Anal. Chem. 1987, 59, 617-623 (6) Occobwltz. J. L.; Hamill, R. L. fdyettmf Antibiotics; Wlley: New York, 1982. (7) Tabet, J. C.; Fraisse, D.; David, L. Int. J . Mess Spechom. Ion fromsses 1085, 63, 29. (8) Barber, M.; Bordoll, R. S.; Elliot, 0. J.; Sedgwlch, R. D.; Tyler, A. N. .Anal. .. . Chem. -. .- ... . W82. . - -, 54. .. , 645A. . . (9) Chang, T. T.; Lay, J. O., Jr.; Francel, R. J. Anal. Chem. 1984, 56,
109.
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(10) Slegel, M. M.; McGahren, W. J.; Tomer, K. B.; Chang, T. T. The 33rd Annual Conference on Mass Spectrometry, San Dlego, CA, 1985. (11) Slegel, M. M.; Tomer, K. B.; Chang, T. T. J . Biomed. Environ. Mess Specfrom ., In press.
RECEIVED for review July 23,1986. Accepted October 15,1986.
Comprehensive Trace Level Determination of Organotin Compounds in Environmental Samples Using High-Resolution Gas Chromatography with Flame Photometric Detection Markus D. Muller Swiss Federal Research Station, CH-8820 Wadenswil, Switzerland
A comprehensive method for trace analysis of mono-, dC, trl-, and some tetrasubstltuted organotln compounds is presented. The Ionic compounds are extracted from diluted aqueous 80lutlons as chlorides by using a Tropoion-C,, silica cartrldge and from sediment and sewage sludge by using an ethereal tropoion solution. The extracted organotln compounds are ethyiated by a Grlgnard reagent and analyzed by using hlghresolutlon gas chromatography with flame photometric detectlon (HRGWFPD). Gas chromatography/mass spectrometry (GC/MS) was used for conflrmatlon. The extraction behavior, gas chromatographk retention, and photometric response of a series of organotln compounds are descrlbed, and the ldentlfication via electron Impact (EI) and chemlcal Ionization (CI) mass spectrometry Is discussed. The main organotln compounds detected In varlous samples are butyltlns; cyciohexyi- and phenyltins were ldentlfled In some of the sediment and sewage sludge samples. Methylbutyltlns and tetrabutyltln were not detected. Concentratlons were found to range from low ng/L (parts per trillion) In surface water to low mg/kg (parts per million) In sewage sludge.
Organotin compounds have found applications in many fields, such as stabilizers for PVC, fungicides and miticides in agriculture, and biocides (1-4), because their properties can be tailored by the variation of the type and the number of substituents to meet widely different requirements. Annual world production was estimated to be 33000 tons in 1983, most of it dioctyltin maleate (2,5). The toxicity and degradation in the environment depend strongly on the number and nature of the substituents ( 1 , 5 ) . Organotin compounds with short alkyl chains or phenyl substituents generally exhibit considerable toxicity toward both aquatic organisms and mammals. Alkyltins with small alkyl chains degrade slowly in the environment (6, 7);phenyltins are less stable and may, under certain conditions, rapidly loose the phenyl substituents (3). Organotin compounds may accumulate in sediments and aquatic organisms (6). Trace.determination of organotin compounds in environmental samples is complicated by the fact that organotins with one to three substituents are polar, involatile substances due to their ionic character. In the last few years, a series of publications dealing with different approaches for trace 0003-2700/87/0359-0617$01.50/0
analysis of organotin compounds appeared, marking a growing concern over the fate of these persistent and toxic compounds in the environment and their impact especially on aquatic organisms. Trace level determination of these compounds can be carried out either by nonchromatographic methods (e.g., electrochemical or fluorometric assays ( 8 , 9 ) )or by chromatography with an appropriate detection method. High-performance liquid chromatography (HPLC) coupled with fluorescence detection ( 1 0 , I I ) or ion-exchange HPLC with detection by graphite furnace atomic absorption spectroscopy (GF/AAS) (12)proved to be sensitive methods, but may lack from limitations in separation power and ease of identification of unknown products. The preparation of volatile derivatives makes the ionic organotin compounds amenable to evaporative separation techniques (purge and trap or gas chromatography (GC)). Hydride formation in dilute aqueous solutions is becoming a routine method for determination of methyltins (13-16), methyl- and butyltins (17-19),and phenyl- and various other organotin compounds (20-22) to form the volatile hydrides (stannanes), which are analyzed either by purging and AAS or flame photometric detection (FPD) or by liquid-liquid extraction with subsequent GC analysis. Unfortunately, stannanes are rather labile thus preventing further cleanup steps (2). Therefore, alkylation is often preferred over hydride formation, as the resulting tetrasubstituted organotin compounds can easily be purified and concentrated, which is necessary for low-level samples and complex matrices such as animal tissue or sewage sludge. A Grignard reagent