- Email: [email protected]
Distribution and speciation of platinum group elements in environmental matrices
702
trends in analytical chemistry, vol. 18, no. 11, 1999
[ 25 ] E.N. Fung, E.S. Yeung, Anal. Chem. 67 ( 1995 ) 1913. [ 26 ] A.C. Peacock, C.W. Dingman, Biochemistry 7 ( 1968 ) 668. [ 27 ] A. Guttman, in J.P. Landers ( Ed. ), Handbook of Capillary Electrophoresis, CRC Press, Boca Raton, FL, 1994. [ 28 ] D. Tietz, M.H. Gottlieb, J.S. Fawcett, A. Chrambach, Electrophoresis 7 ( 1986 ) 217. [ 29 ] P. Trost, A. Guttman, Anal. Chem. 70 ( 1998 ) 3930.
[ 30 ] S. Cassel, A. Guttman, Electrophoresis 19 ( 1998 ) 1341. [ 31 ] J.E. Stanch¢eld and D.W. Batey, Poste Presentation at Genome Mapping and Sequencing Symposium, Cold Spring Harbor, May, 13^17, 1998, p. 214. [ 32 ] S. Hjerten, J. Chromatogr. 347 ( 1985 ) 191. [ 33 ] A. Guttman, N. Cooke, Anal. Chem. 63 ( 1991 ) 2038. [ 34 ] H.A. Erlich ( Ed. ), PCR Technology, Stockton Press, New York, 1989.
Distribution and speciation of platinum group elements in environmental matrices R.R. Barefoot*
Department of Geology, University of Toronto, Toronto, Ont. M5S 3B1, Canada The use of platinum group elements (PGEs ) as components of autocatalytic converters attached to motor vehicles has resulted in serious contamination of the environment by Pt, Rh and Pd in nanocrystalline forms. Trace concentrations of PGEs, particularly the major component Pt, in environmental samples have been measured by sensitive instrumental procedures. These data have raised further questions about the nature of Pt species in contaminated soils and in plants grown in them. The focus of attention is changing from accumulations of data expressing total concentrations to investigations of speciation. Application of analytical procedures for research on speciation has provided information concerning transformations of Pt compounds in contaminated soils, the uptake of Pt by plants and the nature of Pt compounds in vegetation. Determination of background levels of precious metals in clinical and environmental matrices has required the development of analytical methods which combine uses of minimal quantities of reagents, and as small a number of chemical operations as possible to yield very low procedural blanks. Sensitive instrumental methods based upon high resolution inductively coupled plasma mass spectrometry and adsorptive stripping voltammetry have proven to be valuable for this *Fax: +1 (416) 978 3938.
work. z1999 Elsevier Science B.V. All rights reserved. Keywords: Platinum group elements; Autocatalytic converters; Catalysts; Exhaust gases
1. Introduction For over 20 years, autocatalytic converters containing platinum group elements (PGEs ) have been employed successfully in the treatment of pollutants in exhaust gases from motor vehicles. Of the PGEs used for this purpose, Pt has been the main and most important component, together with Pd and Rh. About 90% of the three major gaseous pollutants, namely carbon monoxide, unburned hydrocarbons and nitrogen oxides, are transformed to harmless products by autocatalysts. Along with the bene¢cial aspects of the technology, a disadvantage was a widespread distribution of ¢ne particulate matter, or dust, containing PGEs. The dust originated from abrasion and deterioration of the bulk catalysts. Thus, PGEs have been deposited along roadways, on vegetation and soil surfaces adjacent to roadways, and in streams, rivers and waterways either directly or as runoff. Concerns have arisen that PGEs may have deleterious effects on the health of the general population by direct contact with the dust, by inhalation of particulate matter and through food and water [ 1 ]. Research has been carried out on developing reliable analytical methods for accurate determinations of traces of PGEs in environmental and clinical samples.
0165-9936/99/$ ^ see front matter PII: S 0 1 6 5 - 9 9 3 6 ( 9 9 ) 0 0 1 7 3 - 9
ß 1999 Elsevier Science B.V. All rights reserved.
TRAC 2589 21-10-99
703
trends in analytical chemistry, vol. 18, no. 11, 1999
Most of the attention has been focused on Pt determinations. A considerable volume of data has been accumulated on low level Pt determinations at polluted sites and trends in concentrations of Pt over a period of years. This work is being extended to include data on Rh and Pd. Accurate measurement of total concentrations of each of the elements in phases of the environment has presented dif¢cult problems. Recently, more attention has been given to determinations of background levels of PGEs, particularly in clinical samples. In addition, investigations of transformations of Pt in soils have been undertaken in order to gain an understanding of the forms in which the element is taken up by vegetation. Research has involved studies of Pt speciation both in polluted soil matrices and in plants grown in these soils. Development and application of analytical methods suitable for determinations of traces of metallic species in such matrices have played a major role in the projects. The purpose of this review is to describe some of the signi¢cant accomplishments which have occurred, mainly during the past 3 years. It includes determinations of background levels of PGEs, especially in clinical samples, bioavailability and speciation of Pt in soils and speciation of Pt in vegetation. The lack of reference materials for work in this ¢eld is noted also.
2. Analytical techniques Accurate determinations of low levels of PGEs in environmental and clinical samples have been possible using instrumental methods which possess good sensitivities. Care in sample preparations in order to diminish the effects of contamination and to avoid losses of analytes is equally important. Samples collected for analysis have included soil [ 2 ], dust [ 3 ], vegetation [ 4 ], water [ 5 ], snow [ 6 ] and ash from sewage treatment [ 5 ]. The metals contents of vegetation growing outdoors, as contrasted with plants grown under controlled conditions in greenhouses, include metals both deposited on the foliage and metabolized by the plants. In order to keep procedural blanks at the lowest practical levels, plastic tools ( scissors, scoops, etc. ) are used in collecting samples. Storage vessels must be clean and, when possible, acid washed. Acids and other chemicals used in the laboratory are high-purity grades. Electrothermal atomization-atomic absorption spectrometry ( ETA-AAS ) is a well-established technique with excellent sensitivity, and the equipment is available in many research laboratories. An instru-
ment equipped with Zeeman effect background correction was used for very low concentrations of Pt, Pd and Au in urine after the metals had been separated from the matrix as their pyrrolidinedithiocarbamate complexes [ 7 ]. A method suitable for determining traces of Pd in environmental samples was based upon the preconcentration of Pd by complexation with N,N-diethyl-NP-benzoylthiourea [ 8 ]. Pd concentrations were measured using ETA-AAS. Another technique, ICP-MS, has been used by many workers for determinations of PGEs because of its sensitivity and multi-element capability. Applications to analyses of soils has involved ¢re assays ( FA ) employing both nickel sul¢de (NiS^FA ) and lead (Pb^FA ) as collectors [ 2,3 ]. NiS^FA was also used to prepare soil samples for determinations of PGEs by instrumental neutron activation analysis ( INAA ) [ 9 ]. Plant samples were decomposed in a high-pressure asher for ICPMS determinations of Pt [ 10 ]. In ICP-MS, one of the most important spectral interference in determinations of Pt isotopes was caused by HfO ions; ZrO, Cd and Rb ions interfered with Pd determinations. HfO interferences were overcome by means of mathematical corrections [ 10 ] and by chromatographic separations [ 4 ]. Some of the instrumental techniques possess suf¢cient sensitivities that preconcentration steps are not required. One of these, adsorptive stripping voltammetry ( AV ), has been used for determinations of both Pt and Rh in environmental materials [ 11 ]. Complete decompositions of organic materials were necessary in order that carbon contents of sample solutions were below 0.5%; nitric acid must be absent also. Ultraviolet irradiation of acidi¢ed samples was necessary to overcome serious interferences from surface-active compounds in determinations of Pt in sea water [ 12 ]. Electrothermal atomization laser-excited £uorescence spectrometry ( ETA-LEAFS ) has been applied to determinations of traces of Pt in environmental materials directly after dilution or acid digestions of samples [ 13 ]. High resolution ( HR )-ICP-MS, also known as magnetic sector- or sector ¢eld-ICP-MS, is a new technique which has been applied to determinations of very low levels of PGEs in blood and urine. Descriptions of high resolution instruments and the theory of operation have appeared in a recent review [ 14 ]. Although the sensitivity of HR-ICP-MS decreases with increases in resolution, in a low-resolution mode, m / vm = 300, detection limits of non-interfered isotopes were improved by two orders of magnitude when compared to those of quadrupole ICP-MS [ 15 ]. Very low
TRAC 2578 21-10-99
704
trends in analytical chemistry, vol. 18, no. 11, 1999
instrumental background levels ( 6 1 count s31 ) meant that method detection limits depended mainly upon reagent blanks, memory effects and any spectral interferences. Additional details of this technique applied to determinations of precious metals in clinical samples are found in the next section.
