Poly-xanthurenic acid modified electrodes: An amperometric sensor for the simultaneous determination of ascorbic and uric acids

The poly-xanthurenic acid (poly-Xa)/multi-walled carbon nanotube (MWCNT)/glassy carbon modified electrode (poly-Xa/MWCNT/GCE) was successfully applied for the simultaneous determination of ascorbic (AA) and uric (UA) acids. Cyclic voltammetric results show that the modified electrode displays an excellent eletrocatalytic activity toward the oxidation of AA at a low potential (0.05 V versus Ag/AgCl) and anodic peak resolution (ΔEpa), close to 300 mV versus Ag/AgCl, in solutions containing AA and UA. Values in the order of 106 L mol−1 s−1 were obtained for the kinetic constant kcat for the catalytic oxidation of AA, upon evaluation by cyclic voltammetry, chronoamperometry and RDE. Furthermore, the sensor provided limits of detection of 0.19 μmol L−1 and 0.31 μmol L−1 for AA and UA, respectively. The sensor was applied for the simultaneous determination of AA and UA in urine samples and the average recoveries for these samples were 99.9 (±2.5)% and 99.9 (±2.6)%, respectively.