INTER-LABORATORY NOTE Determination of total tin in environmental and geological samples by electrothermal atomic absorption spectrometry using a tungsten furnace after pretreatment by solvent extraction and cobalt(III) oxide collection Tomohiro Narukawa Department of Chemistry, Chiba Institute of Technology, 2-1-1 Shibazono, Narashino, Chiba 275-0023, Japan Received 19th March 1999, Accepted 12th May 1999 Solvent extraction and cobalt(III) oxide collection has been studied for the determination of total tin in environmental and geological samples by electrothermal atomic absorption spectrometry using a tungsten furnace. Tin iodide was extracted into benzene under acidic conditions using sulfuric acid, and cobalt(III ) oxide powder was added to the benzene to collect the extracted tin.The cobalt(III ) oxide powder was separated from benzene by vacuum filtration and then suspended in 5 ml water. Part of the slurry thus obtained was introduced into the tungsten furnace and the determination of tin performed. A relative standard deviation of 1.8% (n=6) was obtained for the determination by the proposed method of 0.20 mg l-1 tin in the slurry.The calibration curve was linear up to 0.40 mg l-1 (4.0 ng per 10 ml ) tin, and the detection limit (3 s) was 6.00 mg l-1 (0.06 ng per 10 ml ) tin. The proposed method was applied to marine sediment, fish tissue and rock as examples of environmental and geological samples. The determination of total tin obtained was in good agreement with the certified value or reference value of the environmental and geological samples.Organotin compounds are widely used to inhibit marine tellurium23 and arsenic24 by ETAAS using a tungsten furnace and reported the eVects of using cobalt(III ) oxide powder as a organisms from adhering to the bottom of ships or fishing nets. These organotin compounds are eluted by seawater and chemical modifier and collector. In this study, cobalt(III) oxide powder is used to collect tin, and pretreatment by solvent concentrate in the marine sediment or in the bodies of marine organisms having a harmful influence upon the ecosystem.extraction is performed to determine traces of tin in the environment. Recently, some organotin compounds have been specified as being endocrine disrupters. Hence, the development of an easy, precise method for the determination of tin is desired. Experimental Organotin compounds are easily decomposed into inorganic Reagents tin in the presence of light, etc.; however, in the bodies of organisms, organotin compounds remain unchanged.Thus, Tin(II) standard solution. This was prepared by diluting the chemical nature of tin in the environment is complex. AAS-grade tin solution (1000 mg l-1, SnCl2 in 6.0M HCl, Therefore, it is important to determine the amount of total Wako, Osaka, Japan) with 3 M HCl. tin in a sample, in addition to the amount of each specific chemical species of tin.Tin(IV) standard solution. This was prepared as follows: The sensitivity of ETAAS and ICP-AES for the determi- Precisely 0.301 g of tin(IV) chloride pentahydrate nation of tin is relatively high, and that of ICP-MS is very (98.0%<SnCl4 5H2O; Wako) was dissolved in 6 M HCl to high.1 However, the determination of trace amounts of tin in make a 100 ml solution, and the resulting solution was estabcomplex matrices is diYcult due to large interference from lished as the 1000 mg l-1 standard solution of tin(IV); this matrix components.Therefore, pretreatment procedures such standard solution was diluted with 3 M HCl and used in the as organic solvent extraction2–7 and other methods8–10 are experiments. necessary to separate tin from its matrix components or to Organotin compound was prepared by diluting tri-n-butyltin determine tin in each chemical species present in the matrix. chloride, triphenyltin chloride and tri-n-pentyltin chloride stan- Ni et al.11 and Ferri et al.12 have studied organic solvent dard solution (1000 mg l-1, Kanto, Tokyo, Japan) with extraction methods for tin(IV) and organotin compounds.toluene. Since tin(II) easily oxidizes to tin(IV), most previous studies Cobalt(III ) oxide powder. 