3. Background levels of precious metals in blood and urine The widespread release of Pt, Pd and Rh into the environment by means of dust emissions from automotive catalytic converters has resulted in concerns about possible health effects on humans. Consequently, measurements of very low levels, called background or baseline levels, of these elements in blood and urine of persons not normally exposed to them are important. Such measurements allow assessments of possible increases in levels after periods of exposure of the general population to new sources of pollution. Analytical methods for determinations of elevated levels of Pt and Au in clinical samples relating to patients receiving treatments for cancer and arthritis, respectively are available [ 16 ]. Ultratrace quantities of Pt in urine and blood were determined by ETA-LEAFS with minimal sample treatment [ 13 ]. An absolute limit of detection of 50 fg was achieved. A precision of 8% at the 10 ng g31 level was reported for complex samples. An analytical procedure based upon high-pressure acid digestion with determination by AV has been applied to measurements of baseline concentrations of Pt in blood and urine [ 17 ]. Pt concentrations were in the ranges of 6 0.8^6.9 ng l31 in blood, and 0.5^14.3 ng l31 in urine. The limit of detection of the method was 0.2 ng l31 . Recently, a new instrumental method has been applied to this work. HR-ICP-MS has provided greater resolution and decreased instrumental background noise than quadrupole ICP-MS as noted in Section 2. Procedures were developed for multi-element analyses with excellent detection limits suitable for measurements of very low levels of precious metals. Work on analyses of blood and urine [ 18 ] showed that detection limits of such procedures were mainly in£uenced by blank values and spectral interferences. Decompositions of blood and urine samples by means of ultraviolet photolysis rather by digestions in acids were preferable because of requirements of minimal additions of reagents. The use of sub-boiling acid condensates obtained from ultrapure acids was essential in reducing the procedural blanks. Scrupulous cleansing
of laboratory apparatus and a clean-air environment were important also. Results of analyses for precious metals concentrations in blood and urine of nonexposed personnel are shown in Table 1. Detection limits were several orders of magnitude better than those obtained by quadrupole ICP-MS or ETV-AAS. Table 1 also contains the results of another study of Pt, Pd and Rh concentrations in urine using a method based upon ultraviolet photolysis and magnetic HRICP-MS [ 20 ]. The samples were obtained from a group of 30 children who lived in urban and suburban areas of Rome, Italy. In a study carried out in the UK, Pt concentrations in samples from nonexposed personnel were analyzed by ICP-MS after acid digestions [ 21 ]. Concentrations of Pt were in the ranges of 0.11^ 0.14 ( mean 0.13 ) Wg l31 in blood, and 0.05^0.22 ( mean 0.11 ) Wg ( g creatine )31 in urine. The detection limit was 0.03 Wg l31 . A comparison of these data with those in Table 1 and reference [ 17 ] shows that Pt concentrations in blood found in the UK study were much larger than the others.
4. Platinum group elements in soil, dust and vegetation The dispersion and accumulation of precious metals in the environment has been monitored over a period of about 8 years by determining totals of Pt, Pd and Rh in various environmental compartments. Most of the investigations have involved samples of soils and vegetation adjacent to heavily traveled highways, and of road dust swept from the surfaces of roadways. The element that has received the most attention is Pt, while Pd and Rh have been monitored in more recent research projects [ 11 ]. Data have shown an upward trend of Pt concentrations over time. Some concentrations in soils near roadways have been as much as 70 Table 1 Precious metal levels ( ng l31 ) in blood and urine of nonexposed persons using HR-ICP-MS Sample Element
Range
Detection limits
Ref.
Blood
0.3^1.3 32^78 0.1^0.4 125^413 0.5^7.6 61 W10 W10
61 61 61 5 0.2 0.03 0.2 0.03
[ 19 ] [ 19 ] [ 19 ] [ 19 ] [ 18 ] [ 20 ] [ 20 ] [ 20 ]
Urine
TRAC 2578 21-10-99
Pt Pd Ir Au Pt Pt Pd Rh
705
trends in analytical chemistry, vol. 18, no. 11, 1999
times larger than background levels [ 22 ]. In a typical investigation, soil samples were obtained for a distance of 20 m from the traf¢c lane along a line drawn perpendicular to the roadway; sampling depths were 0^2 cm, 2^5 cm and 5^10 cm [ 23 ]. Concentrations of Pt, Pd and Rh decreased with increasing distance from the road, and decreased signi¢cantly with depth of sample. Ratios of Pt /Rh were about 5:1; other workers have reported ratios of 5:1 and 6:1. The probable emission rate of Pt from vehicles equipped with catalytic converters has been estimated as 0.5^0.8 Wg Pt km31 [ 24 ]. This rate was calculated from test stand experiments and from Pt concentrations in samples of plants and soils. Factors of uncertainty were included in the calculations. Platinum deposited along roadways has been studied also by measuring accumulations of Pt in standardized grass cultures. These have been planted adjacent to heavily and lightly traveled roads [ 25 ]. The largest concentrations of Pt ranged from 0.8 to 2.9 Wg kg31 dm31 . In locations far removed from heavy traf¢c, the concentrations ranged from 0.2 to 0.5 Wg kg31 dm31 . Platinum concentrations of dust in air sampled in a bus traveling in dense urban traf¢c averaged 7.3 pg m33 ; along less traveled routes, the average was 3.3 pg m33 [ 26 ]. Collections of data on Pt and Pd concentrations in compartments of the environment are found in other publications [ 5,27 ]. Table 2 contains some additional data from more recent reports.
