Flow injection analysis-amperometric determination of ascorbic and uric acids in urine using arrays of gold microelectrodes modified by electrodeposition of palladium

Abstract

Uric acid (UA) and ascorbic acid (AA) present in urine were rapidly determined by the amperometric method in association with flow injection analysis. An array of gold microelectrodes modified by electrochemical deposition of palladium was employed as the working electrode. Uric and ascorbic acids were quantified in urine using amperometric differential measurements at +0.75 and +0.55 V, respectively. This method is based on three steps involving the flow injection of: (1) the sample spiked with a standard solution, (2) the pure sample, and (3) the enzymatically treated sample. The enzymatic treatment was carried out with ascorbate oxidase, uricase, and peroxidase at pH 7. The calibration curves for freshly prepared ascorbic and uric acid standards were very linear in the concentration ranges of 0.44–2.64 mg l −1 (AA) and of 0.34–1.68 mg l −1 (UA) with a relative standard deviation (RSD) <1 %. For uric acid, the real sample analyses where compared with the classical spectrophotometric method, showing deviations between 3.1 and 8.6% ( n = 9).