Open-focused microwave-assisted digestion for the preparation of large mass organic samples

Abstract

Microwave-assisted wet digestions of large sample masses (up to 10 g) of biological materials and hydrocarbon-based oil were successfully accomplished at atmospheric pressure using an open-focused system. The per cent. residual carbon contents (RCC) of the resulting solutions, trace element recovery and extent of contamination (magnitude of the blank) were used to characterize the performance of the methodology. A Prolabo Maxidigest M 401 unit, fitted with a modified reaction vessel, was used to solubilize samples of National Research Council of Canada (NRCC) certified reference materials TORT-1 and LUTS-1 (Lobster Hepatopancreas) as well as Conostan 75 base oil, using either HNO₃ or a mixture of HNO₃—H₂SO₄. Digestion efficiency increased with increased digestion time and sample mass (15% RCC with 0.25 g sample, 2% RCC with 8 g sample). The minimum spike recovery of added elements (As, Cd, Cr, Co, Cu, Fe, Pb, Mn, Ni, Se, Sr and Zn) was 94.5%(Sr) and averaged 99% in HNO₃ and 97% in the mixed acid. Certified reference values for trace element content were achieved for TORT-1 and LUTS-1.