A1 extracted as tfa chelates in CC14. Linear up to 60 ng of Cu, 100 ng of Al. Detection limits 0.5 ng of Al, 1 ng of Cu c u 9 324.8 A1 , 396.2 See refs40,43. Ar plasma 3 ft x 5 mm i.d. glass MeHgCl in water samples MeHgCl extracted as Hg 3 5-10 Torr pressure 18 W 6% FFAP on 80-100-mesh quaternary amine adducts. 253.7 forward power Gas-Chrom Q. Detection limit: Ar = 130-150~m~min-~, T = 180-190"C samples 1-2.5 ng I-' for water TI = 200 "C Atmospheric pressure Used exponential diluter to Gas mixtures He plasma using TMolo cavity demonstrate the applicability of MIP for GC detection Demonstrates advantages of atmospheric pressure He plasma and discusses excitation mechanism.Three to four orders of magnitude linear ranges. Detection limits: 2 x 10-11-2 x lo-' moll-' Low-pressure (3-5 Torr) Glass column Mixture of n-alkanes and Dual FID - MPD Ar plasma; see refs 40 and 6 ft x 3.5 mm 4% OV-101 43 on Chromosorb G-HP carboxylic acids specificity of response to 80-100 mesh. TMS derivatives. Linear Ar = 80 ml min-1 TMS derivatives of (5 1 split) to demonstrate range 0.5-150 ng Low-pressure (90 Torr) He Constant sample Various organic plasma observation introduction for compounds 9 mm downstream from centre of discharge, 75 W forward power. 0.25% VIVO as scavenger or 0.4% VIV NZ.h Evenson cavity Model 214L and 4 h coaxial cavity Model 217L optimisation studies Optimised plasma conditions for gas flow-rates observation position microwave power and gas pressure with the 217L cavity up to 10% of power reflected with 217L only 1 YO reflected. Three to four decades except for H where a non-linear response is found. Detection limits: 0.01-0.5 ng s-l c , 193.1 247.9 H, 486.1 c1, 479.5 481 .O Br, 470.5 478.5 I, 516.1 206.2 s, 545.4 Si, 251.6 Br, 470.47 c , 247.86 c1, 479.45 F, 685.6 H, 486.13 I, 516.12 N, 746.88 0, 777.19 s, 545.39 48 49 50 51 5 1120 ANALYST OCTOBER 1986 VOL. 111 Table l-continued Detector See ref. 33. Reduced pressure He plasma Chromatography Sample See ref.33. Reduced pressure He plasma None given Mixed Ar - He plasma, 110 W forward power 0 W reflected Atmospheric He plasma, TMolo cavity 75-80 W, forward power axial viewing Various organic compounds Trace S in MeOH, yellow P in PC13 specific detection of vinylidene and PCBs Polypenco Nylaflow Hydrides generated from pressure tubing 4.7 mm i d . 1 3 and 6 ft lengths. Packed with Chromosorb 102 60-80 mesh from solutions of As, Ge Sb Se and Sn 3 ft X 4 in i.d. 5% OV-17 Diphenylmercury on 100-120-mesh Chromosorb 750. He = 70 cm3 min-1. 3 ft X & in i.d. 3% QF-1 on 100-120 mesh Varaport 30. He = 50 cm3 min-1. 6 ft X & in i d . 6% Carbowax 20M on 100-120-mesh Chromosorb P.He = 50 cm3 min-1. 6 ft x 4 in i d . 2.5% Dexsil300 on 100-120-mesh Chromosorb TEL 2,5-dimethyl-750. He = 50 (311113 min-1 TBP Tetravinylsilane MMT thiophene. Halobenzenes Comments Signals for four elements monitored simultaneously, added by a SYNC signal and stored for later computer analysis, resulting in inter-element ratios; main concern is in data acquisition and processing Using MPD 850 to obtain accurate empirical formulae obtained detection limits comparable to manufacturers’ claims Hydride trapped in liquid N2 then chromatographed. Elements determined sequentially. Linear over 2 orders of magnitude A design for heating the interface between GC and plasma utilising nichrome resistance wire coupled to a variac given.Detection limits 0.49-63 pg S-1 Element and wavelength/ nm Reference c 53 247.8 H, 486.1 D, 656.2 0, 777.2 N, 746.9 F, 685.6 (21, 479.4 Br, 470.5 I, 516.1 s, 545.4 c 54 247.8 H, 486.1 D, 656.2 0, 777.2 F, 685.6 c1, 479.4 Br, 470.5 I, 516.1 p, 253.6 s, 545.4 Ge 55 303.9 As, 193.7 Se 3 196.0 Sn 7 317.5 Sb , 259.8 Hg 7 56 253.7 p, 253.6 Si , 251.6 Mn , 257.6 Pb > 283.3 s, 545.4 c1, 481 .O Br, 470.5 F, 685.6 I, 206. ANALYST OCTOBER 1986 VOL. 111 1121 Table l-contznued Detector Chromatography Sample Element and wavelength/ Comments nm References 3 h cylindrical cavity 1.8 m x 3.1 mm i.d. 3% Tetraalkyllead compounds Samples cold trapped Pb 15 125 W forward power OV-1 on 80-100-mesh in the atmosphere on SE-50 on Chromosorb 405.78 Ar plasma Chromosorb W.P at -80 "C. Removed background correction Ar = 22 cm3 min-1 by freeze-drying and by wavelength modulation T = 80 "C. concentrated in Ti = 130 "C organic solvent. Detection limit 6-40 pg Low-pressure (5 Torr) He and Ar plasmas. Tapered rectangular cavity, 100 W forward power. 0.3% O2 added to plasma gas See ref. 15 Reduced pressure He plasma. See ref. 33 See ref. 33 Beenakker (3 A), Evenson (4 h) and Broida (3 A) cavities were compared with He - Ar or Ar plasmas 100 W forward power Beenakker TMolo cavity viewed axially He plasma Mixed Ar (400 ml min-1) and He (300 cm3 min-1) plasma power.110 W for forward Evenson a h cavity See ref. 63 Stainless steel H in organic compounds He plasma twice as 3 m X 3 mrn i.d. 3% mlm Dexsil300 on 80-100-mesh Chromosorb W AW. 6 m X 3 mm i.d. Squalane on 80-100-mesh Detection limit: Chromosorb W AW sensitive as Ar plasma due to higher energy and therefore more complete fragmentation. 10-11 g s-1 See ref. 15 H isotope ratios in OSM measures organic compounds in alternately 1H and water samples 2H emissions of hydrocarbons. Major disadvantage is high signal to noise ratios PCBs in seal blubber, cleaning fluids in water Applications of MPD 850 in analysis and also empirical formula determinations. Detection limits: 50 pg s-1 range Biological tissues, coal tars pesticides Brief resum6 of the possible uses of the MPD 850 system 2.5 in x 4.7 mm i.d.Standard solutions Semi-automated hydride packed with Chromosorb 102. Served only to reduce rate of sample throughput to give stable plasma generation from stock solution containing As, Ge Sb and Sn. Beenakker cavity proved easiest to operate. Detection limit 1 p,p.b. at 3 o level for all cavities 10 ft x Q in i d . , stainless-steel Tenax GC water HECD. Found that MIP Haloforms in drinking Compared MIP with was preferable as it gave a uniform molar response and selective detection. Detection limit 1 p.p.b. H, 656.28 'H, 656.28 2H, 656.10 57 58 c H p N 59 F C1 Br, I p Se, As Hg Pb C1 Br I, s p Hg As , 234.984 Ge, 303.906 Sb , 259.806 Sn, 3 17.502 a , 481.0 Br, 470.5 I, 206.2 3 ft X 4.7 mm i.d.Whole blood enriched Hydrides trapped on As , tubing packed with leaves (SRM 1571) condensation tube packed Ge , Polypenco Nylaflow flour NBS orchard liquid N2-cooled 193.7 Chromosorb 102,60-80 with glass helices prior to 303.9 separation on GC column. Se , Detection limits 196.0 3-40 ng Sb , 259.8 Sn , 317.5 mesh. T = 23 k 3°C 60 61 62 63 See ref. 63 NBS orchard leaves; Elements except Ge hydride generation determined both sequentially and simultaneously the former giving lower detection limits. Detection limits: 2C600 ng Simultaneous 64 As , 235.0 Se , 196.0 Sb , 259.8 (2nd order) Sn 317.5 (2nd order) (for sequential, see ref.63 1122 ANALYST OCTOBER 1986 VOL. 111 Table l-continued Element and wavelength1 Reference Detector Chromatography Sample Comments nm See ref. 57 See ref. 57 He plasma TMolo cavity viewed axially 12.5 m X 0.2 mm i d . fused-silica WCOT SP 2100 capillary column, TI = 80-116 "C at 4 "C min-1 to 170 "C; 0.1-p1 injections. Column passed to within 5 mm of plasma He plasma TMolo cavity viewed axially. OV-225 SCOT column. He = 450 (31x13 min-1 100 m X 0.25 mm i.d. He = 4 cm3 min-1, T = 40 "C then 4 "C min-1, TI = 210 "C, Tin = 250 "C H emission from Characterisation of H 65 organic compounds emission from atomic H 656.28 in MIP accounts for non-linearity observed Toluene solutions of The low volume of GC volatile organometailic column (cu.80 p1) compounds [CpV(CO),] is ideally compatible with MMT,[Cp2Fe] [Cp2Ni] MIP. Specificity of detec-[CpCo(NO)(CO),] and tion aids identification of [(CH,),CpCo(CO),] the unresolved [Cp,Ni] and [CpCr(NO) (CO),] complexes Friedel - Crafts 35 redistribution catalysed alkyl group products are formed. redistribution Owing to the requirement reaction of to vent the solvent the methylethyl-n-propyl- low MW products that n-butylsilane elute with the solvent are not recorded He atmospheric plasma, using TMolo cavity 2% OV-101 on compounds 85-90 W forward power Glass 1.5 m x 4 mm i.d., 80-100-mesh Chromosorb He = 60 cm3 min-1, T = 238 "C PBB and related W-HP. He plasma in a 30 m capillary column Pesticides Surfatron cavity coated with OV-101 (see ref.69) methylsilicone. He = 5.9 ml min-1, T = 250 "C for pesticides TI = 275 "C, See refs 56 and 62 See refs 56 and 62 See ref. 72 See ref. 72 TMolo cavity He plasma 80 W forward power o2 as scavenger. He = 40-70 cm3 min-1 15.2 m x 0.508 mm i*d. SCOT column packed with finely ground diatomaceous earth on silica support coated with rn-bis(m-phenoxyphenoxy)-benzene and Apiezon L. He = 0.5-8 cm3 min-1, T = 90 "C c , 247.9 Cr, 267.7 c o , 240.7 Ni , 231.6 Mn , 257.6 Si , 251.6 Br Not as sensitive as the ECD but offers element 478.55 selectivity. Detection limit: 1 ng The Surfatron He plasma gives slightly higher detection limits than those obtained with other cavities.Detection limits: 0.5-20 ng Aqueous chlorination In addition to products of humic and fulvic substances significant number of tnhalomethanes a chlorinated phenolic compounds were found c, 247.8 c1, 479.5 481 .O Br, 470.5 I, 206.2 c1, 479.5 Selenium biomethylation (CH3)2Se (CH3)2Se2 Se , products from soil and and (CH3),Se02 found. 196.0 sewage Detection limit 20 pg for (CH3)2Se Hydrocarbons FID proved 50 times more c , Hg 9 (CH3)2Hg and (C2HJ2Hg sensitive than MIP for C 193.1 and (at 193.1 nm). Both had 247.9 (C2H5)Hg. The MIP was 254.3 twice as sensitive as the FID for (CH3)2Hg using Hg-specific detection. Detection limits: 3.8 X 10-12 and 9.1 X 10-12gs-1 the same sensitivity for 66 67 68 70 71 73 7 ANALYST OCTOBER 1986 VOL.111 1123 Table l-continued Detector Chromatography Sample Comments TMolo cavity He plasma f h Evenson low-pressure (40 Torr). TMolo atmospheric pressure. Ar and He plasmas the latter viewed axially Organic compounds, elemental analysis Linear ranges of 3 orders of magnitude for all elements. Detection limits: 2 x 10-11-8 x 10-10 mol 1-1 C4-C7 n-hydrocarbons Atmospheric pressure SP21OO WCOT fused-silica Trialkyllead chlorides He plasma in a TMolo cavity. Background i.d. and OV-101 SCOT samples correction by quartz glass column refractor plate column 12.5 m X 200 ym in spiked tap water 30 m x 350 ym i.d. TMolo cavity. Atmospheric pressure SP2100 fused-silica B compounds from the He plasma viewed axially WCOT capillary column.pyrolysis of Dexsil T = 60-104 "C at 4 "C min-1 0.1 pl injections 100 1 split. Used for boration studies TMolo cavity. Glass 3 m x 3 mm i.d., Atmospheric pressure columns packed with compounds He plasma 75 W forward either 3% OV-17 on power;He = 80cm'min- 80-100-mesh Shimarate W, 10% Carbowax 6000 on 30-60-mesh Shimarate TPA or Poropak Q, 80-100 mesh. TI = 190 "C 12.5 m X 0.2 mm i.d. Detection of volatile series carborane silicone polymer and from boration of diols with n-butylboronic acid Various organic Tin = 190 "C With the aid of a reference compound it is possible to determine ratio formulae, but the results are inadequate for unknown compounds. Detection limitshg s-1: TM010: He Ar C 0.67 0.2 H 0.13 4.7 2 h Evenson: He Ar C 0.44 0.35 H 0.16 0.36 Gas switches interface illustrated which prevents the solvent from extinguishing the plasma.Linear from 10 p.p.b. to 10 p.p.m. Detection limits: 1S30 p.p.b. H2 doping of the plasma inhibits the formation of oxides of silicates, promotes boron hydride formation and the population of B atomic, rather than ionic states Relative sensitivities for C and H in different compounds were not the same. Attributed to incomplete fragmentation in the low-power plasma used. Detection limits: 1.8-39.0 pg s-* Atmospheric pressure 12.5 m Sp2100 fused- Tetraalkyllead compounds Demonstrates advantages He plasma TMolo silica capillary column. in petrol of element-specific cavity. See ref. 77 detection by comparison of Pb and C responses 100 1 split ratio.T = 40-100 "C at 5 "C min-1 0.01 yl sample Element and wavelength/ nm Reference C? 75 193.1 247.9 H, 486.1 c1, 479.5 481 .O Br, 470.5 487.5 1, 516.1 206.2 s, 545.4 c, 247.86 H, 656.28 C,? 576.52 CH, 431.42 Pb 7 405.8 c , 247.9 B, 247.77 H, 656.279 c , 193.091 F, 685.602 c1, 479.454 Br, 470.486 I, 206.238 s, 545.388 Pb 7 283.3 c, 247.86 76 77 78 79 8 1124 ANALYST OCTOBER 1986 VOL. 111 Table l-continued Element and wavelength/ nm Reference F 81 685.6 Detector Atmospheric pressure, He plasma TMolo cavity. 75 W forward power 12 W reflected Chromatography 1 m X 3 mm i.d. glass column 15% DC-200 on 80-100-mesh Uniport B and 3% OV-17 on 8C100-mesh Uniport HP.He = 80 ml min-1 Sample F in urine Comments F extracted with TCMS and converted to TMFS in toluene. Linear over 4 orders of magnitude. Detection limit 7.5 pg s-* H2 doping of He enables plasma to withstand 1-2 ng s-l throughputs of Pb Ge or Sn. Linear over 3 orders of magnitude. Detection limits: 0.71-6.1 pg Ge, 265,l Sn , 284.0 Pb , 283.3 82 Atmospheric pressure, He plasma TMolo cavity. See ref. 77 12.5 m x 200 pm i.d. SP2100 fused-silica WCOT. Terminated within 1-5 mm of cavity wall Redistribution reactions for Ge Sn and Pb alkyls. Pb alkyls in gasolines Beenakker TMolo cavity He as the support gas. 50 W forward and 0-1 W reflected power.Modified Jarrell-Ash 66000 polychromator 6 ft stainless-steel column (4 in o.d., 2 mm i d . ) packed with 10% Apiezon L on 80-100-mesh Chromosorb P AW at 110 "C. 3 ft silanised glass column (4 in o.d., 4 mm i.d.) packed with 2% OV-101 on 8G100-mesh Chromosorb HP at 270 "C Chlorinated pesticides and brominated flame retardants The polychromator -microcomputer system was developed to monitor four emission wavelengths simultaneously . Detection limits nanogram level with precision in order of 5% RSD c, 247.9 a, 479.5 Br, 470.5 83 84 Atmospheric pressure microwave sustained helium plasma with Beenakker TMolo resonant cavity. Effluent split by 3-way valve with 20% going to FID 2 ft x Q in stainless-steel column packed with Porapak QS 80-100 mesh, using 1-ml gas injections.Bentone 34/DC-550 mixed phase on Chromasorb W HP Application to a number of halomethane and monochlorobiphenyl separations Notes on design, optimisation and utilisation of interface. Detection limits C1 20; P 8.8; Fe, 2.5; Br 10; and S 14.0 ng Cl, 481 .O 479.5 p, 213.6 Fe 7 259.94 Br, 478.6 S, 213.6 545.5 Copper Beenakker cavity 2450 MHz microwave generator and McPherson Model 270 scanning UV - visible monochromator. Interface similar to ref. 77 6 ft x 0.125 in i.d. column packed with OV-17 on Chromosorb W HP. Carrier gas He at 28 ml min-1. Column temperature 85 "C (140 "C for derivatives) Technique used in combination with chemical derivatisation of selected compounds in complex samples e.g., trichloroacetyl derivatives of aliphatic amines Microcomputer used to switch valves; can also be used to control monochromator wavelength settings and acquire analytical data c, 247.9 c1, 479.5 Br, 470.5 85 86 Details not given Modification undesirable c1, in quantitative studies as 479.45 results in degradation of Br, detection limits.Interface 478.55 recommended in ref. 62. Most of paper concerned with hardware and software development for control data acquisition etc. System as described in ref. 68. Minor modification by inserting a stainless-steel tube from the column into the plasma containment tube in hope of reducing dead volume Application to halogenated compounds e.g.Cilex BC-26 Reduced pressure He plasma in parallel with either an FID or ECD. Plasma viewed DB-5. Temperature transversely by a multi-channelspectrometer 10 "C min-1 with a helium Two capillary columns of 30 m X 0.25 mm i.d. with a 1.0 pm thick film of programme 70-300 "C at carrier at 1 ml min-1 Characterisation of fluorine-containing metabolites in blood plasma Inlet splitter to divide F, columns. Interaction of c, fluorine species with 495.7 effluent between the two 685.6 quartz tubing gives rise to peak tailing 8 ANALYST OCTOBER 1986 VOL. 111 1125 Table l-continued Detector Spectrospan IIIB Multi-Element Analyser equipped with a three-electrode DCP-Spectrojet I11 and multi-element cassette.Wavelength scan achieved using Spectrametrics DBC-33 system. Series UV monitor at 280 nm Element and wavelength/ Chromatography Sample Comments nm Reference Gel filtration Speciation of Gel filtration separation c u 88 100 x 2.6 cm column protein-bound requires several hours 324.7 S-300. 5-ml sample and intraVeIlOUS infUSiOIl recalibrated every hour. 213.8 packed with Sephacryl CU Fe and Zn in Serum therefore spectrometer Zn , applied to column fluids Detection limits Cu 3.2; Fe 7 Fe 3.9; Zn 9.3 373.4 Atmospheric pressure Capillary column Pyrolysis products of plasma utilising a 11 m x 0.25 mm i.d., Beenakker type TMolo SE-30 fused silica. He at siloxanes cavity.Low-resolution 1 ml min-1. Temperature scanning monochromator with approximately 0.1 nm after first 6 min.resolution Pyrolysis using Model novel linear silarylene programme 4 " c min-1 100 Pyroprobe Unit Atmospheric He 30 m x 0.25 mm i.d. Organoarsenic plasma operated at thin film DB-1 bonded- compounds 30 W forward power phase fused-silica capillary column Atmospheric He 12 m x 0.25 mm i.d. Chlorinated and plasma TMolo SE-30 fused-silica non-chlorinated cavity. Transfer capillary column organics line similar to ref. 56 As in ref. 91 As in ref. 91. Also a 15 m DB 210 fused-silica capillary column packed with 10% Kel F Oil No. 10 on Chromosorb T and a 3 m Teflon column (Q in o.d., 1/16 in i.d.) packed with 25% dibutyl phthalate on Chromosorb W Organosilicon compounds The interface allowed c , venting of column effluent 253.6 containing large amounts p, of solvents that would 247.6 disrupt helium discharge, while passing labile species without loss Quartz tube extended As , from the interface oven 228.8 into the cavity so that c7 contact with anything 247.9 except column eliminated Use of technique in Se, multi-element detection 203.99 and in determining As 7 empirical formula 228.81 Br, 470.49 CI , 479.45 c , 247.86 p, 253.57 1 7 516.12 s, 545.59 Pb , 283.31 Si , 288.16 H, 656.28 ' F, 685.60 89 90 91 Background emission As in ref.91 92 spectra are compared for plasmas contained within alumina boron nitride and quartz discharge tubes h. coaxial cavity SE-52 FSOT (30 m X Various types of Carrier and scavenger c , No background column and two SCOT with 3-12 carbon atoms use.Determination of H7 DEG 20 m 0, operated at 90 W. 0.315 mm i. d. ) capillary oxygenated compounds gases deoxidised before 247.86 correction used columns empirical formulae 486.13 777.19 (32.5 m x 0.22 mm i.d.) and SE-52 (21 m X 0.22 mm i.d.) 9 1126 ANALYST OCTOBER 1986 VOL. 111 Table l-continued Detector Chromatography Sample System similar to ref. 83 with the internally tuned packed with 2% OV-101. halogenated compounds resonant cavity mounted on the GC oven 3 ft X d in i.d. column Flow-rate 25 ml min-1, Column temperature 300 "C Dioxins and other As in ref. 83 6 ft X 4 mm i.d. glass, OV-101 2% on Chromosorb W HP Pyrethroids and dioxins Comments The H line was monitored with a red-sensitive photomultiplier.Data manipulation as in ref. 83, but modified to store chromatographic data Evaluation of laminar flow torch Element and wavelength/ nm Reference c 94 247.9 Br, 470.5 c1, 479.5 H, 656.3 c , 247.9 p, 253.6 Br, 470.5 C1, 479.5 H, 656.3 F, 685.6 95 The first couplings of GC - ICP were made by Windsor and Denton96.97 in Arizona and Sommer and Ohls99JOO in Dortmund. The former group showed the capability of ICP -optical emission spectrometry (OES) for the elemental analysis of organic compounds96 using an all-argon plasma. This capability was then utilised in a GC - ICP coupling97 for simultaneous multi-elemental analysis of organic and organo-metallic compounds.A natural extension of this work was the derivation of empirical formulae. Windsor and Dentongs used carbon hydrogen and halogen ratios to find the empirical formulae of various organic compounds; however whereas the technique provided the ability to analyse for a large number of elemental constituents suitable lines for oxygen and nitrogen were not found. Sommer and Ohls99 used both all-argon and nitrogen-cooled plasmas for the determination of tetraalkyllead compounds in various petrols by monitoring the lead emission. The same workers100 determined nickel and zinc as diethyldithiocarbamates using a nitrogen-cooled plasma. Fry et al.102 investigated a large number of fluorine atom lines for the selective detection of various fluorine-containing organic compounds using off-line correction to remove interference from the solvent emission.Brown and Fry101 monitored near infrared oxygen emissions to enable oxygen-specific detection. The determination of volatile hydrides of arsenic germanium and antimony by GC - ICP using a sequential slew-scanning monochromator~03 demon-strates how the use of chromatography enables rapid multi-element analysis using a monochromator. Table 2 lists applications of GC - ICP. 4. Coupled Gas Chromatography - Direct Current Plasma The direct current plasma (DCP) is essentially a direct current arc struck between two or more electrodes and stabilised by a flow of inert gas. There are relatively few reported couplings of GC with DCP - OES although the group at Amherst have been particularly active.67@J07JOs They found it possible to use argon helium or nitrogen as a carrier gas,lOs although in certain spectral regions interference from cyanogen bands can occur with nitrogen.The use of a sheathing gas heated to prevent sample condensation around the injector nozzle was found to increase the sensitivity.107JOs The DCP is tolerant to a wide range of gas flow-rates gas and solvent types and this clearly aids versatility even if this is sometimes at the expense of sensitivity. This coupled technique has been used as an element-selective detector for the following manganese as the cyclopentadienyltricarbon yl derivativel07; copper chromium, nickel palladium and zinc chelatesgl; iron in ferrocenellO; and various Group IV metals in an interesting study of Friedel -Crafts catalysed alkyl group redistribution reactions.140 Treybig and Ellebrachtlll utilised a vacuum ultraviolet plasma spectrometer for sulphur-specific detection which compares favourably with MIP detection and has the advantage that solvent venting is not required.The applications of GC - DCP are summarised in Table 3. 