116 Organic compounds in soils, sediments & sludges
isolation and derivatisation procedures. An alternative procedure is described involving a series of selective extractions of tetra-alkylleads, ionic alkylleads, and inorganic
ionic lead salts from soils and street dusts. Alkyllead salts were selectively extracted
complexometrically from samples containing up to 1000 mg ionic lead per kg. The
extracts were then butylated and analysed by gas chromatography-atomic absorption
spectroscopy. Re-extraction of the sample with methyl isobutyl ketone-dithizone permitted the recovery of ionic lead. In the samples tested, ethyllead salts were detected,
but not methyllead salts. Concentrations of these analytes were significantly correlated
with levels of extractable ionic lead, but not with total lead.
4.3 ORGANOTIN COMPOUNDS
The preparation of volatile derivatives makes the ionic organotin compound amenable
to evaporative separation techniques (purge and trap or gas chromatography). Hydride
formation in dilute aqueous solutions has become a routine method for determination
of methyltins [6–15], methyl- and butyltins [5.16.17] and phenyl- and various other
organotin compounds [18,19] to form the volatile hydrides (stannanes), which are
analysed either by purging and atomic absorption spectrometry or flame photometric
detection or by liquid–liquid extraction with subsequent gas chromatographic analysis.
Unfortunately, stannanes are rather labile thus preventing further cleanup steps.
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 sludges. A Grignard
reagent or an alkyllithium compound is used to convert the ionic mono-, di-, or triorganotin compound into the corresponding non-polar tetrasubstituted compound.
The reaction has to be carried out in aprotic solvents and thus requires extraction of
aqueous samples prior to derivatisation. Procedures have been described for the analysis of methyltins [20], butylenes [21, 22], mixed methylbutyltins [23], various alkytins
[24], cyclohexyltins [26], and phenyltins [25]. Alkylation also offers the possibility for
selection of the volatility range of the derivatives, which are in most cases analysed by
gas chromatography.
Gas chromatography
Sinex et al [27] have described a method for the determination of methyltin compounds
based on reaction with sodium borohydride to form tin hydrides then purge and trap
analysis followed by gas chromatography with mass spectrometric detection. Down to
3–5 pg absolute (as tin) of methyltin compounds equivalent to the sub µg kg
−1 range
can be determined by this procedure.
Lobinski et al [28] optimised conditions for the comprehensive speciation or
organotin compounds in soils and sediments. They used capillary gas chromatography coupled with helium microwave induced plasma emission spectrometry to
determine mono-, di-, tr- and some tetraalkylated tin compounds. Ionic organotin compounds were extracted with pentane from the sample as the organotindiethyldithiocarbamate complexes then converted to their pentabromo derivatives
prior to gas chromatography. The absolute detection limit was 0.5 pg as tin; equivalent
to 10–30 µg kg
−1 .
isolation and derivatisation procedures. An alternative procedure is described involving a series of selective extractions of tetra-alkylleads, ionic alkylleads, and inorganic
ionic lead salts from soils and street dusts. Alkyllead salts were selectively extracted
complexometrically from samples containing up to 1000 mg ionic lead per kg. The
extracts were then butylated and analysed by gas chromatography-atomic absorption
spectroscopy. Re-extraction of the sample with methyl isobutyl ketone-dithizone permitted the recovery of ionic lead. In the samples tested, ethyllead salts were detected,
but not methyllead salts. Concentrations of these analytes were significantly correlated
with levels of extractable ionic lead, but not with total lead.
4.3 ORGANOTIN COMPOUNDS
The preparation of volatile derivatives makes the ionic organotin compound amenable
to evaporative separation techniques (purge and trap or gas chromatography). Hydride
formation in dilute aqueous solutions has become a routine method for determination
of methyltins [6–15], methyl- and butyltins [5.16.17] and phenyl- and various other
organotin compounds [18,19] to form the volatile hydrides (stannanes), which are
analysed either by purging and atomic absorption spectrometry or flame photometric
detection or by liquid–liquid extraction with subsequent gas chromatographic analysis.
Unfortunately, stannanes are rather labile thus preventing further cleanup steps.
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 sludges. A Grignard
reagent or an alkyllithium compound is used to convert the ionic mono-, di-, or triorganotin compound into the corresponding non-polar tetrasubstituted compound.
The reaction has to be carried out in aprotic solvents and thus requires extraction of
aqueous samples prior to derivatisation. Procedures have been described for the analysis of methyltins [20], butylenes [21, 22], mixed methylbutyltins [23], various alkytins
[24], cyclohexyltins [26], and phenyltins [25]. Alkylation also offers the possibility for
selection of the volatility range of the derivatives, which are in most cases analysed by
gas chromatography.
Gas chromatography
Sinex et al [27] have described a method for the determination of methyltin compounds
based on reaction with sodium borohydride to form tin hydrides then purge and trap
analysis followed by gas chromatography with mass spectrometric detection. Down to
3–5 pg absolute (as tin) of methyltin compounds equivalent to the sub µg kg
−1 range
can be determined by this procedure.
Lobinski et al [28] optimised conditions for the comprehensive speciation or
organotin compounds in soils and sediments. They used capillary gas chromatography coupled with helium microwave induced plasma emission spectrometry to
determine mono-, di-, tr- and some tetraalkylated tin compounds. Ionic organotin compounds were extracted with pentane from the sample as the organotindiethyldithiocarbamate complexes then converted to their pentabromo derivatives
prior to gas chromatography. The absolute detection limit was 0.5 pg as tin; equivalent
to 10–30 µg kg
−1 .