or an alkyllithium compound is used to convert the ionic mono-, di-, or triorganotin compounds into the corresponding nonpolar tetrasubstituted compound. The reaction has to be carried out in aprotic solvents and thus requires extraction of aqueous samples prior to derivatization. Procedures have been described for the analysis of methyltins (23), butyltins (24,25),mixed methylbutyltins (26), various alkyltins (27),cyclohexyltins (28),and phenyltins (29). Alkylation also offers the possibility for selection of the volatility range of the derivatives, which are in most cases analyzed by GC. However, there are few methods for the sensitive determination of a broad range of organotin compounds in environmental samples. Recently, the sensitive determination of butyltin residues in sediment and surface water was described on the basis of extraction/methylation and high@ 1987 American Chemical Society
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resolution GC/FPD (30). A revised procedure is now presented allowing sensitive, rapid, and simultaneous detection of a series of organotin compounds, including their degradation and conversion products. After extraction as chlorides, the organotins are ethylated with a Grignard reagent and analyzed by using HRGC/FPD. Combined HRGC/mass spectrometry (GC/MS) in the electron impact (EI) and chemical ionization (CI) mode was used for identification and confirmation. A series of alkyltin standard compounds was synthesized as reference materials. The method was applied to surface water, sewage sludge, and sediment samples and showed the presence of various organotins a t concentrations ranging from ng/ kg (parts per trillion, pptr) (water) to mg/kg (parts per million, ppm) in sewage sludge. For briefness, the chemical names of organotins are given as follows: The abbreviated names for the side chains together with the sign for tin designate a certain organotin compound; e.g., HexBuzSnEt denotes hexyldibutylethyltin. Substituents placed on the right side of the tin sign originate from derivatization. (Me, methyl; Et, ethyl; Pr, propyl; Bu, n-butyl; Hex, n-hexyl; Cyhex, cyclohexyl; Oc, n-octyl; Phe, phenyl.) Charges of ionic species are indicated but do not imply the presence of true ionized organotin compounds in the environment. EXPERIMENTAL SECTION Materials and Solvents. All solvents were purchased either from Merck (Darmstadt,FRG) or Fluka AG (Buchs, Switzerland) and were at least of purissimum grade. Hydrochloric acid and silica gel (Silica Gel 60) was from Merck, Alumina (Alox basisch) from Woelm, Eschwege (FRG),and ascorbic acid (drug quality) from Siegfried (Zofingen, Switzerland). Sep-PAK C18cartridges were from Waters (Milford, MA), organotin reference compounds (cf. section "standard material"), SnCl, and 2-hydroxy-2,4,6cycloheptatrien-1-one (tropolone) were obtained from Fluka; Grignard reagents were synthesized from Mg chips and alkyl bromides (methyl, ethyl, butyl, hexyl, octyl, and phenyl bromide) from Fluka. Triphenyltin chloride and tricyclohexyltin hydroxide were obtained from Merck and R. Maag, AG, Dielsdorf, Switzerland, respectively. Stock solutions of 1mg/mL in toluene were prepared and kept in the dark; fresh dilutions of appropriately derivatized standards were prepared weekly. The stationary phases for preparing the capillary columns were obtained from Fluka (Pluronic L 64, an analogue of Ucon 50 HB 5100, produced by Wyandotte Chemicals Corp.) and from Petrarch Systems, Inc., Bristol, P A (PS 255, a SE 54 analogue). Preparation of Grignard Reagents. These reagents were prepared according to standard synthetic methods (31) by reacting 6.1 g of Mg (0.25 Mol) in tetrahydrofuran (THF) with equimolar quantities of the corresponding alkyl or aryl bromides, respectively. The Grignard reagent solutions were diluted with THF to give approximately 2 M solutions and were stored in the dark. Caution: Alkyl bromides are very toxic-use good ventilation. Grignard reagents are extremely reactive and should be handled with great care. Standard Material. The following types of standard reference materials were used: (a) A quantitative standard, Bu4Sn,was prepared by weighing and diluting the material with specified purity (99%). (b) Quantitative standards were prepared by weighing and diluting of material of known purity with subsequent ethylation. (c) Qualitative standards were prepared by reacting dilute solutions of SnC1, with controlled amounts of the corresponding Grignard reagents. In this way, complex mixtures, e.g., mixed MeBuSnEt compounds, can easily be obtained for GC retention time studies and as reference compounds for GC/MS. (d) An internal standard, HexBu,SnCl, was used as described earlier (30). A solution containing 2 ng/pL acetone was used and added to the samples prior to extraction. The compound was added at various levels: about 10 ng/L (10 pptr) in surface water samples, 100 kg/kg (100 ppb) in sediment samples, and 1 mg/kg (1 ppm) in sewage sludge samples. Extraction Procedure. For surface water, 100-500 mL of water is acidified to pH 2-3. Internal standard, HexBuzSnCl, in acetone, tropolone (0.5 mL of a 1% solution in methanol), and
