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), Δ E AA–DA = 222 mV; Δ E AA–UA = 360 mV and Δ E DA–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.
Published Version
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