30 mg of cobalt(III ) oxide powder on inorganic tins have focused on pretreatment methods and (purity 99.5%;Wako) were passed through a 200 mesh (74 mm) methods for the determination of inorganic tin(IV); there are sieve, weighed and used for the experiments.few reports on tin(II). In the case of tin determination by The acids used were of poisonous metal analysis (PMA)- ETAAS using a graphite furnace, detailed reports on chemical grade (Wako), and benzene and potassium iodide used were modifiers13–15, and their eVect and behavior during the charof gravimetric analysis grade (Kanto). Caution: benzene is ring and atomization stages,16–21 have been studied. However, both toxic and carcinogenic and care should be exercised in in the case of tin determination by ETAAS using a tungsten its use.furnace only a limited number of reports are available on the Ultrapure grade water purified with a Milli Q-Labo filter eVects of chemical modifiers. We have studied the determination of lead,22 bismuth,22 (Nippon Millipore, Tokyo, Japan) was used throughout. J. Anal. At. Spectrom., 1999, 14, 1081–1085 1081Apparatus samples by acid, the residue was dissolved by adding 5 ml of 3 M HCl, and the resulting solution was poured directly into The analysis was conducted using an SAS 7500A atomic a separating funnel. absorption spectrometer connected to a PS200A electrothermal In addition, a blank test of the acids used to dissolve the atomizer (Seiko Instruments, Chiba, Japan).25 An L-233 tin solid samples, as well as measurement of water content in the hollow cathode lamp (Hamamatsu Photonics, Shizuoka, solid samples (85 °C, 4 h), was performed to compensate for Japan) was used.A deuterium lamp was used for the back- the determined values. ground correction, and the furnace was a high capacity (50 ml ) U-type metal boat made of tungsten. Results and discussion Procedure EVect of charring temperature Five ml of sample solution (total Sn!2.0 mg), which was Both organotin and inorganic tin are present in the environacidified with 3.0 M HCl, were introduced into a separating mental samples studied.In this study, organotin was comfunnel, to which 5 ml of 5 M KI were added. To this solution pletely decomposed when the solid sample was dissolved in 10 ml of 7.0M H2SO4 were added to give 20 ml of aqueous acid; therefore, to evaluate various experimental conditions, solution (concentration of H2SO4: 3.5 M). An equal volume inorganic tin was used. of benzene was added to this aqueous solution, and the funnel According to the procedure described above, a slurry was was placed on a shaker for 5 min to extract tin.After shaking, prepared using aqueous solutions which contained 1.0 mg of the benzene was separated from the aqueous solution into a either tin(II ) or tin(IV). The eVect of charring temperature on 100 ml PTFE beaker, to which 3 ml of 4-methyl-2-pentanone the slurry (1.0 mg per 5 ml=0.2 mg l-1) during tin atomization (MIBK) and 30 mg of cobalt(III) oxide powder were added. was studied when the atomization temperature was set at The beaker was placed in an ultrasonic bath, and the organic 2500 °C and the charring temperature was varied from 400 to phase was stirred for 10 min to collect tin that was adsorbed 1600 °C.At the same time, the following solutions were used onto the cobalt(III) oxide powder. Vacuum filtration was then for comparison. (i) 0.20 mg l-1 tin(II ) or tin(IV) standard performed using a PTFE membrane filter (diameter, 