5. Bioavailability of platinum Platinum attached to particulate matter, which has been emitted as deterioration products of automotive catalysts, exists mainly in the metallic form. In this form, it is not available to plants. Over a period of time, Pt and other precious metals in the catalysts which can accompany Pt are subject to biological
and chemical agents in soils. The metallic species may be transformed to other species which are bioavailable. Properties of the soil are important in experimental programs involving studies of bioavailabilities. Most of the work in this area to date has been focused on Pt. A detailed study was undertaken of transformations of selected Pt compounds occurring in a clay-like humic soil [ 28 ]. The samples studied included dust ( containing Pt ) collected from a road tunnel in Austria, Pt black, PtO2 , K2 PtCl4 and Na2 PtCl6 . The Pt materials were mixed with soil. Water was added to some of the mixtures and no water to others. Reaction times of 1^60 days at room temperature were chosen prior to analyses of the soil samples. Speciation of Pt was investigated by eluting the soils with water, complexing agents and some organic solvents. Platinum contents of the extracts were determined by ICP-optical emission spectrometry and ICP-MS. Uptake of Pt in plants grown in soils containing tunnel dust varied from 0.02 to 0.6% of the total Pt present [ 6 ]. Oxidation of Pt occurred to a larger extent in soil treated with tunnel dust than the Pt in soil treated with Pt black. The authors concluded that the explanation was the degree of dispersion and nanocrystalline particle size of Pt in the tunnel dust. The chlorocomplexes of Pt were absorbed strongly by the soil. Detailed results of the work were presented in a series of bar graphs. More detailed information is available in reference [ 10 ]. Measurements of transfers of Pt, Pd and Rh from contaminated roadside soil to several species of plants were reported [ 29 ]. Plants such as spinach and cress were grown in a controlled environment in both contaminated and uncontaminated sandy and clay soils. After 6 weeks, plants and soils were analyzed for their precious metals contents. These were determined by ICP-MS. There were measurable transfers of Pt, Pd and Rh from contaminated soils to plants. Transfer coef¢cients were calculated and were then used as descriptors for comparisons of uptakes of elements
Table 2 Precious metals in soil, dust and vegetation Sample
Element
Method
Technique
Detection limits
Ref.
Soil Soil Soil Dust, ( soil ) Dust ( air ) Grass
Pt Pt Pt, Pd, Rh Pt Pt Pt, Rh
Acid digestion NiS^FA NiS^FA Pb^FA Acid digestion Acid digestion
ETA-LEAFS ICP-MS INAA ICP-MS AV AV
50 fg 0.5 Wg kg31 0.3 ng g31 ( typical ) 0.1 ng g31 0.5 pg m33 55 ng kg31 (Pt ) 33 ng kg31 (Rh )
[ 13 ] [2] [5] [3] [ 26 ] [ 11 ]
TRAC 2578 21-10-99
706
trends in analytical chemistry, vol. 18, no. 11, 1999
by the plants. The coef¢cients were de¢ned as ratios of concentrations of elements in the plants to concentrations in the soil. Pd was the most available to plants. However, mobilities of the three elements could be described as low on a qualitative basis. Additional studies of Pt species formed in humic soils treated with tunnel dust, Pt black and water-soluble Pt salts were undertaken [ 30 ]. Aqueous extracts of these soils were analyzed by high performance ( HPLC )^ICP-MS and capillary electrophoresis ( CE )^ICP-MS in parallel. In the HPLC studies, the interface between the chromatograph and the spectrometer included an ultrasonic nebulizer combined with a membrane desolvator. In this way, organic solvents as well as aqueous solutions containing dissolved salts were transferred directly to the ICP instrument without adverse effects on the plasma. Information about the polar character of the eluted Pt species was obtained. CE^ICP-MS studies provided some information about the nature of Pt species present. Changes in compositions were monitored after periods of 3, 7, 14 and 30 days ( at room temperature ). The detection limit of the HPLC system was 25 ng Pt l31 , and 1 Wg Pt l31 for the CE system. Detailed results of the experiments were presented as chromatograms and electropherograms. Pt concentrations in the extracts of soils treated with soluble Pt salts tended to increase with time. For tunnel dust, Pt concentrations in extracts were close to the method detection limits. Electropherograms of tunnel dust extracts showed species patterns different from those of the other contaminants. The soluble Pt species formed from interactions of Pt black and the chlorocomplexes of Pt with the soils were very polar, and were probably inorganic Pt species. In contrast, Pt in the tunnel dust formed humic acid complexes. The bioavailability of Pt contained in a model substance containing Pt, that was said to be similar in respect to the Pt in exhaust particulates, was tested by administration of extracts to rats [ 31 ]. About 10% of the total Pt content of this substance was soluble in physiological chloride solutions. After 8 days, Pt was detected in tissues and body £uids of the treated animals. All Pt in samples of blood plasma was bound to proteins.
6. Speciation of platinum in vegetation Platinum deposited in soils and water may be taken up by vegetation. Subsequently, plants and agricultural products such as meat and dairy products act as
sources for transfers of Pt from the environment to humans. Studies of the speciation of precious metals, particularly Pt, in plants are essential in gaining an understanding of the potential risks to the health of human populations. Total Pt concentrations in vegetation are small, but accurate determinations of Pt are possible using instrumental techniques described in earlier sections of this report. However, signi¢cant analytical data are more dif¢cult to obtain in speciation studies because of even smaller concentrations of the species themselves. A number of recent investigations are outlined here. Research programs were undertaken with the objectives of separations and identi¢cations of Pt species in grass grown in soils containing a water-soluble Pt compound [Pt(NH3 )4 ](NO3 )2 . Welches Weidelgras was chosen for this work. There was no contact between the grass and the Pt complex so that absorption was limited to the roots. Samples for analysis were obtained by extracting the cut grass with solvents. Dissolved compounds were separated by ultra¢ltration and gel permeation chromatography ( GPC ). Platinum contents of the fractions were detected and investigated by means of AV [ 32,33 ], ICP-MS [ 34 ], pulsed amperometric methods and cyclic voltammetry [ 35 ]. Grass grown in soil that had not been treated with the complex contained Pt in a fraction of high molecular mass ( 160^200 kDa ) [ 32 ]. In grass from treated soil, 90% of total Pt appeared in a low molecular mass fraction ( 6 10 kDa ) [ 33 ]. The low molecular mass fraction was investigated further by coupled GPC^ICP-MS, and ¢ve Pt containing fractions were detected. Information about possible binding partners ( C, S, Ca, Pb ) of Pt in the fractions was obtained by applying the multi-element capability of ICP-MS [ 34 ]. In this manner, the authors arrived at some tentative conclusions about the chemical compositions of the Pt species. Pulsed amperometric detection together with cyclic voltammetry were used in investigations of electroactive Pt species and ligands such as carbohydrates [ 35 ]. The instrumental techniques did not provide suf¢cient information for positive identi¢cations of Pt species. However, there were indications that Pt was associated with carbohydrates which were either partly oxidized sugars or glycosidically bound sugars.
