178 Organic compounds in soils, sediments & sludges
spectroscopy (XANES). It was found that the method can provide the “organic extent’’,
the average number of organic ligands bound to tin, for environmental samples. For Sn
XANES at the L 111 , L 1 , and K edges, systematic variations were found in the spectra
for butyl-, phenyl-, and methyl-substituted tin compounds depending on the organic
extent. A quantitative relationship between the organic extent and the characteristics
in the XANES spectra was determined based on the peak position, peak area ratio,
and peak width. The detection limit was better than 10 µg/g tin when using the K
edge, which is sensitive enough for some environmental samples, e.g., sediments, biological samples, and antifouling paints, and the sensitivity would be better if a more
intense X-ray source such as an undulator or Wiggler was used. This XANES method
is totally non-destructive, having the advantage that no complicated pre-treatment
procedures are needed, whereas such procedures are essential in conventional chromatographic analysis, and may cause experimental error by alteration of tin species
and poor recovery during analyses. Although the XANES method only provides the
average number of organic ligands, the direct speciation using XANES will be helpful
for estimating roughly the ratio of organic and inorganic tin species, which can be used
to study organotin transformation in sediment cores and the inspection of organotin
compounds in antifouling paints. In particular, micro-XANES analysis based on the
present method is a promising tool in obtaining the distribution of organotin species
in biological samples and specific phases in sediments.
Staniszewska et al [49] have recently pointed out that the determination of organotin compounds in bottom sediments is a complex process that requires a number of
analytical steps i.e. sample collection, transport and storage; extraction of analytes
from sediment; derivatisation; extract purification; enrichment; and the final chromatographic measurement. The whole process is time and labour consuming, and is
subject to securing a representative sample. These workers review the most frequently
encountered problems and the examples of possible analytical solutions are presented,
which encompass the specific steps of speciation analysis of these toxic compounds.
Detection limits achievable for organotin compounds in non-saline sediments are
listed below in Table 7.2.
7.4 ORGANOMERCURY COMPOUNDS
Earlier work on the determination of total mercury in river sediments includes that of
Iskandor et al [51]. Iskandor applied flameless atomic absorption to a sulphuric acidnitric acid digest of the sample following reduction with potassium permanganate,
potassium persulfate and stannous chloride. A detection limit of 1 µg kg
−1 is claimed
for this somewhat laborious method. Langmyhr and Aamodt et al [52] determined
down to 0.1 µg L
−1 of organomercury and Matsunaga and Takahashi et al [53], Craig
and Mortan et al [54] and the AOAC [54] also determined organic mercury in river
sediments using cold vapour atomic absorption spectrometry.
A method [55,56] has been described for the determination of down to 2.5 µg kg
−1
alkylmercury compounds and inorganic mercury in river sediments. This method uses
steam distillation to separate methylmercury in the distillate and inorganic mercury
in the residue. The methylmercury is then determined by flameless atomic absorption spectrophotometry and the inorganic mercury by the same technique after wet
spectroscopy (XANES). It was found that the method can provide the “organic extent’’,
the average number of organic ligands bound to tin, for environmental samples. For Sn
XANES at the L 111 , L 1 , and K edges, systematic variations were found in the spectra
for butyl-, phenyl-, and methyl-substituted tin compounds depending on the organic
extent. A quantitative relationship between the organic extent and the characteristics
in the XANES spectra was determined based on the peak position, peak area ratio,
and peak width. The detection limit was better than 10 µg/g tin when using the K
edge, which is sensitive enough for some environmental samples, e.g., sediments, biological samples, and antifouling paints, and the sensitivity would be better if a more
intense X-ray source such as an undulator or Wiggler was used. This XANES method
is totally non-destructive, having the advantage that no complicated pre-treatment
procedures are needed, whereas such procedures are essential in conventional chromatographic analysis, and may cause experimental error by alteration of tin species
and poor recovery during analyses. Although the XANES method only provides the
average number of organic ligands, the direct speciation using XANES will be helpful
for estimating roughly the ratio of organic and inorganic tin species, which can be used
to study organotin transformation in sediment cores and the inspection of organotin
compounds in antifouling paints. In particular, micro-XANES analysis based on the
present method is a promising tool in obtaining the distribution of organotin species
in biological samples and specific phases in sediments.
Staniszewska et al [49] have recently pointed out that the determination of organotin compounds in bottom sediments is a complex process that requires a number of
analytical steps i.e. sample collection, transport and storage; extraction of analytes
from sediment; derivatisation; extract purification; enrichment; and the final chromatographic measurement. The whole process is time and labour consuming, and is
subject to securing a representative sample. These workers review the most frequently
encountered problems and the examples of possible analytical solutions are presented,
which encompass the specific steps of speciation analysis of these toxic compounds.
Detection limits achievable for organotin compounds in non-saline sediments are
listed below in Table 7.2.
7.4 ORGANOMERCURY COMPOUNDS
Earlier work on the determination of total mercury in river sediments includes that of
Iskandor et al [51]. Iskandor applied flameless atomic absorption to a sulphuric acidnitric acid digest of the sample following reduction with potassium permanganate,
potassium persulfate and stannous chloride. A detection limit of 1 µg kg
−1 is claimed
for this somewhat laborious method. Langmyhr and Aamodt et al [52] determined
down to 0.1 µg L
−1 of organomercury and Matsunaga and Takahashi et al [53], Craig
and Mortan et al [54] and the AOAC [54] also determined organic mercury in river
sediments using cold vapour atomic absorption spectrometry.
A method [55,56] has been described for the determination of down to 2.5 µg kg
−1
alkylmercury compounds and inorganic mercury in river sediments. This method uses
steam distillation to separate methylmercury in the distillate and inorganic mercury
in the residue. The methylmercury is then determined by flameless atomic absorption spectrophotometry and the inorganic mercury by the same technique after wet