Evaluation of Closed-Vessel Conductively-Heated Digestion System with Diluted Acid for Analysis of Animal Feed by ICP-MS

A conductively-heated digestion system (CHDS) with closed-vessel and diluted acid was evaluated for the preparation of animal feed for subsequent determination of As, Cd, Mo, Ni, Pb, Se and V by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The analytical performance of the digestor was checked by analyzing fish tissue, tuna and corn bran certified reference materials (CRMs) using 1 mL of 30% (w w-1) hydrogen peroxide plus 2 mL of nitric acid at 14, 7 and 3.5 mol L-1 HNO3. The recoveries of analytes in CRMs digested at different acid concentrations varied from 80 – 116% (3.5 mol L⁻¹ HNO₃) 86 – 118% (7 mol L⁻¹ HNO₃) e 80 – 123% (14 mol L⁻¹ HNO₃). The method was applied to real animal feed samples, and the CHDS results were like those of comparative microwave digestion (MWD). Quantification limits of analytes found by CHDS and MWD were also similar, concerning different acid concentrations. However, the use of diluted nitric acid in the preparation of animal feed samples proved to be a viable and efficient approach, allowing lower residual acidity, reduction in reagent consumption and acid waste generation, in accordance with the principles of Green Chemistry.