Page 251 - Tandem Techniques

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The chromatograms of an eleven-component synthetic mixture, monitored for elements, carbon,
hydrogen, deuterium, nitrogen, oxygen, sulfur, fluorine chlorine, bromine, silicon and phosphorus, are
shown in Figure 6.4. The advantages of the technique are clearly seen. The chromatograms monitored
by measuring the carbon and hydrogen elements are very similar as would be expected. The other
chromatograms show single peaks, indicating the unique nature of their element content.

The GC/ES combination, employing microwave plasma emission, has been used by a number of
analysts in various environmental studies. In particular, Lobinski et al. [4] have used it for determining
tin compounds in soils and ground water. There has been a growing interest in the determination of
organotin, due to the increasing number of anthropogenic sources. Tin is used largely in the plastics
industry, the paint industry and in agriculture. The toxicity of tin compounds depends on their structure
and in the R SnX(4-n) series of tin compounds, where (R) and (X) are alkyl groups, the maximum
n
biological activity appears to occur when n = 3.

The use of GC as the chosen separation process appears to arise from the very high efficiencies that are
readily available and the associated short analysis times. Nevertheless, most tin compounds are highly
polar, consequently they must be derivatized before separation on a GC column. Popular preparation
procedures involve extraction of the ionic tin compound after chelation, followed by reaction with an
ethyl, pentyl or hexyl Grignard reagent [5-7]. The alkyl tin compounds so formed are then injected onto
the column, and the separation monitored with an atomic emission spectrometer. As the extracts are
usually loaded with a wide variety of interfering organic compounds, monitoring the chromatogram
with a conventional FID detector would provide a bemusing mass of peaks. By selecting a particular
emission wavelength associated with elemental tin, a chromatogram showing only tin compounds can
be reconstructed. An example of the procedure to separate and identify three organotin compounds is
shown, as a two-dimensional emission wavelength/retention time chromatogram, in Figure 6. 5.