7. Reference materials At the present time, there is a need for environmental reference materials (RMs ) containing certi¢ed low
TRAC 2578 21-10-99
707
trends in analytical chemistry, vol. 18, no. 11, 1999
levels of PGEs, particularly Pt, Pd and Rh. These could be used in projects involving the development of analytical methods for determinations of traces of PGEs. A list of some RMs used in various research projects related to determinations of Pt in environmental and biological matrices is available [ 27 ]. However, it included used catalysts containing high levels of Pt, and geological certi¢ed RMs that are not really suitable for the current requirements of investigators. A project has been proposed with the objective of the production and certi¢cation of a reference material, namely road dust, for Pt and Pd [ 1 ].
8. Conclusions Investigations involving determinations of background and very low levels of PGEs have led to the development of new analytical methods. Instrumental methods using HR-ICP-MS, AV and ETA-LEAFS have been important because preparations of solutions to determinations of analytes have not required preconcentration steps. Research on speciation and bioavailability of Pt in contaminated soils and in plants has yielded information on the uptake and metabolism of Pt by plants. There is a continuing need of RMs suitable for analyses of environmental materials containing traces of PGEs.
References [ 1 ] T. Hees, B. Wenclawiak, S. Lustig, P. Schramel, M. Schwarzer, M. Schuster, D. Verstraete, R. Dams, E. Helmers, Environ. Sci. Pollut. Res. Int. 5 ( 1998 ) 105. [ 2 ] M. Cubelic, R. Pecoroni, J. Schafer, J.D. Eckhardt, Z. Berner, D. Stuben, Umweltwiss. Schadst.-Forsch. 9 ( 1997 ) 249. [ 3 ] M.E. Farago, P. Kavanagh, R. Blanks, J. Kelly, G. Kazantzis, I. Thornton, P.R. Simpson, J.M. Cook, S. Parry, G.E.M. Hall, Fresenius' J. Anal. Chem. 354 ( 1996 ) 660. [ 4 ] M. Parent, H. Vanhoe, L. Moens, R. Dams, Fresenius' J. Anal. Chem. 354 ( 1996 ) 664. [ 5 ] E. Helmers, M. Schwarzer, M. Schuster, Environ. Sci. Pollut. Res. Int. 5 ( 1998 ) 44. [ 6 ] U. Kestel, Forum Staed-Hyg. 47 ( 1996 ) 293. [ 7 ] J. Begerow, M. Turfeld, L. Dunemann, Anal. Chim. Acta 340 ( 1997 ) 277. [ 8 ] M. Schuster, M. Schwarzer, At. Spectrosc. 19 ( 1998 ) 121. [ 9 ] E. Heinrich, G. Schmidt, K.-L. Kratz, Fresenius' J. Anal. Chem. 354 ( 1996 ) 883. [ 10 ] S. Lustig, S. Zang, B. Michalke, P. Schramel, W. Beck, Fresenius' J. Anal. Chem. 357 ( 1997 ) 1157.
[ 11 ] E. Helmers, N. Mergel, Fresenius' J. Anal. Chem. 362 ( 1998 ) 522. [ 12 ] C.M.G. van den Berg, G.S. Jacinto, Anal. Chim. Acta 211 ( 1988 ) 129. [ 13 ] R.Q. Aucelio, V.N. Rubin, B.W. Smith, J.D. Winefordner, J. Anal. At. Spectrom. 13 ( 1998 ) 49. [ 14 ] N. Jakubowski, L. Moens, F. Vanhaecke, Spectrochim. Acta B 53B ( 1998 ) 1739. [ 15 ] J. Begerow, L. Dunemann, J. Anal. At. Spectrom. 11 ( 1996 ) 303. [ 16 ] R.R. Barefoot, J.C. Van Loon, Anal. Chim. Acta 334 ( 1996 ) 5. [ 17 ] J. Messerschmidt, F. Alt, G. Tolg, J. Angerer, K.H. Schaller, Fresenius' J. Anal. Chem. 343 ( 1992 ) 391. [ 18 ] J. Begerow, M. Turfeld, L. Dunemann, J. Anal. At. Spectrom. 11 ( 1996 ) 913. [ 19 ] J. Begerow, M. Turfeld, L. Dunemann, J. Anal. At. Spectrom. 359 ( 1997 ) 427. [ 20 ] M. Krachler, A. Alimonti, F. Petrucci, K.J. Irgolic, F. Forastiere, S. Caroli, Anal. Chim. Acta 363 ( 1998 ) 1. [ 21 ] M.E. Farago, P. Kavanagh, R. Blanks, J. Kelly, G. Kazantzis, I. Thornton, P.R. Simpson, J.M. Cook, H.T. Delves, G.E.M. Hall, Analyst 123 ( 1998 ) 451. [ 22 ] F. Zereini, F. Alt, K. Rankenburg, J.M. Beyer, S. Artelt, Umweltwiss. Schadst.-Forsch. 9 ( 1997 ) 193. [ 23 ] J. Schafer, H. Puchelt, J. Geochem. Explor. 64 ( 1998 ) 307. [ 24 ] E. Helmers, Environ. Sci. Pollut. Res. Int. 4 ( 1997 ) 100. [ 25 ] M. Waeber, D. Laschka, L. Peichl, Umweltwiss. Schadst.-Forsch. 8 ( 1996 ) 3. [ 26 ] R. Schierl, G. Frumann, Sci. Total Environ. 182 ( 1996 ) 21. [ 27 ] R.R. Barefoot, Environ. Sci. Technol. 31 ( 1997 ) 309. [ 28 ] S. Lustig, S. Zang, B. Michalke, P. Schramel, W. Beck, Sci. Total Environ. 188 ( 1996 ) 195. [ 29 ] J. Schafer, D. Hannker, J.-D. Eckhardt, D. Stuben, Sci. Total Environ. 215 ( 1998 ) 59. [ 30 ] S. Lustig, B. Michalke, W. Beck, P. Schramel, Fresenius' J. Anal. Chem. 360 ( 1998 ) 18. [ 31 ] S. Artelt, O. Creutzenberg, H. Kock, K. Levensen, D. Nachtigall, U. Heinrich, T. Ruhle, R. Schlogl, Sci. Total Environ. 228 ( 1999 ) 219. [ 32 ] J. Messerschmidt, F. Alt, G. Toelg, Electrophoresis 16 ( 1995 ) 800. [ 33 ] J. Messerschmidt, F. Alt, G. Toelg, Anal. Chim. Acta 291 ( 1994 ) 161. [ 34 ] D. Klueppel, N. Jakubowski, J. Messerschmidt, D. Stuewer, D. Klockow, J. Anal. At. Spectrom. 13 ( 1998 ) 255. [ 35 ] G. Weber, F. Alt, J. Messerschmidt, Fresenius' J. Anal. Chem. 362 ( 1998 ) 209. Ronald R. Barefoot is a research associate in the Department of Geology, University of Toronto, Toronto, Ont. M5S 3B1, Canada. He has worked with Prof. J.C. Van Loon ( retired ) on projects involving determinations of precious metals, instrumental methods of analysis and chemical speciation applied to environmental studies. He is an author and co-author of a number of publications and textbooks in these areas. Formerly, he was Senior Research Scientist in the Chemicals Research Laboratory of ICI Canada.
