Organometallic compounds in non-saline sediments 175
carbon-containing particles, the sediment taken at the deepest (and anoxic) part of the
lake accumulates higher organotin residues and is therefore more representative of the
overall situation in the lake sediment.
Unger et al [20] have studied the sorption behaviour of tributylin on estuarine
sediments.
Rapsomankis et al [21] have studied of biological methylation of inorganotin
sediments.
Gas chromatography predominates as the preferred method of analysis of organotin compounds.
Gas chromatography
Arakawa et al [22] pointed out that methyltin compounds may be extracted from
complex matrices and analysed by conventional gas chromatography. However, the
procedure is lengthy, involving multiple steps where speciation may be altered and vessel adsorption effects may be large. Detection limits achievable with a flame ionisation
detector are 10–100 µg.
Chau et al [23] have pointed out that butylation of methyl tin species before solvent extraction and the use of atomic absorption spectrometry shortens the extraction
procedure and reduces detection limits to about 0.1 ng.
In the method described by Hattori et al [24], the sediment samples were extracted
into methonolic hydrochloric acid and then, following mixing with water and sodium
chloride, the mixture was extracted with benzene. Following dehydration and concentration, the tin compounds were cleaned up on a silica gel column impregnated with
hydrochloric acid and then hydrides generated using an ethanol solution of sodium
borohydride [44]. The organotin hydrides were determined from sediment samples
and the detection limits 0.02 mg kg
−1 .
Mueller et al [25] has described a method for determining 0.5 µg kg
−1 tributyltin in sediments in which tributylin is first converted to tributymethyltin and
analysed using capillary gas chromatography with flame photometric detection and
gas chromatography-mass spectrometry.
Mueller et al [26] has described a comprehensive method for determining traces
of mono-, di-, tri- and some tetrasubstituted organotin compounds in lake sediment.
The ionic compounds are extracted from acidified sediment as chlorides using ethereal Tropalone solution. The extracted organotin compounds are ethylated using a
Grignard reagent (EtMgBr) and analysed by high-resolution gas chromatography with
flame photometric and mass spectrometric detection. Ethylation using ethyl magnesium bromide was chosen for conversion of the various mono-, di- and tri-substituted
organotin compounds in sediments into tetrasubstituted ones.
Ethylation was preferred over either methylation or alkylation using a larger alkyl
group because methylation of tin (IV) and butylin species seems to occur in the environment leading to methyltins and mixed methylalkyltins. Further methylation of these
environmental metabolites in the derivatisation step would exclude the possibility of
determining these conversion and degradation products. The ethylation reaction of
these compounds leads to a series of tetrabutylin compounds as shown in Table 7.1.
Environmental methylation is easily recognised, as the methylated products show typical relative retention time shifts compared to their ethylbutylin analogues (Figure 7.1).
carbon-containing particles, the sediment taken at the deepest (and anoxic) part of the
lake accumulates higher organotin residues and is therefore more representative of the
overall situation in the lake sediment.
Unger et al [20] have studied the sorption behaviour of tributylin on estuarine
sediments.
Rapsomankis et al [21] have studied of biological methylation of inorganotin
sediments.
Gas chromatography predominates as the preferred method of analysis of organotin compounds.
Gas chromatography
Arakawa et al [22] pointed out that methyltin compounds may be extracted from
complex matrices and analysed by conventional gas chromatography. However, the
procedure is lengthy, involving multiple steps where speciation may be altered and vessel adsorption effects may be large. Detection limits achievable with a flame ionisation
detector are 10–100 µg.
Chau et al [23] have pointed out that butylation of methyl tin species before solvent extraction and the use of atomic absorption spectrometry shortens the extraction
procedure and reduces detection limits to about 0.1 ng.
In the method described by Hattori et al [24], the sediment samples were extracted
into methonolic hydrochloric acid and then, following mixing with water and sodium
chloride, the mixture was extracted with benzene. Following dehydration and concentration, the tin compounds were cleaned up on a silica gel column impregnated with
hydrochloric acid and then hydrides generated using an ethanol solution of sodium
borohydride [44]. The organotin hydrides were determined from sediment samples
and the detection limits 0.02 mg kg
−1 .
Mueller et al [25] has described a method for determining 0.5 µg kg
−1 tributyltin in sediments in which tributylin is first converted to tributymethyltin and
analysed using capillary gas chromatography with flame photometric detection and
gas chromatography-mass spectrometry.
Mueller et al [26] has described a comprehensive method for determining traces
of mono-, di-, tri- and some tetrasubstituted organotin compounds in lake sediment.
The ionic compounds are extracted from acidified sediment as chlorides using ethereal Tropalone solution. The extracted organotin compounds are ethylated using a
Grignard reagent (EtMgBr) and analysed by high-resolution gas chromatography with
flame photometric and mass spectrometric detection. Ethylation using ethyl magnesium bromide was chosen for conversion of the various mono-, di- and tri-substituted
organotin compounds in sediments into tetrasubstituted ones.
Ethylation was preferred over either methylation or alkylation using a larger alkyl
group because methylation of tin (IV) and butylin species seems to occur in the environment leading to methyltins and mixed methylalkyltins. Further methylation of these
environmental metabolites in the derivatisation step would exclude the possibility of
determining these conversion and degradation products. The ethylation reaction of
these compounds leads to a series of tetrabutylin compounds as shown in Table 7.1.
Environmental methylation is easily recognised, as the methylated products show typical relative retention time shifts compared to their ethylbutylin analogues (Figure 7.1).