Simultaneous voltammetric determination of dopamine and ascorbic acid using multivariate calibration methodology performed on a carbon paste electrode modified by a mer-[RuCl3(dppb)(4-pic)] complex

Abstract

A preparação e caracterização eletroquímica do eletrodo de pasta de carbono (EPC) modificado com o mer- [RuCl 3 (dppb)(4-pic)] (dppb= Ph 2 P(CH 2 ) 4 PPh 2 , 4-pic= CH 3 C 5 H 4 N), denominado Rupic, foi investigada. O sistema EPC/Rupic apresentou apenas um par de picos com potencial médio de 0,28 V vs. Ag/AgCl, o qual foi atribuído ao processo de transferência de elétrons do Ru III /Ru II . Este eletrodo modificado apresentou a propriedade de eletrocatalisar a oxidação da dopamina (DA) e do ácido ascórbico (AA) em 0,35 V e 0,30 V, respectivamente. Como a oxidação dos analitos, AA e DA, ocorreu praticamente no mesmo potencial, não foi possível a distinção dos sinais voltamétricos utilizando-se a voltametria cíclica. Esta limitação foi resolvida empregando-se a Regressão de Mínimos Quadrados Parciais (PLSR), a qual permitiu a determinação de quatro amostras sintéticas, com erros de previsão (RMSEP) de 5,55×10 -5 mol L -1 e 7,48×10 -6 mol L -1 para DA e AA, respectivamente.The preparation and electrochemical characterization of a carbon paste electrode (CPE) modified with mer-[Ru0Cl 3 (dppb)(4-pic)] (dppb=Ph 2 P(CH 2 ) 4 PPh 2 , 4-pic=CH 3 C 5 H 4 N), referred to as Rupic, were investigated. The CPE/Rupic system displayed only one pair of redox peaks, with a midpoint potential at 0.28 V vs. Ag/AgCl, which were ascribed to Ru III /Ru II charge transfer. This modified electrode presented the property of electrocatalysing the oxidation of dopamine (DA) and ascorbic acid (AA) at 0.35 V and 0.30 V vs. Ag/AgCl, respectively. Because the oxidation for both AA and DA practically occurred at the same potential, distinguishing between them was difficult with cyclic voltammetry. This limitation was overcome using Partial Least Square Regression (PLSR), which allowed us, with the optimised models, to determine four synthetic samples with prediction errors (RMSEP) of 5.55×10 -5 mol L -1 and 7.48×10 -6 mol L -1 for DA and AA, respectively. Keywords: carbon paste electrodes, ruthenium complexes, dopamine, ascorbic acid, multivariate calibration methodology IntroductionConsiderable progress has been made over the last few years on chemically modified carbon paste electrodes, having an easier and faster procedure to assemble and renew the paste surfaces, low cost, background currents and possibility to incorporate a series of materials. [1][2][3][4][5] Among the materials that may be used in conjunction with carbon paste are the ruthenium-containing compounds such as oxides, mixed valence compounds and complexes. These Ru-based materials possess electrocatalytic properties, which have been used to modify electrodes for electroanalysis of ascorbic acid, 6,7 L-dopa, 8 glucose, 9 benzylic compounds 10 and dopamine. 11 Dopamine (DA) and ascorbic acid (AA), in particular, are relevant from the biomedical and neurochemical point of view, for their importance to human metabolism. DA is involved in the functioning of the central nervous system, in addition to the cardiovascular, renal and hormonal systems, and plays an important role in ...

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“…DA, ascorbic acid (AA) and uric acid (UA) usually coexist in physiological samples such as blood and urine [15], and the AA concentration (0.2-0.4 mM) is generally 100 to 1000 times that of DA. This makes it difficult to detect DA electrochemically because AA and UA can be oxidized at a potential close to that of DA at bare electrodes.…”

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