Evaluation of microwave digestion and solvent extraction for the determination of trace amounts of selenium in feeds and plant and animal tissues by electrothermal atomic absorption spectrometry.

A sensitive method for the accurate determination of Se in agricultural products at sub-ppm levels is described. The proposed procedure involves the wet oxidation of samples by using a mixture of nitric, sulphuric and perchloric acids, co-extraction of Se and added Pd with diethylammonium N,N-diethyldithiocarbamate in chloroform, and electrothermal atomic absorption spectrometric determination of Se in the organic extract. Atomization and extraction conditions are discussed. Special attention is given to the wet oxidation step, and its advantages in speed and simplicity over conventional heating have been evaluated using an automated microwave digestion system. The results reported, obtained from several reference materials, confirm the accuracy of the method with which a detection limit of 0.002 micrograms g-1 of Se can be achieved.