Determination of toxic elements in yerba mate by ICP-MS after diluted acid digestion under O₂ pressure

In this work, a procedure allowing effective digestion of a high mass of yerba mate (up to 1500 mg) using diluted HNO_3, in a system pressurized with oxygen, is proposed. Digests were suitable for direct analysis by ICP-MS, virtually free of interferences. Digestion was performed using 7 mol l^-1 HNO₃ and 8 bar O₂. The digestion efficiency was better than 92% and digests presented a relatively low acidity (<10 mmol HNO₃). The limit of quantification was 4.0, 1.0 and 1.0 ng g^-1 for As, Cd and Pb, respectively. Under optimized conditions up to 1500 mg of sample were digested and no interferences were observed during analyses by ICP-MS, making this approach suitable for routine determination of As, Cd and Pb in yerba mate and also in agreement with the quality control requirements.