TRAC 2578 21-10-99
trends in analytical chemistry, vol. 18, no. 11, 1999
[ 25 ] E.N. Fung, E.S. Yeung, Anal. Chem. 67 ( 1995 ) 1913. [ 26 ] A.C. Peacock, C.W. Dingman, Biochemistry 7 ( 1968 ) 668. [ 27 ] A. Guttman, in J.P. Landers ( Ed. ), Handbook of Capillary Electrophoresis, CRC Press, Boca Raton, FL, 1994. [ 28 ] D. Tietz, M.H. Gottlieb, J.S. Fawcett, A. Chrambach, Electrophoresis 7 ( 1986 ) 217. [ 29 ] P. Trost, A. Guttman, Anal. Chem. 70 ( 1998 ) 3930.
[ 30 ] S. Cassel, A. Guttman, Electrophoresis 19 ( 1998 ) 1341. [ 31 ] J.E. Stanch¢eld and D.W. Batey, Poste Presentation at Genome Mapping and Sequencing Symposium, Cold Spring Harbor, May, 13^17, 1998, p. 214. [ 32 ] S. Hjerten, J. Chromatogr. 347 ( 1985 ) 191. [ 33 ] A. Guttman, N. Cooke, Anal. Chem. 63 ( 1991 ) 2038. [ 34 ] H.A. Erlich ( Ed. ), PCR Technology, Stockton Press, New York, 1989.
Distribution and speciation of platinum group elements in environmental matrices R.R. Barefoot*
Department of Geology, University of Toronto, Toronto, Ont. M5S 3B1, Canada The use of platinum group elements (PGEs ) as components of autocatalytic converters attached to motor vehicles has resulted in serious contamination of the environment by Pt, Rh and Pd in nanocrystalline forms. Trace concentrations of PGEs, particularly the major component Pt, in environmental samples have been measured by sensitive instrumental procedures. These data have raised further questions about the nature of Pt species in contaminated soils and in plants grown in them. The focus of attention is changing from accumulations of data expressing total concentrations to investigations of speciation. Application of analytical procedures for research on speciation has provided information concerning transformations of Pt compounds in contaminated soils, the uptake of Pt by plants and the nature of Pt compounds in vegetation. Determination of background levels of precious metals in clinical and environmental matrices has required the development of analytical methods which combine uses of minimal quantities of reagents, and as small a number of chemical operations as possible to yield very low procedural blanks. Sensitive instrumental methods based upon high resolution inductively coupled plasma mass spectrometry and adsorptive stripping voltammetry have proven to be valuable for this *Fax: +1 (416) 978 3938.
work. z1999 Elsevier Science B.V. All rights reserved. Keywords: Platinum group elements; Autocatalytic converters; Catalysts; Exhaust gases
1. Introduction For over 20 years, autocatalytic converters containing platinum group elements (PGEs ) have been employed successfully in the treatment of pollutants in exhaust gases from motor vehicles. Of the PGEs used for this purpose, Pt has been the main and most important component, together with Pd and Rh. About 90% of the three major gaseous pollutants, namely carbon monoxide, unburned hydrocarbons and nitrogen oxides, are transformed to harmless products by autocatalysts. Along with the bene¢cial aspects of the technology, a disadvantage was a widespread distribution of ¢ne particulate matter, or dust, containing PGEs. The dust originated from abrasion and deterioration of the bulk catalysts. Thus, PGEs have been deposited along roadways, on vegetation and soil surfaces adjacent to roadways, and in streams, rivers and waterways either directly or as runoff. Concerns have arisen that PGEs may have deleterious effects on the health of the general population by direct contact with the dust, by inhalation of particulate matter and through food and water [ 1 ]. Research has been carried out on developing reliable analytical methods for accurate determinations of traces of PGEs in environmental and clinical samples.
0165-9936/99/$ ^ see front matter PII: S 0 1 6 5 - 9 9 3 6 ( 9 9 ) 0 0 1 7 3 - 9
ß 1999 Elsevier Science B.V. All rights reserved.
TRAC 2589 21-10-99
703
trends in analytical chemistry, vol. 18, no. 11, 1999
Most of the attention has been focused on Pt determinations. A considerable volume of data has been accumulated on low level Pt determinations at polluted sites and trends in concentrations of Pt over a period of years. This work is being extended to include data on Rh and Pd. Accurate measurement of total concentrations of each of the elements in phases of the environment has presented dif¢cult problems. Recently, more attention has been given to determinations of background levels of PGEs, particularly in clinical samples. In addition, investigations of transformations of Pt in soils have been undertaken in order to gain an understanding of the forms in which the element is taken up by vegetation. Research has involved studies of Pt speciation both in polluted soil matrices and in plants grown in these soils. Development and application of analytical methods suitable for determinations of traces of metallic species in such matrices have played a major role in the projects. The purpose of this review is to describe some of the signi¢cant accomplishments which have occurred, mainly during the past 3 years. It includes determinations of background levels of PGEs, especially in clinical samples, bioavailability and speciation of Pt in soils and speciation of Pt in vegetation. The lack of reference materials for work in this ¢eld is noted also.
2. Analytical techniques Accurate determinations of low levels of PGEs in environmental and clinical samples have been possible using instrumental methods which possess good sensitivities. Care in sample preparations in order to diminish the effects of contamination and to avoid losses of analytes is equally important. Samples collected for analysis have included soil [ 2 ], dust [ 3 ], vegetation [ 4 ], water [ 5 ], snow [ 6 ] and ash from sewage treatment [ 5 ]. The metals contents of vegetation growing outdoors, as contrasted with plants grown under controlled conditions in greenhouses, include metals both deposited on the foliage and metabolized by the plants. In order to keep procedural blanks at the lowest practical levels, plastic tools ( scissors, scoops, etc. ) are used in collecting samples. Storage vessels must be clean and, when possible, acid washed. Acids and other chemicals used in the laboratory are high-purity grades. Electrothermal atomization-atomic absorption spectrometry ( ETA-AAS ) is a well-established technique with excellent sensitivity, and the equipment is available in many research laboratories. An instru-
ment equipped with Zeeman effect background correction was used for very low concentrations of Pt, Pd and Au in urine after the metals had been separated from the matrix as their pyrrolidinedithiocarbamate complexes [ 7 ]. A method suitable for determining traces of Pd in environmental samples was based upon the preconcentration of Pd by complexation with N,N-diethyl-NP-benzoylthiourea [ 8 ]. Pd concentrations were measured using ETA-AAS. Another technique, ICP-MS, has been used by many workers for determinations of PGEs because of its sensitivity and multi-element capability. Applications to analyses of soils has involved ¢re assays ( FA ) employing both nickel sul¢de (NiS^FA ) and lead (Pb^FA ) as collectors [ 2,3 ]. NiS^FA was also used to prepare soil samples for determinations of PGEs by instrumental neutron activation analysis ( INAA ) [ 9 ]. Plant samples were decomposed in a high-pressure asher for ICPMS determinations of Pt [ 10 ]. In ICP-MS, one of the most important spectral interference in determinations of Pt isotopes was caused by HfO ions; ZrO, Cd and Rb ions interfered with Pd determinations. HfO interferences were overcome by means of mathematical corrections [ 10 ] and by chromatographic separations [ 4 ]. Some of the instrumental techniques possess suf¢cient sensitivities that preconcentration steps are not required. One of these, adsorptive stripping voltammetry ( AV ), has been used for determinations of both Pt and Rh in environmental materials [ 11 ]. Complete decompositions of organic materials were necessary in order that carbon contents of sample solutions were below 0.5%; nitric acid must be absent also. Ultraviolet irradiation of acidi¢ed samples was necessary to overcome serious interferences from surface-active compounds in determinations of Pt in sea water [ 12 ]. Electrothermal atomization laser-excited £uorescence spectrometry ( ETA-LEAFS ) has been applied to determinations of traces of Pt in environmental materials directly after dilution or acid digestions of samples [ 13 ]. High resolution ( HR )-ICP-MS, also known as magnetic sector- or sector ¢eld-ICP-MS, is a new technique which has been applied to determinations of very low levels of PGEs in blood and urine. Descriptions of high resolution instruments and the theory of operation have appeared in a recent review [ 14 ]. Although the sensitivity of HR-ICP-MS decreases with increases in resolution, in a low-resolution mode, m / vm = 300, detection limits of non-interfered isotopes were improved by two orders of magnitude when compared to those of quadrupole ICP-MS [ 15 ]. Very low
TRAC 2578 21-10-99
704
trends in analytical chemistry, vol. 18, no. 11, 1999
instrumental background levels ( 6 1 count s31 ) meant that method detection limits depended mainly upon reagent blanks, memory effects and any spectral interferences. Additional details of this technique applied to determinations of precious metals in clinical samples are found in the next section.