5. Coupled Gas Chromatography - Atomic Absorption Spectrometry Coupled GC - AAS applications are summarised in Table 4. Generally these can be seen to involve either flame (FAAS) or electrothermal (ETA) atomisation systems. Flame atomisa-tion offers the advantages of continuous operation simplicity and inexpensive instrumentation. Often it is cited that the low nebulisation efficiency of about 10% for solutions is a disadvantage compared with ETA in which the whole sample is atomised.This is unimportant in coupled GC - AAS as the analyte is in the gas phase prior to entry into the atom cell. However FAAS does suffer the disadvantage of higher detection limits owing to the shorter atomic residence times in the flame. In addition to the increased sensitivity it is also claimed that ETA is safer and lends itself to the possibility of unattended operation. The simplest way of interfacing a gas chromatograph with an atomic absorption spectrometer is to pass the column effluent via an interface tube into the nebulisation chamber, where it is swept by the oxidant and fuel gases into the flame. The first reported GC - FAAS coupling by Kolb et al.112 used this method to determine tetraalkyllead compounds in petrol with an air - acetylene flame. This interfacing method has bee ANALYST OCTOBER 1986 VOL. 111 1127 Table 2. Coupled gas chromatography - inductively coupled plasma optical emission spectrometry Element and wavelength/ nm Reference Detector Chromatography Sample Commen ts 6 ft X fi in i.d. packed with Elemental analysis of Used single and All-Ar plasma Br 97 700.57 c , 247.86 (21, 725.67 F, 634.67 H, 656.28 I, 206.16 Si , 251.61 Fe , 371.99 Pb , 217.00 Sn, 284.00 observations made 9 mm 8% Carbowax 1540 on above load coil. 80-100-mesh firebrick Computer-controlled data acquisition system. See ref. 96 various organic compounds multi-channel monochromators.Using the latter monitored C and H channels for TMT, toluene and p-xylene. Detection limits: 0.8 ng- 1 mg depending on the element All-Ar plasma. See refs 96 and 97. Power 0.8 kW; coolant 12 1 min-1; plasma 0.5 1 min-1; sample 0.9 1 min-1; make-up 0.9 1 min-1 Uses both high-power Ar - SP1000. N2 and low-power Ar - Ar N = 30 cm3 min-1. See ref. 96 98 c, 247.86 H, 656.28 I, 206.16 a, 725.67 Si , 212.4 288.1 Halogen-containing hydrocarbons Elemental ratio determinations for each peak. Typically 200 elemental ratio determinations were taken to yield an average figure 99 100 Determined lead in petrols using standard addition, also TML - TEL ratio and C background at 220.35 nm T = 140 "C (Si), T = 150 "C (Pb) ' plasmas Pb , 220.35 10% Carbowax 20M on Chromosorb P 80-100 mesh.Ar = 25 cm3 min-1, T = 100 "C Tin = 100 "C All-Ar plasma 1.75 kW forward power. Used elongated torch, observation zone 5.5 mm above load coil Monitored near-IR oxygen emissions for various gases and organic liquids Studied effect of varying various plasma gas flows on signal and background levels. Detection limit: 650 ng 0, 777.194 101 6 ft X Q in i.d. packed with Amine 200. Ar = 25 cm3 min-1 T = 105 "C sampling loop used Separation of trifluorobenzene and o-fluorotoluene F/C selectivity of 1.0 at 685.602 nm without background correction. By using "off-line" correction, solvent peak disappears F 102 considered lines in the region 350-895 1 ccg 56 All-Ar plasma All-Ar plasma with slew scanning monochromator.1 kW forward power. Observation 15 mm above load coil 3.5 ft x 3 mm i.d. Chromosorb 102 at ambient temperature Sequentially eluting hydrides monitored. Linear over 2-3 orders of magnitude. Detection limits 4 ng of Ge 50 ng of As and Sb Ge , 303.9 As, 278.0 Sn , 317.5 Sb , 287.8 103 Hydrides generated cold trapped and passed through column into plasma Spherisorb C,,-ODs 10 pm 250 x 4.6 mm 120 x Interface via a 10 cm 1/16 in 0.d. PTFE capillary from column to the nebuliser AII-Ar plasma. Data acquisition via chart Alkyllead compounds Pb , 405.78 105 recorder or microcomputer 4.6 mm. LiChrosorb RP-2, as in ref. 104 10 pm 120 X 4.6 mm.Partisil-10 SCX 25 cm. Various mobile phases examined Effluent from column passed directly into the nebuliser y, 328.937 Also 13 additional elements Ar plasma. All observations 15 mm above LC cartridge in earths in geological load coil. 1.1 kW forward conjunction with a Z material power module Radial 8 PSCX 10 pm Radial Pak Yttrium and selected rare Compression separation system 10 1128 ANALYST OCTOBER 1986 VOL. 111 Table 3. Coupled gas chromatography - direct current plasma optical emission spectrometry Detector Prototype Spectraspan I11 d.c. plasma Cchelle spectrometer See ref. 107. Details of heated interface design given. Dual detection with FID used sheathing gas heated to 230 "C to prevent condensation of eluents.Ti = 230 "C For spectrometer and interface see ref. 109. A 3-electrode jet was used rather than a 2-electrode jet. Ar flow-rates: sheathing 1.42-1.65, cathode = 2.0 and anode = 1.3 1 min-1. Current = 7 A voltage = 40-60 V See refs. 67 and 108 Vacuum UV spectrometer with Spectrametrics d.c. plasma Chromatography 6 ft X Q in i.d. stainless-steel 2% Dexsil 300 GC on 100-120-mesh Chromosorb 750. 1 1 split with FID. He = 25 cm3 min-1 T = 130 "C, TI = 160 "C Ti = 170 "C 6 ft X Q in i.d. 3% Dexsil 300 on 100-120-mesh Chromosorb 750. T = 170 "C He = 60 cm3 min-1 T = 220 "C. 6 ft X + in i.d. 2.5% Dexsil 300 GC. T = 230 "C T = 280 "C. 6 ft X Q in i.d. 3.2% Dexsil300 GC on 100-120-mesh Chromosorb 750. T = 190 "C.6 ft X Q in i d . , 10% SE-30 on 60-80-mesh Gas-Chrom S . T = 170 "C 6 ft x Q in i.d. stainless-steel 5% OV-101 on 100-120-mesh Chromosorb 750. He = 40 cm3 min-1 T = from 80 "C at 6 or 8 "C min-l TI = 210 "C Ti = 220 "C. Nickel tubing 1 m x Q in i.d. 3% OV-201 on 100-120-mesh Ultrabond 20M. He = 40 cm3 min-1, T = from 80 "C at 8 "C min-l TI = 210"C Ti = 220 "C Sample MMT in gasoline, standards in isooctane. Eymantrene as internal standard Cr(tfa), Friedel - Crafts catalysed alkyl group redistribution reactions 100 ft x 0.03 in i.d. Ferrocene and stainless-steel OV-101 haloderivatives PLOT column. T = 170 "C 122 cm X 2 mm i.d., Poropak Super Q. 183 cm x 2 mm i d . 3% OV-101 on Chromosorb W HP, 80-100 mesh. N2 = 80 CS2 thiophene 3-methylthiophene, hexanethiol benzenethiol and dimethyl sulphoxide.Detection limit 0.3 ng s-l cm3 min-1 of s Comments Only sample modification required was addition of the internal standard. 3 min analysis time. Upper limit of linear range was 340 ng. Detection limit: 3 ng Sheathing gas around the issuing GC effluent prevented excessive diffusion as the sample travelled into the plasma from the interface tubing. Linear from 2 to 150 ng for Cr. Detection limits: 0.28-320 pg s-1 Redistribution reactions of the following pairs: n-Pr4Sn+Et4Pb; Et4Sn +n-Bu4Ge; n-Pr4Si+n-Bu4Ge; n-Bu4Ge+Et,Pb; Vn4Si+Et4Sn; and Vn4Si+n-Bu4Ge studied. Formation of PbR3CI and SnR3CI by reactions with AIC13 also studied Paper contains many other organome t allic separations; however the detector used is the FID Element and wavelength1 nm Reference Mn 107 279.8 c u , 324.7 Ni , 341.7 Pd , 340.4 c , 247.8 Cr, 267.7 c , 247.8 Si , 251.6 Ge 7 265.1 Sn 7 286.3 Pb , 368.3 Pb , 368.3 Sn, 286.3 Fe 7 372.0 s, 180.7 108 67 110 111 utilised by various workers.113J20J24 Morrow et al.113 used the dinitrogen oxide - acetylene flame for the silicon-specific detection of silylated alcohols and an air - acetylene flame for atomic emission detection of the same species. A similar coupling was used to determine lead in petro17120J24J37 and in the atmosphere.124 Hahn et al.145 used such an arrangement to determine As Ge Se and Sn after hydride generation using a hydrogen diffusion flame.Cokerl" realised that dilution of the sample and the excessive peak broadening caused by passage through the nebulisation chamber could be avoided. He passed the chromatographic effluent into a manifold just below the burner slot and achieved lower detection limits for tetraalkyllead compounds in petrol than the previous coupl-ings. Wolf130J36 used a similar coupling to specifically determine chromium in standard orchard leaves after chela-tion with trifluoroacetylacetone as did Chanlso when investi-gating tetraalkyllead ratios in petrols from various sources. Work in our laboratories15lJ52 has emphasised that in order to enable true trace level determinations by GC - FAAS the residence times of atoms in the flame must be increased.This was achieved using a flame-heated ceramic tube suspended over a flame in various configurations. The system described by Ebdon et al. 151 or variations of it are now used routinely in a number of laboratories,l52-155 particularly for the speciation of alkyllead compounds. The electrothermal devices used in coupled GC - AAS fall into three main categories (i) laboratory-made electrother-mally heated quartz or ceramic tubes; (ii) commercial graphite furnaces; and (iii) commercial cold vapour mercury analysers. This latter atom cell has been used for mercury-specific detection of organomercurials in various samples. Heyl14 passed the effluent from the chromatograph into a continuous wet chemical reduction cell the reduced Hg(0) being swept into the cold vapour absorption cell of a commercial system (MAS 50 Coleman Instruments).Other workers116119 used a flame-ionisation detector flame to atomise the organomercury species which were then passed into the same cell. Dress-man116 used this method to speciate dialkylmercur ANALYST OCTOBER 1986 VOL. 111 1129 Table 4. Coupled gas chromatography - atomic absorption spectrometry Element and wavelength/ nm Reference Detector Chromatography Sample Comments Flame AAS GC effluent passed via a heated tube Apiezon M on and TEL GC - AAS coupling for into the nebulisation Chromosorb R. N2 = 40 element-specific detection. chamber ml min-1 T = 150 "C Linear range 50-700 2 m x 2 mm i.d. 10% Pb alkyls in petrol TML First paper to describe p.p.m.Pb 112 217.0 Flame AES N 2 0 - C2H2, FAAS air - C2H2 flame. column 20% SE-30 on of n-alcohols C1-C7 stainless-steel (0.0345 in Coupling was through the i.d.) heated in excess of nebulisation chamber T,. Linear ranges AAS 4-20 pg AES 3-100 pg. Detection limits AAS, 0.11 pg; AES 0.72 pg 6 ft X 0.25 in i.d. steel 30-60-mesh Chromosorb W. He = 100 ml min-1, T = 130 "C Silylated pyridine solutions Interface tube Si 113 251.6 Hg 114 253.7 Using cold vapour analyser Organomercury Passed GC effluent into a compounds continuous wet chemical reduction vessel; Hg then flushed into cold vapour cell. Linear up to 10 pg. Detection limit 50 ng Glass 6 ft x 0.25 in i.d. Alkylmercury compounds GC effluent passed into a column 5% HIEFF-2AP in fish tissue MeHgCl and quartz tube combustion on Chromosorb W HP EtHgCl furnace (780 "C) prior to 80-100 mesh.N2 = 120 passing into the cold r.1 min-I TI = 200 "C T vapour cell. Linear up to = 170 "C Ti = 200 "C 45 ng. Detection limit: 2.5 x 10-11 g of MeHgCl gives 1% absorption As ref. 114 Hg 115 253.7 See ref. 114 6 ft x 2 mm i.d. glass column 5% DC-200 + 3% compounds in spiked river QFI on 80-100-mesh waters combust the mercury Chromosorb Q. T = 70 "C hold 2 min then 20 "C min-1 to 180 "C Dialkylmercury The effluent was passed through the FID to compounds prior to entry into the cold vapour analyser. Detection limit: 0.1 ng Hg 7 253.7 116 See ref. 116 Dialkylmercury See ref. 60. Linear from compounds Me2Hg 0.05 to 100 ng. Detection Et2Hg n-Pr,Hg n-Bu2Hg limit 0.02 ng for Me2Hg See ref.114 See ref. 114 Hg 7 253.7 117 118 See ref. 116 Dialk ylmercury See ref. 60. Linear from compounds 0.05 to 100 ng for Me2Hg and Et2Hg. Detection limit 0.02 ng for Me2Hg Hg , 253.7 See ref. 114 6 ft X 0.125 in glass column 5% SP2100 + 3% involved in pathways in SP2401 on 80-100-mesh transformations of microorganisms Supelcon AW DCMS. N2 = 20 ml min-1, T = 60 "C hold 2 min then 32 "C min-1 to 180 "C Mercury compounds Study of methylation microorganisms in soils and sediments Hg 7 253.7 119 120 Air - acetylene flame 3 m x 3 mm PTFE tube. N2 = 40 ml min-1 T = 110 "C Pb alkyls in gasoline samples Effluent passed from GC into spray chamber; 5-cm burner. Linear from 0.2 to 40 pg Pb , 217.0 Graphite furnace kept at 10 cm W transfer line 2700 "C with background connected into an enlarged correction OV-210 on Gas-Chrom Q.hole in graphite tube. Detection limit 10 ng of 6 ft X %16 in i.d. on glass column 4% SE-30 + 6% Ar = 50 ml min-1 T = 150 "C 2 . 0 4 injections Pb Pb alkyls in gasoline Pb 121 217. 1130 ANALYST OCTOBER 1986 VOL. 111 Table k o n t i n u e d Detector Electrothermally heated silica tube (60 x 7 mm i d . T = 1000 "C). Furnace gases air = 120 ml min-1; H2 = 120 ml min-1 Air - C2H2 flame AAS using an electrothermally heated silica furnace. See ref. 122 Air - C2H2 flame. All-glass lining for nebulisation chamber used to prevent absorption of organolead on chamber walls Electrothermally heated silica tube.See ref. 122 Electrothermally heated silica tube. See ref. 122 T furnace atomiser (900-1000 "C; 100 x 20 mm i.d.). Flows into atomiser Hz = 1 1 min-1, N = 6 I min-l. Quartz T furnace Chromatography 1.8 m X 6 mm i.d. glass column 3% OV-1 on Chromosorb W 80-100 mesh. T = 40 "C hold 2 min then 15 "C min-1 to 120 "C. TI = 225 "C 3 ft x 3/16 in i.d. steel column 10% Carbowax 20M on 100-120-mesh Porasil C. H2 = 120 ml min-l T = 130 "C. Laboratory-made column heating system. 5-pI injections See ref. 122 1.8 m x 6 mm i.d. glass column 3% OV-1 on 80-100-mesh Chromosorb W. N2 = 65 ml min-l T, = 40 "C hold for 2 min then 5 "C min-1 to 90 "C Column (see ref. 68). N, Element and wavelength/ Sample Comments nm Reference Me2Se and Me2Se2 in synthetic air samples Se , 196.0 Air samples trapped at -80 "C on 3% OV-1 on Chromosorb W and desorbed into the GC at 80 "C.The trap was heated in a commercial "toaster." Linear up to 50 ng. Detection limit 0.1 ng 122 Pb alkyls in gasoline The effluent from the GC Pb 7 111 passes into a manifold just below the burner slot which evenly distributes the effluent along the flame. Linear up to 200 p.p.m. for TML and 1000 p.p.m. for TEL. Detection limit 0.2 p.p.m. 283.3 TML from methylation of Reported that Me,Pb+ Pb 123 Me,Pb+ salts salts were readily 217.0 converted to TML by microorganisms in lake water or nutrient medium Tetraalkyllead compounds The air sample was Pb 124 in the atmosphere and trapped (see ref.66) then 217.0 gasolines passed through a nebulisation chamber into the flame. Detection limit: 80 ng Tetraalkyllead compounds For sample trap and Pb 125 = 70 ml min-1 T = 56°C in the atmosphere for 2 min then 15 "C min-* to 150 "C, TI = 150 "C chromatographic interface 217.0 see ref. 122. Linear up to 200 ng. Detection limit: 0.1 ng 1.8 m x 6 mm i.d. 3% OV-1 on Chromosorb W, 80-100 mesh. Lead see ref. 68. Selenium NZ = 70 ml min-l T = 40 "C for 2 min then 15 "C min-1 to 120 "C, TI = 225 "C. Arsenic 10% OV-1 on Chromosorb W. N = 30 ml min-1, T = 25 "C = T I , Ti = 100 "C. Mercury, 5% DEGS on Chromosorb W. N2 = 80 ml min-1, Ti = 150 "C. Cadmium, N2 = 70 ml min-1, T = 70 "C, TI = Ti = 80 "C Organometallic compounds in liquid or gaseous samples.For gaseous sample trapping method see ref. 122 T = 145 "C TI = 150 "C, Compounds determined were tetraalkylleads, methylseleniums, methylarsines, alkylmercury chlorides and dimethylcadmium. Detection limits 0.1 ng for each element Hg 9 126 253.6 Pb , 217.0 Cd , 228.5 As, 193.7 Se , 196.0 122 cm x 3 mm i.d. A1 Dialkylselenium The laboratory-made Se 7 127 tube 20% polymetaphenyl compounds chromatographic system 196.0 ether on 60-80-mesh Chromosorb W. N2 = 23 ml min-l T = 82 "C, was contained in the quartz T arrangement TI = 180 " ANALYST OCTOBER 1986 VOL. 111 1131 Table k o n t i n u e d Detector See ref. 127 Flame with chromatographic effluent being delivered directly to the burner cavity Electrothermally heated silica furnace see ref.122, or directly coupled through the nebulisation chamber to an air - C2H2 flame see ref. 124 H2 diffusion flame burning in quartz cuvette. H2 = 250 ml min-1 air = 150 ml min-1 See ref. 117 Graphite furnace with pyrolytic or alumina lining or standard graphite tubes, at various temperatures with and without Ar - H2 (90 + 10) flow (20 ml min - 1 ) Graphite furnace at 2000 "C. The furnace was kept at this temperature throughout the chromatographic run Air - C2H2 flame; see ref. 130 Chromatography See ref. 127 2 ft x 3 mm i.d. PTFE tubing 10% SE-30 on Chromosorb W HP, 80-100 mesh. N2 = 65 ml min-1 T = 180 "C 20-1.11 injection See ref.125 6 m stainless-steel column, 16.5% DC-550 on 80-100-mesh Chromosorb W AW DMCS, He = 80 ml min-1 80 cm x 6 mm i.d. glass column 10% Carbowax 20M on Chromosorb W AW. 5-100-yl injections, N2 = 15 ml min-' for Me2Hg 200 ml min-1 for MeHgCl TI = 200 "C Tc = 60 "C for Me2Hg 200 "C for MeHgCl Element and wavelength/ Sample Comrnen ts nm Reference Organoselenium compounds transpired Astraaalus racernosus The transpired compounds Se 128 129 on Chromosorb W in a dry ice-bath and desorbed at 175 "C into the chromatographic column. Detection limits Me2Se = 10 Me2Se2 = 20 and Et,Sez = 20 ng by were trapped on DC-550 196.0 Inorganic Cr in NBS SRM After a H2SO -k H Z ~ Z 1571 orchard leaves as digestion Cr chelated with Cr(tfa) chelates Htfa (0.1 ml) then extracted with hexane (0.5 ml) prior to injection.Linear from 0.5 to 5 p.p.m. of Cr. Detection limit 1 ng Cr Tetraalkyllead compounds For atmospheric sampling Pb , 217.0 in petrol and air samples see ref. 122. Linear up to 200 ng for furnace. Detection limit 0.1 ng for furnace system Reducible As species in The hydrides of the As As , compounds isolated by 193.7 cold trapping passed down a column and into a furnace. Linear up to 50 ng. Detection limit 0.05 ng for ASH, natural waters MezHg MeHgCl Detection limit 10 p.p.b. Hg 7 Hg 253.7 6 ft X Q in i.d. glass Me3As Me& and Me,Se Best detection levels column 5% SP2100 and in Nz. To simulate an achieved using standard 3% SP2401 on atmosphere over a lake graphite tubes with an 80-100-mesh Supelcon system Ar - H2 flow at 1800 "C.AW DMCS. Ar = 30 Linear up to As 320 Se ml min-l T = 40 "C 313 and Sn 363 ng. Ti" = 100 "C Detection limits 5-12 ng PTFE column 8 ft x 4 in i.d. 20% TCP on Chromosorb W. Ar = 30 atmosphere limit 0.1 ng ml min-I T = 100 "C TI Tetraalkyllead compounds TEL undetected in all 10 in gasoline and the air samples. Detection = 125 "C Ti = 100 "C 18 in x 3 mm i.d. PTFE Inorganic Cr in NBS SRM tubing 5% SE-30 on 1571 orchard leaves and Chromosorb P AW SRM 1569 brewers yeast Fe(tfa)3 and Cu(ofhd),. DMCS 80-100 mesh. N2 as chelates also Co Fe = 120 ml min-1 and Cu chelates Detection limits 1.&500 The chelates determined were Co(fod), Fe(fod),, Linear from 0.5 to 8.0 pg. ng Tc = 160 "C TI = 150 "C As , 193.7 Se , 196.0 Sn, 224.6 Pb , 283.3 130 131 132 133 134 135 Cr 136 c o Fe c 1132 ANALYST OCTOBER 1986 VOL.111 Table 4-continued Detector Element and wavelength/ Sample Comments nm Reference Chromatography Both a flame air - C2H2 20% SE-52 on Tetraalkyllead compounds The furnace technique was Pb 137 the effluent introduced Chromosorb W. Ar = 90 in gasoline samples 100 and 75 times more 283.3 through the nebuliser and a graphite furnace at 1300 "C TEL respectively. ml min-1 T = TI = 125 "C Ti = 130 "C sensitive than the flame coupling for TML and Detection limits flame, TML = 17 and TEL = 81 ng; furnace TML = 0.12 and TEL = 1.1 ng anelectiically heated quartz furnace at 620 "C Hg compounds atomised in 10% SP2300 on Alkylmercury compounds Rapid method for Hg , Chromosorb W.N2 = 90 in fish quantitative extraction of 254.0 ml min-1 T = 145 "C, TI = 200 "C Electrothermally heated See ref. 122 silica tube. See refs. 122 and 125 Graphite furnace atomisation at 1700 "C Various atom cells, air - C2H2 flame flame and electrothermally heated quartz tubes, graphite cup and furnaces Graphite furnace atomisation (see ref. 135) at 1500 "C Electrothermally heated silica furnace see ref. 122 Electrothermally heated silica tube furnace see refs 139 and 125 Graphite furnace atomiser organomercury compounds from fish given. Linear up to 120 ng. Detection limit: 3.5 ng Tetraalkyllead compounds Extraction procedures for Pb , 217.0 in water sediment and fish three sample types given.Detection limits water (200 ml) = 0.5 pg 1-1, sediment ( 5 g) = 0.01 pg g-1 fish (2 g) = 0.025 Pg g-l 150 cm X 6 mm i d . glass Tetraalkyllead compounds The Pb compounds from Pb, column 3% OV-101 on in air 70-1 air samples were 283.3 Chromosorb W 80-100 mesh. Ti = 80 "C T = 90 "C then 40 "C min-1 to 200 "C or isothermal at 150 "C trapped at -72 "C on the chromatographic packing. Detection limit 40 pg 150 cm x 6 mm i.d. glass Tetraalkyllead compounds If Ti > 300 "C Pb , column 3% OV-101 on decomposition of lead 283.3 Chromosorb W 80-100 mesh. N2 = 140 ml min-1 T = 50 "C then 40 "C min-1 up to 200 "C compounds occurred and interference from remobilisation by the solvent resulted.Detection limit 30 pg with HGA 2100 furnace 18 in X i in i.d. PTFE column 20% Ucon surface and evaporates. 