Low volume microwave digestion and direct determination of selenium in biological samples by hydride generation-atomic fluorescence spectrometry

A low volume microwave digestion (LVMWD) procedure has been developed to have all forms of selenium (Se) compounds in biological samples decomposed to Se (IV) and allow total Se be directly determined by hydride generation-atomic fluorescence spectrometry (HG-AFS), or voltammetrically. Between 0.3 and 0.4 mL of mixed digestion reagents consisting of concentrated (15.4 M) HNO₃-(18.5 M) H₂SO₄ (v:v = 10:1) and >5 to <40 mg sample were found ideal systems with an optimized MW digestion program. Total Se in five certified reference materials was accurately determined. The results obtained by the conventional and LVMWD techniques agreed well. By avoiding pre-reduction step, this method, suitable for a wide range of biological samples, fully takes the advantages of HG-AFS or voltammetric techniques for their high sensitivity, high tolerance to matrix-related interference and accessibility in instrumentation. LVMWD not only enhances the sample output by 3 times and reduces the operational cost and acid wastes, but also makes the small sample analysis possible for many environmental and medical related research objectives. The digestion pathways of Se containing organic samples are also discussed based on the experimental results.