title: Simultaneous voltammetric detection of ascorbic acid, dopamine and uric acid using a pyrolytic graphite electrode modified into dopamine solution.
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), DeltaE(AA-DA)=222 mV; DeltaE(AA-UA)=360 mV and DeltaE(DA-UA)=138 mV, avoiding the superficial poisoning effects. The calculated detection limits were: 1.4x10(-6) mol L(-1) for uric acid, 1.3x10(-5)molL(-1) for ascorbic acid and 1.1x10(-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.
authors.affiliation: Institute of Chemistry, University of São Paulo, C.P. 26077, São Paulo, SP, 05513-970, Brazil.
authors.forename: Robson P
authors.initials: RP
authors.lastname: da Silva
authors.forename: Antonio William O
authors.initials: AW
authors.lastname: Lima
authors.forename: Silvia H P
authors.initials: SH
authors.lastname: Serrano
mesh_terms: D001205:Ascorbic Acid / Q000032:analysis*; D004298:Dopamine / Q000032:analysis*; D004563:Electrochemistry / Q000379:methods*; D004566:Electrodes; D006108:Graphite; D012996:Solutions; D014527:Uric Acid / Q000032:analysis*
chemical_list: D012996:Solutions; D014527:Uric Acid; D006108:Graphite; D001205:Ascorbic Acid; D004298:Dopamine