Anal. Chem. 1995, 67, 4250-4254
Microwave-Assisted Leaching of Organotin Compounds from Sediments for Speciation Analysis Olivier F. X. Donard,* Beatrice Lalere, Fabienne Martin, and Ryszard Lobinski Laboratoire de Photophysique et Photochimie Mol&ulaire, CRNS URA 348, Universiti2 de Bordeaux I, 33 405 Talence, France
The behavior and stability of organotin compounds in a microwave field is discussed. An extremely rapid procedure for the separation of butyl- and phenyltin derivatives from sediments is developed. The analyte species are quantitatively leached with acetic acid in a focused microwave field during a period of 3 min. The procedure followed by capillary GC-FPD offers a detection limit of 1 ng/g (as Sn). The procedure developed was validated by the analyses of two certified reference materials: the NRCC PACS-1 and the BCR CRM 462. The most widely used organotin biocides, tributyltin (TBT) and triphenyltin (I'PhT), have been recognized as toxic also to nontarget marine The introduction of relevant environmental legislation in many countries including the European Community has stimulated the development of analytical methods for the determination of the trisubstituted organotin compounds and the products of their degradation (mono- and dibutylphenyltin) in the aquatic environment. Analysis of sediments is particularly important because they act as the ultimate sink of organotins. The accumulated species can be released under favorable conditions into the aquatic environment and create a long-term ecotoxicological risk after the anthropogenic sources had been banned from the given area.4 The analytical protocols available are based mostly on the coupling of gas chromatography and atomic spectrometry and were recently r e v i e ~ e d . They ~ . ~ all suffer from the need for a cumbersome sample preparation step which, for more complex samples such as, e.g., sediments, is the virtual Achilles heel of the whole analytical p r o c e d ~ r e .Indeed, ~ the procedures reported so far are not only extremely time-consuming (they take from 1 h to 2 days) but are also usually inefficient in terms of analyte recovery and reliability. As shown by Chau and co-workers, only 3 out of 10 sample preparation methods described in the literature for the analysis of sediments were able to recover more than 90% of TBT whereas none of them was able to recover monobutyltin ~~
(1) Blunden, S. J.; Chapman, A. In Organometallic Compounds in the Environ-
ment, Principles and Reactions; Craig, P. J., Ed.; Longman: Essex. UK, 1986 pp 346-350. (2) World Health Organization, Tri'butyltin Compounds; Environ. Healths Criteria 116; Geneva, 1990. (3) Maguire, R J. Appl. Orgunomet. Chem. 1987,1, 475-498. (4) D i r k . W. M. R.: Lobinski, R.; Adams, F. C. Anal. Chim. Acta 1994,286, 309-318.
(5) Lobinski, R. Analusis 1994,22, 37-48. (6)Donard, 0.;Martin, F. Trends Anal. Chem. 1992,11, 17-26. (7) Donard, 0.;Ritsema, R. In Techniquesfor Environmental Analysis; Barcelo, D., Ed.; Elsevier: Amsterdam, 1993; pp 549-606.
4250
Analytical Chemistry, Vol. 67, No. 23, December 1, 7995
(MBT) in a nonerratic and reproducible manner! Extraction of phenyltins from sediments has hardly been inve~tigated.~-l~ Substantial progress toward faster and potentially automated speciation analysis of sediments for organotin was made with supercritical fluid extraction.13-15 Besides the high equipment cost, however, the extraction step still requires 10-50 min and the recoveries of di- and, especially, monosubsituted compounds (even when added as spikes) are far from being quantitative. Microwave-assisted digestion has gained wide acceptance as a rapid method for sample decomposition in inorganic analysis.16-1g An attack with a mixture of concentrated acids in a pressurized vessel at temperatures reaching 200-300 "C is the most popular to achieve complete dissolution, often associated with the destruction of carboncontaining bonds. The potential of selective microwave heating of constitutional water to enhance extraction of various compounds from emulsions, biological tissues, biomass, and soils was discu~sed.'