Enzymic Digestion–High-pressure Homogenization Prior to Slurry Introduction Electrothermal Atomic Absorption Spectrometry for the Determination of Selenium in Plant and Animal Tissues

Abstract

Homogenization, in combination with partial enzymic digestion with a crude protease alone or admixed with lipase or cellulase, was investigated as a means of releasing Se residues from zoological and botanical matrices prior to slurry introduction ETAAS. Preliminary timed trials with two zoological certified reference materials (CRMs), one botanical CRM and one animal feed indicated that Se release became quantitative with 4–8 h of digestion, that homogenization prior to digestion increased the initial rate of analyte release, but that homogenization post-digestion and immediately prior to ETAAS did not significantly improve the precision of replicate digestions. Storage of the crude botanical digests at 4 °C for 5 d resulted in quantitative recoveries of Se from each of the digests. Storage at 4 °C for 10 d of 4 and 8 h lipase/protease digests of six other CRMs resulted in quantitative recoveries of Se unless their certified concentrations were appreciably less than the levels determined in control digests containing the enzyme(s) alone. Apparently, Se residues were transferred virtually quantitatively to the liquid phase of the digested suspension and showed no tendency to segregate during the 10 d of storage. Eight other mixtures of ground plant matter (0.13 ≤ [Se] ≤ 1.31 µg g ^{- 1} ), formulated as animal feed supplements, behaved identically when stored post-digestion. The technique was also applied successfully to freeze-dried fresh and boiled fish tissues The principal advantages of the enzymic digestion procedure are its simplicity and lack of operator intervention.