Anal. Chem. 1989, 61. 109R-128R (569)Beauchaine, J. P.; Peterman, J. W.; Rosenthal, R. J. Mkrochim. Acta 1087, 7(1-6),133. (570) Schwanebeck, W.; Wenz, H. W. Fresenius’ Z . Anal. Chem. 1088, 337(1),61. (571) Walsh, K. A. J.; Axon, B. W.; Buckleton, J. S. Forensk Sci. Int. 1088, 32(3),193. (572) Grieve, M. C. J . Forensic Sci. SOC. 1087, 27(6),405. (573) Zeichner, A. Powder Dlff. 1087, 2(1),5 . (574) Catterick, T.; Taylor, M. C. Forensic Sci. Int. 1087, 33(3),197. (575) Shegal, V. N.; Slngh, S.R.; Dey. A.; Kumar, M. R.; Jain, C. K.; Grover, S. K.; Dua, D. K. Forensic Sci. Int. 1088, 36(1,2),21. (576) Cohen, I. M.; Pla. R. R.; Mlla, M. I.; Gomez, C. D. J . Trace Microprobe Tech. 1088. 6(i),113. (577) Daus, R. J. J . Can. SOC.Forensic Sci. 1088, 27(3),98. (578) Laskowski, G. E. J. Forensic Sci. 1087, 32(4),1075. (579) Cousins, D. R.; Fuller, N. A.; Fysh. R. R.; Russell, L. W. J . Forensic Sci. SOC. 1087, 27(4), 247. (580) Leigh, A. G.; Griffiths. Green, M. A. J . Forensic Sci. Soc. 1088, 28(4). 227. (581) Petraco, N. J. Forensc Sci. 1087, 32(5),1422. (562) Turley, D. M. J. Forensic Sci. 1087, 32(3),640. (563)Lauten, M. E.; Buckleton, J. S.; Walsh, K. A. J. J. Forensic Sci. SOC. 1088, 28(4),243. (584) Evett, I. W. J . Forensic Sci. SOC. 1087. 27(6),375. (585) Maehly, A.; Williams, R. L., Eds. Forensic Science Progress; Vol. I. Springer-Verlag: New York, 1986. (586) Maehly, A.; Willlams, R. L., Eds. Forensic Science Progess; Vol. 11. Sprinwr-Verlag: New York, 1988. (587)Maehly, A,: Williams, R. L., Eds. Forensic Science Progress; Vol. 111. Sprlnger-Verlag: New Ywk, 1988. (568)Saferstein, R., Ed. Forensic Science Handbook, Volume I I ; PrenticeHall: Englewood Cliffs, NJ. 1988.
(589)Saferstein, R. Cfiminalistics: An Introduction to Forensic Science, 3rd ed., Prentice-Hall: Englewood Cliffs, NJ, 1987. (590) Giannelli, P. C.; Imwinkelried, E. J. Scientific Evidence; The Michie Co.: Charlottesville, VA, 1986. (591) Moenssens, A. A.; Inbau, F. E.; Starrs, J. E. Scientific Evldence in Criminal Cases, 3rd ed.; Foundation Press: New York, 1986. (592)Clement, J. L. Sciences Legales et Police Scientifique;Masson: Paris, France, 1987. (593) Dominquez, A. M., Ed. Comprehensive Index to the Journal of Forensic Sciences 7972-7986;ASTM: Philadelphia, PA, 1987. (594)Moffat, A. C.; Franke, J. P.; Stead, A. H.; Gill, R.; Flnkle, 8. S.; Moeller, M. R.; Muller, R. K.;Wunsch, I.; de Zeeuw, R. A. Thin-Layer Chromatoraphic Rf Values of Toxicologically Relevant Substances on Standardized Systems; VCH Publishers: New York, 1987. (595) Curry, A. S.Poison Detection in Human Organs, 4th ed.; C. C. Thomas: Springfield, IL, 1968. (596) Mills, T.; Roberson, J. C. Instrumental Data for Drug Analysis, Vols. I-IV, 2nd ed.; Elsevier: New York. 1987. (597) Curry, A. S., Ed. Analytcal Methods for Human Toxicology; Vol. 2; Verlag Chem.: Weinheim, Fed. Rep. Gen.. 1986. (598)Yinon, J. Forensic Mass Spectrometry: CRC Press; B o a Raton. FL,
1987. (599) Proceedings of the International Symposium on Questioned Documents; US. Government Printing Office: Washington, DC. 1987. (600)Proceedings of the International Forensic Symposium on Latent Prints ; US. Government Printing Office: Washington, DC, 1987. (601) Proceedings of the International Symposium on Forensic Hair Comparisons; U S . Government Printing Office: Washington, DC, 1987. (602) Basu, S.;Millette, J. R., Eds. Electron Microscopy in Forensic, Occupational and Environmental Health Sciences ; Plenum Press: New York,
1986.