~ Studies of selective leaching of organic analytes from an inorganic matrix have been scarce and focused mainly on polyaromatic hydrocarbons and pesticides.20~21 This study is, to our knowledge, the first one that aims at investigating the behavior of organometallic compounds in a microwave field with the purpose of improving the recovery of organotins from aquatic sediments (wet and dry) and reducing dramatically the time necessary for sample preparation. EXPERIMENTAL SECTION Apparatus. Organotin compounds were extracted using a Microdigest model A301 (2.45 GHz, maximum power 200 W) microwave digester Brolabo) equipped with a TX32 programmer. It allows us to change the applied energy from 20 to 200 W by a (8) Zhang, S.; Chau, Y. K.; Li, W. C.; Chau, A. S. Y. Appl. Organomet. Chem. 1991,5,431-434. (9) Ashby, J. R; Craig, P. J. Appl. Organomet. Chem. 1991,5,173-181. (10) Muller, M. D. Anal. Chem. 1987,59, 617-623. (11) Tolosa, I.; Bayona, J. M.; Albaiges, J.; Alencastro, L. F.; Tarradellas. X. Fresenius J. Anal. Chem. 1991,339, 646-653. (12) Harino, H.; Fukushima, M.; Tanaka, M. Anal. Chim. Acta 1992,264, 9196. (13) Liu, Y.; Lopez-Avila, V.; Alcaraz, M.; Beckert, W. F. J High Resolut. Chromatogr. 1993,16, 106-112. (14) Cai, Y.; Alzaga, R; Bayona, J. M. Anal. Chem. 1994,66, 1161-1167. (15) Liu, Y.; Lopez-Avila,V.; Alcaraz, M.; Beckert, R. F. Anal. Chem. 1994,66, 3788-3796. (16) Kingston, H. M., Jassie, L. B., Eds. Introduction to Microwave Sample Preparation; American Chemical Society: Washington, DC, 1988. (17) Matusiewicz, H.; Sturgeon, R. E. Prog. Anal. Spectrosc. 1989,4,14. (18)Kimber, G. M.; Kokot, S. Trends Anal. Chem. 1990,9, 203. (19) Pare, J. R J.; Belanger, J. M. R.; Stafford, S. S. Trends Anal. Chem. 1994, 13, 176-184. (20) Lopez-Avila, V.; Young, R Anal. Chem. 1994,66, 1097-1106. (21) Onuska, F. I.; Teny, K. A. Chromatographia 1993,36, 191-194.
0 1995 American Chemical Society 0003-2700/95/0367-4250$9.00/0
Table I. Operating GC-FPD parameters
GC parameters
injection port injection volume @L) column column head pressure (kg/cm2) oven program initial temp (“C) (time) ramp rate (“C/min) final temp (“C) (time) detector parameters HZpressure (kg/cm2)
air pressure (kg/cm2> Hz flow rate (mL/min) cavity temp (“C)
hot splitless 2
Chrompack CP-SIL8CB,
25 m x 0.25 mm x 0.41 pm
2.5
60 (2 min) 15 280 (6 min)
1 0.8 60 280
step of 10 W. The time of exposure up to 99 min can be set by steps of 1 min. A 5@mLround-bottom open vessel (150 mm x 35 mm id.) made of borosilicate glass (prolabo) was used. This co&uration allows a 6@mm part of the vessel (-20 mL of solution) be actually exposed to the microwave field. The determination of the recovered species was carried out using a Shimadzu Model GC 14A gas chromatograph equipped with a flame photometric detector (FPD) with a 61@nmband-pass filter. Reagents. Analytical grade chemicals (Merck) and Milli-Q water were used throughout unless otherwise stated. A 10% (w/v) solution of sodium tetraethylborate (NaBEk, Strem) was prepared daily by dissolving the reagent in water. Individual stock solutions (0.5 mg/mL as Sn) of BuSnCh (MBT) , BuzSnClz @BT), BuBnCl flBT),PhSnCls (MW, PhzSnClZ (DW,P h 3 S n C 1 0 , and Pr3SnC1 (TPrT) (Aldrich) were prepared in methanol. The standards were checked to be free of other organotin compounds by extraction into isooctane and Grignard ethylation. Mixed working solutions (usually in the range 0.5-5 pg/mL) were prepared daily by the dilution of the stock solutions with methanol. Reference Sediments. Two sediments with certi6ed contents of butyltin species were used. They were the PACSl from the National Research Council of Canada (NRCC) and the CRM 462 from the EC Reference Bureau (BCR). Studies of the recovery of butyl- and phenyltin spikes were made using a sediment with a nondetectable organotin concentration5‘( ng/g as Sn), referred to later as the blank sediment, collected at Capbreton (French Atlantic Coast). Procedure. A sample of 0.1-1.0 g of sediment, 10 mL of 0.5 M acetic acid solution in methanol, and 100 pL of the V r T solution (1 pg/mL) was placed in an extractiontube and exposed to microwaves at 70 W and for 3 min. The supernatant solution was separated by means of a Pasteur pipet, made up to 100 mL of water and analyzed according to the procedure of Michel and The latter was based on ethylation of ionic organotins in the aqueous phase with sodium tetraethylborate and simultaneous extraction of the derivatized species into isooctane. The extract was desulfurized by adding tetrabutylammonium sulfite to the organic phase as described by Jensen et aLz3 After the organic phase was rinsed with water, it was analyzed by GGFPD at the conditions shown in Table 1. RESULTS AND DISCUSSION
The preservation of the organometallic moiety is the prerequisite of a succesful digestion procedure prior to speciation (22) Michel, P.; Averty, B. Appl. Organomet. Chem. 1991,5, 393-397. (23) Jensen, S.;, Renberg, L.; Reutergardh, L. Anal. Chem. 1977,49, 316.
