Comparison of methods to determine selenium species in saturation extracts of soils from the western San Joaquin Valley, California

Methods to determine soluble concentrations of selenite, selenate, and organic selenium were compared on saturation extracts of soil samples collected from three sites on the Panache Creek alluvial fan in the western San Joaquin Valley, California. The methods were used in combination with hydridegeneration atomic-absorption spectrometry for detection of selenium and included a selective chemical digestion method and three chromatography methods using XAD-8 resin, Sep-Pac C₁₈ cartridge, and a combination of XAD-8 resin and activated charcoal.

Undigested organic matter in some of the extracts inhibited selenium detection when using the digestion and Sep-Pac C18 methods, but the interference was removed by using the XAD-8 method. Combining XAD-8 resin and activated charcoal was an unacceptable method, because the activated charcoal removed selenite and selenate. Ninety-eight percent of the selenium in the extracts was selenate and about 100 percent of the isolated organic selenium was associated with the humic acid fraction of dissolved-organic matter.