Geological and Inorganic Materials L. L. Jackson,*,I D. M. McKown,’ J. E. Taggart, Jr.,I P. J. Lamothe,2 and F. E. Lichte’ U S . Geological Survey, P.O. Box 25046, Denver Federal Center, Denver, Colorado 80225, and U S . Geological Survey, 345 Middlefield Road, Menlo Park, California 94025
INTRODUCTION This review surveys the literature for the two-year period since our previous review ( A I ) ,November 1986 through October 1988. We have followed a similar format and emphasis as our last review. Our intent is to focus on techniques and their application to the analysis of geological and inorganic materials that offer significant changes to research and routine work, as well as highlight current trends. The majority of the articles in this review pertain to the determination of inorganic species in naturally occurring, nonprocessed, geological materials. The analysis of processed materials such as cement or inorganic materials such as ceramics, glasses, or semiconductors are largely not covered in this review. There are several related reviews in this issue covering solid fuels and ferrous metals. In order to prepare this review we performed a computerized keyword search of Chemical Abstracts and manually searched several of the primary journals. Our literature search identified more than 2600 references pertaining to our topic. A similar number was found in our previous review. We have cited about 400 of those references herein. For many of the topics covered the references are simply too numerous to cite and only representative examples are included. The analysis of geological materials has spawned a variety of international meetings. In June 1990, in Canada, a number of international organizations will sponsor “Geoanalysis 90”. This meeting will emphasize new/definitive methodology, analysis of special matrices, development and use of geostandards, and geoanalysis in the third world and a t remote locations. In the past few years several other international meetings or symposia have focused on similar topics. The International Union of Pure and Applied Chemistry sponsored the “Second International Symposium on Analytical Chemistry in the Exploration, Mining and Processing of Materials” U.S. Geological Survey, Denver Federal Center.
‘US.Geological
Survey, M e n l o Park.
in 1985. The full text of 21 invited lectures, covering fundamentals and applications of major techniques currently in use, has been published (A2).The abstracts of the symposium on “New Analytical Techniques in Geochemistry” from the International Congress of Geochemistry and Cosmochemistry, Paris, 1988, provide a brief glimpse of the areas of most active research in technique development and application (A3). The trend is clearly toward the application of multielement instrumental techniques such as inductively coupled plasma (ICP) atomic emission spectroscopy, ICP mass spectrometry, X-ray fluorescence spectrometry, and neutron activation analysis. Potts speaks to this trend in the preface of his new book A Handbook of Silicate Rock Analysis (A4). With the growth in utilization of complex instrumentation for multielement determinations “users have become more remote from the data production process ...The resultant lack of interaction between user and machine leads to the danger of a ‘black-box’attitude towards analytical chemistry.” In the text he has described the fundamentals of the major techniques, both old and new, and their practical applications. Hence, the volume is a good resource for both the user of geochemical data and the practicing analytical chemist and it may indeed help obviate the black-box attitude. Also toward this end, the US.Geological Survey has published descriptions, which include methodology and limitations, of many of the analytical techniques used for elemental determinations in their laboratories (A5). One other good addition to the practicing geochemist’s library is Principles of Environmental Sampling (A6)-a topic all too frequently neglected. This book includes sections on planning and sample design, quality assurance and quality control, and sampling of solids.