analysis. It can be achieved by a careful optimization of the conditions of the microwave attack. Open-vessel digestion was preferred to pressurized bomb systems commonly used in the analysis for total metals because it offers milder reaction conditions (the increase in temperature is controlled to a large degree by the boiling point of the solvent) and an easier control of process variables. The essential parameters involved include not only the microwave power applied and the exposure time but also the medium of the propagation of microwaves and the presence of extraction-enhancing reagents, such as, for example, acids or complexing agents. The volume of the sample, which is closely related to the design of the microwave system, should also be taken into account. Because of the virtual lack of literature data on the stability of the carbon-metal bond in a microwave field, a two-step optimization was found necessary. In the first step, an extraction medium was chosen and the upper limits of the microwave power applied and exposure time which do not lead to the destruction of the organotin moiety were determined in the absence of the sediment. In the second step, the operating conditions were fine-tuned to maximize the extraction yield. Behavior of Organotin Compounds in a Microwave Field. The choice of extraction medium should ta!!e into account its ability to absorb and to propagate the microwaves. The parameter that determinesthe capacity of a medium to absorb the microwave energy and thus to transfer it to the analyte species is its dielectric constant ( E ) . Four solvents, isooctane, methanol, deionized water, and artificial seawater, which have different (increasing in the enumeration order) E values were examined in detail. Each of the solvents was spiked with an organotin compound (always one at a time to eliminate possible interferences with degradation products) and exposed to a microwave field of varying energy for a preset time. The results are presented in Tables 2 and 3 for butyl- and phenyltin compounds, respectively. Tables 2 and 3 show that the analytical signal obtained is strongly dependent on the species investigated (the degree of alkylation) and on the reaction medium. The monosubstituted compounds are stable in isooctane throughout the whole power range investigated and are fairly stable in salt-rich water, whereas they degrade rapidly at higher powers and in other solvents. The degradation of disubstituted compounds is independent of the microwave conductivity of the medium and is generally less pronounced. The disubstituted organotins are, however, readily degraded in artificial seawater, probably because of the substitution of the alkyl (aryl) group(s) by chlorine atom($. Tributyltin and triphenyltin are generally stable in isoctane and in methanol but rapidly degrade (especially TBT) in aqueous solutions (especially salt-rich ones) proportionally to the power applied. Since in general the organotins are more stable in organic solutions than in aqueous ones, an organic medium was chosen for a detailed study of sediment leaching. Methanol was preferred to isooctane because of its miscibility with water and, thus, compatibility with the derivatization reaction. Exposure times longer than 10 min and powers exceeding 100 W (50% of the maximum power applied) should be avoided since they lead to rupture of the tin-carbon bond. The major product of degradation is inorganic tin, which was identified by hydride generation cryotrapping GC AASz4 Little to no intermediary organotin degradation products were observed. (24) Martin, F. M.; Donard, 0. F. X. J. Anal. At. Spectrom. 1994,9,1143-1151.
Analytical Chemistty, Vol. 67, No. 23, December 7, 7995
4251
Table 2. Effect of the Microwave Power Applied on the Stability of Butyl- and Phenyitin Compounds In Different Media-
MBT recovery 20 w iwoctane methanol
water artificial seawater a
60w
95.5f1.5 92.7f1.8 73.8f1.9 57.7f1.6 94.6f2.1 69.6f2.3 103 f 2.3 102 f 1.7
@)
lOOW
I60W
2ow
91.3f2.2 51.7f2.1 42.5f1.7 86.4 f 2.0
91.0f1.2 50.2f1.7 17.0f2.5 72.7 5 2.7
87.3f0.7 95.0f1.1 99.4f0.9 98.1 f 1.0
DBT recovery (sa) 6Ow 1ww 85.8f0.9 94.5f0.9 99.7f2.0 89.4 f 1.3
83.2f1.4 94.0f1.0 85.2f0.8 71.4 f 0.9
16Ow
2ow
TBT recovery @) 6Ow IOOW
1mw
78.1f1.3 94.4f1.1 69.5f1.5 88.4f1.8 88.312 93.5f1.3 101f2.1 86.5f1.7 86.2f1.8 77.5f2 0 80.4f2.1 4 9 . 4 f l . l 4.0f2.5 0 27.9 5 1.4 41.7 5 2.5 7.3 f 2.7 0 0
Xeld normalized to that for a solution nonexposed to microwaves (mean of three replicates).