283.3 Non-Polar on Chromosorb P. Ar = 60 ml min-1, T = 140 "C TI = 150 "C, Ti = 140 "C TEL in sea water Some TEL migrates to the Pb , The majority forms the soluble Et3PbC1. Evidence of further degradation was found. Detection limit: 1 pg rnl-1 See ref. 122 TML in methylation of Found a chemical Pb 9 Pb" salts in aqueous methylation pathway for 217.0 solution converting PbI1 salts into methyl derivatives 138 139 16 140 141 158 See refs. 125 and 139 Tetraalkyllead compounds Samples were analysed for Pb 142 in fish sediment total Pb volatile Pb 283.3 vegetation and water tetraalkyllead and samples hexane-extractable Pb 2.3 m X 6 mm i.d.3% MMT in air samples The air samples were Mn 143 OV-101 on Chromosorb collected (see ref. 84) at 70 279.5 W HP 80-100 mesh. N = 80 ml min-l T = 115 "C, ml min-* for 8 h. Detection limit 0.05 ng m-3 TI = 150 "C Ti = 150 " ANALYST OCTOBER 1986 VOL. 111 1133 Table Aontinued Element and wavelength/ nm Reference Detector Chromatography Same as ref. 142 Sample Comments Determination of total, hexane-extractable, volatile and tetraalkyllead in fish water sediment and vegetation samples. See ref. 142 Graphite furnace atomisation Coupling of chromatograph transfer line to the furnace was via friction-fitted Ta connector (ref. 140). Detection limits 2 p.p.b. of hexane-extractable, 0.5-1.5 p.p.b. of volatile and 0.5 p.p.b.of tetraalkyllead Pb 7 144 283.3 3 ft X 4.7 mm i.d. Polypenco Nylaflow tubing Chromosorb 102. T = 23 "C Determination of As Ge, Se and Sn after hydride generation and cold trapping of hydrides H2 diffusion flame, samples introduced through nebuliser Chromatographic separation allowed manual lamp change and monochromator change between peaks. The overlap of SeH2 and SnH, required their separate detection. Detection limits 60-260 ng As 7 193.7 Ge , 265.2 Se, 196.0 Sn 7 224.6 145 Coupling via 1 m x 0.5 Pb 7 mm i.d. glass tube. Linear up to 50 ng. Detection limits 40 pg of TML and 90 pg of TEL 283.3 Graphite furnace atomisation at 2000 "C. External gas flow of 0.9 1 min-1 Glass column 180 cm X 2 TML and TEL in petrol mm i.d.3% OV-101 on Gas-Chrom Q 100-120 mesh. Ar = 30 ml min-', T = 50 "C then 20 "C min-' up to 150 "C, Ti, = 200 "C 146 Pb 7 283.3 147 Graphite furnace atomisation see ref. 96 Same as ref. 146; samples desorbed from short glass column of 6 1 min-1 chromatographic material at 90 "C into chromatograph Tetraalkyllead compounds in air sampled for 1 h at Pb compounds sampled on to glass beads at -130 "C, then transferred to a short column of chromatographic packing at - 196 "C. Detection limits TML = 0.1 and TEL = 0.3 ng m-3 2 m x 6 mm i.d. glass column 3% SE-30 on Chromosorb G AW DMCS. For R = Me N2 = 16 ml min-1 T = 120 "C. For R = Et N2 = 50 ml min-1 T = 180 "C Tetraalkyltin and alkyltin chlorides (R,SnCl,-,, R = Me and Et) Owing to column rearrangements all four methyltin compounds cannot be examined.Passed column effluent directly to atomiser and also generated hydrides prior to atomisation. Linear up to 400 ng. Detection limits 1 .O ng for Me,Sn 2.0 pg for Me$n if hydride is atomised Electrothermally heated quartz tube Sn , 286.3 148 Graphite furnace atomisation see ref. 96 Same as ref. 146 149 Tetraalkyllead compounds in air (cf. ref. 97) petrol (cf. ref. 96) river and rain water Degradation of TML and Pb , TEL in river water 283.3 investigated. Detection limits TML = 0.2 TEL = 0.5 pg 1-1 Interface line was 4 ft X 0.02 in i.d. stainless steel. Linear up to 400 ng for TML 1400 ng for TEL Pb 7 217.0 Air - C2H2 flame; effluent from chromatograph introduced just below burner slot 10 ft X i) in i d .steel column 20% Carbowax 20M on Chromosorb P. N2 sources = 120 ml min,-' T = 120 "C 2 p1 injected Tetraalkyllead compounds in petrol from a variety of "C TI = 140 "C Ti, = 110 15 1134 ANALYST OCTOBER 1986 VOL. 111 Table A o n t i n u e d Element and w avel e ng t hl Comments nm Reference Chromatography Detector Sample 4 ft glass column 20% OV-3 on Chromosorb W, 80-100 mesh. N2 = 80 ml min-l T = 30 "C for 3 min then 20 "C min-1 up to 110 "C TI = 85 "C, Tin = 76 "C Electrothermally heated silica furnace (see refs 122 and 125) at 850 "C. H2 = 150 ml min-1 Methyltin compounds sampled from the headspace above sediment samples in a methylating environment Headspace sampling (see Sn 156 ref.122). Experiments 224.6 indicated that SnrI was methylated by CH31 but SnIV was not. Detection limit 0.1 Electrothermally heated silica furnace; see refs 122 and 125 For chromatographic conditions see refs. 124, 125 and 126 Methylated derivatives of As Hg Pb and Se Study of the effect of pH on methylation in the 193.7 aquatic environment. Detection limits 0.1 ng of each element 253.6 As, Hg, 157 Pb , 217.0 Se , 196.0 Tetraalkyllead compounds in the atmosphere. Samples taken from rural, urban and gasoline station environments Elevated levels of Pb , tetraalkyllead compounds 283.3 were found around gasoline stations and in areas with heavy traffic.Linear up to 50 ng. Detection limits 40 pg of TML and 90 pg of TEL 159 Graphite furnace atomisation; see refs. 146 and 147 See refs. 146 and 147 Electrothermally heated silica tube see ref. 122 180 cm X 6.4 mm i.d. 3% OV-1 on Chromosorb HP, 80-100 mesh. N2 = 25 ml min-1 T = 70 "C, TI = 150 "C Tetraalkyllead compounds formed in study of methylation pathways in coastal sediments Reported that Pb , bioconversion of Pb" to 217.3 TML unlikely in marine environments 160 Electrothermally heated quartz tube (cf. ref. 125) at 980 "C 8 cm X 3.2 mm i d . stainless-steel column, Porapak Q 80-100 mesh. TML was trapped on column and flushed off with N2 (150 ml min-l) by placing the column in a toaster (cf. ref. 125) at T = 235 "C Methylation was affected Pb, by methyllithium and only 283.3 a 50% conversion was achieved.Linear up to 200 ng. Detection limit 5 ng 167 Determination of inorganic Pb in aqueous samples as tetramethyl derivative formed by methylation of the extracted dithiocarbamate complex Sn , 224.6 162 Electrothermally heated quartz tube (see ref. 125) 1.8 m X 6 mm i.d. glass column 3% OV-1 on Chromosorb W 80-100 mesh. N2 = 65 ml min-', TI = 180 "C T = 90 "C then 20 "C min-1 up to 190 "C Tin = 165 "C Organotin compounds, Me,SnBu+ in water Tin compounds were extracted with a 0.1% tropolone in benzene solution from spiked water samples. Linear up to 33 ng. Detection limit 0.1 ng Flame and a flame-heated ceramic tube 1.5 m X 4 mm i.d.glass column 5% Carbowax 20M on Chromosorb 750, 80-100 mesh. T = TI = Ti = 159-175 "C Tetraalkyllead compounds Pb 9 Various atom cells developed and simplex 283.3 optimised. Detection limit: 17 pg for most sensitive atom cell 151 Mo furnace surrounded by an alumina sleeve heated at 250 K s-' to 2473 K 247 mm X 1.22 mm i.d. Mo column with a wall thickness of 0.81 mm. Carrier gas of either Ar at 44.7 k 2.1 p1 s-1 or Ar + H2 at 35.1 k 0.8 and 13.5 k 0.4 p1 s-l respectively. T = 2093 K Na Cu Mn and Mg in inorganic salts Ar (3.8 1 min-1) and H2 Na 7 provide an air-free c u 7 Mn 9 (1.2 1 min-1) used to atmosphere around tube 16 ANALYST OCTOBER 1986 VOL. 111 1135 Table k o n t i n u e d Detector Modified form of flame AAS system used in ref.151 to permit the use of Perkin-Elmer burners requiring high gas flow-rates Silica furnace consisting of an electrically heated quartz T-tube encased in a shaped firebrick. Assembly mounted in an aluminium cradle positioned within the optical beam of the spectrometer Flame AAS system based on ref. 151 Element and waveleng thl Comments nm Reference Chromatography Sample 1.5 m X 6 mm 0.d. X 2 Ionic alkvllead comDounds Problem of sample Pb 7 153 mm i.d. column packed with 10% OV-101 on Chromosorb W 80-100 mesh. Temperature programme 50-250 "C at 10 "C min-1 in water 1.8 m x 6 mm i.d. glass column packed with 10% OV-101 on 80-100-mesh Supelcoport. He flow-rate: 35 ml min 1-1. Temperature programme up to 250 "C Alkyllead compounds in environmental samples 1 m x 6 mm 0.d.2 mm i.d. glass column in air containing 3% OV-101 on Gas-Chrom Q (100-120 mesh) Tetraalkyllead compounds introduction into the atom 283.3 cell overcome using commercially available open silica cell normally employed with the Perkin-Elmer MHS-10 mercury - hydride system. Detection limits ng 1-1 Furnace operating conditions 900 "C and hydrogen make-up gas at 50 ml min-l. Detection limits about 30 pg with claims of possible improvement by improving the chromatographic efficiency Pb 7 217.0, 283.3 Samples collected using Pb , cryogenic trapping at 283.3 -196 "C then flash-hea ting 164 154 compounds in spiked river waters. Blair et al.119 also used this method in a study of mercury transformations in aquatic environments. Gonzalez and Ross115 used a quartz combus-tion furnace prior to the detector to determine methyl- and ethylmercury chlorides in fish tissues and found better selectivity towards mercury than that exhibited by electron-capture detectors towards the organomercury chloride. The use of an electrothermally heated silica tube as an atom cell for coupled GC - AAS was pioneered by Chau et a1.122 The furnace heated to around 1000 "C with a through flow of air and hydrogen was used with a selenium-specific detector in the determination of dimethyldiselenium and dimethylsele-nium.122 Chau with a number of co-workers then used this coupled technique for numerous environmental applica-tions.122~239126~56,157 This group later developed the same technique for the metal-specific detection of organolead in the atmosphere,124J25 the aquatic environmentl39J42 and for methylation studies of lead,123J58 tin,156 arsenic mercury and selenium.157 Thompson160 utilised a similar atom cell to study methylation pathways in coastal sediments whereas Brueg-gemeyer and Carus0161 used the same. system for the determination of inorganic lead in aquatic samples after methylation of the extracted dithiocarbamate lead complex. Van Loon and Radziuk127-129 developed a silica T-tube for coupled GC - AAS. This inexpensive arrangement had the chromatographic column contained in the long arm of the T and the effluent then passed into the cross-piece atomiser purged with flows of hydrogen and nitrogen.The system was used as a metal-specific detector for organoselenium com-pounds127 and in the study of organoselenium transpiration by Astragalus racernosus.128J29 Bye and Paus138 used an elec-trothermally heated quartz furnace to atomise organomer-curial compounds prior to their detection in an unheated silica cuvette. In a comprehensive study of various tetraalkyl, methyl- and ethyltin chloridqs148 Burns et al. used an electrothermally heated quartz tube as an atomiser. They found that detection limits could bed lowered substantially if the hydrides were generated prior to atomisation. In a comparison of various atom cells for coupled GC - AAS by Radziuk et a1.140 the graphite furnace proved the most sensitive for lead and gave a 50-fold increase in response compared with the early Kolb-type flame coupling.It is clear from the work of Ebdon et a1.151 reported above that by using ceramic tube atomic traps FAAS couplings can be as sensitive if not more so than furnace couplings as the vital parameter in optimisa-tion is the residence time of the atoms in the absorption cell. The first GC coupling to a commercial graphite furnace was rather crudely achieved by Segar.121 The end of a tungsten transfer line was passed through an enlarged hole in the graphite tube so that the effluent impinged on the hot tube wall. Parris et al. 134 considered the effect of using pyrolytically coated alumina-lined and standard graphite tubes at various atomisation temperatures with and without hydrogen (10%) added to the chromatographic effluent.The best detection levels were achieved for As Se and Sn using standard graphite tubes with hydrogen added to the effluent flow and an atomisation temperature of 1800 "C. Robinson et al.135 passed the chromatographic effluent through a graphite electrode into the optical path of a laboratory-made atomiser which was kept at 2000 "C throughout the chromatographic run. This atomiser was used for lead-specific detection of tetraalkyllead compounds in petrol135 and in a study of the degradation of tetraethyllead in sea water.141 Bye et al. 137 found that graphite furnace atomisation was 100 times more sensitive than flame atomisation for the determination of tetramethyllead in petrol. The determination of tetraalkyllead compounds in various matrices had been well researched; for example by Cruz et al.165 in fish water sediment and vegetation samples. The group in Antwerp developed the most sensitive GC -GFAAS coupling for tetraalkyllead compounds146 and used it to determine these compounds in petro1,146J49 the atmo-sphere147J49 and in a preliminary study of their degradation in river water.149 The determination of another anti-knock petrol additive methylcyclopentadienylmanganesetricar 1136 ANALYST OCTOBER 1986 VOL. 111 Table 5. Coupled gas chromatography - atomic fluorescence spectrometry Detector Chromatography Sample Element and wavelength/ Comments nm Reference Circular N2 shielded See Table 4 in ref. 140 Tetraalkyllead compounds FAFS 3 times more Pb 140 circular air - C2H2 flame Electrothermally heated no better than quartz tube furnace electrothermal AAS sensitive than FAAS.Electrothermal AFS was Graphite cup furnace at 1000 “C bonyl in the atmosphere was achieved by Coe et a1.143 at levels down to 0.05 ng m-3 concentrations. Winefordner et a1.163 have demonstrated a novel method of avoiding matrix interference by selective volatilisation using coupled high-temperature (ca. 2093 K) GC - AAS. They used a molyb-denum column - atomiser for the separation of sodium, copper manganese and magnesium ions with an excellent correlation of analytical signals for each metal in both pure and mixed solution. This work opens a new area of application for GC - AAS as prior to this only elements that formed volatile hydrides or chelates in inorganic matrices could be separated.The technique thus offers a possible method for separating interfering concomitants from the analyte prior to atomic spectroscopic analysis. 6. Coupled Gas Chromatography - Atomic Fluorescence Spectrometry To date chromatographic applications of FAFS have utilised only line sources (Table 5). Van Loon166 first suggested the possible use of non-dispersive AFS as a detector for chromato-graphy noting its multi-element capability ability for low level detection and simplicity of usage. Although this latter point is debatable the most likely reason for the dearth of published work using GC - AFS is probably the lack of sufficiently intense stable and simple light sources. Van Loon’s group in Toronto have published the only GC - AFS work,140 in which they used il nitrogen separated circular air - acetylene flame, an inert gas shielded electrothermally heated quartz tube and a modified graphite cup atomiser.In the lead-specific detection of tetraalkyllead compounds flame AFS proved a factor of three more sensitive than FAAS; however no increase in detectability was found using AFS over AAS when the graphite cup or quartz tube atomisers were used. The availability of a commercial AFS instrument should increase the usage of the technique as the advantages of multi-element analysis and sensitive detection make AFS an excellent method for the determination of metals. 7. Conclusion Historically the MIP has proved the most popular excitation source to couple with gas chromatography.This is probably a reflection of the MIP’s ability to monitor certain non-metallic elements in addition to metals and particular mention should be made of the ability of the helium MIP to monitor halogens. Commercially available GC - MIP systems have unfortunately used low-pressure He plasmas and thus have suffered from the attendant problems of vacuum lines and gas transfer from atmospheric pressure in the chromatograph to low pressure in the detector. The availability of the Beenakker TWlo cavity, which allows an atmospheric He plasma to be sustained yields a more satisfactory GC - MIP coupling. All the plasma emission detectors offer a multi-element facility and long linear ranges which makes them attractive as GC detectors.Unfortunately the ICP and to a lesser extent the DCP involve high capital investment and high operating costs so that coupling of these detectors to GC may not prove cost effective to any but the largest laboratories. Atomic absorption detectors although having short work-ing ranges offer adequate sensitivity for trace metal specia-tion work especially if electrothermal atomisation or atom traps are used. It has been shown that the use of simple ceramic tube traps in conventional flames offers low levels of detection. It is therefore not surprising that most laboratories with a trace metal speciation requirement in which the analytes are a thermally stable volatile organometallic species favour coupled GC - AAS systems. 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Newsl. 1977, 16 79. Wolf W. R. Anal. Chem. 1976,48 1717. Chau Y. K. Wong P. T. S. and Goulden P. D. in Branica, M. and Konrad Z. Editors “Lead in the Marine Environ-ment,” Pergamon Press Oxford 1980 pp. 72-82. Andreae M. O. Anal. Chem. 1977 49 820. Grimm P. Libs S . Cressely J. and Deluzarche A. Ann. Falsif. Expert. Chim. 1977 70 523. Parris G. E. Blair W. R. and Brinckman F. E. Anal. Chem. 1977,49 378. Robinson J. W. Kiesel E. L. Goodbread J. P. Bliss R. and Marshall R. Anal. Chim. Acta. 1977 92 321. Wolf W. R. J. Chromatogr. 1977 134 159. Bye R. Paus P. E. Solberg R. and Thomassen Y. At. Absorpt. Newsl. 1978 17 131. Bye R. and Paus P. E. Anal. Chim Acta. 1979 107 169. Chau Y. K. Wong P. T. S . Bengert G. A. and Kramar O., Anal. Chem. 1979 51 186. Radziuk B. Thomassen Y. Butler L. R. P. Van Loon, J. C. and Chau Y. K. Anal. Chim. Acta 1979 108 31. Robinson. J. W Kiesel. E. L and Rhodes. I. A. L., pp. 215-225. 142. 143. 144. 145. 146. 147. 148. 149. 150. 151. 152. 153. 154. 155. 156. 157. 158. 159. 160. 161. 162. 163. 164. 165. 166. Chau Y. K. Wong P. T. S . Kramar O. Bengert G. A , Cruz R. B. Kinrade J. O. Lye J. and Van Loon J. C. Bull. Environ. Contam. Toxicol. 1980 24 265. Coe M. Cruz R. and Van Loon J. C. Anal. Chim. Acta, 1980 120 171. Van Loon J. C. Anal. Chem. 1979 51 1139A. Hahn M. H. Mulligan K. J. Jackson M. E. and Caruso, J. A. Anal. Chim. Acta 1980 118 115. De Jonghe W. Chakraborti D. and Adams F. Anal. Chim. Acta 1980 115 89. De Jonghe W. R. A. Chakraborti D. and Adams F. C., Anal. Chem. 1980 52 1974. Burns D. T. Glockling F. and Harriott M. Analyst 1981, 106 921. Chakraborti D. Jiange S. G. Surkign P. De Jonghe W., and Adams F. Anal. Proc. 1981 18 347. Chan L. Forensic Sci. Znt. 1981 18 57. Ebdon L. Ward R. W. and Leathard D. A. Analyst 1982, 107 129. Ebdon L. Ward R. W. and Leathard D. A. Anal. Proc., 1982 19 110. Chakraborti D. De Jonghe W. R. A. Van Mol W. E., Van Cleuvenbergen C. and Adams F. C. Anal. Chem., 1984 56 2692. Hewitt C. N. and Harrison R. M. Anal. Chim. Acta 1985, 167 277. Harrison R. M. and Radojevic M. Environ. Technol. Lett., 1985 6 129. Chau Y. K. Wong P. T. S . Dramar O. andBengert G. A., in “Proceedings of the 3rd International Conference on Heavy Metals in the Environment September 1981 Amsterdam,” CEP Consultants Edinburgh 1981 p. 641-643. Baker M. D. Wong P. T. S . Chau Y. K. Mayfield C. I . , and Innis W. E. in “Proceedings of the 3rd International Conference on Heavy Metals in the Environment September 1981 Amsterdam,” CEP Consultants Edinburgh 1981, Ahmad I. Chau Y. K. Wong P. T. S. Carty A. J. and Taylor L. Nature (London) 1980 287 716. De Jonghe W. R. A. Chakraborti D. and Adams F. C. in “Proceedings of the 2nd International Conference on Heavy Metals in the Environment Amsterdam September 1980.” Thompson J. A. J. in Proceedings of the 3rd International Conference on Heavy Metals in the Environment September 1981 Amsterdam,” CEP Consultants Edinburgh 1981, p. 653-656. Brueggemeyer T. M. and Caruso J. A. Anal. Chem. 1982, 54 872. Chau Y. K. Wong P. T. S . and Bengert G. A. Anal. Chem. 1982 54,246. Ohta K. Smith B. W. and Winefordner J. D. Anal. Chem., 1982,54 320. Forsyth D. S. and Marshall W. D. Anal. Chem. 1985 57, 1299. Cruz R. B. Loronso C. George S . Thomassen Y., Kinrade J. D. Lye J. and Van Loon J. C. Spectrochim. Acta Part B 1980 35 775. Van Loon J. C. At. Absorpt. Newsl. 1976 15 72. pp. 645-647. Paper A61100 Received March 25th I986 Accepted May 16th 198