about 100 mg of ascorbic acid are added and, after mixing, the water is slowly passed through a Tropolon-Sep-PAK CIScartridge. This cartridge is prepared by elution of a Sep-PAK C18cartridge with methanol (1.5 mL) and 0.5 mL methanol containing 1% tropolone; after being dried for 1min (vacuum),the cartridge is ready for use. When all water has passed, the cartridge is eluted with 3 mL of diethyl ether; the extract is dried with anhydrous CaCl, and is ready for derivatization. Sewage Sludge and Sediment. The sample (1-20 g) is weighed in a large-mouthed flask, internal standard is added, and the sample acidified with HCl t o pH 2-3. (Caution: H,S and COz are evolved, use a hood.) When the evolution of gas has ceased, the slurry is extracted with three portions (10, 5, and 5 mL) of a 0.25% ethereal tropolone solution. After being shaken vigorously and centrifuged, the organic phases are combined, filtered through anhydrous CaCl,, and reduced in volume to about 2 mL at room temperature by a rotary evaporator. The extract is then ready for derivatization. Derivatization and Cleanup. Small portions (0.5 mL) of the Grignard reagent, ethylmagnesium bromide (2 M in THF), are carefully added to the extracts prepared as described above. Reagent is dropwise and carefully added until an excess (indicated by a steady evolution of ethane) is present. The mixture is allowed to stand at least for 10 min and the excess of reagent is destroyed by careful, dropwise addition of about 3 mL of 2 M HCl. The organic layer, containing the compounds of interest, is dried over anhydrous sodium sulfate, reduced in volume to about 0.5 mL, and purified by adsorption chromatography on silica gel (0.5 g of silica gel in a Pasteur pipet, elution with 10 mL of 10% diethyl ether / hexane). Analysis by GC/FPD. A Carlo Erba 2101 gas chromatograph fitted with a split/splitless injector, glass capillary column (30 m in length, 0.3 mm i.d., coated with either a 0.15-gm film of Pluronic L 64 or a 0.5-pm film of PS 255) and a Carlo Erba flame photometric detector SSD 250 were used. The detector was operated without a filter and with a hydrogen-rich flame (32). Injector and detector temperature were set at 250 "C and 225 "C, respectively. Hydrogen (0.6 bar) served as carrier gas. Sample aliquots of 2 pL were injected at room temperature in the splitless mode (45 9); the compounds of interest were eluted with a temperature program of 4 OC/min. GC/MS. A Finnigan 4000 GC/MS system with a combined EI/CI ion source and a Finnigan 6000 data system were used. The source temperature was 200 "C for E1 and 120 "C for CI. Methane (source pressure of 0.6 mbar) served as reagent gas for CI. A mass range of 100-500 u was recorded. The capillary columns were coupled via an open split fused silica interface to the ion source and the same conditions were applied as for GC/FPD to elute the compounds of interest.
RESULTS AND DISCUSSION General Remarks. The procedure for trace determination of organotin compounds includes four steps: (a) acid digestion of the sample; (b) extraction; (c) derivatization; (d) analysis. Though these steps have been described at least partially by several authors, they had to be checked and modified to meet the requirements discussed later on. Acid Digestion a n d Extraction. Treatment with hydrochloric acid has two purposes: (a) Inorganic particles (carbonates, sulfides) should be dissolved to release eventual inclusions of organotin compounds. (b) The different forms of mono-, di-, and trisubstituted organotin compounds (hydroxides, sulfides (33))present in the environment are converted into the respective chlorides, which are suited for extraction into an organic solvent. On the other hand, organotin compounds may undergo nucleophilic attack by hydrochloric acid resulting in cleavage of side groups ( 2 ) . This would mimic environmental degradation. Therefore, acid digestion was checked for eventual degrading effects on tributyl-, tricyclohexyl-, and triphenyltin chloride. Diluted aqueous solutions of these compounds were acidified to pH 2, allowed to stand 1 h at ambient temperature and extracted, derivatized, and analyzed as described above.
ANALYTICAL CHEMISTRY, VOL. 59, NO. 4, FEBRUARY 15, 1987
Table I. Recoveries for Selected Tin Species from Tap Water level spiked,” recovery,* recovery,c blank, ppb or pg/L % (SD) % PPb
tin
species Sn(1V) BuSn3+ BuzSnZC Bu3Sn+
2.5 0.55 0.475 0.225
71 (&lo) 98 (&8) 97 (&8) 91 (f7)
10 2 24 75
0.25 0.001 0.002 0.002
Calculated as the respective chlorides. *Four samples analyzed in parallel by using tropolone, ascorbic acid, and HC1 (cf. Experimental Section). One samDle analvzed bv using onlv HC1. Comparison with a standard solution of the pure, unhydrolyzed product and with a standard containing all possible degradation products gave the following results: (a) Bu3SnCl showed no detectable degradation products (
