POSSIBILITIES AND LIMITATIONS IN MINIATURIZED SENSOR DESIGN FOR URIC-ACID

Uric acid (UA) has been under intensive investigation by electrochemis ts owing to its important role as a metabolite in biological fluids. O ne of the major problems in biological determinations of uric acid com es from electrochemical interferences such as ascorbic acid (AA), whic h has a similar oxidation potential, E-1/2 approximate to 200 mV versu s SCE, at graphite electrodes, and is present at high concentrations i n biological systems. UA undergoes a 2 H+, 2 e(-) oxidation in aqueous buffers, The oxidation product, a diimine, is an unstable intermediat e with a half-life of less than 22 ms. A follow-up hydration reaction converts the diimine to an imine alcohol. Results of previous work sho w that UA weakly adsorbs and undergoes a fast electron transfer reacti on, k(s) = 54 s(-1), at carbon fiber electrodes. These characteristics make UA an excellent candidate for fast scan voltammetric (FSV) deter minations. This paper presents the results of FSV at bare carbon fiber electrodes. The results show good selectivity and sensitivity in the determination of low concentrations of UA in the presence of high conc entrations of AA, By increasing the scan rate above 500 V s(-1), volta mmograms of UA in the presence of AA can be resolved because of the ki netic differences in the response of the two anions, without the need for a permselective film on the electrode. Results are also presented that demonstrate an effective way to reach a stable background current at bare carbon fiber electrodes, which is required in FSV because the signal from the analyte is smaller than the electrochemical signal fr om the background current. Signal-to-noise ratios at bare carbon fiber electrodes in FSV are improved, because the high temporal resolution in fast scan methods allows the acquisition of a large number of scans that can be signal averaged in a short period of time. In addition, l arge signals can be measured because the voltammetric peak current inc reases with increase in scan rate.