ISSN:0003-2654    

DOI:10.1039/AN9861101113

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

ANALYST OCTOBER 1986 VOL. 111 1139 Use of a Matrix Modifier and L‘vov Platform in the Determination of Copper in Pooled Human Saliva by Electrothermal Atomic Absorption Spectrometry lnes Game,* Leonard0 Balabanoff Rita Valdebenito and Luz Vivaldi Facultad de Ciencias Departamento de Quimica Universidad de Concepcion Casilla 3-C Concepcion, Chile The L’vov platform was used with a common matrix modifier HN03 and NH4N03 to eliminate matrix interferences present in saliva samples during the determination of copper by furnace atomic absorption spectrometry. The NaCl matrix effects were evaluated from a graph of the absorbances versus charring temperatures using a copper solution of 20 pg I-’ with NaCl added. The results obtained by atomisation of the standard either by tube or by L‘vov platform indicate that severe interferences are observed if the modifier is absent.Precision was improved by using a combination of platform matrix modifier and standard additions techniques. The analysis of ten samples of pooled saliva gave an average of 16.7 _+ 1.6 pg I-’ of Cu and a recovery of 99 k 1.6%. The sensitivity was increased from 0.1 ng (common tube) to <0.1 ng (L‘vov platform tube). Keywords Copper determination; pooled saliva; a tomic absorption spectrometry; electrothermal a tom isa -tion; L‘vov platform matrix modifier effects During the last decade worldwide interest in trace elements has stimulated a number of studies of their concentrations in biological fluids and human tissues in order to establish their natural concentrations and to detect illnesses occupational diseases and possible toxic effects.One of the most useful methods for the determination of these trace elements is atomic absorption spectrometry with electrothermal atomisation (ETA-AAS) However the appli-cation of ETA-AAS to the determination of trace elements in biological samples is complicated by the high content of sodium chloride. This compound interferes with the determi-nations producing broad band absorption and also lowers the absorption peak of the analyte. In order to reduce interference from sodium chloride matrix modification can be performed using matrix modifiers. The following reagents have been proposed for this purpose ammonium nitrate I sodium peroxide,2 ascorbic acid,’ carbon dioxide ,4 formic acid5 and thiourea .6 This study was initiated in order to improve the ETA-AAS method for the determination of trace amounts of copper in samples with a sodium chloride matrix.A sample of human saliva was chosen. This fluid contains up to 0.10% m/V of NaCl. In order to reduce or eliminate matrix interferences we propose the use of nitric acid and ammonium nitrate as matrix modifiers. We used a combination of a graphite tube and a L’vov furnace platform (which has been proposed for improv-ing the ETA-AAS methodcs) and compared the results with those obtained using the common graphite tube. Initially we analysed sodium chloride solutions spiked with copper (synthetic solutions) and then analysed samples of pooled human saliva for copper. Experimental A Perkin-Elmer Model 503 atomic absorption spectrometer, equipped with an HGA 2100 graphite furnace and a graphite tube with a L’vov platform was used.The light source was a copper element hollow-cathode lamp intensitron and sample solutions were injected into the graphite tube by an auto-sampler (Perkin-Elmer AS-1). * To whom correspondence should be addressed. Materials and Reagents The glass containers were cleaned by soaking for 48 h in a 1 + 1 mixture of 10% V/V H2S04 and 10% V/V HN03, followed by several rinses with doubly distilled water. Drying was carried out at room temperature in a plastic-covered hood. Flasks and polyethylene containers were filled with 50% V/V HCl for 48 h. All reagents were of Merck Suprapur quality and high-purity distilled water was used for the preparation of all solutions.The furnace was purged with argon (purity 99.998% by volume). Standard solutions A 100 mg 1-1 copper standard solution was diluted such that 20 1.11 contained 0.4 0.8 1.2 and 2.0 ng of copper in each of four solutions. Analysis of Synthetic Solutions Working solutions were prepared according to the compo-sition summarised in Table 1. The synthetic solutions were used in the study of the maximum charring temperature with the L’vov platform. The results obtained are plotted in Fig. 1. Table 1. Composition of synthetic samples used for the study of absorbance vs. maximum charring temperature. Each synthetic sample always contains 0.4 ng of Cu (20 pl of 20 pg 1-’ solution). The concentrations of NaCl HN03 and NH4N03 are 1.5,189 (3 M) and 40 g 1-1 respectively Composition of the matrix * Symbols as used in Fig.1 1140 ANALYST OCTOBER 1986 VOL. 111 0.040 I I 500 1000 C h a r r i ng tern pe rat u re/"C Fig. 1. Absorbance versus charring temperature using L'vov plat-form and synthetic solutions. Symbols and matrix composition as in 500 1000 Charring temperaturePC Fig. 2. Effect of charrin temperature on absorbance for saliva pool sample with (A) HNO, ?B) HN03 + NH4N03 (L'vov platform) and (C) HNO + NH4N03 (common tube) Determination of Copper in Saliva Saliva collection method Samples of saliva were obtained in our laboratory from voluntary donors by a spitting method.9 No stimulation was used. The collected samples were mixed and homogenised by stirring and stored at 4 "C in polyethylene containers.Sample treatment and procedure Slow but substantial precipitation of protein occurred during storage at 4 "C. Consequently the total pooled sample is again homogenised by shaking for 5 min shortly before removing aliquots for analysis. Treat 5 ml of saliva* with 2 ml of concentrated nitric acid. Add 1 ml of ammonium nitrate (40 g 1-I) digest for 3 h at 80 "C and dilute to 10 ml with doubly distilled water. Using the autosampler inject 20-p1 aliquots of the sample solution ( a ) into a graphite L'vov platform tube; and ( b ) into a graphite tube without a platform. Repeat the injection five4imes for each selected charring temperature. The results are plotted in Fig. 2. * This work is part of a project that includes the analysis of saliva for a series of elements i e .Ca Mg Na and K by flame AAS P043- by spectrophotometric analysis with flow injection F- with an ion-selective electrode and Cu Mn and Zn with an HGA graphite furnace. Hence we use 5-ml aliquots of saliva because we try to analyse for all the above elements in the same (pooled) sample. If one were to analyse only for Cu the saliva sample volume could be reduced. Table 2. Instrument conditions used for the determination of copper in pooled saliva samples. Instrument parameters wavelength 325.4 nm; spectral band width 0.7 nm; lamp current 20 mA; argon flow-rate 20 ml min-1 Procedure Temperature/"C Time/s Charring . . . . . . . . 500 30-40* Drying . . . . . . . . 100-200* 40-SO* Atomisation .. . . . . 2700 8-8 * * L'vov platform. ~ Table 3. Determination of copper in pooled saliva Common tube L'vov platform tube Modifier Cu k s.d. R* k s.d. Cu f s.d. R* +_ s.d., p.p.b. Y O p.p.b. YO ACT 13.8 5 1.1 84.6 k 2.8 ACT 14.3 f 1.6 91.0 k 1.6 HN03 CCfl0.0 k 0.1 CCS14.6 I! 0.1 ACT 13.7 k 1.0 84.5 k 4.4 ACT 16.7 k 1.6 99.0 k 1.6 HN03 + NH4N0, CCf 8.2 _t 3.6 CCf 15.2 k 0.1 * R% Recovery. Each value is the mean of five determinations t AC Standard addition mean value for 10 samples of pooled f CC Calibration graph mean value for 10 samples of pooled with two additions. saliva. saliva. Procedure for measurements A temperature of 500°C was chosen for the ashing stage. Copper was determined in 5-ml aliquots of saliva that had received two standard additions of 0.4 and 0.8 ng per 20 pl and that had been treated with concentrated nitric acid and ammonium nitrate as described above.The blanks were determined by the standard additions method.10 The temperature and time of drying and atomisation of the saliva sample were determined in the usual way." The instrument parameters and conditions are given in Table 2 and the analytical results in Table 3. The recoveries of the two copper additions of 0.4 and 0.8 ng to 2 0 4 aliquots of sample solution are also given in Table 3. Results and Discussion The experimental results presented in Fig. 2 allowed us to choose 500°C as an adequate charring temperature. If the temperature is approximately 1000 "C there is diminished absorbance probably owing to the loss of part of the free atomic population of copper in the vaporisation stage.A temperature of 2700 "C was chosen for atomisation. From Fig. 1 it may be concluded that the absorption signal of the standard copper solutions with sodium chloride is lower than that of the standard copper solution without sodium chloride at different charring temperatures even when using the L'vov platform. A loss of sensitivity is observed if nitric acid is added to a copper solution that contains sodium chloride. Nevertheless the nitric acid is required to destroy the organic matter present in the saliva.12 Fig. 2 showing the maximum absorbance vs. charring temperature for saliva with nitric acid and with nitric acid and ammonium nitrate, respectively under L'vov platform analysis leads to the conclusion that the ammonium salt greatly increases the sensitivity.From Table 3 showing the results for copper in saliva it may be concluded that a sample treated with acid shows a low recovery of this element even though the L'vov platform is used. This conclusion is consistent with the graphs in Fig 2 ANALYST OCTOBER 1986 VOL. 111 The mean value found for copper with standard additions and nitric acid and ammonium nitrate treatment in a graphite tube is 13.7 k 1.0 p.p.b. with an 84.5 k 4.4% recovery. With the L’vov platform the mean value of copper rises to 16.7 k 1.6 p.p.b. and an optimum recovery of 99.0 k 1.6%. The results for the determination of copper in saliva derived from the calibration graph are lower than those obtained using the standard additions method.The combination of matrix modifier L’vov platform and standard additions allows one to obtain reproducible results. This is an indication that the L’vov platform by itself does not eliminate the sodium chloride interference. The absolute sensitivity of the method was calculated as the amount of copper in a sample that produced a 1% absorption or 0.0044 absorbance unit. This was found to be <O. 1 ng with the L’vov platform tube and 0.1 ng with the graphite tube. For artifical standarised samples of copper sodium chloride and nitric acid Figs. 1 and 2 show that treatment with ammonium nitrate substantially improves the sensitivity. Finally it can be concluded that for the determination of copper in human saliva it is convenient to add ammonium nitrate with nitric acid to digest the sample and to analyse for copper in a graphite tube with a L’vov platform using the method of standard additions.This research is part of a project (20.13.17) financed by the Direccion de Investigacion of the University of Concepcion, Chile. 1141 The authors thank Prof. P. C. Minning and Prof. M. Zamudio for their critical reading of the manuscipt. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. References Ediger R. Peterson G . and Kerber J. At. Absorpt. Newsl., 1974 13 61. Churella D. J. and Copeland T. R. Anal. Chem. 1978,50, 309. Hides D. Anal. Chem. 1980 52 959. Tominaga M. and Umezaki Y . Anal. Chim. Acta 1983,148, 285. Susuki M. Ohta K. and Yamakita T. Anal. Chem. 1981, 53,9. Bezur L. Marshall Y. Ottaway J. M. and Fakhrul-Aldeen, R. Analyst 1983 108 553. Hindeberger E. J. Kaiser M. L. and Koirtyohann S. R. At. Spectrosc. 1981 2 1. Harezov I. and Ivanova E. Fresenius 2. Anal. Chem. 1983, 315 26. Navazesh M. Christensen M. J . Dent. Res. 1982,61 1158. Camrnan K. Fresenius 2. Anal. Chem. 1982 312 515. “Analytical Methods for Atomic Absorption Spectroscopy Using the HGA Graphite Furnace,” Perkin-Elmer Norwalk, CT 1977 p. 4-1. Game I . Balabanoff L. Valdebenito R . and Vivaldi L., Bol. Soc. Chil. Quim. 1982 27 340. Paper A51455 Received December 18th 1985 Accepted April 3rd 198

