Fractionation of selenium and detection of selenomethionine in a soil extract

Abstract

A procedure is described to fractionate, identify and quantify organic selenium compounds at .mu.g/kg levels in soil extracts. The fractionation is based first on the different solubility of humates and fulvates at low pH, followed by adsorption chromatography with XAD-8 resin. The latter uses a pH gradient to elute the acidic and basic hydrophobic fulvates as well as hydrophilic fulvates. The neutral hydrophobic fulvates were retained on the column and determined by difference from the total extractable selenium. A 0.1 M NaOH/0.1 M Na4P2O7 solution extracted 33% of the total soil selenium. In the soil studied, organic selenium was 20% of total extractable selenium. One of the hydrophilic fulvates has been identified as selenomethionine by gas chromatography-mass spectrometry. The quantity of organic selenium and the presence of selenomethionine suggests that organoselenium compounds could be an important source of plant available selenium.