GEOSTANDARDS The United States National Institute of Standards and Technology (NIST), formerly the National Bureau of
This article not subject t o U.S. Copyright. Published 1989 by the American Chemical Society
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GEOLOGICAL AND INORGANIC MATERIALS
Standards, published a compilation of analytical data for 166 NIST clinical, biological, geological, and environmental standard reference materials ( B I ) . Means, uncertainties, analytical techniques, and the raw data are included. The manual has been produced in a “living format” with automatic updates to be sent to purchasers as sufficient new data is available. Gladney and Roelandts (B2,B3) have compiled elemental data for 11of the newer U.S. Geological Survey rock standards. Govindaraju and Roelandts (B4)have done similarly for five Centre de Recherches Petrographiques e t Geochimiques geologic standards, all of which have been distributed for more than 20 years and with an additional 20 years’ supply. Ando et al. (B5) have also compiled results for 15 Geological Survey of Japan igneous rock series standards. In September 1986, the International Working Group “Analytical Standards of Minerals, Ores, and Rocks” launched a collaborative study of the Ailsa Craig microgranite, AC-E (B6),which contains rare-earth elements a t about 100 times chondritic abundance. One hundred twenty eight laboratories from 29 countries contributed to the establishment of working values for seventy major, minor, and trace elements (B7).The investment of the geochemical community in the development of well-characterized standard reference materials is clear from a project of this magnitude. Other new standards are being distributed as well. Lister (B8)described the preparation and compiled working values for three base-metal concentrates: P b concentrate IGS-42, Zn concentrate IGS-43, and Cu matte IGS-44. Hosterman and Flanagan (B9) listed provisional values for two new USGS clay mineral samples: attapulgite, Am-1,and bentonite, CSB-1. Five Belgian sedimentary rock standards: shale AWI-1, schist SBO-1, psammite PRI-1, limestone CCH-1, and dolomite DWA-1, were described by Roelandts and Duchesne (BlO). Results for four new gypsum rock samples were reported (B11). NIST has also released three new standards: SRM 2704, Buffalo River sediment (B12);SRM 679, brick clay, and SRM 2430, scheelite ore (B13). Roelandts has continued to provide annual bibliographies of articles related to the analysis of geochemical standard reference materials or reporting analytical results of reference B15). The 1986 and 1987 bibliographies cited materials (B14, more than 400 references and were indexed by element. In addition, he summarizes the analytical techniques most used to report results of reference materials. Gladney and Roelandts (B16)also summarized and examined trends for both techniques and literature source for publication of analytical data on NIST, USGS, and Canadian Certified Reference Materials Project (CCRMP) standards for the period 1951-1985. The trend toward the use of multielement instrumental techniques for the routine analysis of geological materials is entirely obvious. Moody et al. (E17) reported on the recommended inorganic chemicals for instrumental calibration. Their compilation includes both NIST standards and commercial compounds along with comments on purity, use, and preparation.
DISSOLUTION TECHNIQUES The biggest change to occur in recent years in the dissolution of geological and inorganic materials is in the application of microwave heating. This has been the subject of two “Focus” articles in Analytical Chemistry (C1, C2) and a recently published book by the American Chemical Society (3). The book contains chapters on digestion methods for geological, metallurgical, and biological samples, as well as on microwave oven and digestion vessel design. Safety precautions are also emphasized. Numerous other articles have appeared as well that have been concerned with the analysis of sediments with both completely closed and pressure relief vessels ( C 4 ) ,Cu-Ni sulfide samples (C5),sequential extractions of sediments (C6), and digestion of peat cores (C7).
