SIMULTANEOUS DETERMINATION OF URIC-ACID, XANTHINE AND HYPOXANTHINE WITH AN ELECTROCHEMICALLY PRETREATED CARBON-PASTE ELECTRODE

A simple method is presented for the simultaneous differential pulse v oltammetric determination of uric acid, xanthine and hypoxanthine. It is based on the improved current responses of the three analytes at ca rbon paste electrodes polarized in a dilute alkaline medium (0.002 mol /l NaOH, 0.1 mol/l NaClO4) at 1.3 V vs. SCE for a short time. Compared with the methods reported in the literature, this procedure has a muc h wider linear range (2 to 3 orders of magnitude in concentration), lo wer detection limits (5 to 10 mug 1(-1) and less interference by ascor bic acid. The electrochemical responses were found to be dependent on the pre-anodization potential and the time imposed on the electrodes a s well as on the alkalinity of the supporting electrolyte. The propose d procedure was used to determine uric acid, xanthine and hypoxanthine in human urine without any preliminary treatment.