Table 3. Effect of the Microwave Power Applied on the Stability of Butyl- and Phenyltin Compounds In Different Media'
MPhT recovery (%) 20 w isooctane
methanol water d c i d Seawater
60W
IOOW
DPhT recovery (%) 16OW
92.5f1.5 87.652.1 87.4f2.6 86.3f2.9 68.6f1.6 61.0f1.9 58.7f2.6 44.2f2.5 74.1 f 1.5 50.3 f 1.3 22.0 5 2.0 9.1 f 1.8 105f3.1 103f2.5 78.9f2.7 75.7f3.2
2OW
WW
102f1.5 103f1.3 101 f 1.4 101f1.1
101f2.1 102+1.8 100 f 2.6 101i1.0
1WW
TPhT recovery 16OW
2OW
102f1.9 101f2.3 89.7f0.8 101f2.5 103f2.8 73.8f0.6 97.8 f 1.0 103 f 1.7 104 f 3.0 102f0.9 58.6f1.9 102f1.9
6)
6OW
ICOW
160W
82.0f0.6 57.7f0.8 97.2 f 0.6 77.0f1.0
78.7f0.8 51.7f1.2 94.5 f 0.8 55.0f2.6
74.4+0 50.252 93.3 f 1 13.5f3
Xeld normalized to that for a solution nonexposed to microwaves (mean of three replicates).
Exwction of Organoh Compounds from Sediments. Extraction of butyltins was investigated by use of two different certified reference materials: PACSl and CRM 462. The former contains relatively high concentrations of organotin species but is certified for all three butyltin species. The latter is certified for only two butyltins (TBT and DBT), however at a factor 1020 lower levels (an indicative value for MBT is, in addition, available). Taking into account also the different content of total organic carbon in PACSl and CRM 462 (3.0 and 1.5%, respectively), these sediments can be considered representative for anthropogenically contaminated sites. Analysis of CRMs was preferred to spike recovery experiments because the naturally occurring organotins are considered to interact more strongly with the matrix than with spikes, especially if the material was dried afterward. Only extradon of phenyltins was investigated by spiking a blank sediment as no certified sediment is availablefor these compounds. The presence of acid and a polar solvent was found necessary to enhance the recovery of organotins from the sediment mahix. Hydrochloric and acetic acids, and methanol, respectively,which have been the most widely reported in the literature for this purpose were examined in detail." Figure 1 shows that quantitative recovery of all the analytes could be obtained with acetic acid at a concentration of 0.5 M in methanol. At higher acid concentrations degradation of TBT and DBT was observed, especially in the presence of hydrochloric acid. In the case of the BCR 462, which contains much more organic matter for a mass unit of organotin, the presence of HCI at the 0.5 M level not only can be tolerated but also improves the recovery for monobutyltin compared to that obtained in acetic acid. The highest recoveries were obtained using 10 mL of the methanolic acetic acid solution with a marked decrease in the leaching yield for larger volumes. Optimization of the leaching time and the microwave power applied was carried out by the univariate procedure and lead to an optimum at 60 W for Smin leaching. Figure 2 shows that for a given microwave power applied the recovery varies significantly 4252
Analytical Chemistry, Vol. 67, No. 23,December 1, 1995
Acid
Acetic acid Concentration, M
Effectof (a) differentacids (0.5 M each) and (b) acetic acid concentration on the recovery of organotin from the P A C - I sediment in methanol SoIutions: power, 60 W: time, 3 min; volume, 10 mL. Error bars represent standard deviation of three measurements. with time, reaching a maximum at 3 min for TBT and DBT and at 4 min for MET. Whereas the recoveries of TBT and DET are quantitative at their maxima, only -40% of MBT (with respect to the indicalive value) is extracted at optimum conditions. The same extraction conditions applied to the PACS show, however, a quantitative recovery of MBT. The shift in extraction maximum of MBT vs DBT and TBT is apparently caused by stronger interaction of this compound with the sediment This shift may be also interpreted, however, in terms of the appearance of MBT produced by the degradation of DBT and/or TBT at harsher conditions. To validate either of the hypotheses, a blank sediment was spiked with TBT only and monitored for the presence of MET and DBT during exposure to microwaves. It was observed that Figure 1.