ATOMIC ABSORPTION SPECTROMETRY Atomic absorption spectrometry (AAS) has now been used for over 30 years (01,02). The technique is well established, and current publications reveal mostly subtle though important improvements. The primary modes of application are flame atomic absorption (FAA), graphite furnace atomic absorption (GFAA), and hydride generation atomic absorption (HGAA). In this review, each of these techniques is discussed llOR
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separately although the major innovations that have been reported during the past two years in sample preparation, separation, or preconcentration could generally be applied to any of the atomization techniques. Reviews by Ebdon, Cresser, and McLeod (03)and Cresser, Ebdon, and Dean (04) describe recent developments and applications in AAS for environmental samples, including soils. Most laboratories employ at least two of the AAS operational modes in their analytical program. Macalalad et al. (05) published a paper describing the use of AAS in their laboratory for the determination of 16 elements in geological materials. They applied nearly all of the current techniques for these determinations including flame, graphite furnace, hydride generation, cold vapor cells, and organic solvent extraction. Flame atomic absorption spectrophotometry (FAAS) remains a widely used method, and the major instrument manufacturers have published standard operating procedures for all of the elements. This technique offers better precision and ease of operation compared with electrothermal atomizers or hydride generation. It is also less sensitive by 1-2 orders of magnitude than the other two types of atomization. It is ideally suited for the determination of major, minor, and some trace constituents in geological materials. Either an air/ acetylene or nitrous oxide/acetylene flame is used for atomization depending on the element of interest and in some cases depending on the presence of interfering elements. In this application, solutions are analyzed. For geological materials, the sample must be dissolved prior to measurement, although, slurries of solid samples can be introduced through conventional nebulizers. The sensitivity of the flame technique can be improved by approximately 1 order of magnitude using preconcentration procedures including chelate extraction into organic solvents, coprecipitation, or ion exchange. The inclusion of flow injection techniques with flame atomization can improve sample throughput as well as reduce the total amount of sample required for quantification. Flow injection FAAS for Na and K was reported by Nara et al. (06). They used the standard Li2C03/H3B03fusion and analyzed 120 samples per hour with relative standard deviations of 1.0 reand 0.5% for Na and K, respectively. Matusiewicz (07) ported using the NzO CzHzflame in the conventional setup for the analysis of roc salt and brine for Li, K, Rb, Mg, Ca, Sr, and Ba. Methods of analysis for ore grade material and concentrates were reported for several elements. Chong and Merian (08)determined W by N O/C2H2FAAS in ore grade materials. The sample was fused with KHS04, and Na4Si04 was used to suppress the interference caused by Ca. A direct method for Ta and Nb was developed by Malhotra et al. (09) for samples containing >5% Nbz05/Taz06. They used a KHS04 fusion and dissolved the cake with citric acid. Al was added a t 1000 pg/g to suppress interferences and improve sensitivity. Cr in spinels was determined by Yamashige and Terashima (010). The spinel was dissolved by using a NaZCO3/H3BO3fusion. La was added at 4OOO pg/g to reduced various potential interferences. Sen Gupta (011)determined Rb, Sr, and Ba in barite. The barite was dissolved by refluxing the sample with ammoniacal disodium ethylenediaminetetraacetic acid. The silicate residue was dissolved in H F / HzSO4 and combined with the EDTA solution. Ba and Sr were then easily determined by FAAS and the Rb by GFAAS. Lau, Ure, and West (012) reported a method for 16 elements using ion trapping from an air/C2Hz flame. The durability of the quartz cell used for trapping was improved by coating the cell with alumina. More applications of this technique should be appearing during the next few years. Rozanska and Lachowicz (013)reported that extractions of metals using tetrabutylammonium bromide/thioyltrifluoroacetone into methyl isobutyl ketone (MIBK) were stable for up to 3 weeks. This stability should enable greater flexibility in scheduling the measurement step of the analysis. Rubeska et al. (014) reported on the multielement extraction into 4-methylpentan-2-one. Several elements were determined from a single extraction. He conserved the solution by using a microsampling syringe to introduce 50-pL aliquots into the flame through the nebulizer. Then he used GFAA for determining Se, Te, and T1 with limits of detection of 0.2, 0.1, and 0.1 pg/g, respectively. Pleskach et al. (015)reported that ultrasonic agitation improved the extraction time of Cu and Pb in minerals. They extracted the metals by using standard KCN or thiourea procedures.
