Evaluation of a cost-effective and environmentally friendly digestion method for preparing animal feed samples for elemental analysis

A novel method using a closed-vessel conductively heated digestion system (CHDS) with diluted nitric acid was developed for the decomposition of animal foods and determination of B, C, Ca, Cu, Fe, K, Mg, Mn, P, S and Zn by inductively coupled plasma optical emission spectrometry (ICP-OES). The effects of acidity were evaluated by digesting samples using 2 mL of HNO₃ at 3.5, 7.0, and 14 mol L⁻¹ plus 1 mL of 30 % (w w⁻¹) H₂O_2, and the accuracy was checked by analyzing certified reference materials. Recoveries for all analytes varied in the 81–113 % (3.5 mol L⁻¹), 83–114 % (7.0 mol L⁻¹), and 80–114 % (14 mol L⁻¹) intervals. Commercial samples of cat, dog, rabbit, bird, fish, and horse foods were analyzed, and the results found by CHDS were equivalent to those obtained by the comparative benchmark microwave-assisted digestion (MW-AD) method. Limits of quantification obtained by CHDS using HNO₃ 3.5 mol L⁻¹, 7 mol L⁻¹, and 14 mol L⁻¹ were also comparable to those observed with MW-AD. The dissolved organic carbon (DOC) determined in all digests was lower than 2000 L^−1, which is considered acceptable for determinations by ICP techniques. The analytical greenness metric for sample preparation (AGREEprep) furnished a score of 0.50 for digestions with 3.5 mol L⁻¹, suggesting a sustainable and environmentally friendly alternative method for sample preparation.