25 mm; solution (3 M HCl ); (ii) 5 ml of 0.20 mg l-1 tin(II) or tin(IV) pore size, 3.0 mm) to separate cobalt(III) oxide powder from standard solution into which 30 mg of cobalt(III) oxide powder the organic phase.The entire membrane filter including the was dispersed. The results obtained are shown in Fig. 1, and cobalt(III) oxide powder was inserted into a plugged test tube, the absorption signals of tin obtained using these solutions to which 5 ml of water were added. The test tube was shaken are shown in Fig. 2. by hand to obtain homogeneously dispersed slurry.Part of The absorbance was almost constant regardless of charring the slurry was introduced into the furnace, and the absorbance temperature, when tin(II) or tin(IV) standard solution was of tin (atomized under the conditions shown in Table 1) was used. In addition, the absorbance of tin(II) is similar to that measured. Manual pipetting was employed for injecting the of tin(IV). Sensitivity was also similar regardless of valence. slurry. In cases of tin standard solutions into which cobalt(III) oxide powder was dispersed, the absorbance obtained during Acid decomposition of solid samples atomization of tin(II) corresponds to that of tin(IV), which was also similar to that of the standard solutions.No influence To dissolve the solid sample, a mixed solution of HNO3, of cobalt(III) oxide powder on background absorption was HClO4 and HF was used. A precisely weighed solid sample observed. (from 0.5 to 3.0 g) was transferred into a PTFE beaker to On the other hand, in slurries prepared using the proposed which the mixed solution consisting of HNO3 (30 ml ), HClO4 method, the absorbance was lower than that of standard (10 ml ) and HF (3 ml ) was added.After the beaker was left solutions treated with cobalt(III ) oxide powder, due to the to stand for 15 min, it was placed on a hot plate (230 °C) to influence of iodide which was adsorbed onto the cobalt(III) dissolve the solid sample; the sample was then solidified oxide powder at charring temperatures of 1000 °C or less.through evaporation. If a sooty residue was obtained or the However, the absorbance almost reached that of the standard decomposition of the organic substance was incomplete, solutions with cobalt(III ) oxide powder at charring tempera- additional nitric acid was added for complete decomposition. The residue was then dissolved in 10 ml HCl (1+10) solution, and the resulting solution was poured into a measuring flask, to which 12.5 ml of concentrated HCl and a suYcient amount of water were added to obtain 50 ml of the solution.The molarity of HCl in the obtained solution was set at 3 M for convenience. If the amount of tin contained in the solid samples was extremely small after decomposition of the solid Table 1 Instrumental operating parameters for tin Parameter Ramp time/s Hold time/s Temperature/°C Dry 10 20 130 Char 10 15 1400 Atomize 0 2 2500 Clean 0 1 2600 Wavelength 224.6 nm Spectral bandwidth 0.5 nm Fig. 1 EVect of charring temperature. +,6: Sn standard solution Lamp current 20 mA (0.20 mg l-1); &,%: 5 ml of Sn standard solution (0.20 mg l-1) Gas flow rate Ar: 5.0 l min-1 containing dispersed cobalt(III ) oxide powder; $,#: slurry (Sn: 1.0 mg H2: 1.0 l min-1 per 5 ml ) of the proposed method; +,&,$: SnII; 6,%,#: SnIV; Injection volume 10 ml injection volume: 10 ml. 1082 J. Anal. At. Spectrom., 1999, 14, 1081–1085Fig. 2 Atomic absorption profiles of tin on atomization.