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GEOLOGICAL AND INORGANIC MATERIALS
Larry L. J a c k m is a Research Chemkt with Me Ranch of Ogochemistry. U S . Geohim1 Survev. He reCeivBd a B.S. deoree inChemistry~irmKansas state U&S& in 1973 and a W.D. in analytical chemistry hom Colorado State University in 1978. His research interests include the application 01 electroanaMica1 technirrues to the analysis
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t David M. McKovn is a Researdl Chemist at Me U.S. GeOlDgiCal SUNBY. Branch 01 GeeChemlSlN. He received his B.S. dwree in chemist6 hom West Virginia Universilty and his m.D. h nuclear and radiochemistry from Me University of Kentucky in 1969. He was a reSBBrCh facuity member at Me Missouri University Research Reactw faclllty lor 9 years belwe joining the USGS in 1978. He cvrentiy SBNBJ as the activation analysis proiect chief at the USGS nuclear faciiii. His research interests are in radioanalytical geOchemistry.
Joseph E. Tawart, Jr.. is presently a Research Geologist with the h n c h of W chemistry. U.S. Gaalogical SUNBY. He received his 0,s. degree In geol~glhom S Y ~ C M BUniversity (1967) and his M.S. d e aree In oeoIoov from Miami Universlw cl969). f i s re&ch interests Include & analysis 01 geological materials by waveiansfh dispersive X-ray Spectrometry and the analysis of mherals by various chemical and X-ray diffractiontechniques.
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Pad J. Lamothe is a R e m r c h Chemist at Me U S . Geological SUNBY. Branch of Oeochernktry. He received his 0,s. in chemistry hom Me Universlty 01 Sa" Francisco in
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1968 and his Ph.D. in analytical chemishy
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;ear& chemist wHh the Environmental Protection Agency. Research Triangle Park. NC. His research interests are in analvtical specnoscopy and trace element analyses. Fred E. Uchte Is a Research Chemist at the U S Geological Survey. .Branch Of Gemhemishy. He received his B.A. degree in chemistry from Wartburg College. Waverty. IA. in 1963 and his Ph.D. in chemistry *om Colorado state university m 1973. prior to joining the USGS in 1977. he was a Research Chemist With Atlantic Richfield Corp. and the Environmental Trace SubStances Research Center. Universihr of Missouri. His research intereMs include the application of inductiiety coupled plasma emission and mass spectrometry to geochemical studies.