‘7 z-z
t certified values
Sb4
m,
Em W
25
c
: 1
3
4
7
TIME,min
UCROWAVE POWER.WITIME.
*
Recovery of triphenyltin from a spiked sediment under different extraction conditions. Error bars represent standard deviation of three measurements. Figure 4.
TIME. min
Effectof time on the recovery of butyltin compounds from sediments: (a, top) BCR CRM 462; (b, bottom) PACS-I: 0.5 M acetic acid in methanol; power, 60 W. Error bars represent standard deviation 01 three measurements. Figure 2.
I
OBT
HMBT @H DBT I TBT
t
certified values
POWER, W
-1
POWER. W
of microwave power on the recovely of butyltin compounds from sediments: (a)BCR CRM 462; (b) PACS-1; 0.5 M acetic acid in methanol; time, 3 min. Error bars represent standard deviation of three measurements, Figure 3. Effect
after 3 min the decrease in TBT was not accompanied by the appearance of DBT or MBT, which indicates that the only degradation product is inorganic tin. figure 3 shows that, at a constant extractiontime, an increase in power has an effect similar to that of an increase in exposure time at a constant applied microwave power. Figure 4 shows that a quantitative recovery of a mixed spike of phenyltins is possible under optimum conditions similar to those found for butyltins in the certified sediments. Figure l b shows that the concentrations for MBT found exceed the certified value regularly, in some cases (at 1-2 M acid
concentration) even 2-fold. A slight decrease in the DBT and TBT concentrations does not compensate for a dramatic increase in the amount of MBT found. This, together with an indication that inorganic tin is the major degradation product, lead to the conclusion that the certified value may be too low. Indeed, except for one value, 0.03 f 0.01 ~ g / g , ’ ~the literature values, 0.36 f 0.17,* 0.52 f0.15,260.41iO.O4,2’ and 1.03 f 0.01 /rg/g, are higher than the certified value. It is evident that the presence of sediment modifies the behavior of organotins exposed to microwaves compared to when in a pure solvent. The release of low-polar compounds (e.g., polyaromatic hydrocarbons) decreases the dielectric constant of the medium and results in a smaller transfer of energy from the leaching solvent to the analytes (screening effect). This may explain the observed presemtion of the organotin entity during extraction from the sediment under harsher conditions than in pure solvents. The observed n m w range of stabilityof organotin compounds in a microwave field that is, in addition, a function of the content of organic matter may require an intemal standard to control the degradation of the analytes. Tripropyltin,which was found to show a behavior similar to the analyte organotins, is recommended for this purpose. The analyses of over 100 sediments in our laboratory showed, however, that the correction factor necessary has never exceeded 10%.This, in view of the overall precision of the method, leads to the conclusion that variations in the recovery due to the different release of organic matter from different sediments are practically nonexistent. The presence of the internal standard is nevertheless recommended, if the origin of the sediments analyzed varies from one sample to another. Analylical figures of Merit Table 4 shows a statistical evaluation of the results obtained for the two certified sediments investigated. A precision of 5-10% for the di- and hisubstituted compounds is rontinely obtained. In the absence of the tissue, the precision of the determination is 3-5%. The poorer precision (20-30%) obtained for monobutyltin is partly due to problems associated with its ethylation after leaching. Indeed, the presence of complexing agents in sediments was shown to suppress the (25) Range, A. Jantzen.
E.) Anal. Af. Specfrom. 1995, IO, 105-110. Kuballa, J.; Wilken. R. D.;Jantzen. E.; Kwan, K K; Chau. Y. K Analyst 1995, 120.€6-673. (27) Chau. Y.K; Yang. F.: Bmwn. M. A n d Chim. Acta 1995.304, 85-88. (28) Quewuviller, ph.: hmc. M.;Ebdon. L: Desauziers. Y; Sarradin. P. M.: Asme, A h e r , G. N.; Griepink. B. Appl. ognnomrf. Chrm. 1994.8, (26)
629.