(A): SnII Fig. 3 Recovery of SnII and SnIV from extraction process as a function standard solution; (B): SnIV standard solution; (C): SnII standard of H2SO4 concentration. Organic solvent: benzene, #,%: without KI; solution containing dispersed cobalt(III ) oxide powder; (D): SnIV $,&,6: with KI;$,#: SnII;&,%: SnIV;6: SnII in 3 MHCl aqueous standard solution containing dispersed cobalt(III ) oxide powder; (E): solution; cobalt(III) oxide powder: 30 mg; concentration of KI: 1.25 M.slurry of SnII for the proposed method; (F): slurry of SnIV for the proposed method; (G): blank of the proposed method; charring temperature: 1400 °C; concentration of Sn: 0.20 mg l-1. recovery of tin(II) increased to 100% (6). For HCl concentrations of 2.5 M or less and HClO4 concentrations of 2.0–4.0 M, the recovery was 70–98%. Tin is extracted by benzene in tures of 1300–1500 °C. The measurement of the slurry H2SO4 solution in the form of SnI4, upon the addition of absorbance was repeated (n=6) at charring temperatures of potassium iodide.Therefore, when tin(II) is present in an 1300–1500 °C. The results indicate that the highest reproducaqueous solution, recovery is considered to increase through ibility was observed at a charring temperature of 1400 °C, oxidation of tin(II) to tin(IV) by the addition of an oxidizing where the relative standard deviation (RSD) was 1.8%. The agent. However, in this study, recovery was increased upon optimal charring time was determined to be 15 s.the addition of potassium iodide, a reducing agent, to the HCl solution. EVect of atomization temperature When arsenic iodide was extracted by an organic solvent, the following phenomena were confirmed: the production of The eVect of atomization temperature on the absorbance of slurries containing tin was examined when the charring tem- free iodine was promoted with increasing HCl concentration, arsenic(III) was oxidized to arsenic(V) due to the I2 produced, perature was set at 1400 °C and the atomization temperature was varied from 2000 to 2700 °C.When the atomization and arsenic was extracted by the solvent in the form of arsenic(V).26 Similar to the phenomena observed in arsenic, temperature was 2300 °C or less, wide peak signals were obtained. As the atomization temperature increased, the width free iodine may promote the oxidation of tin(II ) to tin(IV) through the addition of potassium iodide to the HCl solution.of the peak signal decreased and the absorbance increased sharply; the highest absorbance was obtained at an atomization With respect to tin(IV), the recovery was constant regardless of when potassium iodide was added, however, the extraction temperature of 2700 °C (RSD=4.3%, n=6). However, RSD for a repeated 6 measurements was minimal (1.8%) at an process could not be clarified. Based on the above results, the concentration of HCl in the atomization temperature of 2500 °C.The optimal atomization time was determined to be 2 s. aqueous solution was set at 3 M, and the concentration of H2SO4 maintained at 3.5 M after potassium iodide was added. With respect to other measurement conditions, detailed analysis was performed and the optimal conditions shown in Table 1 were determined. Selection of organic solvent The following three organic solvents used for tin extraction, Extraction conditions of tin the specific gravities of which are lower than that of water, were studied: (i) diethyl ether, (ii) benzene and (iii) MIBK.Aqueous solutions containing 1.0 mg of tin(II) or tin(IV) and 1.25 Mpotassium iodide were acidified with 2.0–4.0 Msulfuric Fig. 4 shows the recovery of tin(II ) and tin(IV) at various concentrations of H2SO4 with a constant concentration of acid. The solutions were diluted to give a final volume of 20 ml. Tin was then extracted by benzene (20 ml ) and the 1.25 M of potassium iodide.In the experiment, the ratio of the aqueous to the organic phase was 151. extract treated with cobalt(III) oxide powder to recover the tin. Fig. 3 shows the results. The recovery of tin(II ), obtained with H2SO4 concentrations of 2.5–4.0M was 100%, when benzene was used. Recoveries When potassium iodide was added to