3. Background levels of precious metals in blood and urine The widespread release of Pt, Pd and Rh into the environment by means of dust emissions from automotive catalytic converters has resulted in concerns about possible health effects on humans. Consequently, measurements of very low levels, called background or baseline levels, of these elements in blood and urine of persons not normally exposed to them are important. Such measurements allow assessments of possible increases in levels after periods of exposure of the general population to new sources of pollution. Analytical methods for determinations of elevated levels of Pt and Au in clinical samples relating to patients receiving treatments for cancer and arthritis, respectively are available [ 16 ]. Ultratrace quantities of Pt in urine and blood were determined by ETA-LEAFS with minimal sample treatment [ 13 ]. An absolute limit of detection of 50 fg was achieved. A precision of 8% at the 10 ng g31 level was reported for complex samples. An analytical procedure based upon high-pressure acid digestion with determination by AV has been applied to measurements of baseline concentrations of Pt in blood and urine [ 17 ]. Pt concentrations were in the ranges of 6 0.8^6.9 ng l31 in blood, and 0.5^14.3 ng l31 in urine. The limit of detection of the method was 0.2 ng l31 . Recently, a new instrumental method has been applied to this work. HR-ICP-MS has provided greater resolution and decreased instrumental background noise than quadrupole ICP-MS as noted in Section 2. Procedures were developed for multi-element analyses with excellent detection limits suitable for measurements of very low levels of precious metals. Work on analyses of blood and urine [ 18 ] showed that detection limits of such procedures were mainly in£uenced by blank values and spectral interferences. Decompositions of blood and urine samples by means of ultraviolet photolysis rather by digestions in acids were preferable because of requirements of minimal additions of reagents. The use of sub-boiling acid condensates obtained from ultrapure acids was essential in reducing the procedural blanks. Scrupulous cleansing
of laboratory apparatus and a clean-air environment were important also. Results of analyses for precious metals concentrations in blood and urine of nonexposed personnel are shown in Table 1. Detection limits were several orders of magnitude better than those obtained by quadrupole ICP-MS or ETV-AAS. Table 1 also contains the results of another study of Pt, Pd and Rh concentrations in urine using a method based upon ultraviolet photolysis and magnetic HRICP-MS [ 20 ]. The samples were obtained from a group of 30 children who lived in urban and suburban areas of Rome, Italy. In a study carried out in the UK, Pt concentrations in samples from nonexposed personnel were analyzed by ICP-MS after acid digestions [ 21 ]. Concentrations of Pt were in the ranges of 0.11^ 0.14 ( mean 0.13 ) Wg l31 in blood, and 0.05^0.22 ( mean 0.11 ) Wg ( g creatine )31 in urine. The detection limit was 0.03 Wg l31 . A comparison of these data with those in Table 1 and reference [ 17 ] shows that Pt concentrations in blood found in the UK study were much larger than the others.
4. Platinum group elements in soil, dust and vegetation The dispersion and accumulation of precious metals in the environment has been monitored over a period of about 8 years by determining totals of Pt, Pd and Rh in various environmental compartments. Most of the investigations have involved samples of soils and vegetation adjacent to heavily traveled highways, and of road dust swept from the surfaces of roadways. The element that has received the most attention is Pt, while Pd and Rh have been monitored in more recent research projects [ 11 ]. Data have shown an upward trend of Pt concentrations over time. Some concentrations in soils near roadways have been as much as 70 Table 1 Precious metal levels ( ng l31 ) in blood and urine of nonexposed persons using HR-ICP-MS Sample Element
Range
Detection limits
Ref.
Blood
0.3^1.3 32^78 0.1^0.4 125^413 0.5^7.6 61 W10 W10
61 61 61 5 0.2 0.03 0.2 0.03
[ 19 ] [ 19 ] [ 19 ] [ 19 ] [ 18 ] [ 20 ] [ 20 ] [ 20 ]
Urine
TRAC 2578 21-10-99
Pt Pd Ir Au Pt Pt Pd Rh
705
trends in analytical chemistry, vol. 18, no. 11, 1999
times larger than background levels [ 22 ]. In a typical investigation, soil samples were obtained for a distance of 20 m from the traf¢c lane along a line drawn perpendicular to the roadway; sampling depths were 0^2 cm, 2^5 cm and 5^10 cm [ 23 ]. Concentrations of Pt, Pd and Rh decreased with increasing distance from the road, and decreased signi¢cantly with depth of sample. Ratios of Pt /Rh were about 5:1; other workers have reported ratios of 5:1 and 6:1. The probable emission rate of Pt from vehicles equipped with catalytic converters has been estimated as 0.5^0.8 Wg Pt km31 [ 24 ]. This rate was calculated from test stand experiments and from Pt concentrations in samples of plants and soils. Factors of uncertainty were included in the calculations. Platinum deposited along roadways has been studied also by measuring accumulations of Pt in standardized grass cultures. These have been planted adjacent to heavily and lightly traveled roads [ 25 ]. The largest concentrations of Pt ranged from 0.8 to 2.9 Wg kg31 dm31 . In locations far removed from heavy traf¢c, the concentrations ranged from 0.2 to 0.5 Wg kg31 dm31 . Platinum concentrations of dust in air sampled in a bus traveling in dense urban traf¢c averaged 7.3 pg m33 ; along less traveled routes, the average was 3.3 pg m33 [ 26 ]. Collections of data on Pt and Pd concentrations in compartments of the environment are found in other publications [ 5,27 ]. Table 2 contains some additional data from more recent reports.