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ature furnace developed and reported by Woodriff e t al. (D16) is still perhaps the benchmark for developing an electrothermal atomizer free of gas-phase interferences. With the commercial availability of isothermal atomizers, many of the old rationales need to he reexamined with reeard to inclusion of matrix modifiers and separation routines in the method. In fact, most of the published work during the past two years is an iteration of previous methods' development with one of the modes of vapor heating. Even so, interferences caused hy concomitant elements frequently require calibration using standard additions even though the magnitude of the interference can he reduced by using matrix modifiers and one of these accessories. There also seems to he a better recognition of an improved lifetime for the graphite tubes when a secondary surface such as a platform or probe is used (017). Chakraharti (018) in a review published following the Analytical Chemistry in the Exploration, Mining and Processing of Materials Symposium reported that the severe matrix problems experienced in electrothermal atomizers had been largely solved. In a similar review by Kumar e t al. (0191, they reached the same conclusion, but went on to state that in severe cases matrix modifiers are required. As is the case for FAAS, GFAAS has been app!ied to virtually every element and is most useful for situations where the analytical requirements require measurement of concentrations below the limits of detection offered by FAAS. Most of the methods for transition and chalcophillic elements have been previously reported. The application of a probe was reported by Corr and Littlejohn (020) for the measurement of Cu, Mn, and Ph. The determination of S n continues to he difficult with conventional methods and new methods have been reported. Sturgeon, Willie, and Berman (D21)analyzed environmental reference standards for tin. They used hydride generation with NQBH, to introduce the Sn onto the graphite tube a t 800 OC followed by atomization and measurement in the tube. They reported a limit of detection of 0.3 pg/g. Lundherg and Bergmark (022) reported a method for Sn which used all of the newer instrumental accessories including a platform and Zeeman background correction, as well as an NH, matrix modifier. Complete dissolution of Sn when it is present as casserite requires either a NHJ sublimation technique or a fusion. They used LiBO, fusion to dissolve the sample and achieved a limit of detection of 0.7 pg/,g and relative standard deviation of 12% at the 3 pg/g level wthout further separation or preconcentration. Taga e t al. (D23) found that K2W0, was effective as a matrix modifier for the GFAA determination of Sn. Knowledge of the concentration of Re is important for many petrogenetic and meteoritic studies. Because of its relative abundance and association with Mo, very few analytical methods are available for the determination of Re at the trace level. Koide e t al. (024) reported a method for Re in marine sediments. They separated Re from Ma as the tetraphenylarsonium perrhenate into CHC1, and then used GFAA for the measurement. Probably the greatest need for GFAAS is for the determination of the noble metals (Au, Ag, Pt, Pd, Rh) for exploration of new resources. Fletcher and Horsky (025)reported a relatively fast and very sensitive method for the determination of Au. A large (100g) sample is extracted with CN- and the solution analyzed by GFAA. Detection levels below 1 ng g were reported. Luo (026) reported using the L'vov plat orm GFAAS for the determination of ultratrace concentrations of gold. He dissolved the sample with aqua regia and extracted the Au on a polymer foam. Thiourea was used as a matrix modifier on the platform. Wang and Lin (027) reported a method for preconcentrating Au, Pt, and Pd as the chloride complex on esteramine foam followed by a desorption step using thiourea. Limits of detection were 0.5, 1.0, and 10 ng/g for Au, Pd, and Pt, respectively. Terashima (028) reported a method for the determination of Pt in Mn nodules. He used an aqua regia digestion on 0.1-g samples and determined the Pt directly by GFAA. In a method reported by Branch and Hutchinson (029) Pt and Pd were determined by GFAA. The sample was treated with aqua regia and noble metals were adsorbed onto Dowex 1-X8 in a batch mode, The resin was separated and ignited, and then the metals were dissolved. The method is designed for rapid screening of a large number of samples. Brooks and Lee (030) reported a method of separation of Pt and P d as their iodo complexes into MIBK. A direct determination of Ag was
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Graphite furnace atomic absorption has achieved widespread usage due to its ability to detect lower levels of concentration than those achieved by FAAS. Several of the newest methods of analysis have been developed based on isothermal conditions within the tube of the graphite atomizers which reduce interferences from the incomplete dissociation of moleculer gases. Platforms, probes, or capacitive heating can be used to produce better isothermal conditions during the vaporization step of the analysis. The constant temper-
ANALYTICAL CHEMISTRY, VOL. 61. NO. 12. JUNE 15, 1989
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GEOLOGICAL AND INORGANIC MATERIALS