the aqueous solution, the recovery of tin(II) for H2SO4 concentrations of 2.5–4.0 M of 100% and 62%, respectively, were obtained when diethyl ether was used with 2.5M H2SO4 and MIBK with 2.0M was approximately 80% ($).However, tin(IV) was extracted by benzene in the form of SnI4, and the recovery for H2SO4 H2SO4. Similarly, the recovery of tin(IV), obtained with H2SO4 concentrations of 2.0–4.0M was 100% (&). As explained above, the recovery of tin(II) diVered from concentrations of 2.0–4.0 M was 100%, when benzene was used. Recoveries of 69% and 38%, respectively, were obtained that of tin(IV) when potassium iodide was added to H2SO4 solutions containing tin.Based on the above results, we first when diethyl ether and MIBK were used with 2.0M H2SO4. Based on these results, it was found that a recovery of 100% acidified the aqueous solution with 1.0–6.0 M HCl or 2.0–4.0 M HClO4, and then controlled H2SO4 concentration could be obtained with benzene in the presence of H2SO4 at a wide concentration range (2.5–4.0 M) for both tin(II ) and after potassium iodide was added.As a result, by adding potassium iodide to 2.0–6.0M HCl and then controlling tin(IV). However, MIBK was superior to benzene in terms of operation since MIBK has higher viscosity and loss of H2SO4 concentrations of the solution at 2.5–4.0 M, the J. Anal. At. Spectrom., 1999, 14, 1081–1085 1083added to 50–200 ml of benzene containing 1.0 mg of both tin(II) and tin(IV), the recovery was 100%, indicating that 30 mg of cobalt(III) oxide powder can also be eVective when the volume of benzene is large.EVect of coexisting ions The eVect of coexisting ions on the recovery was studied in order to apply the proposed method to environmental samples. Various kinds of ions were added to the aqueous solution containing 1.0 mg of tin(II) or tin(IV). According to a previously determined procedure, a slurry was prepared by solvent extraction and collection of tin by cobalt(III) oxide powder. Ten ml of the slurry was introduced into the furnace and absorbance during atomization was measured.The obtained results were compared with absorbance obtained without coexisting ions, and recovery was determined. Fig. 4 Recovery of SnII and SnIV from extraction process using various To determine the amount of coexisting ions added, those organic solvents in the case of H2SO4 system. $,#: benzene; &,%: contained in 2 g of rock or sediment samples were used. diethyl ether; +,6: MIBK; $,&,+: SnII in 3 M HCl aqueous Chlorides of each ion were used as cations to be added.Table 2 solution; #,%,6: SnIV in 3M HCl aqueous solution; cobalt(III ) oxide summarizes the results. Because of pretreatment which powder: 30 mg; concentration of KI: 1.25 M. included solvent extraction and collection using cobalt(III) oxide powder, the recovery was 100±2%, regardless of the cobalt(III) oxide powder was suppressed during the recovery quantity of coexisting ions. operation such as a vacuum filtration. For these reasons, we employed the following procedure in this study: tin was first Calibration curve extracted by benzene to which 3 ml of MIBK was added; then, Calibration curves were obtained using slurries prepared tin was collected using cobalt(III) oxide powder.according to the determination procedure using an aqueous solution containing tin(II) or tin(IV). The results indicate that EVect of concentration of potassium iodide the calibration curve of tin(II) corresponds to that of tin(IV).Potassium iodide (0.1–2.0 M) was added to the aqueous The calibration curve was linear up to 0.40 mg l-1 (4.0 ng per solution containing 1.0 mg of tin(II) or tin(IV) to give 20 ml of 10 ml ), and the detection limit (3 s) was 6.00 mg l-1 (0.06 ng 3.5 M H2SO4 solution. per 10 ml ). A recovery of 100% was obtained in the presence of potass- When