5. Bioavailability of platinum Platinum attached to particulate matter, which has been emitted as deterioration products of automotive catalysts, exists mainly in the metallic form. In this form, it is not available to plants. Over a period of time, Pt and other precious metals in the catalysts which can accompany Pt are subject to biological
and chemical agents in soils. The metallic species may be transformed to other species which are bioavailable. Properties of the soil are important in experimental programs involving studies of bioavailabilities. Most of the work in this area to date has been focused on Pt. A detailed study was undertaken of transformations of selected Pt compounds occurring in a clay-like humic soil [ 28 ]. The samples studied included dust ( containing Pt ) collected from a road tunnel in Austria, Pt black, PtO2 , K2 PtCl4 and Na2 PtCl6 . The Pt materials were mixed with soil. Water was added to some of the mixtures and no water to others. Reaction times of 1^60 days at room temperature were chosen prior to analyses of the soil samples. Speciation of Pt was investigated by eluting the soils with water, complexing agents and some organic solvents. Platinum contents of the extracts were determined by ICP-optical emission spectrometry and ICP-MS. Uptake of Pt in plants grown in soils containing tunnel dust varied from 0.02 to 0.6% of the total Pt present [ 6 ]. Oxidation of Pt occurred to a larger extent in soil treated with tunnel dust than the Pt in soil treated with Pt black. The authors concluded that the explanation was the degree of dispersion and nanocrystalline particle size of Pt in the tunnel dust. The chlorocomplexes of Pt were absorbed strongly by the soil. Detailed results of the work were presented in a series of bar graphs. More detailed information is available in reference [ 10 ]. Measurements of transfers of Pt, Pd and Rh from contaminated roadside soil to several species of plants were reported [ 29 ]. Plants such as spinach and cress were grown in a controlled environment in both contaminated and uncontaminated sandy and clay soils. After 6 weeks, plants and soils were analyzed for their precious metals contents. These were determined by ICP-MS. There were measurable transfers of Pt, Pd and Rh from contaminated soils to plants. Transfer coef¢cients were calculated and were then used as descriptors for comparisons of uptakes of elements
Table 2 Precious metals in soil, dust and vegetation Sample
Element
Method
Technique
Detection limits
Ref.
Soil Soil Soil Dust, ( soil ) Dust ( air ) Grass
Pt Pt Pt, Pd, Rh Pt Pt Pt, Rh
Acid digestion NiS^FA NiS^FA Pb^FA Acid digestion Acid digestion
ETA-LEAFS ICP-MS INAA ICP-MS AV AV
50 fg 0.5 Wg kg31 0.3 ng g31 ( typical ) 0.1 ng g31 0.5 pg m33 55 ng kg31 (Pt ) 33 ng kg31 (Rh )
[ 13 ] [2] [5] [3] [ 26 ] [ 11 ]
TRAC 2578 21-10-99
706
trends in analytical chemistry, vol. 18, no. 11, 1999
by the plants. The coef¢cients were de¢ned as ratios of concentrations of elements in the plants to concentrations in the soil. Pd was the most available to plants. However, mobilities of the three elements could be described as low on a qualitative basis. Additional studies of Pt species formed in humic soils treated with tunnel dust, Pt black and water-soluble Pt salts were undertaken [ 30 ]. Aqueous extracts of these soils were analyzed by high performance ( HPLC )^ICP-MS and capillary electrophoresis ( CE )^ICP-MS in parallel. In the HPLC studies, the interface between the chromatograph and the spectrometer included an ultrasonic nebulizer combined with a membrane desolvator. In this way, organic solvents as well as aqueous solutions containing dissolved salts were transferred directly to the ICP instrument without adverse effects on the plasma. Information about the polar character of the eluted Pt species was obtained. CE^ICP-MS studies provided some information about the nature of Pt species present. Changes in compositions were monitored after periods of 3, 7, 14 and 30 days ( at room temperature ). The detection limit of the HPLC system was 25 ng Pt l31 , and 1 Wg Pt l31 for the CE system. Detailed results of the experiments were presented as chromatograms and electropherograms. Pt concentrations in the extracts of soils treated with soluble Pt salts tended to increase with time. For tunnel dust, Pt concentrations in extracts were close to the method detection limits. Electropherograms of tunnel dust extracts showed species patterns different from those of the other contaminants. The soluble Pt species formed from interactions of Pt black and the chlorocomplexes of Pt with the soils were very polar, and were probably inorganic Pt species. In contrast, Pt in the tunnel dust formed humic acid complexes. The bioavailability of Pt contained in a model substance containing Pt, that was said to be similar in respect to the Pt in exhaust particulates, was tested by administration of extracts to rats [ 31 ]. About 10% of the total Pt content of this substance was soluble in physiological chloride solutions. After 8 days, Pt was detected in tissues and body £uids of the treated animals. All Pt in samples of blood plasma was bound to proteins.
6. Speciation of platinum in vegetation Platinum deposited in soils and water may be taken up by vegetation. Subsequently, plants and agricultural products such as meat and dairy products act as
sources for transfers of Pt from the environment to humans. Studies of the speciation of precious metals, particularly Pt, in plants are essential in gaining an understanding of the potential risks to the health of human populations. Total Pt concentrations in vegetation are small, but accurate determinations of Pt are possible using instrumental techniques described in earlier sections of this report. However, signi¢cant analytical data are more dif¢cult to obtain in speciation studies because of even smaller concentrations of the species themselves. A number of recent investigations are outlined here. Research programs were undertaken with the objectives of separations and identi¢cations of Pt species in grass grown in soils containing a water-soluble Pt compound [Pt(NH3 )4 ](NO3 )2 . Welches Weidelgras was chosen for this work. There was no contact between the grass and the Pt complex so that absorption was limited to the roots. Samples for analysis were obtained by extracting the cut grass with solvents. Dissolved compounds were separated by ultra¢ltration and gel permeation chromatography ( GPC ). Platinum contents of the fractions were detected and investigated by means of AV [ 32,33 ], ICP-MS [ 34 ], pulsed amperometric methods and cyclic voltammetry [ 35 ]. Grass grown in soil that had not been treated with the complex contained Pt in a fraction of high molecular mass ( 160^200 kDa ) [ 32 ]. In grass from treated soil, 90% of total Pt appeared in a low molecular mass fraction ( 6 10 kDa ) [ 33 ]. The low molecular mass fraction was investigated further by coupled GPC^ICP-MS, and ¢ve Pt containing fractions were detected. Information about possible binding partners ( C, S, Ca, Pb ) of Pt in the fractions was obtained by applying the multi-element capability of ICP-MS [ 34 ]. In this manner, the authors arrived at some tentative conclusions about the chemical compositions of the Pt species. Pulsed amperometric detection together with cyclic voltammetry were used in investigations of electroactive Pt species and ligands such as carbohydrates [ 35 ]. The instrumental techniques did not provide suf¢cient information for positive identi¢cations of Pt species. However, there were indications that Pt was associated with carbohydrates which were either partly oxidized sugars or glycosidically bound sugars.
