Decomposição de amostras de alimentos empregando ácido nítrico diluído e pressurização com diferentes gases em sistema de câmara única de reação assistida por radiação micro-ondas

Abstract

In the present work the use of a microwave-assisted wet digestion using a single reaction chamber system (MAD-SRC) at high pressure and temperature was evaluated for digesting food samples. It was evaluated the use of dilute solutions of HNO3 for sample digestion. Oxygen was used as auxiliary reagent for sample digestion using diluted HNO3. The gas phase influence over the efficiency of sample digestion was performed by using different gases (compressed air, Ar, N2 and O2). Whole milk powder was used as a model sample for all the evaluations using different gases. Modified covers were developed to check the influence of gaseous phase in the digestion of whole milk powder, as well as provide a better understanding of the reactions of the organic matter oxidation. For comparison purposes, a sample digestion was performed using a high pressure asher (HPA), which is conventionally heated. This system was employed for evaluating. For the digestion using HPA system it was evaluated the use of HNO3 solution (1 to 7 mol L- 1) with H2O2. The digestion temperature, the concentration of HNO3, volume of H2O2 and the time of digestion was systematically evaluated. For both digestion system, MAD-SRC and HPA, the digestion efficiency was performed by means of residual carbon content (RCC) and residual acidity (RA) in the final digests. In the optimized sample digestion condition metals (Ba, Ca, Cu, Fe, K, Mg, Mn, Na, Sr, and Zn) were determined by ICP-OES. The obtained results indicated that the MAD-SRC system using O2 presented a better digestion efficiency, as well as enabling multiple samples with different compositions to be digested in the same run. The accuracy was evaluated by using certified reference materials (CRMs) of whole milk powder (NIST 8435 Whole Milk Powder), bovine liver (NIST 1577a Bovine Liver) and corn bran (NIST 8433 Corn Bran). The proposed method was used for simultaneously digestion of samples of linseed, parsley, bovine liver and whole milk powder.