Determination of L- Ascorbic Acid in Plasma by Voltammetric Method

Voltammetric techniques have been considered as important methods among the analytical techniques used for the identification and determination of trace concentrations of many biological molecules such as L-ascorbic acid (AA). L-ascorbic acid is an electro-active molecule, though it is difficult to determine its value directly with a majority of electrodes made of carbon and transition metals, because of electrode surface problems. The present study is based on I-E curves for AA analysis at various pH. Furthermore, the effects of the presence of other electro-active substances; such as copper, as well as the effect of the sweep rate of potential will be studied. The present study is based on analysis of the current-voltage curves for L-ascorbic acid at varying pH and sweep rate scan values. An analysis was also carried out to measure the influence of the concentration of some electro active species. The peak height of the first oxidation wave is used for L-ascorbic acid assay. L-ascorbic acid was determined in aqueous media by linear-scan voltammetry on a gold electrode; ranging between (1-175 µg/mL). In biologic samples, for elimination of uric acid or some sugars and effects, a significant interference of copper ions whose presence reduces the height of the L-ascorbic acid oxidation peak was used. The optimum pH and sweep rate were 3.2 and 7500mV/s, respectively. Under these conditions, the detection limit of the method was 0.3 µg/mL. Repeatability of the method based on relative standard deviation (RSD) 50, 10 and 1 µg/mL concentrations was 0.83, 2.1 and 10.3%, respectively. The calibration curve was linear over the range 1-175µg/mL (r2 = 0.9977, p < 0.001). The advantage of this method lies in the fact that the use of copper eliminates the interference of different substances such as uric acid.