Resumo

CARMO, D. Ribeiro do; SILVA, R. Moutinho da  e  STRADIOTTO, N. Ramos. Electrochemical Behaviour of Copper Nitroprusside Generated in situ Onto the Graphite Paste Electrode Surface, and its Application in the Determination of N-Acethylcysteine. Port. Electrochim. Acta [online]. 2005, vol.23, n.4, pp.457-470. ISSN 0872-1904.

Copper nitroprusside (CuNP) was generated on the graphite paste electrode using a new methodology of the preparation. The electrochemical studies were carried out by cyclic voltammetry technique. The cyclic voltammogram of the modified electrode, CuNP showed two redox couples (E^0’)₁=0.22 and (E^0’)₂=0.88 V vs. SCE attributed to Cu^(I)/Cu^(II) and Fe^(II)(CN)₅NO/Fe^(III)(CN)₅NO, respectively. The nature of the cation affect the (E^0’)₁ and (E^0’)₂, as current intensity, shifting the E^0’ for more positive potentials, for two redox processes. The voltammograms obtained with different KCl concentrations (0.1-3.0 mol L^-1) exhibit a shift in the (E^0’)₁ to more positive potentials; this change was linear with the supporting electrolyte concentrations change. It was verified that the (E^0’)₁ remained practically constant at pH between 6 and 3. However, a new process with (E^0’)₃ (0.48 V) appears at pH<3 and it was ascribed to formation of intermediary species. The redox couple at (E^0’)₂=0.88 V presents an electrocatalytic response for N-acethylcysteine. The modified graphite paste electrode gives a linear response between 5.0´10^-4 to 1.0´10^-2 mol L^-1 of N-acethylcysteine with a detection limit of 4.5´10^-4 (±5%) mol L^-1 (n=3) and an amperometric sensitivity of 4.9 mA/mmol L^-1. The electrocatalytic oxidation of N-acethylcysteine compounds by the mediator has been used for the determination of N-acethylcysteine in a commercially pharmaceutical available product.

Palavras-chave : copper nitroprusside; modified electrode; electrocatalysis; N- acethylcysteine; oxidation.

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