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 SC E for a short period of time, exhibit a great shift of the oxidation p otential of uric acid in cathodic direction and a marked enhancement o f its current response, compared to unpretreated electrodes. These eff ects are dependent on the preanodization potential and the time impose d on the electrodes as well as on the alkalinity of the supporting ele ctrolyte. 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 1 0(-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 interf ere. For multiple determinations (5 runs), the relative standard devia tion is 2.1% at a concentration of 1 mg/l uric acid. The proposed proc edure can be used to determine uric acid in human urine and serum with out any preliminary treatment of the samples in an accurate, rapid and simple way.