reported by Hamalainen et al. (031). The sample was digested with aqua regia and (NH4)2HP04was used as a matrix modifier. The limit of detection reported was 0.01 pg /g. There has been continued development and refinement of the GFAA application to the rare-earth elements (REE). In the latest publications, GFAA is primarily used for the determination of the heavy REE, whereas the light and more abundant elements are determined by X-ray fluorescence spectrometry or inductively coupled plasma atomic emission spectroscopy. Juras et al. ( 0 3 2 ) combined GFAA with pressed pellet XRF in their latest publication. The sample was dissolved with and H F and the REE separated by using BioRad AG50W-X8 resin. Sen Gupta ( 0 3 3 ) precipitated the REE and used GFAA and ICP-AES for the measurement of the solution. Hasegawa et al. ( 0 1 7 ) reported a method for Ga using the platform with a Ni matrix modifier. Their reported limit of detection was 0.1 pgfg. They also pointed out that approximately 300 measurements could be made from a single tube. De Castro et ai. ( 0 3 4 ) separated Ag, Cd, T1, and Mo as C1- or I- complexes into MIBK using trioctylphosphine oxide (TOPO). They reported limits of detection of 0.02 pgfg for Cd and 0.2 pg /g for Ag, Mo, and T1. Mitchell et al. ( 0 3 5 )reported a direct method for the determination of Co in soils. The soil was extracted with acetic acid and introduced into the furnace tube as an aerosol. The dream of many chemists, and certainly laboratory managers, is to develop analytical methods that can be accomplished without the dissolution requirement. It is possible to vaporize and atomized several elements from solid materials in graphite tubes. Samples are either weighed directly into the tube or pipetted as a slurry. Several investigators have reported their work in this area during the past two years. Yuan et al. ( 0 3 6 ) introduced the solid as a suspension for the determination of T1 and Cd. P d and ascorbic acid were used as matrix modifiers. They reported that with the method of standard additions reliable results could be obtained. Hinds and Jackson ( 0 3 7 ) reported that P b could be determined by using the L’vov platform and the combination of Pd and Mg as matrix modifiers. They used slurry injection onto the platform and added the modifiers to the solution. Rygh and Jackson ( 0 3 8 ) used slurry injection into the Delves cup for a fast method for the determination of Cd. De Kersabiec et al. ( 0 3 9 ) reported the direct introduction of sample mixed with graphite into a Hitachi cup cuvette. They studied As, Cd, Pb, Hg, Sb, and Se. They concluded that this type of sample analysis scheme is better for the medical and biological fields than geological because of matrix effects. Schmidt and Falk ( 0 4 0 ) designed a graphite tube specifically for the analysis of solid samples. The design allows the light path of the tube to reach an isothermal temperature prior to the vaporization of the sample. They studied Ag, Cu, and Ni in several different matrices. Nakamura et al. ( 0 4 1 ) reported a method for the determination of Cu in scale and carbonate rocks by direct atomization. They determined the Cu by mixing 1 mg of sample with 1 mg of graphite and used standard furnace conditions. T o date, the direct analysis of solid geological materials seems to be limited to very volatile elements or elements captured in known mineral phases. Hydride generation atomic absorption (HGAA) has been reported for several elements (As, Sb, Te, Bi, Sn, Se, Pb). These elements are typically found at low concentrations and are important environmentally and as “pathfinder” elements for sulfide mineralization. Hydride generation has gained attention not only because of its high sensitivity but also because the method is quite easily automated. Wang and Fang ( 0 4 2 ) reported a rate of measurement of 250-300 samples per hour using flow injection combined with hydride generation. The primary problem associated with HGAA is a suppression interference caused by the presence of transition elements, other hydride forming elements, and some of the platinum group elements. Kuldvere ( 0 4 3 ) reported a method for determining As in Se metal. He oxidized the Se to Se(V1) with permanganate prior to analysis and determined the As(V). The method was tested up to 25 pg /mL Se. Itoh et al. ( 0 4 4 ) reported the reduction of interference on the Se determination by Cu and Bi using Fe(II1) in 6 M HC1. They reported a limit of determination of 0.012 pg /g. A method for P b determination in geological materials was reported by Zhang and Hu (045).Interferences were minimized by adding potassium ferrocyanide, sodium thiocyanide, and oxalic acid. 112R
ANALYTICAL CHEMISTRY, VOL. 61, NO. 12, JUNE 15, 1989
Sanzolone and Chao ( 0 4 6 ) reported the application of continuous-flow hydride AAS to 32 geochemistry reference materials. Ohyama et d. (047)reported using an argon-hydrogen flame as the atom cell for the determination of Bi in environmental and geological materials. Zhang and Yin ( 0 4 8 ) examined the interferences for 44 elements on the measurement of Sn. They used 1% tartaric acid to suppress the interference and achieved a limit of detection of 0.01 pg/g. Methods for determining Hg using cold vapor generation into AA cells continue to be published. Kennedy and Crock ( 0 4 9 ) reported on a continuous flow technique that gave a 0.01 pg g limit of detection from a 0.1-g sample. Zelyukova et al. ( 50) reported on the use of GeC1, to reduce the Hg. They compared the efficiency or SnCl:, with the Ge. Ge was more efficient. Citric acid was used as a catalyst in the Ge study.
