Abstract
After the pressure decomposition of biological sample materials with 69% nitric acid at 180°C, organic decomposition products frequently remain, leading to interference effects during inverse voltammetric trace metal determination. It is shown by the example of the determination of Zn, Cd, Pb and Cu by inverse square-wave voltammetry that the interference signals are caused by the two-stage reduction of nitrated benzoic acids to amines at the mercury electrode. Nitrobenzoic acids arise in the degradation of phenylalanine during decomposition. In addition, they also cause, as do oxidation products of tryptophan, an increased current due to hydrogen deposition in the potential range of Zn oxidation. Decomposition solutions of biological materials free from phenylalanine and tryptophan, on the other hand, can be analysed by inverse voltammetry without any interference.
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