7. Reference materials At the present time, there is a need for environmental reference materials (RMs ) containing certi¢ed low
TRAC 2578 21-10-99
707
trends in analytical chemistry, vol. 18, no. 11, 1999
levels of PGEs, particularly Pt, Pd and Rh. These could be used in projects involving the development of analytical methods for determinations of traces of PGEs. A list of some RMs used in various research projects related to determinations of Pt in environmental and biological matrices is available [ 27 ]. However, it included used catalysts containing high levels of Pt, and geological certi¢ed RMs that are not really suitable for the current requirements of investigators. A project has been proposed with the objective of the production and certi¢cation of a reference material, namely road dust, for Pt and Pd [ 1 ].
8. Conclusions Investigations involving determinations of background and very low levels of PGEs have led to the development of new analytical methods. Instrumental methods using HR-ICP-MS, AV and ETA-LEAFS have been important because preparations of solutions to determinations of analytes have not required preconcentration steps. Research on speciation and bioavailability of Pt in contaminated soils and in plants has yielded information on the uptake and metabolism of Pt by plants. There is a continuing need of RMs suitable for analyses of environmental materials containing traces of PGEs.
References [ 1 ] T. Hees, B. Wenclawiak, S. Lustig, P. Schramel, M. Schwarzer, M. Schuster, D. Verstraete, R. Dams, E. Helmers, Environ. Sci. Pollut. Res. Int. 5 ( 1998 ) 105. [ 2 ] M. Cubelic, R. Pecoroni, J. Schafer, J.D. Eckhardt, Z. Berner, D. Stuben, Umweltwiss. Schadst.-Forsch. 9 ( 1997 ) 249. [ 3 ] M.E. Farago, P. Kavanagh, R. Blanks, J. Kelly, G. Kazantzis, I. Thornton, P.R. Simpson, J.M. Cook, S. Parry, G.E.M. Hall, Fresenius' J. Anal. Chem. 354 ( 1996 ) 660. [ 4 ] M. Parent, H. Vanhoe, L. Moens, R. Dams, Fresenius' J. Anal. Chem. 354 ( 1996 ) 664. [ 5 ] E. Helmers, M. Schwarzer, M. Schuster, Environ. Sci. Pollut. Res. Int. 5 ( 1998 ) 44. [ 6 ] U. Kestel, Forum Staed-Hyg. 47 ( 1996 ) 293. [ 7 ] J. Begerow, M. Turfeld, L. Dunemann, Anal. Chim. Acta 340 ( 1997 ) 277. [ 8 ] M. Schuster, M. Schwarzer, At. Spectrosc. 19 ( 1998 ) 121. [ 9 ] E. Heinrich, G. Schmidt, K.-L. Kratz, Fresenius' J. Anal. Chem. 354 ( 1996 ) 883. [ 10 ] S. Lustig, S. Zang, B. Michalke, P. Schramel, W. Beck, Fresenius' J. Anal. Chem. 357 ( 1997 ) 1157.
[ 11 ] E. Helmers, N. Mergel, Fresenius' J. Anal. Chem. 362 ( 1998 ) 522. [ 12 ] C.M.G. van den Berg, G.S. Jacinto, Anal. Chim. Acta 211 ( 1988 ) 129. [ 13 ] R.Q. Aucelio, V.N. Rubin, B.W. Smith, J.D. Winefordner, J. Anal. At. Spectrom. 13 ( 1998 ) 49. [ 14 ] N. Jakubowski, L. Moens, F. Vanhaecke, Spectrochim. Acta B 53B ( 1998 ) 1739. [ 15 ] J. Begerow, L. Dunemann, J. Anal. At. Spectrom. 11 ( 1996 ) 303. [ 16 ] R.R. Barefoot, J.C. Van Loon, Anal. Chim. Acta 334 ( 1996 ) 5. [ 17 ] J. Messerschmidt, F. Alt, G. Tolg, J. Angerer, K.H. Schaller, Fresenius' J. Anal. Chem. 343 ( 1992 ) 391. [ 18 ] J. Begerow, M. Turfeld, L. Dunemann, J. Anal. At. Spectrom. 11 ( 1996 ) 913. [ 19 ] J. Begerow, M. Turfeld, L. Dunemann, J. Anal. At. Spectrom. 359 ( 1997 ) 427. [ 20 ] M. Krachler, A. Alimonti, F. Petrucci, K.J. Irgolic, F. Forastiere, S. Caroli, Anal. Chim. Acta 363 ( 1998 ) 1. [ 21 ] M.E. Farago, P. Kavanagh, R. Blanks, J. Kelly, G. Kazantzis, I. Thornton, P.R. Simpson, J.M. Cook, H.T. Delves, G.E.M. Hall, Analyst 123 ( 1998 ) 451. [ 22 ] F. Zereini, F. Alt, K. Rankenburg, J.M. Beyer, S. Artelt, Umweltwiss. Schadst.-Forsch. 9 ( 1997 ) 193. [ 23 ] J. Schafer, H. Puchelt, J. Geochem. Explor. 64 ( 1998 ) 307. [ 24 ] E. Helmers, Environ. Sci. Pollut. Res. Int. 4 ( 1997 ) 100. [ 25 ] M. Waeber, D. Laschka, L. Peichl, Umweltwiss. Schadst.-Forsch. 8 ( 1996 ) 3. [ 26 ] R. Schierl, G. Frumann, Sci. Total Environ. 182 ( 1996 ) 21. [ 27 ] R.R. Barefoot, Environ. Sci. Technol. 31 ( 1997 ) 309. [ 28 ] S. Lustig, S. Zang, B. Michalke, P. Schramel, W. Beck, Sci. Total Environ. 188 ( 1996 ) 195. [ 29 ] J. Schafer, D. Hannker, J.-D. Eckhardt, D. Stuben, Sci. Total Environ. 215 ( 1998 ) 59. [ 30 ] S. Lustig, B. Michalke, W. Beck, P. Schramel, Fresenius' J. Anal. Chem. 360 ( 1998 ) 18. [ 31 ] S. Artelt, O. Creutzenberg, H. Kock, K. Levensen, D. Nachtigall, U. Heinrich, T. Ruhle, R. Schlogl, Sci. Total Environ. 228 ( 1999 ) 219. [ 32 ] J. Messerschmidt, F. Alt, G. Toelg, Electrophoresis 16 ( 1995 ) 800. [ 33 ] J. Messerschmidt, F. Alt, G. Toelg, Anal. Chim. Acta 291 ( 1994 ) 161. [ 34 ] D. Klueppel, N. Jakubowski, J. Messerschmidt, D. Stuewer, D. Klockow, J. Anal. At. Spectrom. 13 ( 1998 ) 255. [ 35 ] G. Weber, F. Alt, J. Messerschmidt, Fresenius' J. Anal. Chem. 362 ( 1998 ) 209. Ronald R. Barefoot is a research associate in the Department of Geology, University of Toronto, Toronto, Ont. M5S 3B1, Canada. He has worked with Prof. J.C. Van Loon ( retired ) on projects involving determinations of precious metals, instrumental methods of analysis and chemical speciation applied to environmental studies. He is an author and co-author of a number of publications and textbooks in these areas. Formerly, he was Senior Research Scientist in the Chemicals Research Laboratory of ICI Canada.
TRAC 2578 21-10-99