Total organic content chemical methods

Hydride generation AAS is a well-established technique for the determination of selenium because of its selectivity and sensitivity. The detection limits are improved by concentrating the hydride prior to the transfer to the spectrometer. Cryogenic condensation in a U-tube at liquid nitrogen temperature is a preferred method of pre-concentration. However, selenium hydride is formed essentially only from Se. The selectivity for Se has been combined with various chemical preparation steps to determine the sum of SeIV and Se and the total selenium content of samples. Se concentrations are measured by the difference between the (Se + Se ) and Se contents. The difference between total selenium and (Se + Se ) contents represents the concentrations of Se° and Se2- species. These methods have been used for determinations of selenium species in natural waters. Soluble organic matter in some groundwater samples interferes with the hydride generation determination of selenium. Isolation of humic substances by their adsorption on resins has overcome this problem. 

The determination of various oxidation states of elements is of great interest as well. Until recently, analytical methods allowed analysts to determine only the total content of analytes, but it was soon realized that this analytical information was insufficient. Biochemical and toxicological investigation has shown that, for living organisms, the chemical form of a specific element or the oxidation state in which that element is introduced into the environment is as important as its quantity. 

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