the calibration curves are compared with the standard ium iodide concentrations of 0.1–2.0 M. At this concentration solution, the absorbance of the slurry at tin concentrations of range, potassium iodide concentration did not aVect both the 0.25 mg l-1 (2.5 ng per 10 ml ) or higher is slightly lower than absorption signal and the background absorption, obtained that of the standard solution; the slopes of the two calibration by tin atomization during ETAAS using a tungsten furnace.Therefore, we set the potassium iodide concentration at 1.25 Table 2 EVect of coexisting ions on the determination of tin(II) M.and tin(IV) EVect of extraction time Found/mg l-1 bc Recovery (%) Approximately 100% of tin iodide can be extracted by benzene Ion Added/mga SnII SnIV SnII SnIV in approximately 1 min, when the ratio of the aqueous to the organic phase is 151. In this study, in order to completely SnII/SnIV — 200.0 200.0 — — extract tin in a single extraction operation, the extraction time NaI 150 197.4 198.9 99 99 KI 150 199.8 200.7 100 100 was set at 5 min. MgII 150 200.1 200.0 100 100 CaII 150 197.6 198.3 99 99 Collecting condition on cobalt(III ) oxide powder SrII 1 199.6 198.6 100 99 BaII 5 197.4 199.5 99 100 Tin(II) and tin(IV) were extracted into benzene; then 30 mg of MnII 3 199.9 197.4 100 99 cobalt(III) oxide powder were added.The thus-prepared sample CoII 0.1 200.0 200.1 100 100 was stirred for various time periods and recovery carried out. NiII 0.1 201.3 200.8 101 100 A recovery of approximately 70% was obtained for a stirring CuII 0.5 199.8 200.6 100 100 time of 1 min.Recovery was increased with increased stirring ZnII 0.2 201.1 199.7 101 100 CdII 0.01 199.9 200.2 100 100 time; a recovery of 100% was obtained with a stirring time of PbII 0.1 200.1 200.0 100 100 5 to 30 min. Considering the requirements for rapid operation, AlIII 200 199.4 202.6 100 101 the stirring time was determined to be 10 min. CrIII 0.2 202.8 201.4 101 101 Five to 50 mg of cobalt(III) oxide powder was added to FeIII 200 197.3 196.9 99 98 20 ml of benzene containing both tin(II) and tin(IV), and the AsIII 0.1 200.0 199.9 100 100 resulting organic phase was stirred for 10 min to obtain the SbIII 0.1 200.1 199.9 100 100 BiIII 0.1 200.1 200.0 100 100 recovery.The recovery was 100% when 10–50 mg of cobalt(III) TiIV 20 196.9 198.2 98 99 oxide powder was added; it was approximately 80% when SeIV 0.1 199.9 199.8 100 100 5 mg of cobalt(III) oxide powder was added. In this study, VV 1 200.3 201.8 100 101 since the volume of the slurry was set at 5 ml, an insuYcient MoVI 0.01 201.3 202.2 101 101 amount of cobalt(III) oxide powder was present in the slurry SiO32- 500 196.7 197.6 98 99 due to the decrease in the solid: water ratio; the organic phase PO43- 3 198.6 199.7 99 100 contained no tin. The amount of cobalt(III) oxide powder was aSample volume, 20 ml; bslurry, 5 ml; cinjection volume, 10 ml.set at 30 mg. When 30 mg of cobalt(III) oxide powder was 1084 J. Anal. At. Spectrom., 1999, 14, 1081–1085Table 3 Recovery of organotin compounds Organotin compound Taken/mga Found/mg l-1 bc Recovery (%) Tri-n-butyltin 1.0 200.0 100 0.5 100.5 101 Triphenyltin 1.0 201.6 102 0.5 99.7 100 Tri-n-pentyltin 1.0 199.8 100 0.5 99.4 99 Taken/mga Tri-n-butyltin Triphenyltin Tri-n-pentyltin Found/mg l-1 bc Recovery (%) 0.2 0.3 0.5 101.5 102 0.3 0.5 0.2 98.9 99 0.5 0.2 0.3 100.2 100 aAmounts as tin; bslurry, 5 ml; cinjection volume, 10 ml.Table 4 Analytical results for total tin in environmental and are used as pretreatment.The method can also determine the geological samples amount of inorganic tin with a diVerent valence number using the same determination procedure. The current pretreatment Mean/mg g-1 Reference value or method is proven to be eVective in the determination of tin, Sample ± (n=6) certified value/mg g-1 including organotin, in environmental samples. JG-1a 4.43±0.06 4.47 (Granodiorite) References JB-3 0.94±0.01 0.94 (Basalt) 1 A. B.Pandyn and J. C. Van Loon, Fresenius’ Z. Anal. Chem., JF-1 0.25±0.02 0.3 1988, 331, 707. (Feldspar) 2 H. N. Elsheimer, Anal. Sci., 1993, 9, 681. NIES No. 11 2.35±0.01 2.4±0.1 3 H. N. Elsheimer and T. L. Fries, Anal. Chim. Acta, 1990, 239, 145. (Fish tissue) 4 R. Pinel, M. Z. Benabdallah, A. Astruc and M. Astruc, J. Anal. NIES No. 12 9.38±0.04 10.7±1.4a At. Spectrom., 1988, 3, 475. (Marine sediment) 5 M. Chamsaz and J. D. Winefordner, J. Anal. At. Spectrom., 1988, 3, 119. aRef.No.: 27. 6 K. Tanaka, Bunseki Kagaku, 1962, 11, 332. 7 S. Terashima, Bull. Geol. Surv. Jpn, 1985, 36, 375. 8 E. Lundberg and B. Bergmark, Anal. Chim. Acta, 1986, 188, 111. curves do not agree. For this reason, in this study, we used 9 K. Ide, S. Hashimoto and H. Okochi, Bunseki Kagaku, 1995, the calibration curve prepared using the slurry. 44, 617. 10 J. Kuballa, R. D. Wilken, E. Jantzen, K. K. Kwan and Y. K. Acid decomposition and recovery of organotin Chau, Analyst, 1995, 120, 667. 11 Z.-M. Ni, H.-B. Hang, A. Li, B. He and F.-Z. Xu, J. Anal. At. Since organotins are contained in the environmental samples Spectrom., 1991, 6, 385. used in this study, the current pretreatment method was 12 T. Ferri, E. Cardarelli and B. M. Petronio, Talanta, 1989, 36, 513. applied to some organotin compounds. According to pro- 13 R. Pinel, M. Z. Benabdallah, A. Astruc and M. Astruc, Anal. cedure described above, recovery of tin was obtained through Chim. Acta, 1986, 181, 187. 14 M. Taga, H. Yoshida and O. Sakurada, Bunseki Kagaku, 1987, acid decomposition, solvent extraction and collection of tin 36, 597. using cobalt(III ) oxide powder. Recovery was almost 100% for 15 M. Tominaga and Y. Umezaki, Anal. Chim. Acta, 1979, 110, 55. every organic compound used, which means that the current 16 K. Yasuda, Y. Hirano, T. Kamino and K. Hirokawa, Anal. Sci., method can also be applied to environmental samples 1994, 10, 623. (Table 3). 17 K. Yasuda, Y. Hirano, K. Hirokawa, T. Kamino and T. Yaguchi, Anal. Sci., 1993, 9, 529. 18 Y. Terui, K. Yasuda and K. Hirokawa, Anal. Sci., 1991, 7, 599. Application to environmental and geological samples 19 K. Oishi, K. Yasuda and K. Hirokawa, Anal. Sci., 1991, 7, 883. The proposed method was applied to environmental samples 20 M. Taga, O. Sakurada and H. Takahashi, Bunseki Kagaku, 1988, 37, 164. from the National Institute for Environmental Studies (NIES) 21 W.-M. Yang and Z.-M. Ni, Spectrochim. Acta, Part B, 1997, 52, and geological standard rock samples from the Geological 241. Survey of Japan (GSJ). 22 T. Narukawa, W. Yoshimura and A. Uzawa, Bunseki Kagaku, First, these samples were precisely weighed, and one of the 1998, 47, 707. following procedures was carried out: (i) dissolution in 5 ml 23 T. Narukawa, J. Anal. At. Spectrom., 1999, 14, 75. of 3 M HCl solution, or (ii) dissolution in a suYcient amount 24 T. Narukawa, W. Yoshimura and A. Uzawa, Bull. Chem. Soc. Jpn., 1999, 72, 701. of acid to make 50 ml (3 M HCl solution) and 5 ml of the 25 T. Narukawa, A. Uzawa, W. Yoshimura and T. Okutani, J. Anal. resulting solution was used for a later experiment. At. Spectrom., 1997, 12, 781. The results revealed that values obtained in this study agree 26 S. Tagawa, Bunseki Kagaku, 1980, 29, 563. with the certified or reference value reported for each standard 27 J. Yoshinaga, H. Kon, T. Horiguchi, M. Morita and K. Okamoto, sample (Table 4). Anal. Sci., 1998, 14, 1121. Use of the proposed method enables the determination of trace amounts of tin in complex matrices when solvent Paper 9/02207D extraction and collection of tin using cobalt(III ) oxide powder J. Anal. At. Spectrom., 1999, 14, 1081–1085 1085