Enzymatic digestion-high-pressure homogenization prior to slurry introduction graphite furnace atomic absorption spectrometry for selenium determination in plant and animal tissues

Homogenization using a new flat valve homogenizer in combination with enzym atic digestion with a crude protease was investigated as a means of releasi ng Se compounds fi om zoological and botanical matrixes prior to slurry int roduction GFAAS. Timed trials with four zoological certified reference mate rials (CRMs), three botanical reference materials (RMs), and a food crop in dicated that Se release into 5% (v/v) ethanol-0.03 M TRIS containing 20 mg of protease was quantitative after homogenization or became quantitative wi thin 1 h of digestion at 60 degrees C. For each of the zoological RMs (whol e egg powder, dogfish muscle, and dogfish liver), three passes through the homogenizer in the presence of protease provided a quantitative release of selenium, and incubation with the enzyme was not necessary. No separation o f the Se between the liquid phase and the particulate phase was evident eve n after several days of subsequent storage at 4 degrees C. The botanical ma trixes (three milled wheat RMs and a rapeseed sample) were more resistant t o selenium release and required up to 1 h of digestion with protease at 60 degrees C. Alternatively, 10 passes through the homogenizing valve (in the presence of the enzyme) resulted in the quantitative release of analyte.