Analytical Chemistry, Val. 67,No. 23, December 1. 1995 4253
Table 4. Determination of Butyltin Compounds In Certified Reference Materials.
concn*in PACSl found certified (ng/g) (ndd
compd monobutyltin dibutyltin
372 f 96 1092 f 84 1208 110
*
tributyltin
concn in CRM 462
found
280 k 17 1160 f 180 1270 & 220
(ndd
certified (ng/g)
28 f 4 108 f 11 70 & 4
128 i 16 70 i 14
C
S i experiments. * As Sn, calculated for dry mass. Not available. Literature values: 13-244,28102 f 38,26and 14.1 f 5.6 ng/g.15
loo
1
0
2
4
6
0
EXTRACTION TIME, min
Figure 5. Leaching of butytin compounds from the PACS-1 with 0.5 M acetic acid in methanol at 65 "C in the absence of a microwave field. Error bars represent standard deviation of three measurements.
derivatization yield for MBT.24 The signal increases linearly with sample amount taken for analysis to 1 g with regression coefficients of 0.965, 1.000, and 0.996 for mono- di- and tributyltin, respectively. The larger sample intake is particularly important for less contaminated sediments or for insufficiently sensitive techniques. The detection limit was at the level of 1 ng/g (for a 1-g sample of dry sediment). R e method developed has been successfully used in our laboratory for the routine determination of organotin compounds in natural sediments. Microwave-AddedEffect. Figure 5 shows the recovery of butyltin compounds as a function of extraction time in the absence of a microwave field at a temperature equal to that which would be achieved as a result of microwave interaction. Only 50% of DBT and TBT and virtually no MBT can be recovered even for a much longer period of time compared to the yields observed in a microwave field. It is thus evident that the microwave field accelerates the extraction and enhances its yield by a sort of mechanism which needs yet be investigated. On the basis of the literature indication^,^^^^^ it is possible, however, to put forward some hypotheses. A combination of several mechanisms that act more simultaneously than sequentially apparently needs to be considered. Most organotin compounds are xenobiotic and are likely to occur in sediment in surface coatings with little geochemical evolution. Their release into the leaching solvent can thus be accelerated by an increase in the sediment surface associated
with the physical desintegration of the sediment. Indeed, such a phenomenon is directly related to the action of the microwave field by very intensive heating not only of the clay and oxides matrix but also the water or solvent. At elevated temperatures, cavities, pits, and scratches in the sediment become a source of nucleation sites for gas bubbles to form, which since entrapped are responsible for local pressure buildups and destruction of the initial macrostructure of the sediment, leading to an increase in sediment surface available for the leaching solvent. It is worth noting that at the limited power and times applied under our experimental conditions this solid/surface/liquid interaction usually remains limited to the heart of the sediment, which hampers the evaporation of the leaching solvent. Another important factor is the increase in the solubility of the analytes in the solvent superheated in a microwave field by 12-26 "C above the normal boiling p0int.2~ The macroscopic mechanisms alone are apparently not able to explain the accelerated leaching of organotin from dry sediments and to account for the unusully high increase in the microwave-assisted recovery of monobutyltin compared to that observed in the absence of a microwave field (Figure 5). The gain in time compared to sonication is hypothesized to be due to different targets for the energy delivered. Whereas the sonication desintegrates the sediment aggregates thus increasing the surface available for the leaching solvent, the frequency of the microwaves makes them ready to be absorbed by the analyte molecules directly and thus allows them to overcome the adsorption forces. The highly polar character of monobutyltin makes its a particularly suitable target for the microwave energy and thus explains the especially high microwave-added effect for this compound. CONCLUSIONS
The paper presents the first evidence that the microwaveassisted leaching can be an inexpensive and useful method for the recovery of organometallic compounds in speciation analysis of complex matrices, e.g., sediments. The analysis time can be dramatically (20-100 times) decreased, and yields from some species can be increased compared to conventional methods. Careful optimization of the extraction medium, power applied, and exposure time is required. The extension of the method developed to other environmentally important organometals (organolead, -mercury, -arsenic) and matrices (algae, fish, oysters) is in progress. ACKNOWLEDGMENT
We thank Mr. D. Mathe (Prolabo) for putting at our disposal a prototype of the microwave digester. M. Ceulemans (University of Antwerp, ULA) is acknowledged for valuable discussion. Received for review January 9, 1995. Accepted August 8, 1995.B
AC950029Z (29) Baghurst, D. R.; Mingos, D. M. P.J. Chem. SOC., Chem. Commun. 1992, 674-677.
4254
Analytical Chemistry, Vol. 67,No. 23, December 1, 1995
@Abstractpublished in Advance ACS Abstracts, October 15, 1995.
