AN IMPROVED VOLTAMMETRIC METHOD FOR THE DETERMINATION OF TRACE AMOUNTS OF URIC-ACID WITH ELECTROCHEMICALLY PRETREATED CARBON-PASTE ELECTRODES

Carbon paste electrodes, preanodized in alkaline medium at 1.4 V vs SCE for a short period of time, exhibit a great shift of the oxidation potential of uric acid in cathodic direction and a marked enhancement of its current response, compared to unpretreated electrodes. These effects are dependent on the preanodization potential and the time imposed on the electrodes as well as on the alkalinity of the supporting electrolyte. The enhanced voltammetric response can be used to determine uric acid in the concentration range of 5.0-4.0 x 10(4) mug/l (3.0 x 10(-8)-2.4 x 10(-4)M) with a detection limit (3sigma) of 2.0 mug/l (1.2 x 10(-8)M). Ascorbic acid in less than 30-fold excess does not interfere. For multiple determinations (5 runs), the relative standard deviation is 2.1% at a concentration of 1 mg/l uric acid. The proposed procedure can be used to determine uric acid in human urine and serum without any preliminary treatment of the samples in an accurate, rapid and simple way.