Automatic Determination of Uric Acid in Urine in a FIA System with a Tubular Amperometric Detector

Abstract

This paper describes the use of a FIA system for the automatic determination of uric acid in urine, using a tubular amperometric detector. In this system, glassy carbon electrodes of tubular configuration were activated by successive cyclical scans from - 0.30 to 2.00 V versus Ag/AgCl reference electrode in 0.50 mol.L -1 sulphuric acid solution. Samples were diluted in supporting electrolyte before analysis and no other pre-treatment was employed. Such dilution enabled the matrix effects to be reduced and therefore improving the sensitivity provided by the activation step that allows the uric acid (UA) to be detected at lower concentration levels after dilution. Uric acid determination was performed in a single channel FIA manifold, which provided reproducibility of sample transport to the detector and enabled a sampling rate of 120 samples per hour to be achieved. The tubular configuration of the cell offered robustness to the system since it was rigidly fixed to the manifold, allowing the manifold to be generalised for routine analysis application. The results obtained with the FIA system for UA determination in urine were compared with those from the enzymatic method used in clinical analysis laboratories. No statistical difference between methods was found at the 95% confidence level. Relative deviations between both methods were within ± 4% and the proposed system showed good repeatability (about 3%, n = 10).