ISSN:0003-2654    

DOI:10.1039/AN9861101139

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

ANALYST OCTOBER 1986 VOL. 111 1143 Selective Reduction of Arsenic Species by Continuous Hydride Generation Part 1. Reaction Media Robert K. Anderson Michael Thompson and Elisabeth Culbard Applied Geochemistry Research Group Department of Geolog y Imperial College London S W7 2BP UK Continuous hydride generation using sodium tetrahydroborate(ll1) as a reductant in conjunction with atomic absorption spectrometry (AAS) and inductively coupled plasma atomic emission spectrometry (ICP-AES) has been used to form arsines selectively from arsenate (Asv) arsenite (AsV monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA). The reaction media studied have been shown to allow the rapid determination of As111 alone DMAA alone Aslll + AsV and “total” arsenic i.e. As111 + AsV + MMAA + DMAA.Interference effects produced by heavy metal ions are suppressed by the addition of masking agents. Keywords Arsenic speciation; continuous h ydride generation; selective reduction; atomic absorption spectrometry; inductively coupled plasma atomic emission spectrometry Arsenic is a ubiquitous trace element and can be mobilised via a plethora of geochemical pathways.1 The danger of exposure of mammals and fish to the element remains a major international concern as many of its compounds are known to be toxic; this has provided a stimulus for research into its chemistry. Historically “total” arsenic has been monitored in environ-mental samples but currently there is considerable interest in establishing methods for determining the concentrations of individual species of the element.Such interest stems from the fact that toxicity decreases in the order arsine > arsenite > arsenate > alkylarsenic acids > arsonium compounds > metallic arsenic.2 The problems associated with monitoring such species have been highlighted by recent comments such as “various techniques can be used to differentiate between the many species of arsenic which are found in environmental samples. However this type of analysis is time consuming and difficult to apply routinely”.3 Many analytical techniques have been employed to detect arsenic in environmental samples including spectropho-tometry,4-12 flame atomic absorption spectrometry,13-25 elec-trothermal atomic absorption spectrometry,2G43 atomic emis-sion ~pectrometry,~“-55 voltamrnetry,5&63 gas chromato-graphy 17964-67 neutron activation analysis,68 X-ray fluores-cence spectrometry,by ion chromatography70 and atomic fluorescence spectrometry.24.71 Techniques for separating the different arsenic species are equally varied and include column chromatography,23J9) cold-trapping,17>22>4-9>74 voltammetry,56-63 liquid - liquid extraction30.36.40.43~75~76 and selective hydride genera-It can be seen that analytical techniques for the detection and speciation of arsenic are diverse.Each approach possesses both advantages and disadvantages that must be considered with respect to the scope of the study and also the laboratory facilities available. In general spectrophotometric methods are applicable only to the speciation of inorganic arsenic and are less sensitive than other alternatives.The silver diethyldithiocarbamate procedures are susceptible to interferences from both trace rnetals6.79 and methylated arsenic species.? Pre-treatment using chelation solvent extraction or ion exchange can prevent this but these operations simultaneously introduce additional analytical steps and may disturb the equilibrium between 33-35,37,39,54,62 HpLC,32,54,72,73 gas chromatography,l7,64-67 tion. 16,20,77-79 species. The procedure also employs disagreeable solvents such as pyridine benzene or chloroform which should be avoided if possible. Full colour development in arseno-molybdate methodsllJ2 requires a reaction time of 2-4 h and such methods are consequently slow.Electrometric methods can be used for the direct speciation of inorganic arsenic but indirect determination of methylated arsenicals demands perchloric acid digestion.62 Stripping voltammetric methods are however extremely sensitive. Solvent and liquid - liquid extraction are certainly applic-able to trace arsenic determination and have distinct advan-tages. The procedures can separate the analyte from complex and potential interfering matrices with simultaneous pre-concentation the latter being a distinct benefit with aqueous samples. Published methods for the speciation of both inorganic and organic arsenic species are rare and the existing methods for separating As111 and As” are time consuming. They generally involve multi-stage cycles of chelation - solvent extraction phase separation evaporation and/or back-extraction into a more suitable analytical phase prior to quantification by GFAAS.Despite its ability to separate individual species of arsenic and pre-concentrate them from large-volume water samples, ion-exchange chromatography requires multiple elutions with a range of reagents. The fractions of eluent are collected in a fraction collector and normally analysed by GFAAS. As with solvent extraction this is a tedious and time-consuming process as slow flow-rates are needed for quantitative recovery although multi-sample batches could probably be run simultaneously in routine analysis. Cold-trapping procedures established by Braman et al. 47 and Andreae,17 effectively pre-concentrate several arsenic species from 10-50-ml sample volumes allow their sequential determination with a suitable detector and have found widespread application.These procedures are relatively slow, with a minimum time of approximately 30 min per sample being required. The literature concerning selective reduction highlighted the potential for further research as the data presented were inconsistent and demanded investigation. Braman et al. 47 commented that the reduction of arsenic compounds with sodium tetrahydroborate(II1) was pH dependent and was related to the pK of the individual arsenic acids. This statement warranted an inspection of the relationship between the pH and the fraction of each undissociated arsenic aci 1144 ANALYST OCTOBER 1986 VOL. 111 present at equilibrium in aqueous solution.These functions are shown in Fig. 1 and are based on the equation where a = fraction of undissociated arsenic species present at equilibrium K1 = first dissociation constant of the arsenic acids and [H+] = hydrogen ion concentration. It is obvious from Fig. 1 why Hinners20 found that monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA) interfered with the determination of As111 and As". If it is assumed that each acid must be totally protonated in order to allow arsine formation,46 then MMAA and DMAA can be reduced between pH 1 and 8 (kinetic factors and complex formation may however affect such reduction reactions). As described previously a number of workers have utilised the pK differences of AsV and As111 in order to speciate them, but only Pahlavanpour and Thompson80 have attempted to apply selective reduction and continuous hydride generation also to the determination of organic arsenic species.However, there appeared to be discrepancies between the responses of MMAA and DMAA in the media used by Hinners,2O Arbab-Zavar and Howard21 and Pahlavanpour and Thomp-son .a0 Hydride generation by means of the continuous mixing of sample and reagents is a reliable rapid and convenient technique well suited to the analysis of large numbers of water samples in a geochemical laboratory. The technique has been in use only in the last 4-5 years and few workers have utilised its advantages for arsenic speciation studies. The research described here concerns the use of pH, reaction matrix chelating agents and redox agents for the determination of AsV AsIII MMAA and DMAA using continuous hydride generation with sodium tetrahydrobor-ate(II1) as reductant and AAS for detection.The studies were orientated so that ICP-AES could be used as an alternative detector but most of the details provided below are related specifically to the use of AAS. Experimental Apparatus The equipment and reagent requirements are similar for both AAS and ICP-AES detectors. For AAS the instrumental configuration is represented schematically in Fig. 2. It consists of a peristaltic pump uptake tubes for sample and sodium tetrahydroborate(II1) solutions a gas - liquid separator inert gas supply lines and an atomic absorption spectrometer. With this detector a quartz tube is suspended in the optical path 3 0.2 -0 1 2 3 4 5 6 7 8 9 1 0 1 1 PH Fig.1. Relationship between fraction of undissociated arsenic acids present at equilibrium and pH. Calculated from K values given by Braman et aL4' above an air - acetylene flame.15 The operating conditions of the apparatus are shown in Table 1. Reagents Unless stated otherwise the reagents were of analytical-reagent grade or better. De-ionised water (DIW) was used for dilution as this was found to be sufficiently pure for research purposes. For all routine work a 1% mlV solution of sodium tetrahydroborate(II1) in 0.1 M sodium hydroxide solution was prepared fresh daily from the powder (Aldrich). In this matrix NaBH4 has been found to be stable for up to four days.81 The arsenic reagents used were as follows: sodium arsenate Na2HAs04.7H20 (Sigma) ; sodium arsenite NaAs02 (Sigma); disodium monomethylarsonate CH3As03Na2.6H20 (Pfaltz and Bauer via Phase Separations and ICN Pharmaceuticals New York); dimethylarsinic acid (CH3)2AsO( OH) (Sigma). B 1 1 I F- 2 Fig. 2. Schematic diagram of hydride generation atomic absorption system. 1 Reductant; 2 sample; 3 peristaltic pump; 4 carrier gas; 5 , gas - liquid separator; 6 liquid waste outlet; 7 arsines pass into quartz glass absorption cell; 8 arsenic EDL; 9 carrier gas inlet for side vents; 10 burner gases inlet; 11 burner; 12 quartz glass absorption cell; 13, carrier gas outlet for side vents; 14 atomic absorption spectrometer; and 15 signal output Table 1. Operating conditions of the hydride generation atomic absorption spectrometry system AAspectrometer .. . . . . Peristaltic pump . . . . . . Wavelength . . . . . . . . Slit width . . . . . . . . Lamp . . . . . . . . . . Flame . . . . . . . . . . Uptaketubes . . . . . . Uptakerates . . . . . . Carriergases . . . . . . Carrier gas flow-rate (through phase separator) . . Gas flow-rate (through silica tube side vents) . . Pre-integration time . . . . Integration . . . . . . . . Reductant . . . . . . . . Fusedquartztube . . . . Perkin-Elmer 403 and 5000 Watson Marlow 501 193.7 nm 1 mm but spectral band Perkin-Elmer EDL (8 W) Air - acetylene Sample silicone-rubber, 0.8 mm bore Reductant silicone-rubber, 0.5 mm bore Sample 8.4-8.6 ml min-1 Reductant 3.6-3.8 ml min-' Argon width = 0.7 nm 500 ml min- 1 2 lmin-1 15 s 2 x 10s 1% mIVNaBH in 0.1 M NaOH 15 cm path length 8 mm i.d ANALYST OCTOBER 1986 VOL.111 1145 These reagents were soluble in DIW and stock solutions were prepared at 1000 pg ml-1 of As in 1 M HC1 (Aristar grade BDH Chemicals). Each of the standards was stored individually in the dark at 4 "C in stoppered glass calibrated flasks for 2-3 weeks. During this period no perceptible changes in concen-tration or speciation were noticed but fresh solutions were prepared as a matter of routine at this frequency. Each reagent was checked initially for total arsenic content by ICP-AES with conventional nebulisation. The sensitivity of this technique is not affected by speciation.The stock solutions were serially diluted (1 + 99) with DIW on a daily basis to provide working standards of 100 pg 1-1 of arsenic. Standard metal solutions (1000 pg ml-I) used during the studies on interference effects were prepared from the chlorides of analytical-reagent grade reagents. During analytical method development the concentrations of the arsenic species in the test solutions were maintained at 10 pg 1-1. Analytical Procedures The test solution and reductant solution are pumped from their respective containers by a peristaltic pump and mixed continuously in narrow-bore tubing (see Fig. 2). Simul-taneously the reduction of arsenic and decomposition of sodium tetrahydroborate( 111) occur producing arsine and hydrogen respectively. Hydrogen evolution degasses the resulting solution during its passage through the tubing, following which the gas - liquid mixture passes into the separation cell.Here the gas phase is swept by an inert carrier gas (argon) into the heated quartz atomiser tube of the spectrometer. The gaseous arsines are decomposed into arsenic atoms which absorb radiation from the source and are detected spectrometrically . When species response versus matrix constituent concentra-tion profiles were monitored matrix blanks were also analysed at each concentration. In each analytical batch some solutions were analysed in duplicate in order to ensure high-quality data. For each test matrix response profiles were generated by analysing solutions containing a constant concentration of the arsenic species (10 pg 1-I) but varying the concentrations of the reaction matrix or other reagents.Results and Discussion Mineral Acid Reaction Media Hydrochloric acid The responses generated from AsV As"' MMAA and DMAA in hydrochloric acid are shown as a function of acid concentration in Fig. 3. 0.225 . 1 rn W 0.200 - As1'' I 0.175 '2 0.150 8 0.125 v) c 3 C ; 0.100 a 2 0.075 0.050 0.025 0 1.0 2.0 3.0 4.0 5.0 HCiiM In hydrochloric acid the responses of A+ DMAA and MMAA increased rapidly with increasing acid concentration, with As111 reaching a constant value at concentrations above 0.4 M. By analysing samples over a narrow range of acid concentrations the responses for DMAA and MMAA were shown to reach maxima at 0.3 M but fell thereafter with the absorbance of DMAA approaching zero in 5 M acid.The response for AsV was low reaching a plateau between 3 and 5 M acid concentrations. These results are almost identical with those obtained recently by Narasaki and Ikeda,*2 who developed an auto-mated system for determining "total" arsenic. However the response profiles obtained by Arbab-Zavar and Howard21 and Pahlavanpour and Thompson80 differ markedly. With the former the MMAA response did not decrease with increasing HC1 concentration and the DMAA signal did not decay to zero but to only 40% of the maximum signal of the other three species. In the latter publication it is implied that the responses of both MMAA and DMAA decrease to zero. The reasons for the differences are not known although kinetic factors or mixing dynamics may be responsible.As a mixing coil was used in the method of Arbab-Zavar and Howard,21 a 24-turn reaction coil was inserted between the mixing point and the gas - liquid separator in order to assess the relative effects and increase the contact time to approximately 15-20 s. (The research by Narasaki and Ikeda82 had not been published when this work was carried out although they too used a reaction coil.) Fig. 4 shows the resulting effects and suggests that arsine formation from As" is kinetically slow with the response being increased at higher acid concentrations to a level slightly less than that of As"'. At all acid concentrations studied the responses of MMAA and DMAA were also increased relative to those obtained in the absence of a reaction coil.On the basis that the rate of reduction of AsV was inherently slow initial attempts to suppress it further by cooling the sample in an ice-bath failed to cause any significant difference in the absorbance of any species. Other mineral acid reaction media With nitric acid the results obtained were similar to those with hydrochloric acid and are shown in Fig. 5. The results obtained with sulphuric acid (Fig. 6) show that the responses for AsIII MMAA and DMAA increased rapidly with increas-ing sulphuric acid concentration but all reached maxima at about 0.1 M acidity. Unlike the responses in hydrochloric and nitric acid at concentrations above 0.1 M sulphuric acid the signals for all species decayed considerably.The reasons for this are not understood but are possibly a combination of factors including rapid reductant decomposition at higher acid 0.225 0.200 0.175 v) w y 0.150 $ 0.125 3 c ; 0.100 0 $ 0.075 a 0.050 0.025 I I I I I J 0 1.0 2.0 3.0 4.0 5.0 6.0 HCVM Fig. 3. Effect of hydrochloric acid concentration on the response of As" AsIII MMAA and DMAA during reduction by NaBH and AAS analysis and AAS analysis Fig. 4. Effect of a 26-turn mixing coil on the response of AsV As"', MMAA and DMAA in hydrochloric acid during reduction by NaBH 1146 0.200 1 I ANALYST OCTOBER 1986 VOL. 111 0.175 v) 0.150 c .-C 0.125 0 6 0.100 e a 0" 0.075 0.050 0.025 1 I I I I 0 1.0 2.0 3.0 4.0 5.0 6.0 H N 0 3 / ~ Fig. 5. Effect of nitric acid concentration on the response of AsV, As"' MMAA and DMAA during reduction by NaBH4 and AAS analysis 0.175 M'I 0.150 c 0.125 v) 4- .-a m I) 2 0.100 $ 0.075 n a 0.050 0.025 0 1.0 2.0 3.0 4.0 5.0 HZS04/M Fig.6. Effect of sulphuric acid concentration on the response of AsV Asrrr MMAA and DMAA during reduction by NaBH4 and AAS analysis concentrations sulphate interference or unknown characteris-tics of degassing. Orthophosphoric acid as a reaction matrix was found to give high background values compared with other reaction mat-rices probably owing to arsenic contamination and hence no further work was performed with this reagent. These investigations showed that some reduction selectivity can be achieved depending on both the acid matrix and the acid concentration employed.Organic Acid Reaction Media The response profiles of AsV A+ MMAA and DMAA in oxalic acid citric acid tartaric acid acetic acid and mercap-toacetic acid are shown in Figs. 7-13. With oxalic acid (Fig. 7) the maximum responses of As111 and DMAA were obtained at approximately 1% mlV oxalic acid concentration. At higher concentrations the DMAA signal decayed steadily whereas that of As111 passed through a minimum value and then increased again. The responses from MMAA and AsV were considerably lower than those of As111 and DMAA both reaching broad plateaus above 1% mlV oxalic acid concentration with MMAA giving a signal twice that of AsV. The responses produced by using citric acid (Fig. 8) were similar to those obtained with oxalic acid except that the response of MMAA was relatively slightly lower at higher acid concentrations.These results differ from these of Pahlavan-pour and Thompson.8O Attempts to separate the response profiles of As111 and DMAA by introducing a 26-turn reaction coil (15-20 s delay time) provided the data displayed in Fig. 9. It shows that the response of As111 was enhanced relative to v MMAA i AsV I 1 . 1.0 2.0 3.0 4.0 5.0 Oxalic acid % miV Fig. 7. Effect of oxalic acid concentration on the response of AsV, As"' MMAA and DMAA during reduction by NaBH and AAS analysis v) 0.125 C 4- .- 0.100 u 2 0.050 0.025 0 1.0 2.0 3.0 4.0 5.0 Citric acid % m/V Fig. 8. Effect of citric acid concentration on the response of AsV, AsIII MMAA and DMAA during reduction by NaBH and AAS analysis 0.5 1 .o 1.5 2.0 Citric acid Yo m/V Fig.9. Effect of a 26-turn mixing coil on the response of AsV AsIII, MMAA and DMAA during reduction by NaBH and AAS analysis that of DMAA. The extent of arsine formation from As"' was increased at lower citric acid concentrations without an undue increase in the signals from AsV and MMAA. However this approach did not provide a means of distinguishing adequately between As111 and DMAA in this matrix. Tartaric acid was employed in order to assess its effect on AsV as it was thought to be capable of reducing it to As"'. It can be seen from Fig. 10 that the response from AsV in this matrix was high suggesting that in the 2-3-hour contact time allowed prior to analysis there had been either partial conversion of -4s" into As111 or that the extent of arsine generation from AsV was dependent on the tartaric acid concentration.The response of MMAA was relatively higher than in other organic acid matrices studied ANALYST OCTOBER 1986 VOL. 111 1147 0.175 0.150 5 0.125 + .