RESUMO
In this work, a procedure allowing effective digestion of a high mass of yerba mate (up to 1500â¯mg) using diluted HNO3, 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 7â¯molâ¯l-1 HNO3 and 8â¯bar O2. The digestion efficiency was better than 92% and digests presented a relatively low acidity (<10â¯mmol HNO3). The limit of quantification was 4.0, 1.0 and 1.0â¯ngâ¯g-1 for As, Cd and Pb, respectively. Under optimized conditions up to 1500â¯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.
Assuntos
Contaminação de Alimentos/análise , Ilex paraguariensis/química , Espectrometria de Massas/métodos , Chás de Ervas/análise , Arsênio/análise , Cádmio/análise , Chumbo/análise , Limite de Detecção , Micro-Ondas , Ácido Nítrico/química , Oxigênio , PressãoRESUMO
The present work evaluates the influence of vessel cooling simultaneously to microwave-assisted digestion performed in a closed system with diluted HNO3 under O2 pressure. The effect of outside air flow-rates (60-190 m(3) h(-1)) used for cooling of digestion vessels was evaluated. An improvement in digestion efficiency caused by the reduction of HNO3 partial pressure was observed when using higher air flow-rate (190 m(3) h(-1)), decreasing the residual carbon content for whole milk powder from 21.7 to 9.3% (lowest and highest air flow-rate, respectively). The use of high air flow-rate outside the digestion vessel resulted in a higher temperature gradient between liquid and gas phases inside the digestion vessel and improved the efficiency of sample digestion. Since a more pronounced temperature gradient was obtained, it contributed for increasing the condensation rate and thus allowed a reduction in the HNO3 partial pressure of the digestion vessel, which improved the regeneration of HNO3. An air flow-rate of 190 m(3) h(-1) was selected for digestion of animal fat, bovine liver, ground soybean, non fat milk powder, oregano leaves, potato starch and whole milk powder samples, and a standard reference material of apple leaves (NIST 1515), bovine liver (NIST 1577) and whole milk powder (NIST 8435) for further metals determination by inductively coupled plasma atomic emission spectroscopy (ICP-OES). Results were in agreement with certified values and no interferences caused by matrix effects during the determination step were observed.