Evaluation of a digestion procedure based on the use of diluted nitric acid solutions and H2O2 for the multielement determination of whole milk powder and bovine liver by ICP-based techniques

Abstract

Many efforts have been made in order to reduce the amount of reagents and waste produced in analytical laboratories. However, suitable digestion efficiency must be considered, and depending on the sample preparation procedure, incomplete digestion can result in severe matrix effects during analysis by spectrometric techniques such as ICP OES and ICP-MS. In the present work a procedure based on the use of H₂O₂ was developed in order to minimize the consumption of HNO₃ without decreasing the efficiency of digestion. Although H₂O₂ has been used combined with HNO₃ for sample digestion, its role is still not completely elucidated even as its action combined with O₂ in pressurized systems. The performance obtained using H₂O₂ was similar to that observed when adding O₂ to the reaction vessel, driving the better understanding of the role of H₂O₂ in closed digestion procedures. Digestion using H₂O₂ allowed the use of HNO₃ solutions as diluted as 1 mol L⁻¹ to digest sample masses of biological materials as high as 500 mg. The proposed procedure allowed a reduction of up to 14 and 9.3-fold in the HNO₃ amount normally used in whole milk powder and bovine liver digestions, respectively, without decreasing the digestion efficiency. Calcium, Cu, Fe, K, Mg, Mn, Mo, Na, and Zn were determined by ICP OES, while Cd, Co, and Pb were determined by ICP-MS. Using diluted HNO₃ solution low blank values were obtained resulting in relatively lower limits of detection and relative standard deviations. The accuracy was evaluated by using certified reference materials of milk powder and bovine liver (agreement was better than 95% to certified values for all evaluated analytes).