-0) 6 0.100 e 2 0.075 0.050 0.025 0 2.0 3.0 4.0 5.0 Tartaric acid YO m/V Fig. 10. Effect of tartaric acid concentration on the response of As"' MMAA and DMAA during reduction by NaBH and 0.175 0.1 50 0.125 MMAA As" t AsV, AAS 0 0.5 1 .o 1.5 2.0 Acetic aCid/M Effect of acetic acid concentration on the response of AsV, A@] MMAA and DMAA during reduction by NaBH4 and AAS analysis The results obtained with acetic acid are shown in Fig.11, where it can be clearly seen that this matrix allowed the generation of arsines from both As111 and DMAA to almost identical extents over the entire concentration range stud-ied.The response for AsV was low and gave a broad plateau at acetic acid concentrations greater than 0.2 M. The signal from MMAA showed a steady increase over the entire acetic acid concentration range. Good separation between the responses of ASIT' - DMAA and AsV - MMAA can be seen at 0.1-0.2 M acetic acid concentration. As with citric acid investigations with reaction coils were carried out but again no distinct separation of AsIII and DMAA profiles could be produced, despite significant enhancement of the As"' signal relative to that from DMAA at low acid concentrations.With mercaptoacetic acid as shown in Fig. 12 all arsenic species followed similar response profiles with signals rising to maxima and then decaying to zero. This was a surprising result as it was expected that results similar to those with other organic acids would be obtained. It is thought that the sulphur-containing ligand must play a significant role in effecting rapid hydride generation either through the forma-tion of a more volatile arsine or by altering the reaction mechanism. By studying a narrower range of acid concentra-tions it was seen that optimisation could be achieved with 0.1 M mercaptoacetic acid (Fig. 13). As the maximum response of each species was lower than with the other organic acid reaction media reaction coils were inserted as before in order to increase the contact and degassing time.With 0.1 M mercaptoacetic acid a 15-20% increase in response for all species was found by inserting a 14-turn coil whereas the relative increase using a 26-turn coil was only 1628%. Hence 0 0.5 1 .o 1.5 Me rca ptoaceti c aci d/M Fig. 12. Effect of mercaptoacetic acid concentration on the response of AsV A s I I I MMAA and DMAA during reduction by NaBH and AAS analysis 2 0.1 50 As" c .-DMAA 0.100 0.05 0.07 0.09 0.1 1 0.13 Mercaptoacetic aCid/M Fig. 13. Effect of a narrow range of mercaptoacetic acid concentra-tions on the response of AsV As111 MMAA and DMAA during reduction by NaBH and AAS analysis a 14-turn reaction coil was employed in all subsequent studies with this matrix in order to improve the sensitivity without unduly increasing the analysis time.In summary there were distinct differences between the responses of the arsenic species in each of the organic acid reaction media investigated. In oxalic citric and acetic acid, As111 and DMAA were reduced probably to their respective arsines and produced large signals whereas AsV and MMAA responded poorly. Of these media 0.16 M acetic acid provided the maximum separation between the responses of AslI1 or DMAA and As" or MMAA suggesting that this matrix should be further studied for determining As111 and/or DMAA in the presence of AsV and MMAA. Tartaric acid allowed the partial reduction of AsV in addition to giving high responses from As111 and DMAA whereas mercaptoacetic acid pro-duced similar peak responses for all four arsenic species.The latter was considered as a potentially valuable matrix for further study as the "total" arsenic content (AsV + As"' + MMAA + DMAA) of a sample could be measured rapidly, without the need for pre-treatment or sample digestion prior to analysis suggested in some published methods ,21325,82 Buffered Reaction Media A survey of the available literature concerning the use of buffers that are suitable for the reduction of As"' in the presence of AsV suggested that no standard matrix or constant pH had been employed. Table 2 shows the wide range of buffers pHs and reducing media that have been utilised for this purpose. The primary aim of this research was to find a chemically inert buffer that would allow the selective reduction of As111 using continuous hydride generation with minimum interfer-ence from AsV MMAA and in particular DMAA.Hence, with regard to Fig. 1 consideration was given to buffers whose working ranges covered the pH range 4-9 ANALYST OCTOBER 1986 VOL. 111 1148 Table 2. Buffers reaction media and pHs reported in previous publications for the determination of As111 in the presence of other arsenic species Publication Reaction matrix Braman etal.47 . . . . . Oxalic acid pH 1-1.5 Aggett and Aspelll6 . . . . Citrate IPH 5.5 Howard and Arbab-Zavar2' . . Acetate pH 5.0 Nakahara53 . . . . . . . HCl 2 M KHP pH 3.5-4.0 Acetatel HCl 5 M HC1,1 M Thompson and Thomerson15 . . HCI 1-4 M Ebdon et al. 24 . . . . . . HCl 5 M + KI Nakashima78 .. . . . . ZrIV + HCl 0.25 M Shaikh andTallman90 . . . . Acetate). HCI 2 M + KI citrate jPH5 HCl pH 0 Oxalic acid pH 1 Tris - HCI pH 6.2 HC1,6 M Oxalic acid 1 YO Andreae l7 . . . . . . . , F e ~ ~ ~ a n 4 9 . . . . . . . . Tris - Tris maleate pH 6.5 Thompson et d . S 0 . . . . . . HCI 5 M Hinners20 . . . . . . . Acetate pH 4.8 Gifford and Bruckenstein91 . . Potassium hydrogen Howard and Arbab-Zavar7 . . Buffers (various) HCl 6 M tartrate Species As"' As"' As"' Total As AsIII+V As111 t V ASllIi V As111 t V As111 t V As"' AslI1 As111 + V As111 + V As"' Total As As111 Total As As111 + V Asi1' Total As Ad1' Total As As111 * Discrete injection of reductant into sample as opposed to continuous hydride generation.Reduct ant 2% NaBH,* not stabilised 5% NaBH,* in 0.1 M NaOH 2% NaBH, unstabilised 1.5% NaBH4 in 0.5% NaOH 1 .0% NaBH4* unstabilised 1 .O% NaBH4 in 0.1 M NaOH 5.0% NaBH4* in 0.1 M NaOH 5% NaBH4* in 0.1 M NaOH 5% NaBH,* in 0.1 M NaOH 4% NaBH,* unstabilised 2% NaBH4* unstabilised 1% NaBH, in 0.1 M NaOH 1% NaBH4* unstabilised 4% NaBH,* in 0.1 M NaOH 1% NaBH,* in 0.1 M NaOH Preliminary experiments were therefore conducted with various buffer media to determine their optimum working pH range and concentration requirements for use in continuous hydride generation with sodium tetrahydroborate( 111) (1 % m/V) stabilised with sodium hydroxide (0.1 M). The buffers initially considered were acetic acid - acetate citric acid -citrate Tris - HC1 and ammonia - ammonium chloride.Con-siderable difficulties were encountered in finding buffer systems that would maintain a reasonably constant pH during mixing with the reductant solution stabilised by 0.1 M NaOH. On attempting to analyse samples containing an ammonia -ammonium chloride buffer (0.4 M in ammonium chloride), spurious signals were observed and the liquid in the gas - liquid separator was ejected. This matrix was excluded from further studies. The Tris - HCl buffer was prepared from 0.25 M Tris and HCl covering the pH range 7.0-8.7. No response was obtained from any of the arsenic species and there was no vigorous hydrogen evolution such as occurs at lower pH values. The responses of the arsenic species in the acetate buffer (0.4 M in acetate) can be seen as a function of pH in Fig.14. The matrix caused the simultaneous evolution of arsines from As111 and DMAA but limited recovery of As" and MMAA. The results are similar to those observed with some organic acids. Fig. 15 shows the absorbance for As111 and DMAA as a function of citrate molarity at initial pH values of 6.0 6.3 and 6.6. The responses of both As" and MMAA were negligible and have therefore been excluded from the diagram. At pH 6.0 the DMAA signal increased steadily with increasing citrate concentration whereas the response from As111 reached a plateau at citrate concentrations greater than 0.3-0.4 M. At 0.175 0.1 50 m 0.125 a 0.100 0.075 a 0.050 c .-C 3 c ((I m I] 4.0 4.5 5.0 5.5 6.0 pH of acetate buffer Fig.14. Effect of acetate buffering on the response of AsV ASIT', MMAA and DMAA during reduction by NaBH and AAS analysis higher pH values the responses of As"' and DMAA were lower for a given citrate molarity. Overall hydrogen evolution and consequently degassing rates in media whose initial pH values were greater than 6.0-6.3 (citric acid - citrate and Tris - HCl) were slow as the rate of decomposition of the reductant is strongly pH dependent. It must be concluded therefore that continuous hydride generation using hydrogen evolution as the only means of degassing arsines from solution is not feasible at pHs approaching neutrality. It must be also stated that the citrate buffer consisting of 5 + 1 sodium citrate (1 M) - citric acid (10% m/V) i.e.pH 6.0 despite its ability to provide a high response from As111 and minimum response from DMAA did no ANALYST OCTOBER 1986 VOL. 111 1149 maintain a constant pH during mixing but increased to approximately pH 9.0. Oxidising and Reducing Agents In order to change the oxidation state of inorganic arsenic species several redox systems have been used in a wide range of analytical procedures. As shown in Table 3 some of these redox systems require heating or long reaction times. The emphasis of this study was towards speed and efficiency in analysis; appropriate reagents were therefore chosen for use with the favoured reaction media. Potassium iodide (0.1% mlV) was shown to effect the rapid reduction (<3G min) of AsV in 5 M hydrochloric acid thereby allowing the selective determination of As"' + AsV with some interference from MMAA but negligible interference from DMAA.However potassium iodide failed to reduce AsV in 0.3 M hydrochloric acid or 0.16 M acetic acid at concentrations up to 0.4% mlV. In fact in the latter reaction matrix As111 was seemingly oxidised thereby providing a matrix suitable for the determination of DMAA alone. Thiourea (up to 3% mlV) and sodium thiosulphate (up to 0.4% mlV) were also employed in 0.3 M hydrochloric acid and 0.16 M acetic acid in an attempt to reduce AsV to A+ but competing reactions were found to be active. In 0.3 M hydrochloric acid the response of AsV increased with increas-ing thiourea concentration whereas the DMAA response 0.1751 1 I pH 6.3 pH 6.0 pH 6.3 0.025 v - ~ 0.1 0.2 0:3 014 0.5 0.6 Citrateh Fig.15. Effect of citrate buffering on the response of As111 and DMAA during reduction by NaBH and AAS analysis decreased. The responses of As"' and MMAA remained constant. In 0.16 M acetic acid thiourea merely caused a decrease in the response of As111 and DMAA. With sodium thiosulphate in 0.3 M hydrochloric acid sulphur precipitation occurred and caused the loss of response from all arsenic species. In 0.16 M acetic acid the extent of sulphur precipita-tion was lower than in 0.3 M hydrochloric acid but in spite of this the As111 and DMAA reponses decreased the latter markedly with increasing thiosulphate concentration. The opposite was true for As111 and MMAA. Potassium permanganate (0.5 pg ml-1) was shown to oxidise As111 to AsV rapidly (<30 s) thereby providing a matrix for the determination of DMAA alone From explora-tory studies it was found that potassium permanganate also oxidised As111 in 0.3 M hydrochloric acid.However it was thought that unless the AsV response in this matrix could be totally suppressed (see Figs. 3 and 4) thereby allowing the selective determination of organoarsenic species there were no gains to be made in pursuing this line of investigation. Interferences The presence of certain transition metal ions can suppress arsine evolution during the reduction stage of hydride generation. In early work Braman et aZ.47 mentioned that Cu and Ag interfered in the generation of arsine from alkaline solution using sodium tetrahydroborate(II1) as the reductant.Since then most workers reporting developments in hydride generation have described adverse suppressive interferences mainly from transition metal elements. Major contributions to the documentation of interference effects have been made by Pierce and Brown,s3 Smith,84 Thompson et al.,j1 Kirkbright and Taddias5 and Welz and Melcher.86 Selective chelating agents have been added to the various reaction media including l,lO-phenanthroline,85 thiosemicarbazide ,8j EDTA,22,s7 iodide j 1 tartaric acids8 and thiourea.89 Although such metal concentrations are normally low in most water bodies and are therefore unlikely to cause analytical problems heavy metal concentrations in some contaminated rivers can be relatively high.High interference effects from FeIJI Co" Ni" CuII ZnlI and MnlI were studied in the media established so far as being suitable for the selective reduction of As" AsIII MMAA and DMAA. The reaction media used in this study were hydrochloric acid (5 M) with potassium iodide (0.1% rnlV) acetic acid (0.16 M) citric acid - sodium citrate (0.4 M in sodium citrate pH 6.0) and mercaptoacetic acid (0.1 M). The last reaction matrix was used in conjunction with a 14-turn reaction coil. The concen-~~ ~~ ~~~ ~~ ~ ~ Table 3. Redox systems used in previous publications for altering the oxidation state of AsV and As1" Publication Redox system Conditions Foa et a1.92 . . . . . . . . Nakahara53 . . . . . . . . Chakraborti et al. 30 . . . . Puttemans and Massart75 .. JohnsonandPilson11 . . . . Maher34 . . . . . . . . Stauffer12 . . . . . . . Stauffer12 . . . . . . Subramanian and Meranger36 Y asui et al. 18 . . . . . . Thompson et ui. 51 . . . . , Nakashima7* . . . . . Forsberg et al. 56 . . . . . . Bodewig et aL58 . . . . . Hinners20 . . . . . . . . Chung et al. 40 . . . . . Terada et al. 93 . . . . . . Terada et al. 93 ' . . . . . KMn0 - HCI HS03- - Sz032- - HCI HS03- - S2032- - HC1 103- - HCI KI - ascorbic acid - HCI 103- - H+ KI - HCl S20S2- - H+ S2032- - HCI KI - HC1 KI - HC1 KI - HC1 S032- - H+ so2 KI - ascorbic acid - HCI TiC13 - HCI K1 - ascorbic acid - HCI S032- - KI - S2032-Is room temp. Not given 3-5 min room temp. 15 min room temp. 15 min room temp.30 min room temp. Heat 15 min room temp. 5 min room temp. 15 min room temp. Not given Not given 20-30 min 80 "C 2-3 min 80 "C 30 min room temp. 15 min room temp. 30 min room temp. 30 min room temp 1150 ANALYST OCTOBER 1986 VOL. 111 tration of each arsenic species used was 10 pg 1-1 (as in all previous studies) a level consistent with concentrations in Cornish rivers. The potentially interfering metal ion was spiked in at concentrations up to 100 pg ml-1 (i.e. up to 10 000-fold excess). Blank solutions were analysed for each matrix and matrix plus interfering ion. Calibrators were run at regular intervals but more frequently when interferences were observed. Tables 4-7 show the effects of various concentrations of metal ions on the response of arsenic species in the different reaction media.The effects are expressed as percentage deviation from the interference-free response. Differences of less than 5% are probably insignificant but those greater than 10% were considered to be a result of metal ion interference effects. In the hydrochloric acid reaction medium only Ni" caused interference at high metal concentrations. This was in agreement with Welz and Melcher.86 In the citric acid - citrate matrix only CU" interfered with signal suppression increasing with increasing Cu" concentration. At 100 pg ml-l a black, finely divided precipitate was formed which was presumably Table 4. Effect of metal ions on the recovery of arsenic species (10 pg 1-1) from the citric acid - citrate reaction matrix Interfering ion CU".. . . . Co". . . . . Ni" . . . . Z n " . . . . . . Mnrl . . * . FelI1 . . . . Concentration/ pg ml-1 1 10 100 1 10 100 1 10 100 1 10 100 1 10 100 1 10 100 Deviation (AS"') O/o - 10 - 23 - 79 0 0 0 0 0 -2 +2 -2 0 +1 -2 0 -1 0 -2 copper metal. This caused the formation of a "mirror" on the glassware which necessitated flushing through with 10% V/V nitric acid in order to effect removal. Unfortunately acetic acid and mercaptoacetic acid suffered interference problems with several metals the effects increasing with increasing metal ion concentration. In acetic acid both Cu" and Ni" gave fine black precipitates at 100 pg ml-l concentrations.In mercaptoacetic acid high concentrations of Cu" caused haziness which was thought to be due to the onset of precipitation. At 10 pg ml-1 in the mercaptoacetic acid matrix, Cu suppressed the signals from AsV and As"' to a greater extent than from MMAA and DMAA suggesting that selective metal interference may allow the selective determi-nation of certain species. In natural waters heavy metal concentrations rarely exceed 1 pg ml-1 let alone 10 or 100 1-18 ml-l and hence further studies were limited to metal concentrations not greater than 10 pg ml-1. The hydrochloric acid reaction matrix was considered to be interference free with respect to the determination of arsenic species in natural waters as nickel concentrations which could interfere are in general low.Table 6. Effect of metal ions on the recovery of arsenic species (10 pg 1-l) from the hydrochloric acid reaction matrix Deviation % AsV As111 Interfering Concentration/ ion pg ml-1 CU" . . . . 1 -1 -2 10 -2 -4 100 -4 -11 CO" . . . . 1 +1 -5 10 +2 -5 100 +3 -5 Ni'I . . . . . . 1 +3 -3 10 -2 -8 100 -22 -31 Zn". . . . . . 1 +2 -2 10 +2 -4 100 +4 -4 Mn" . . . . 1 +1 -4 10 -1 -5 100 -2 -5 Fe"' . . . . 1 +9 -2 10 +5 -2 100 +7 -5 Table 5. Effect of metal ions on the recovery of arsenic species (10 pg 1-1) from the mercaptoacetic acid reaction matrix Deviation O h Interfering Concentration/ ion pgml-1 AsV As"' MMAADMAA CU" . . . . 1 -2 -1 +2 +3 COT' . . . . 1 -1 -2 -1 -2 10 -20 -16 +3 0 100 -40 -34 -12 -22 10 -3 -4 -3 -2 100 -3 -3 -9 -2 MI' .. . . 1 -15 -11 -11 -18 10 -56 -57 -49 -49 100 -83 -89 -91 -88 10 +1 +2 +1 +2 100 +2 +3 + I +3 Mn" . . . . 1 +2 +2 -4 -6 10 0 -7 -13 -13 100 -2 -13 -18 -17 Fe"' . . . . 1 -23 -24 -23 -23 10 -46 -46 -48 -49 100 -53 -55 -57 -58 zh" . . . . 1 0 0 0 0 Table 7. Effect of metal ions on the recovery of arsenic species (10 pg 1-I) from the acetic acid reaction matrix Deviation % Interfering Concentration/ ion pg ml-1 As1r1 DMAA CUT'. . . . . . 1 -4 -12 10 -22 -38 100 -90 -91 COT'. . . . . . 1 -1 -1 10 -1 0 100 0 0 Ni" . . . . . . 1 0 -6 10 -88 -87 100 -100 -100 Z n " . . . . . . 1 -0 -6 10 -23 -33 100 -SO -70 Mn" . . . . 1 1 0 10 0 0 100 -1 -4 Fe"' . . . . 1 -6 -7 10 -4 -11 100 -6 -1 ANALYST OCTOBER 1986 VOL.111 1151 Masking Studies Chelating agents were selected for evaluation with regard to their effectiveness in removing the signal suppression caused by CulI in the citric acid - citrate matrix by Cu" Nil1 and FeII in mercaptoacetic acid and by Cu" Ni" ZnII and Fe"1 in acetic acid without affecting the arsenic species responses. Reagents studied included disodium EDTA 1 ,lo-phenanthroline thiosemicarbazide and thiourea. It was found that in the citric acid - citrate matrix EDTA (0.001-0.04 M) enhanced the interference effect of Cu", whereas both thiosemicarbazide (0.02-0.05 M) and thiourea (0.2-0.4 M) were effective masks. In the acetic acid reaction matrix a combination of EDTA (0.02 M) and thiourea (0.04 M) or thiosemicarbazide (0.02-0.05 M) were shown to prevent interference effects.The oxidation of As111 to As" in this matrix with potassium permanganate (0.5 pg ml-1) was only possible prior to the addition of masking agents and hence the order of reagent addition is critical here if selective determina-tion of DMAA is required. In the mercaptoacetic acid reaction matrix a combination of 1 ,10-phenanthroline (0.005 M) EDTA (0.02 M) and thiourea (0.04 M) was found to prevent interferences from those metals studied. In the latter matrix the haziness observed with high concentrations of Cu" disappeared immediately on addition of thiourea. Also after 10-15 min of analysis with this combination of matrix and reagents a dark ring formed around the neck of the U-section of the gas - liquid separator.This had no adverse effects on the instrument response and could be readily removed with a 2-ml injection of 10% V/V nitric acid. Blank concentrations of arsenic in reaction media contain-ing masking agents were either very low or indistinguishable from the response of the reaction medium alone. Thiourea at high concentrations (>0.06 M) in acetic acid was the only combination that affected the response of any of the arsenic species and was therefore not used at these concentrations in later research. None of the other masking agents at any concentration studied affected the relative response of the various arsenic species. Conclusions Of the media and reagents investigated several combinations have shown promising selectivity towards the reduction of As" As"I MMAA and DMAA.It has been shown clearly that it is not only pH that affects the reduction of individual arsenic species [see equation (l)] but other factors such as kinetic control and complexation are also involved. Where metal ion interference effects were observed in the preferred reduction media masking agents were shown to suppress them. With due consideration towards the research carried out, the reaction media selected for evaluation with natural waters from Cornish rivers were as follows: hydrochloric acid (5 M) with potassium iodide (0.10/, m/V) for the determination of total inorganic arsenic (As"' + AsV) (note that in this matrix a small response from MMAA may be also found); citric acid - sodium citrate (0.4 M in sodium citrate pH 6.0) for the determination of As"'; thiourea (0.4 M) was added to prevent interference from Cu"; acetic acid (0.16 M) for the determination of As111 and DMAA or DMAA alone after oxidation of AsJ1' to As" with potassium permanganate (0.5 pg ml-1); thiourea (0.04 M) and Na2 EDTA (0.02 M) were added to prevent metal interferences; mercaptoacetic acid (0.1 M) for the determination of "total" arsenic (AsV + As"' + MMAA + DMAA); Na2EDTA (0.02 M) thiourea (0.04 M) and 1,lO-phe-nanthroline (0.005 M) were included to prevent metal ion interferences; a 14-turn mixing coil was included in the reaction path.The authors acknowledge the financial support of the Natural Environment Research Council. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 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ISSN:0003-2654    

