Simultaneous voltammetric detection of ascorbic acid, dopamine and uric acid using a pyrolytic graphite electrode modified into dopamine solution |
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Authors: | da Silva Robson P Lima Antonio William O Serrano Silvia H P |
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Institution: | Institute of Chemistry, University of São Paulo, C.P. 26077, São Paulo, SP, 05513-970, Brazil |
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Abstract: | Pyrolytic graphite electrodes (PGE) were modified into dopamine solutions using phosphate buffer solutions, pH 10 and 6.5, as supporting electrolyte. The modification process involved a previous anodization of the working electrode at +1.5 V into 0.1 mol L−1 NaOH followed by other anodization step, in the same experimental conditions, into dopamine (DA) solutions. pH of the supporting electrolyte performed an important role in the production of a superficial melanin polymeric film, which permitted the simultaneous detection of ascorbic acid (AA), (DA) and uric acid (UA), ΔEAA-DA = 222 mV; ΔEAA-UA = 360 mV and ΔEDA-UA = 138 mV, avoiding the superficial poisoning effects. The calculated detection limits were: 1.4 × 10−6 mol L−1 for uric acid, 1.3 × 10−5 mol L−1 for ascorbic acid and 1.1 × 10−7 mol L−1 for dopamine, with sensitivities of (7.7 ± 0.5), (0.061 ± 0.001) and (9.5 ± 0.05) A mol−1 cm−2, respectively, with no mutual interference. Uric acid was determined in urine, blood and serum human samples after dilution in phosphate buffer and no additional sample pre-treatment was necessary. The concentration of uric acid in urine was higher than the values found in blood and serum and the recovery tests (92-102%) indicated that no matrix effects were observed. |
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Keywords: | Pyrolytic graphite modified electrode Uric and ascorbic acids Dopamine Biological fluids Differential pulse voltammetry |
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