Enzymatic probe sonication as a tool for solid–liquid extraction for total selenium determination by electrothermal-atomic absorption spectrometry

A new fast and reproducible approach is described for the application of the enzymatic probe sonication (EPS) methodology [J.L. Capelo, P. Ximénez-Embún, Y. Madrid-Albarrán, C. Cámara, Anal. Chem. 76 (2004) 233–237] for total selenium determination by electrothermal atomic absorption spectrometry, ET-AAS. Ni(NO3)2 and Pd(NO3)2 were studied as matrix modifiers in conjunction with H2O2, being best results obtained with Pd(NO3)2 plus H2O2. The presence of H2O2 as matrix modifier increases up to 66% the time-life of the graphite tubes, by avoiding the building-up of carbonaceous residues. BCR-414 plankton and ERM-CE 278 mussel tissue reference materials were used for proof-of-the-methodology. Different enzymes, protease XIV, substilisin and trypsin were studied. The use of fresh enzyme was found critical. Good Se recoveries were obtained for oyster tissue, 111%; BCR-414 plankton, 106% and ERM-CE 278 mussel tissue, 93%, when protease XIV was used. Data regarding microwave digestion versus EPS methodology is also presented and discussed.