DOI:10.1039/AN9861101143

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

ANALYST OCTOBER 1986 VOL. 111 1153 Selective Reduction of Arsenic Species by Continuous Hydride Generation Part II.* Validation of Methods for Application to Natural Waters Robert K. Anderson Michael Thompson and Elisabeth Culbard Applied Geochemistry Research Group Department of Geolog y Imperial College London S W7 2BP UK Preliminary research has been concerned with the selective determination of arsenate (Asv) arsenite (Aslll), monomethytarsonic acid (MMAA) and dimethylarsinic acid (DMAA) using continuous hydride generation and atomic absorption spectrometric detection. These studies (Part I) highlighted certain media as being suitable for monitoring Aslll As111 + AsV DMAA alone and As111 + AsV + MMAA + DMAA. Details are provided of the application of these procedures to the determination of arsenic species in contaminated streams draining mineralised areas of Cornwall.The data generated have been compared with those produced by a cold-trapping technique and statistical methods have been utilised to test the analytical accuracy. Keywords Arsenic speciation; continuous hydride generation; selective reduction; natural waters In order to test rigorously original analytical methods devel-oped during preliminary research studies three alternative approaches are potentially feasible. In the first approach the new method is applied to certified reference materials. However these are not generally available for speciated analytes. In the second approach known concentrations of the analytes are spiked into a natural sample the analytical procedures are applied and the recovery efficiency is measured.In practice this often may be the only recourse available to the analyst. It is appropriate for speciation methods provided that there is effectively no equilibrium between species within the time scale of the study. In the third approach two dissimilar analytical procedures can be applied to the same set of samples and the resulting data compared. Generally a limitation of this approach is that there may be no alternative method available in speciation studies. Many workers have stressed the importance of testing analytical procedures during their actual development. For example reviewing pre-concentration procedures for waters, Van Griekenl stated that “a common failure of most publications is the lack of thorough and systematic checking of the performance of these procedures for waters containing abundant alkaline earth and alkali metal ions examination of complications caused by humic material and the effects of variable speciation of the trace metals.” Briigmann et a1.2 suggested that one of the reasons for the lack of inter-comparisons found in the literature is that most laboratories specialise in just one method.They advocated the application of several methods in order to furnish accurate metal determinations. Sturgeon et al. 3 suggested that a comparison of data between suitably different analytical methods is a way of testing their validity in those instances where potential interferences must be overcome and standard reference materials are not available.The results give confidence in the ability of individual methods to give accurate analytical data. (An important and useful review of these approaches has been provided by Keith et a1.4) Thompson5 advocated the use of weighted regression methods for the comparison of accuracy and has reviewed this subject. A properly applied statistical approach can provide information regarding rotational and translational bias or a combination of the two in addition to speciation effects. Tests for significant deviations from a slope of unity a zero intercept or linearity therefore highlight bias in analytical accuracy. * For Part I of this series see page 1143. In the light of these comments considerable efforts have been made to test thoroughly the developments described previously.6 In this study the validation was performed by comparison of virtually independent methods.The data were generated from the analysis of freshly collected water samples from contaminated rivers and estuaries. Both the selective reduction procedures and an established cold-trapping tech-nique were employed and the results were compared by simple linear regression and with maximum likelihood estima-tion. Experimental Apparatus The apparatus required for the selective reduction of arsenic species has been described previously.6 The equipment required for the cold-trapping technique has been described by Braman et al.7 and the procedures are well established. In summary the volatile arsines were generated by injecting sodium tetrahydroborate(II1) into a reaction vessel containing a buffered water sample.Potassium hydrogen phthalate allowed the selective determination of As”’ whereas the use of oxalic acid allowed the formation of arsines from all species. Helium was then passed through the sample for a few minutes, thereby carrying the arsines into a glass bead U-trap sus-pended in liquid nitrogen. After removing the cold trap the pre-concentrated arsines were thermally desorbed and passed into a d.c. discharge and detected by emission spectrometry. All glassware electrodes for the d.c. discharge and electronic components were constructed locally the specifications for which have been fully detailed.8 Reagents Selective reduction procedures Acetic acid 1 M stock solution.Prepare from AnalaR or Aristar grade material (BDH Chemicals). Add 1.6 ml to 10-ml sample tubes. Mercaptoacetic acid (thioglycolic acid) 2 M stock solution. Prepare from GPR grade material (BDH Chemicals). Add 0.5 ml to 10-ml sample tubes. Hydrochloric acid 11.4 M. Aristar grade (BDH Chemicals). Add 4.5 ml to 10-ml sample tubes. Citric acid 10% mlV stock solution. Prepare from analyti-cal-reagent grade material (Sigma) 1154 ANALYST OCTOBER 1986 VOL. 111 Sodium citrate 1 M stock solution (29.41 g per 100 ml). Prepare from analytical-reagent grade material (BDH Chem-icals). Citric acid - citrate matrix 30 ml of 10% mlV citric acid + 150 ml of 1 M sodium citrate (PH 6.0). After adding thiourea (see below) add 4.8 ml to 10-ml sample tubes. Potassium iodide 2% mlV stock solution.Prepare from analytical-reagent grade material (BDH Chemicals). Add 0.5 ml to hydrochloric acid reaction matrix. Thiourea 1 M stock solution (7.61 g per 100 ml). Prepare from analytical-reagent grade material (BDH Chemicals). Add 0.4 ml to acetic acid matrix in a 10-ml tube. Also add 11.42 g per 180 ml of citric acid - citrate reaction matrix. l,lO-Phenanthroline 0.1 M stock solution. Initially dissolve 1.98 g of analytical-reagent grade material (Sigma) in 3 ml of 2 M mercaptoacetic acid plus a few millilitres of de-ionised water then dilute to 100 ml (not readily soluble). Add 0.5 ml to a 10-ml sample tube containing the mercaptoacetic acid reaction matrix. EDTA disodium salt 0.1 M stock solution (7.44 g per 100 ml).Prepare from analytical-reagent grade material (BDH Chemicals). Add 2.0 ml to acetic acid and mercaptoacetic acid reaction media. Thiosemicarbazide 0.1 M stock solution (0.91 gper 100 ml). Prepare from analytical-reagent grade material (Sigma). Use as an alternative to thiourea 0.03-0.05 M in the citric acid -citrate matrix. Sodium tetrahydroborate(III) 1% mlV stabilised in 0.1 M NaOH. Prepare from analytical-reagent grade material. The arsenic species used as calibrators (i. e. reference solutions) have been described previously.6 Liquid nitrogen trapping procedures Potassium hydrogen phthalate 5 YO mlV stock solution. Prepare from analytical-reagent grade material (Sigma). Oxalic acid 10% mlV stock solution (saturated). Prepare from analytical-reagent grade material (Sigma).Sodium tetrahydroborate(III) 2% mlV unstabilised aqueous solution. Prepare from analytical-reagent grade material (Aldrich). Sample Collection Samples were collected from the Rivers Hayle Gannel and Carnon in Cornwall UK. These rivers are affected by widespread contamination from mining in a mineral province high in arsenic. All glassware and plasticware was leached for a minimum of 24 h in nitric acid (loyo) rinsed 3-4 times with de-ionised water and allowed to dry. Filters (0.4 pm pore-size Nucle-pore) were treated similarly. For the analysis of natural water samples using selective reduction procedures the preparation of reaction media and masking agents was performed prior to travelling to the field area. Masking agents were weighed and stored in covered beakers awaiting dissolution and dilution immediately prior to analysis.Appropriate volumes of the aqueous reaction media were dispensed into the sample tubes which were then capped ready for sample and masking agent addition. For the analysis of natural water samples using the cold-trapping procedure reagents were prepared on the morning of analysis. On each field expedition a single river was sampled during a period of approximately 6 h with samples being collected from sequential sampling sites travelling upstream from the estuary. This approach was employed primarily to avoid the effects of the disturbance of naturally deposited river sedi-ments which otherwise contaminate the non-filterable fraction (“particulates”) and possibly the filterable fraction (<0.4 pm, “dissolved” phase) of the water samples downstream from the sampling point.The reason for sampling one river in a single day was based on the comments of several workers on the stability of arsenic species in water samples. For the purposes of this study it was concluded that the time delay between sampling and analysis was an important parameter that needed to be addressed especially as a statistical comparison of accuracy was to be made between two analytical tech-niques. Another important consideration was that of field filtration. From early work it was known that arsenic was measurably lost from the filterable fraction of sea water and fresh water samples containing high concentrations of iron and man-ganese when stored for just 5-6 h prior to filtration.It is well known that both As” and AsIxx are adsorbed or coprecipitated on hydrous iron(II1) oxides.9 The sampling scheme adopted prior to the determination of arsenic species was as follows. At each sample site along the river a 1-1 high-density polyethylene sampling bottle was rinsed four times with the sample. A fifth sample was retained for 5 min before discarding in an attempt to saturate adsorption sites on the vessel walls. A sixth sample was taken as the representative sample from that site. In each operation the water sample was taken from below the water surface and where possible well above the sediments in order to avoid contaminating the sample with metal-rich material. A polyethylene syringe was initially rinsed several times with the sample and was then used to force 60-ml portions through a 25 mm diameter 0.4 pm pore size polycarbonate membrane filter (Nuclepore) supported in a Swinnex filter holder (Millipore).The filtrate was collected in a 300-ml high-density polyethylene sample container which was rinsed thoroughly with three 10-ml volumes prior to filling the entire vessel. This procedure was rapid with minimum delay between sampling and removal of non-filterable material. (The par-ticle-loaded membrane filters were stored separately in Petri dishes for each sample location. Details of acid leaching procedures and subsequent analysis of leachates will be published elsewhere .) Delays in filtration have been found seriously to affect “soluble” arsenic results with significant losses even after a few hours of storage.The 300-ml sample containers were packed together in black plastic and returned to the laboratory (overnight) within 18-24 h of collection. Approximately ten samples were taken from each river the number representing the maximum that could be safely collected and filtered during the daylight hours of February March and early April 1985. Also although the selective reduction procedures are rapid the cold-trapping procedure is inherently slow and the maximum number of samples that can comfortably be analysed for the different arsenic species was approximately ten per working day. The sample was not acidified as analysis occurred within 20-26 h of sampling during which time it was believed that speciation changes would be negligible.Also as selective reduction relies to a great extent on pH additional operations may have contaminated the sample and re-adjustment of pH would have been necessary on return to the laboratory. As a check, arsenic speciation was monitored for several days after the first sampling expedition and it was found that most samples were stable for only 3-4 days. Analytical Procedures On returning to the laboratory the samples were prepared for analysis in the media described above (1 + 1 dilution) and then analysed using selective reduction procedures as previously described.6 In order to ensure high-quality data blanks and calibrators (i.e. reference solutions) were analysed at inter-vals of six to eight samples with 10-15% of the samples being run as duplicates.In each analytical batch some samples were analysed repeatedly to provide further precision data. The samples were then stored overnight in the dark at 4 “C in order to limit changes in arsenic speciation. The following day th ANALYST OCTOBER 1986 VOL. 111 1155 samples were analysed once again using the cold-trapping procedures7 with similar emphasis on data quality control. Results and Discussion Comparison of Accuracy Neither MMAA nor DMAA was detected in any of the water samples collected from the contaminated Cornish streams by either method (detection limits were approximately 0.2 pg 1-l for the cold-trapping procedures with a 10-ml sample). The scatter plots in Figs. 1-7 therefore show the correlation between arsenic data generated using selective reduction (SR) and cold-trapping (CT) procedures only for the inorganic arsenic species.The plots display As111 determination in: (i) acetic acid (SR) vs. citric acid - citrate (SR) Fig. 1; (ii) acetic acid (SR) vs. potassium hydrogen phthalate (CT) Fig. 2; and (iii) citric acid - citrate (SR) vs. potassium hydrogen phthalate (CT) Fig. 3; (i) HC1 (SR) vs. mercaptoacetic acid (SR) Fig. 4; (ii) HCl (SR) vs. oxalic acid (CT) Fig. 5; and (iii) mercaptoacetic acid (SR) vs. oxalic acid (CT) Fig. 6. The data for AsV were generated by subtracting AslI1 concentrations measured in the citric acid - citrate matrix (SR) from the total inorganic arsenic concentrations measured in the HCl matrix (SR) and also by subtracting As111 concentrations and As111 + AsV determination in: Asill - acetic acid/pg I-' Fig.1. (selective reduction) us. citric acid - citrate (selective reduction) Scatter plot for the determination of As111 in acetic acid 10-1 1 00 10' 102 As~ll - acetic acid/,ug I-' Fig. 2. Scatter plot for the determination of As"' in acetic acid (selective reduction) vs. potassium hydrogen phthalate (cold trap-ping) measured in potassium hydrogen phthalate (CT) from As111 + As" concentrations measured in the oxalic acid matrix (CT). The scatter diagram for As" determinations is shown in Fig. 7. In order to determine the equation of the "line of best fit" through the data points two regression techniques were employed simple linear regression (SLR) and the maximum likelihood regression (MLR).In order to apply SLR to the statistical comparison of data generated by two analytical 102 r I PI PI Q Q -t 10' .-h E w 8 100 2 I -lo-' 1 00 10' 102 As1ii - citric - citrate/pg I-' Fig. 3. Scatter plot for the determination of As"' in citric acid -citrate (selective reduction) vs. potassium hydrogen phthalate (cold trapping) (AS"' + AS") - HCl/yg I-' 2 + AsV in Fig. 4. hydrochloric acid (selective reduction) vs. mercaptoacetic acid (selective reduction) Scatter plot for the determination of AsI" m 5. PI P Q . .-2 c lo2: 0 10' 8 -%I a + 100 10' 102 (AS"' + AS") - HCI/pg I-' Fig. 5. Scatter lot for the determination of As"' + AsV in hydrochloric acid gelective reduction) us.oxalic acid (cold trapping 1156 ANALYST OCTOBER 1986 VOL. 111 methods the technique with the lower variance was used as the independent variable (abscissa) and that with the larger variance as the dependent variable (ordinate).5 The variance data were initially obtained by plotting the mean of replicate measurements against their standard deviation. The linear functions were then used not only to determine the x and y variances for the SLR routine but also to generate the variance data for MLR. The equations of the "lines of best fit" for SLR were generated using the software package "Minitab" and those for MLR using a program written by Ripley10 and tested by Thompson.5 No outlying data points were excluded from the statistical analyses.It has been shown that SLR gives accurate estimates of bias between methods only if (i) ten or more samples are used (ii) the samples cover the concentration range from zero upwards in a uniform manner and (iii) the results from the method with the smaller variance are used as the independent variable (x value). All these conditions have been satisfied during the statistical analyses. MLR on the other hand is known to give true estimates of bias under all circumstances. To conclude a visual inspection of the scatter plots in Figs. 1-7 suggests that no analytical bias exists. A comparison of the two data sets in Tables 1 and 2 reveals a number of interesting features and indicates that as expected MLR and SLR do not give identical results. In all instances the standard errors for the intercepts generated by SLR are larger than those produced by MLR whereas the standard errors of the slopes are similar.SLR has produced data for intercepts which in all (AsIII + AsV)- mercaptoacetic acid/pg I-' Fig. 6. Scatter plot for the determination of As111 + As" i n mercaptoacetic acid (selective reduction) vs. oxalic acid (cold trapping) AsV - selective reductioniwg I-' Fig. 7. reduction vs. cold-trapping procedures Scatter plot for the determination of As" by selective but one instance are not significantly different from zero (t-test). This is not so for MLR where only two intercepts are shown to be not significantly different from zero. Inspection of the residuals of the regression equations indicated no curva-ture of the lines.Although the application of SLR and MLR techniques produced slightly different regression equations and hence different coefficients with most comparisons they indicated only minimal rotational and/or translational bias. Given the difficult nature of sampling storage and the analysis of arsenic species in natural waters the results show acceptable agree-ment. Table 1. Regression equations coefficients and standard errors generated by simple linear regression analysis for the comparison of accuracy* Y variable HCI Oxal. Oxal . Cit. KHP KHP AsV CT X variable Merc. HCl Merc. Ace t . Acet. Cit. AsV SR Statistical significance n (a = 0.05) a (SE) b (SE) u = -0.197 (0.450) 41 NSo b = 1.023 (0.015) NS1 b = 1.010 (0.020) NSI b = 1.040 (0.013) S1 b = 0.990 (0.012) NSI b = 0.927 (0.017) S* b = 0.935 (0.016) S1 u = -0.242 (0.619) 41 NSo ~ = - 0 .6 0 0 (0.402) 41 NSo u = -0.213 (0.336) 37 NSo ~=-0.204 (0.472) 37 NSo u = 0.021 (0.441) 37 NSo u = 0.554 (0.257) 30 So * Key to HC1 = Merc. = Acet. = Cit. = KHP = Oxal. = AsVCT = AsVSR = CT = SR = a(SE) = b (SE) = so S1 NSo = NS1 = n -- --a - -b = 0.845 (0.047) s1 Tables 1-4: hydrochloric acid matrix (selective reduction). mercaptoacetic acid matrix (selective reduction). acetic acid matrix (selective reduction). citric acid - citrate matrix (selective reduction). potassium hydrogen phthalate matrix (cold trapping). oxalic acid matrix (cold trapping). cold trapping for AsV.selective reduction for AsV. cold trapping. selective reduction. value of intercept (standard error in parentheses). value of slope (standard error in parentheses). significantly different from zero. significantly different from unity. not significantly different from zero. not significantly different from unity. number of pairs of data. level of significance. Table 2. Regression equations coefficients and standard errors generated by maximum likelihood regression analysis for the compari-son of accuracy. For abbreviations see footnote to Table 1 Variables HClIMerc. Oxal./HCl Oxal ./Mere. Cit ./Ace t . KHP/Acet . KHP/Cit . AsV CT/AsV SR a (SE) b (SE) a = 0.391 (0.016) b = 0.941 (0.006) a = 0.397 (0.037) b = 0.904 (0.012) a = 0.039 (0.041) b = 0.959 (0.013) u = -0.013 (0.028) b = 0.945 (0.012) u = -0.154 (0.052) b = 0.862 (0.022) u = -0.135 (0.053) b = 0.923 (0.024) a = 0.114 (0.049) b = 0.974 (0.077) Statistical significance n (a = 0.05) 41 So SI 41 So S1 41 NSo S1 37 NSo s1 37 so s1 37 so s1 30 So NS ANALYST OCTOBER 1986 VOL.111 1157 There is no evidence of interference from transition metal ions such as Fe Cu or Ni despite their high concentrations in some Cornish rivers. This was verified by the results of a separate multi-element analysis using ICP-AES which indi-cated that no interfering metal ions would be present above 10 yg ml-1 in the samples from any of the heavy metal contaminated sampling sites. Analytical Precision Table 3 shows examples of the range of concentrations found in the Cornish rivers sampled and gives details of the means and relative standard deviations of replicate data.It can be seen that for approximately similar concentrations of the arsenic species the analyses using selective reduction proce-dures are more precise than those using cold trapping. The indirect determination of AsV is less precise than the determination of both As"' and As111 + AsV using both types of analytical approach. This is to be expected as the concentration of AsV was determined as the difference between A P and As111 + AsV concentrations both of which have associated analytical errors. At concentrations ap-proaching the practical detection limits the relative standard deviation of any analytical method increases and this effect is reflected in the precision data in Table 3.Table 3. Examples of the precision of replicate determinations using selective reduction and cold-trapping procedures over a wide range of concentrations in natural waters. For abbreviations see footnote to Table 1 Mean of Relative Reaction Number of replicated standard deviation % matrix replicates I-' HCI (SR) 6 1.4 38 4 4.1 1.2 7 33.3 1.5 5 61.6 3.4 Merc. (SR) 6 8.2 3.1 5 20.7 1.7 Acet. (SR) 4 0.6 16 5 4.6 7.1 6 12.5 3.2 5 63.4 2.0 4 4.6 7.1 5 28.6 4.0 5 61.8 3.8 5 82.7 3.4 5 1.3 14.4 5 2.1 2.5 7 4.6 11.3 5 7.8 4.5 9 50.2 7.9 Oxal. (CT) 4 2.3 6.1 7 8.7 4.4 7 9.7 6.1 4 2.8 30 4 7.0 28 4 9.7 29 Cit.(SR) 5 0.5 36 AsV (SR) 4 0.7 32 KHP (CT) 10 0.13 32 AsV (CT) 4 0.2 57 Table 4. Practical detection limits of arsenic determinations in the various reaction media using selective reduction and cold-trapping procedures. For abbreviations see footnote to Table 1 Reaction matrix species Detection limit/vg 1-' HCl (SR) As111 + AsV 0.2-0.6 (n>30) Merc. (SR) As"' + AsV 0.3-0.7 (n>30) Acet. (SR) AslI1 0.3-0.7 (n>30) Cit. (SR) As111 0.3-0.7 (n>30) Oxal. (CT) Asr1' + AsV KHP (CT) As111 0.1 (10-mlsample,n = 10) 0.1 (10-ml sample n = 10) Detection Limits The detection limits expressed as three times the standard deviation of multiple blank determinations for the analysis of arsenic species in the various reaction media using selective reduction procedures are shown in Table 4.The detection limits for the selective reduction procedures were determined on several occasions by repeatedly analysing blank solutions and hence are expressed as a range. It is unlikely that the detection limits of the selective reduction procedures can be improved greatly with existing instrumentation. Calibration Graphs With the selective reduction procedures the calibration graphs were typical of those normally found with atomic absorption spectrometry; they were linear at low arsenic concentrations (0-15 pg 1-1) with curvature increasing at higher levels. The responses in each reaction medium were broadly similar. Calibrations generated with AsV AsIII, MMAA and DMAA in mercaptoacetic acid all follow similar curves.As111 or DMAA in the acetic acid matrix and As111 or AsV in the hydrochloric acid matrix also give similar calibra-tion graphs. Conclusions Environmental data for arsenic are limited although recently research efforts have been orientated towards its monitoring. Unfortunately data for arsenic speciation in UK waters are even more scarce probably because of the general difficulties associated with speciation measurement. This fact was high-lighted in a recent survey of river and estuarine waters in the UK in which water samples from rivers throughout the UK were analysed for arsenic.11 As mentioned previously the authors stated that "various techniques can be used to differentiate between the many species of arsenic which are found in environmental samples.However this type of analysis is time consuming and difficult to apply routinely". It is believed that the speciation procedures studied and de-veloped during this research programme and which are described above can be applied routinely and have been shown to give accurate and precise estimates of detectable species of arsenic in fresh and saline waters. By definition selective reduction allows the determination of arsenic species both individually and in combination with others. The time required for a single determination is approximately 1 min whereas a determination of As111 using cold trapping requires 10 min and that of total inorganic arsenic (i.e. As111 + AsV) as well as methylated species requires about 15 min. The cold-trapping procedures were also found to be less precise than the selective reduction procedures.However there are also some disadvantages to the selective reduction approach to the determination of arsenic speciation. The detection limits are not as low as those which can be and have been attained using the cold-trapping technique. This may be a consequence of the speed of determination. With cold trapping the volatile arsines are pre-concentrated in a liquid nitrogen-cooled U-trap over a period of 5-10 min and ultimately pass as a "plug" of analyte to the detector. With continuous hydride generation the number of arsenic atoms in the quartz glass cuvette of the detector rapidly attains a steady-state concentration within 15-20 s of mixing the sample with reductant but the reaction is unlikely to go to completion and there is no pre-concentration.It was not possible to monitor the efficacy of using the selective reduction procedures for the determination of methylated arsenic species in waters as none was detected, despite the reports that these species can represent a considerable fraction (up to approximately 50%) of the total arsenic present in some water samples.7~12~13 The low temper 1158 atures in February and March when sampling took place may inhibit the biological formation of such species. The direct determination of organoarsenic species using selective reduc-tion procedures may not be possible for some aqueous media, where their natural concentrations are below the practical detection limits of the method. However the procedures could be used to determine directly such species at higher concentrations for example after their addition to the natural environment as agrochemicals such as DMAA.High ratios of combinations of the different species may cause small mutual interferences although in these studies these were not observed presumably because the AsV/AsIII ratios were low. Despite these potential drawbacks during the research described the system has been shown to be reliable accurate, precise and rapid and hence suitable for the routine analysis of large numbers of water samples in a geochemical laboratory. The approach allows minimum sample handling unlike procedures such as solvent extraction or ion exchange and is less likely to suffer from the problems of contamination or alteration of arsenic speciation.It has been shown that the sampling storage and analytical schemes work efficiently and are feasible. It may ultimately be possible to automate the mixing of sample and reaction media in the same way that the sample plus reaction media are currently continuously mixed with reductant. This could follow the research of Arbab-Zavar and Howard,l4 Gum15 and Narasaki and Ikeda16 using multi-channel peristaltic pumps. It appears that the mercaptoacetic acid matrix may be more suitable for the quantitative determination of total soluble arsenic ( i e . AsV + As111 + MMAA + DMAA) in water samples than those media used by the above workers. From their response profiles and comments,14-16 it seems likely that DMAA will be underestimated in hydrochloric acid although Gunnl5 claimed total recoveries for all arsenic species studied after automated digestion with sulphuric acid and potassium persulphate and final determination in hydrochloric acid.The reaction media could also be used to determine arsenic species directly or alternatively in the absence of a graphite furnace atomic absorption spectrometer after pre-concentration or separation by solvent extraction or ion exchange. The detection limits 0.2-0.7 pg 1-1 of As are slightly lower than those reported in the UK river and estuary survey by the Water Research Centre 0.6-1.0 pg 1-1,11 and are therefore thought to be adequate for normal purposes. However for open-ocean or sea water analysis or the determination of methylated species at ultra-trace levels (<1 pg 1-1) sample ANALYST OCTOBER 1986 VOL.111 pre-concentration may be always necessary. Here most workers have used cold-trapping pro~edures~7J7.18 although more recently solvent extraction - hydride generation19 and ion exchange have also been employed.20 Clearly sensitive analytical techniques are important in this type of research, but their successful application is dependent on careful sample handling prior to analysis. The authors acknowledge the financial support of the Natural Environment Research Council and thank Dr. David L. Johnson (Syracuse University New York State) for his assistance during this work. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. References Van Grieken R. E. Anal. Chim. Acta 1982 143 3. Brugmann L. Danielsson L. G. Magnusson B. and Westerlund S . Mar. Chem. 1983 13 327. Sturgeon R. E. Berman S. S . Desaulniers J. A. H., Mykytiuk A. P. McLaren J. W. and Russell D. S . Anal. Chem. 1980,53,2337. Keith L. H. Libby R. A. Crummett W. Taylor J. K., Deegan J. Jr. and Wentler G. Anal. Chem. 1983,55,2210. Thompson M. Analyst 1982 107 1169. Anderson R. K. Thompson M. and Culbard E . Analyst, 1986 111 1143. Braman R. S. Johnson D. L. Foreback C. C. Ammons, J. M. and Bricker J. L. Anal. Chem. 1977 49 621. Anderson R. K. PhD Thesis University of London 1985. Hem J. D. Geochim. Cosmochim. Acta 1977 41 527. Ripley B. unpublished work 1981. Mance G. Musselwhite C. and Brown V. M. Water Res. Centre Tech. Rep. 1984 TR 212. Andreae M. O. Anal. Chem. 1977 49 820. Shaikh A. U. and Tallman D. E. Anal. Chim. Acta 1978, 98,251. Arbab-Zavar M. H. and Howard A. G. Analyst 1980,105, 744. Gunn A. W. Water Res. Centre Techn. Rep. 1983 No. 191. Narasaki H. and Ikeda M. Anal. Chem. 1984 56 2059. Andreae M. O. Deep-sea Res. 1978 25 391. Howard A. G. Arbab-Zavar M. H. and Apte S. Mar. Chem. 1982 11,493. Amankwah S. A. and Fasching J. L. Talanta 1985,32,111. Person J. A. and Irgum K. Anal. Chim. Acta 1982 138, 111. NOTE-Reference 6 is to Part I of this series. Paper A6111 9 Received April 16th 1985 Accepted May 19th 198