b
PLASMAS: ICP-AES, ICP-MS, AND DCP Inductively coupled plasma atomic emission spectrometry (ICP-AES) continues to be a popular analytical tool in the field of applied geology and geochemistry. The technique is noted for low limits of detection, plus wide dynamic range and elemental coverage. Most of the new applications papers published since our last review deal with one of the following topics: (a) novel sample introduction approaches, (b) improved sample decomposition and pretreatment methods, or (c) separation and preconcentration of selected elements from complex matrices. A particularly useful periodical for plasma spectroscopists is the ICP Information Newsletter (R.M. Barnes, Editor) that reports on developments of the technique by listing abstracts of national and international meetings, issuing special reports, and providing an annual bibliogra hy in the January issue. Burman ( E l )prepared a compre ensive review on the use of ICP-AES for the analysis of geological samples. Walsh and Howie (E2)summarized the attributes and limitations of the technique and evaluated its potential in the field of applied geochemistry. Kantipuly and Westland (E3) presented a review of methods for the determination of lanthanides in geological samples which included a section on plasma source emission spectrometry and associated separation techniques. The analysis of minerals and refractories was reviewed by Hickman, Rooke, and Thompson (E4) who compared atomic emission, atomic fluorescence, atomic absorption, and inductively coupled plasma mass spectrometric methods of analysis. It is generally recognized that the dissolution of solid materials is a serious problem and that it is often the most time-consuming step in ICP analyses. In an interesting paper, Govindaraju and Mevelle (E5)described an automated sample dissolution and separation method for rock analysis in the form of a computerized workstation controlled by a traveling robot. They illustrated the application of their system, which they labeled the LabRobStation, by presenting the results of more than 8000 rare-earth element d&erminations. Several papers have appeared that compare and contrast different decomposition procedures. Bettinelli et al. (E6)tried three different procedures for decomposition of fly ash, sediments, and rocks: (1)Li2B407fusion; (2) HF, HN03, HC1, and HCLOl in a PTFE bomb with conventional heating; and (3) the same acids in a bomb in a microwave oven. Hee and Boyle (E7) found that a Parr bombfmixed mineral acid digestion scheme was superior to either microwave oven or hot plate methods for studies involving biological, soil, and phosphate rock samples. Church, Mosier, and Motooka (E8)reported that oxalic acid and aqua regia leaches were the most useful digestion procedures for performin reconnaissance exploration geochemical studies on stream setiment samples. They found that oxalic acid attacks compounds formed during secondary geochemical processes, whereas aqua regia digested primary sulfide phases as well as secondary phases. Brueckner et al. (E9) used a two-stage H202-HF pressure decomposition procedure for the measurement of major and selected trace elements in soil. One way of circumventing the problems associated with the dissolution of solid samples is to introduce the sample in the form of a slurry. Foulkes, Ebdon, and Hill (E10)evaluated two wet grinding techniques for the production of fine slurries from ores and minerals. They found that particle size needed to be reduced to