ISSN:0003-2654    

DOI:10.1039/AN9861101153

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

ANALYST OCTOBER 1986 VOL. 11 I 1159 A/-Oxalylamine(salicylaldehyde hydrazone) as an Analytical Fluorimetric Reagent for the Determination of Nanogram Amounts of Aluminium Fernando de Pablos Jose Luis Gomez Ariza and Francisco Pino Department of Analytical Chemistry Faculty of Chemistry University of Seville Seville Spain The synthesis characteristics and an a lytica I app I icat ions of N-oxa I yla m i ne( sa I icy1 a I de hyde hyd razon e) OSH, are described. The AI(III) - OSH system was studied and a spectrofluorimetric method is proposed for the determination of Al in a medium of water - dimethylformamide (1 + 1) at pH 3.7. Under these conditions the complex has excitation and emission maxima at 387 and 474 nm respectively. The detection limit is 5 p.p.b. and Al can be determined up to 160 p.p.b.Interferences were evaluated; Ga(lll) In(lll) Sb(lll) and Zr(lV) gave the greatest perturbations. The method has been applied to the determination of aluminium in mineral waters. Keywords N-Oxalylamine(salicylaldehyde hydrazone) reagent; aluminium determination; fluorimetry Derivatives of oxalylmonohydrazide and oxalyldihydrazide are structurally related to cuprizone but differ from it in the reactivity of the metal because the ring at the end of the cuprizone molecule is not aromatic. We began to carry out analytical investigations of these compounds in our Depart-mentl as previous work2-6 had shown the affinity of these reagents to metal ions of pseudo-noble gas electronic con-figurations such as Al(III) Ga(II1) and In(II1). Aluminium is an essential element with a low toxicity,7 but aluminium(II1) sulphate which is often added to drinking water in order to clarify it has proved to be highly toxic to patients undergoing dialysis treatment.8 For this reason drinking water standards have been fixed at very low levels; the aluminium concentra-tion in tap or mineral water should be about 50 p.p.b.In this paper the application of N-oxalylamine(salicyla1-dehyde hydrazone) OSH to the determination of aluminium in drinking waters has been tested. \ 0 0 OSH OH OSH exhibits a close structural relationship to N,N’-oxalylbis(salicyla1dehyde hydrazone) (OSBH) previously investigated by US,^ which may be considered to be a molecular duplicate of OSH. Both compounds are used as reagents for the determination of trace amounts of aluminium, gallium and indium as is N N’-oxalylbis(resorcyla1dehyde hydrazone) (OBRH).9 These reagents are therefore of interest owing to the toxicity of the elements concerned.Experimental Apparatus A Perkin-Elmer 554 spectrophotometer equipped with 1 .O-cm glass or quartz cells and a Crison-501 digital pH meter with a combined glass - Ag/AgCl electrode were used. The fluor-escence measurements were made with a Perkin-Elmer LS-5 spectrofluorimeter equipped with a xenon lamp source a Colora KS ultrathermostat and 1 .O-cm quartz cells. Solutions All chemicals were of at least analytical-reagent grade. A standard solution of aluminium(II1) was prepared from aluminium nitrate [Al(N03)3.9H*O] and was standardised gravimetrically with 8-hydroxyquinoline.Working solutions were prepared by appropriate dilution with distilled de-ionised water. Buffer solutions (pH 3.7) of potassium formate - formic acid (0.1 M) were used. Reagents Preparation of OSH Semioxamazide (1 .O g) was dissolved in 450 ml of ethanol and the solution was boiled under reflux. A 1.0-ml volume of salicylaldehyde was added and the mixture was refluxed for 1 h and then allowed to cool to room temperature. The yellowish white powder obtained was recrystallised from ethanol. The melting-point of the reagent was 277-280 “C. Elemental analysis gave a composition of C 51.70 H 3.94 and N 20.49% ; C9H903N3 requires C 52.17 H 4.34 and N 20.28%. The yield of the synthesis was 50%. Solutions of the reagent were prepared weekly in dimethylformamide (DMF).Properties of the reagent OSH is slightly soluble in water ethanol and chloroform and moderately soluble in DMF at room temperature. Infrared spectra (KBr discs) show the characteristic stretching vibra-tion bands of the structure assigned to OSH; N-H (3400 cm-I) 0-H (3250 cm-l) the amide I band and C=N (1665 cm-1) and C=C of the aromatic ring (1610-1475 cm-1). The ultraviolet spectrum of an aqueous 4% V/VDMF solution of the reagent in a neutral medium shows absorbance maxima at 330 and 280 nm; these bands undergo a hypo-chromic effect in acidic media and a bathochromic shift in alkaline media to 374 and 292 nm respectively. The ionisation constants were determined by classical spectro-photometric methods.lG-12 Only an acidic pK value at 2.3 could be accurately determined because the reagent under-goes moderate hydrolysis in alkaline media.The reagent exhibits fluorescence properties in ethanol solution (hex = 385 nm he = 470 nm) and also in aqueous 4% V/V DMF solutions at pH 5.0 (hex = 370 nm he = 470 nm) the wavelength of fluorescence being affected by the pH of the medium (hex = 385 nm he = 480 nm at pH 9.0). Fluorimetric determination of aluminium Transfer 1.0 ml of 0.2% m/V OSH solution in dimethylform-amide into a 25-ml calibrated flask add 11.5 ml of dimethyl 1160 ANALYST OCTOBER 1986 VOL. 111 formamide and adjust the pH of the solution with 1.0 ml of buffer solution (to give an apparent sample pH of 5.1). Add not more than 10 ml of a test solution containing 0.30-1.98 pg of aluminium and dilute to volume with distilled water.Measure the fluorescence at 474 nm with excitation at 387 nm. Determine the amount of aluminium in the sample from a calibration graph prepared under identical conditions. Alternatively a standard additions procedure based on the above can be applied when interfering ions are present and for samples with a high salt content. Results and Discussion Reactions with Metal Ions The chromogenic properties of OSH on reaction with metal ions were tested in both acetic acid - acetate and ammonia -ammonium buffered media; the best results were obtained in acetic acid - acetate media and these are summarised in Table 1. The reagent is most sensitive to AI(III) Ga(II1) and In(III), which exhibit a noble gas electronic configuration.This is in agreement with the presence of oxygen atoms in the structure of the compound. Reactions of OSH with Fe(III) Ni(I1) and Zr(1V) interfere with the determination of Group IIIA elements. The chelates of AI(III) Ga(II1) and In(II1) with OSH exhibit fluorescence properties at pH 4.5. The highest relative fluorescence intensity of the three is that of the aluminium chelate (44); the relative fluorescence intensities of Ga(II1) and In(II1) are 22 and 3.5 respectively. The relative fluor-escence intensity of 0.1 p.p.m. of quinine sulphate is 12.3. The wavelengths of maximum excitation and emission of Al(II1) and In(II1) chelates are at 387 and 474 nm respectively and those of Ga(II1) are at 395 and 480 nm respectively.Study of the Aluminium - OSH System Aluminium solutions rapidly form a yellow chelate in an excess of OSH; the majority of this chelate is formed instantaneously and the chelation reaction is completed within 20 min. The absorbance value only increases by about 7.6% in this time and then remains stable for at least 7 h. The fluorescence intensity of the complex rapidly reaches a high value increasing by about 2% in 20 min and then remains constant for at least 7 h. Influence of pH The effect of pH on the absorbance and fluorescence of the chelate determines the experimental conditions for the determination of aluminium as both the metal and the reagent are affected by the acidity of the medium. Fig. l(a) shows a Table 1. Photometric characteristics of the complexes (acetate-buffered medium) Cation A,,,,/nm E,, /1 mol-l cm-l AI(II1) .. Ga(IT1) . . In(II1) . Ti(1V) . . Zr(IV) . . Fe(I1) . . V(V) . . U(V1) . . Co(I1) . . Cu(I1) . . Ni(I1) . . Pd(I1) . . 373 382 380 362 380 392 365 375 380 382 380 392 1.2 x 104 1.7 x 104 1.6 x 104 3.7 x 103 1.2 x 104 8.7 x 103 7.3 x 103 5.8 x 103 3.2 x 103 1.0 x 104 9.7 x 103 4.8 x 103 narrow pH interval (between 7.0 and 8.0) on the absorbance versus pH graph in which the absorbance is independent of the pH; for this reason a succinic acid - succinate buffer solution (pH 6.3) was selected for the preparation of samples with a final pH of about 7.3. As can be seen by the fluorescence intensity versus pH graph the fluorescence is also independent of pH between pH 3.5 and 4.5 [Fig.1(6)] in a 10% DMF - water medium hence the pH is fixed in the optimum interval with a buffer solution (formic acid - formate) of pH 3.7. In addition the influence of pH on the fluorescence intensity in a 50% DMF - water medium has been tested; the results are analogous to those obtained previously although the optimum fluorescence intensity zone is slightly shifted to pH 5.1-5.7. The same buffer solutions are used to fix the pH in this interval. Stoicheiometry of the complex The molar ratio of OSH to aluminium was determined by the Asmusl3 and the modified Holme - Langmyhr14 methods, which are suitable for the dissociated chelate that OSH forms with the metal ion; other classical methods such as those of Yoe and Jones15 and Job16 do not yield reliable results.The results obtained which indicated a 1:l molar ratio are shown in Fig. 2. The Asmus and modified Holme - Langmyhr methods were also applied to the chelate in the excited state, measuring the fluorescence intensity at 474 nm with excita-tion at 387 nm. The results were in agreement with those of the chelate in the ground state. Fluorimetric Determination of Aluminium with OSH Aluminium can be determined fluorimetrically by following the recommended procedure described under Experimental. The most suitable concentration of the reagent was found to be 3.86 x 10-4 M (for 198 p.p.b. of aluminium) and the I 1 4 6 a 10 0.1 PH 70 .s 60 2 50 > C .-$ 40 $ 30 C 0 5 20 -10 2 3 4 5 6 7 8 9 PH Fig.1. Influence of pH on the aluminium - OSH system. (a) Graph of absorbance versus pH at 380 nm. CAI = 1 p.p.m.; CR = 1 X M in dimethylformamide (10%). ( b ) Grauh of fluorescence versus pH. C, = 1 p.p.m.; CR = 1 x 10-3 M in dimethylformamide (10%). he = 387 nm A, = 474 n ANALYST OCTOBER 1986 VOL. 111 1161 1 2 3 4 5 6 7 8 1 / A -4.6 - ! / 4 2 4.4 ' 3 - I 4.3 L- A 0.2 Log ( x - 1) Fig. 2. Determination of the composition of the aluminium - OSH chelate. (a) Asmus method. A n =2; B n = 1; C n = Yz. ( b ) Modified Holme - Langmyhr method. Conditions pH = 6.3 h = 380 nm. A = absorbance; L = free ligand concentration; V = volume of reagent stock solution taken; x = AmaX./A; n = ratio of ligand to metal ion in the complex Table 2.Effect of foreign ions on the fluorimetric determination of aluminium (39.7 p.p.b.) Foreign ion or species NO,- I- SCN- S2032- B4072-, Br0,- S042- SO3*- 104 ~ 10,-, acetate V(V) C103- Br- C032-, C104- Fe(CN),,- NH,(I) Mn(I1) . . . Hg(II) Bi(III) Ca(II) Ba(II) U(VI), Pb(II) Sr(II) TI(I) La(III) Ti(IV), Zn(II) Th(IV) Ni(I1) . . . . . . . Mo(VI) citrate Ag(I) Pd(II), C2042- Cu(II) Cr(III) Co(II), Mg(II) Au(III) W(VI) S2- Fe(III), Cd(II) As02- Fe(CN)64- . . . . . Sn(II) NO2- tartrate . . . . . . . , Ga(III) In(III) Sb(III) Zr(IV), . Be@) Ce(IV) F- P2072- As043-Tolerance, p.p.b. 1000 500 100 40 <40 Table 3. Determination of aluminium in mineral waters A1 found p.p.b. Sample OSH* AAS Bezoya . . . .. . 20.9 k 2.6 20 Bezoya (tetrabrik) . . 12.8 2 2.3 12 Lanjaron . . . . . . 14.1 k 1.3 16 Veri . . . . . . . . 10.9+ 2.6 10 Fonter . . . . . . 54.3 k 2.9 56 Lanjaron (carbonic) . . 10.4 2 3.1 10 * Average of three determinations. samples were prepared in DMF - water (1 + 1) media. There was a linear relationship between the aluminium concentra-tion and the fluorescence intensity over the range 0-160 p.p.b. The application of the recommended procedure to a series of 11 samples with an A1 content of 39.6 p.p.b. gave a relative error (P = 0.05) of 20.86%. Effect of foreign ions The cations or species that could affect the fluorescence emission of the A1 - OSH chelate were carefully examined. Table 2 summarises the results obtained. A remarkable tolerance of the method towards numerous anions and 12-fold amounts of Cu(II) Cr(III) Co(II) Hg(II) Zn(II) Ni(II), Pb(II) Ca(1I) and Sr(I1) was observed.However attempts to increase the selectivity of the procedure have been restricted to the determination of aluminium in water especially in table waters with some mineral ingredient to increase their digestive and diuretic action. This sample selection is based on the high sensitivity of the method which is in accordance with the low level of aluminium fixed in drinking water standards. In addition the alternative standard additions method proposed under Procedures increases the tolerance of the method for cations that are present in a large excess over aluminium in these types of waters e.g. Mg(I1) can be tolerated up to 10 p.p.m.against 19.4 p.p.b. of aluminium present (ratio 500 1) Ca(I1) up to 25 p.p.m. (ratio 1200 1) and Fe(II1) up to 1 p.p.m. (ratio 50 1). Determination of aluminium in mineral waters The concentration of aluminium in potable waters especially table water is often important in assessing both their quality and the performance of treatment plants. The proposed method was applied to six commercial bottled waters. In these the following ions are generally present; alkali metal ions [Na(I) 10 p.p.m.; K(I) 2 p.p.m.1; alkaline earth metal ions [Mg(II) 10 p.p.m.; Ca(II) 30 p.p.m.1; SO4*- 20 p.p.m.; C1- 5 p.p.m.; and HC03- 150 p.p.m. Veri water contained 0.09 p.p.m. of Fe(II1). The HC03- was removed by an acid and boiling treatment, and then an aliquot of 5.0 ml was used for the aluminium determination.The standard additions method17 was used in all instances. The results obtained are shown in Table 3. There is good accordance between the results obtained by this method and those obtained by atomic absorption spec-trometry with a graphite furnace. Conclusions Many organic reagents have been proposed for the fluori-metric determination of aluminium and Table 4 summarises some of the more important. With OSH it is possible to determine a very low concentration of aluminium and solvent extraction is not necessary. Most of the methods need a heating step to develop the fluorophore or alternatively a standing period; OSH does not require this time-consuming pre-treatment because the measurements can be carried out immediately.OSH is sensitive although it is surpassed by reagents such as 2-hydroxynaphthoic acid and lumogallion; however the OSH method is preferred as it is more rapid and involves fewer manipulations. OSH and OSBH exhibit similar sensitivities but the former is again preferred because in the OSBH method it is necessary to heat the reaction mixture at 60°C for 5 min and to cool it before measurement; a further advantage of OSH is its greater solubility than OSBH which makes the use of an ethanol - water medium possible although a DMF - water medium is recommended as the sensitivity o 1162 ANALYST OCTOBER 1986 VOL. 111 Table 4. Characteristics of reagents for the fluorimetric determination of aluminium Reagent 2-Hydroxy- 1 -naphthaldehyde benzoh ydrazone .. . . . . . . 2-Hydroxy-3-naphthoicacid . . . . . . 8-Hydrox yquinoline . . . . . . . . Lumogallion . . . . . . . . . . Lumogallion . . . . . . . . . . Morin . . . . . . . . . . . . . . Pontachrome BBR . . . . . . . . 2-Quinalizarinsulphonicacid . . . . . . OSBH . . . . . . . . . . . . OSH . . . . . . . . . . . . . . LJ nm 395 370 360 485 365 440 535 500 390 387 A e J nm 475 460 415 576 548 525 600 558 375 474 Experimental conditions pH 4.6; incubate at 40 "C pM5.8; activate after 1 h for 30 min pH 5.0; heat at 80 "C for 20 min With addition of Antarox CO 890 pH 3.0; activate after 20 min pH5.0; heat at 100 "C for 10 min pH 4.8; activate after 1 h pH 5.0; heat at 60 "C for 5 min pH 5.0 Solvent Ethanol - water Water Chloroform Water Water Ethanol - water Ethanol - water Water DMF - water DMF - water Sensitivity, p.p. b. References 100 18 2 19 20 20 4 21 0.5 22 23 50 24 20 25 11 26 5 1 5 This work the method is higher. Therefore the proposed method is fast, reliable and versatile and confirms the suitability of oxalyl-hydrazide derivatives as fluorimetric reagents for aluminium. The authors thank Dr. Domingo Martinez Ruiz and Dr. Miguel Lopez Artigues of the National Institute of Toxicology of Seville for the analysis by atomic absorption spectrometry. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. References G6mez Ariza J. L. Marques M. L. and Montaiia M. T., Analyst 1984 109 885.Narang K. K. and Yadav U. S. Indian J . Chem. 1980 19, 697. Narang K. K. and Bindal A . J . Sci. Res. Banaras Hindu Univ. 1978 28 1. Narang K. K. and Yadav U . S. Curr. Sci. 1980 49 852. Narang K. K. and Lal R. A. Curr. Sci. 1977 46 401. Narang K. K. and Dubey R. M. J. Sci. Res. Banaras Hindu Univ. 1979 30 173. Browning E. "Toxicity of Industrial Metals," Second Edition, Butterworths London 1969. Elliot H. L. Dryburgh F. Fell G. S. and Macdongall A. J . , Br. Med. J . 1978 1 1101. Pastor E. Pablos Pons F. and Gomez Ariza J. L. paper presented at the SAC 8613rd BNASS Conference Bristol UK, July 1986. Maroni P. and Calmon J. P. Bull. SOC. Chim. Fr. 1964,519. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. Agren A. Acta Chem. Scand. 1955 9 49. Sommer L. Folia Fac. Sci. Natur. Univ. Purkyn. Brno 1964, 5 1. Asmus E. Fresenius 2. Anal. Chem. 1960 178 104. Jimenez Sanchez J. C. Muiioz Leyva J. A. and Roman Ceba M. Anal. Chim. Acta 1977 90 223. Yoe J. H . and Jones A. L. Znd. Eng. Chem. 1944 16 111. Job P. Ann. Chim. 1928 10 9. Bader M. J. Chem. Educ. 1980 57 703. Uno T. and Taniguchi H. Bunseki Kagaku 1971 20 113. Kirkbright G. F. West T. S. and Woodward C. Anal. Chem. 1965,37 137. Rees W. T. Analyst 1962 87 202. Nishikawa T. Hiraki K. and Nagano N. Bunseki Kagaku, 1970 19 551. Ishibashi N. and Kina K. Anal. Lett. 1972 5 637. Nishikawa Y . Hiraki K. Morishige K. and Shigematsu T., Bunseki Kagaku 1967 16 692. Will F. 111 Anal. Chem. 1961 33 1960. Donaldson D. E . U.S. Geol. Surv. Pro5 Pap. No. 550-d, 1966 p. 258; cf. Possidoni J. F. An. Assoc. Quim. Argent., 1963 51 96. Capitan F. Roman Ceba M. and Guiraum A. An. Quim., 1974 70 508. Paper A51257 Received July 15th 1985 Accepted April 2nd I98

ISSN:0003-2654    

DOI:10.1039/AN9861101159

出版商:RSC    

年代:1986

数据来源: RSC

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ANALYST OCTOBER 1986 VOL. 111 1163 Spectrophotometric Determination of Vanadium(V) with Desferrioxamine B Svjetlana Luterotti Department of Chemistry Faculty of Pharmacy and Biochemistry University of Zagreb Ante KovaCiCa I , 41000 Zagreb Yugoslavia and Vladimir Grdinic Department of Pharmaceutical Chemistry Faculty of Pharmacy and Biochemistry University of Zagreb, Ante KavaEiCa I 4 1000 Zagreb Yugoslavia A naturally occurring trihydroxamic acid desferrioxamine B reacts with the vanadium(\/) ion in strongly acidic aqueous solutions producing a stable 1 1 complex (log K = 6.09 at 22 'C). This red -violet chelate used for the spectrophotometric determination of trace amounts of vanadium(\/) (Amax = 480 nm molar absorptivity E = 3.15 x lo3 I mol-1 cm-I) obeys Beer's law in the vanadium concentration range 0.5-50.0 p.p.m.The interferences of many foreign substances have been examined and a sensitive highly selective accurate and precise method for the determination of vanadium(\/) is proposed. Keywords Vanadium(V) determination; spectrophotometry; desferrioxamine B Aryl and heterocyclic monohydroxamic acids are well known as analytical reagents for vanadium(V) and iron(II1). They have been widely used as reagents in spectrophotometry as precipitating agents in gravimetric analyses and as metallo-chromic indicators. They have also been proposed as micro-qualitative reagents for the above metals using the same complexation reactions. r3 H3 C0.N H CONH \ / \ / \ .N- c N-c N-6 I II HO 0 I II HO 0 I II HO 0 Desferrioxamine B As yet there have been no reports of the use of desferriox-amine B (H4DFB+) one of the naturally occurring trihydrox-amic acids as a spectrophotometric reagent.Nevertheless it has recently proved propitious for the sensitive and selective micro-scale detection of vanadium(V)l and iron( 111) .2 Desfer-rioxamine B methanesulphonate marketed as Desferal by Ciba-Geigy is well known as a drug for the treatment of both iron toxicity and iron storage diseases in humans.3-5 In this paper a spectrophotometric investigation of the chelation of vanadium(V) with desferrioxamine B is reported. The study included the determination of the composition and the stability of the complex species and the analytical application of H4DFB+ as a spectrophotometric reagent.Experimental Reagents All reagents used were of analytical-reagent grade. Re-distilled water was used throughout. Vanadium( V) standard solutions. Stock solutions were prepared to contain 2.000 g 1-1 of V5+ and were freshly diluted prior to use. An acidic stock solution of the V02+ ion was obtained by the dissolution of 1.78508 g of V2O5 in 500.0 ml of 1 M HN03 by heating and was diluted with 0.6 M HN03. A neutral stock solution of the V03- ion was prepared by the dissolution of 0.22958 g of NH4V03 in 50.0 ml of water by heating. Desferrioxarnine B solution. A 4.0 x 10-3 M solution was obtained by the dissolution in water of 0.26268 g of commer-cially available desferrioxamine B methanesulphonate (Des-feral) previously recrystallised from methanol (m.p.149-152 "C). Solutions of foreign substances. Stock solutions of foreign ions were prepared from alkali metal nitrate chloride or sulphate salts in concentrations of 4.0 2.0 or 1.0 g 1-1. Stock solutions of complexing oxidising and reducing agents were 0.05 M. For the dissolution of solids and further dilutions suitable diluents were used. Apparatus A Pye Unicam SP8-100 UV - visible spectrophotometer with 1-cm silica cells was used for recording spectra and absorbance measurements. For pH measurements an Orion 701 digital pH meter with a glass Ag - AgCl electrode was utilised. Procedure for Determination of Vanadium(V) The acidity of the V(V) solution is regulated to the optimum value of pH 1.0. For a strongly acidic analyte solution this is achieved by the dissolution of the appropriate amount of solid, water-free Na2C03.If a neutral V(V) solution is to be analysed the pH should be regulated by the addition of a few drops of concentrated HN03 and the V(V) ion concentration subsequently corrected. The absorbance of the equivolume analyte - reagent mixture (pH 1.3) is measured at the absorption maximum at 480 nm against a reagent blank. Results and Discussion Preliminary Investigations The spectra of the V(V) solutions obtained from either V205 in nitric acid (pH 1.0) or NH4V03 in water subsequently acidified with HN03 to the same pH were identical (Amax = 340 nm Fig. l) confirming the predominance of the V02+ ion in the solution. The solutions are light yellow and do not absorb at the wavelength of the analytical line at 480 nm.These solutions become more intensely coloured on standing, exhibiting an absorption peak at ca. 420 nm and contributing to the absorbance of the reaction product. For that reason analyte solutions should be freshly prepared. Influence of pH The influence of the acidity of the analyte solution and the reaction mixture is demonstrated in Fig. 1 and Table 1. It is well known that the distribution of the V(V) species depends on the pH of the reaction medium.6 From the data displayed it is evident that the VO2+ species is responsible for the formation of the coloured reaction product. The highes 1164 0.8 0.7 0.6 o) 0.5 + g 0.4 -n Q 0 (IJ 0.3 0.2 0.1 ANALYST OCTOBER 1986 VOL. 111 -- -,I -----/N I I I I I I 200 300 400 500 600 700 800 Wavelengthhm Fig.1. Absor tion spectra of vanadium(V) - H4DFB+ rea media at pH AT0 7 B) 1.3 (C) 2.4 (D) 3.4 (E) 5.8 (F) 6.4 7.6 (H) 7.7 b 8.2 $0 9.0 and (K) 10.0. V5+ 5.0p.p.m.; H4D 2.0 x 10-3 M. (L) V02+ species V5+ 20.0 p.p.m. ; pH 1.0. (M) 7 species; V5+ 5.0 p.p.m.; pH 6.6. (N) H4DFB+ 2.0 x M 01 ion :GI 3+ , 13 -Table 1. Dependence of vanadium(V) species on pH of reaction medium. V5+ 5.0 p.p.m.; H4DFB+ 2.0 x 10-3 M pH of Colour of pH of V(V) Predominant V(V) reaction reaction solution species6 mixture mixture 0.5 v02+ 0.7 Red - violet 1 .o 1.3 Red - violet 2.0 2.4 Orange -violet 3.0 VIOO~~(OH)Z~- 3.4 Violet -orange 4.0 VI 0027 (OH) - 5.8 Light yellow 5.0 6.4 Light yellow 6.0 V3og3- V02(0H)2- and v40124- 7.6 Light yellow 7.0 7.7 Light yellow 8.0 8.2 Light yellow 9.0 V03(OH)2- V2074- 9.0 Colourless 10.0 10.0 Colourless sensitivity is achieved at pH 0.7 whereas the upper usable pH is 3.4.By increasing the pH a loss of sensitivity and a hypsochromic shift of the visible absorption peak from 488 to 460 nm is observed. Stability of the Reaction Product On standing the highly acidic (pH 0.7) reaction mixture exhibits an absorbance decrease followed by a slkht batho-chromic shift of the absorption peak from 488 to 508 nm. In an hour the absorbance decreases by approximately 9%. On prolonged standing a new band appears at ca. 380 nm. This may be because the ligand H4DFB+ tends to degrade in strongly acidic media possibly contributing to the effects observed.7 The influence of pH on reaction product stability was checked by kinetic measurements at pH 0.7 and 1.3.The initial rate of reaction product degradation is 8.4 X and 2.8 x 10-6 M h-1 respectively at the above pHs. From these data a significant increase of reaction product stability with an increase in pH is indicated. An absorbance loss of only 3% is observed within 1 h at pH 1.3. Table 2. Influence of foreign species on the determination of vanadium(V). V5+ 7.5p.p.m.; H4DFB+ 2.0 x 10-3 M; pH 1.3 Tolerance Concentration ratio Foreign species limit p.p.m. relative to V(V) Cu2+ Mg2+ Ca2+ Sr2+, Cdz+ Ba2+ CH3COO-, S O P C1- Mn2+ Br- I-, C4H4062- C,H5073-, Ni2+ . . . . . . . . NHzCSNH2 . . . . . . As043- . . . . . . . . NHzOH-HC1 .. . . . . co2+ . . . . . . . . . . C2042- . . . . Al3+ Cr3+ Na,EDTA . . sn2+ . . . . . . . . . . Ascorbicacid . . . . . . Mo042; . . . . . . . . w04*- . . . . . . . . F- . . . . . . . . . . Fe3+ . . . . . . . . . . 1000.0 750.0 650.0 325.0 187.5 162.5 125.0 93.8 31.3 11.7 7.8 0.7 0.06 133.3 100.0 86.7 43.3 25.0 21.7 16.7 12.5 4.2 1.6 1.0 0.1 0.01 It follows that the stability of the system should be improved by a small loss of sensitivity of the measurement (ca. 5%). Consequently pH 1.3 should be chosen for the determination of the V(V) ion. Stoicheiometry and Stability of the Complex Job’s method of continuous variati0ns83~ and the molar-ratio methodgJ0 were used to determine the stoicheiometry of the complex.A 1 1 stoicheiometric ratio of H4DFB+ to the V02+ ion was found. The apparent stability constant of the complex was calculated from data from the molar-ratio method and a value of log K = 6.09 k 0.12 at 22 “C was obtained. The same experiments indicated that for maximum absor-bance at 480 nm at least a 2-fold molar excess of reagent over vanadium was necessary. Performance of the Analytical Method At 480 nm the wavelength of the absorption peak the system obeys Beer’s law from 0.5 to 50.0p.p.m. of V(V). The optimum concentration range for spectrophotometric deter-mination estimated according to Ringborn’s method is 4.0-10.0 p.p.m. of V(V). The equation of the r$gression line and of the corresponding anaiytical function is A = 0.061~ + 0.014 where c = (16.322A - 0.232) p.p.m.of V(V), respectively. The system is also characterised by the molar absorptivity E = 3.15 x 103 1 mol-l cm-1 the calibration sensitivity H = 61.9 ml mg-1 Sandell’s sensitivity H = 0.016 pg ~ m - ~ and limit of determination = 0.56 p,p.m. of vanadium(V). The precision is evaluated by the relative standard deviation V = 0.5470 and the accuracy of the method using the maximum relative error emax. = 0.86%. Interference Studies The recommended procedure was utilised to analyse standard vanadium(V) solutions in the presence of possible interfering substances. For the determination of 7.5 p.p.m. of V(V) by this method extraneous substances can be tolerated at the levels given in Table 2. The tolerance limits of foreign substances were evaluated using the criterion that deviations of absorbance measurements at 480 nm of +3.O0/o should not be exceeded ANALYST OCTOBER 1986 VOL.111 1165 It is evident that the Fe(II1) ion causes the largest interference. Under suitable conditions it is also possible to determine this cation with desferrioxamine B. 11 According to the data shown in Table 2 the recommended analytical procedure seems to be highly selective. According to Belcher12.13 it should be claimed as p-selective. Conclusions The suitability of the vanadium(V) - H4DFB+ system for the development of a simple sensitive accurate precise and highly selective method for determining small amounts of V(V) has been demonstrated. The acidity of the medium determines the distribution of the V(V) ion species.The VO2+ ion predominates in strongly acidic media and is responsible for the formation of the coloured product. It follows that the method is applicable to the direct analysis of acidic vanadium solutions or to the analysis of neutral solutions after acidifica-tion. The sorption of the red - violet water-soluble product on the strongly acidic ion-exchange resin has indicated the predominance of cationic complex species. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11 12. 13. References Luterotti S. and GrdiniC V. Mikrochim. Acta 1984,III,95. Luterotti S. and GrdiniC V. Zbl. Pharm. in the press. Bunn H. F. Forget B. G. and Ranney H. M. “Human Hemoglobins,” W. B. Saunders Philadelphia 1977. Anderson W. F. and Hiller M. C. Editors “Development of Iron Chelators for Clinical Use,” Department of Health, Education and Welfare Publications US Government Printing Office Washington DC 1977. Summers M. R. Jacobs A. Tudway D. Perera P. and Ricketts C. Br. J . Haematol. 1979 42 547. Baes C. F. and Mesmer R. E. “The Hydrolysis of Cations,” Wiley New York 1976 p. 210. Monzyk B. and Crumbliss A. L. J . Am. Chem. Soc. 1982, 104,4921. Job P. Ann. Chim. Phys. 1928 9 113. Beck M. T. “Chemistry of Complex Equilibria,” AkadCmiai Kiad6 Budapest 1970 pp. 86-91. Yoe J. A. and Jones A. L. Ind. Eng. Chem. Anal. Ed., 1944 16 11. Luterotti S . and GrdiniC V. Acta Pharm. Jugosl. in the press. Belcher R. Talanta 1965 12 129. Belcher R. and Betteridge D. Tulanta 1966 13 535. Paper A6184 Received March 12th I986 Accepted May 5th 198

ISSN:0003-2654    

DOI:10.1039/AN9861101163

出版商:RSC    

年代:1986

数据来源: RSC