Voltammetric determination of ascorbic acid using carbon paste electrode in ginger samples from selected areas of Ethiopia

Abstract

Carbon paste electrode was prepared for the determination of ascorbic acid in ginger (Zingiber officinale) samples from three ginger growing areas (Chilga, Tepi and Dale Sadi) in Ethiopia.  The effect of pH on the oxidation response of ascorbic acid in 0.1 M phosphate buffer was investigated and pH 2 was chosen as an optimum value. The oxidation response of ascorbic acid was predominantly diffusion-controlled reaction with a better determination coefficient R²= 0.9945 on the plot of anodic peak current vs square root of scan rate. A square wave amplitude of 45 mV, step potential of 7.0 mV and frequency of 25 Hz were chosen as optimum values.  Linear calibration curve in the range of 0.1 – 8.0 mM of ascorbic acid standard in pH 2 phosphate buffer solution was obtained with a determination coefficient of 0.998. The amount of ascorbic acid detected in ginger samples collected from the three areas, Chilga was 6.85, Tepi was 6.59 and Dale Sadi was 6.54 mg/g of ginger powder. Percentage recovery in the range of 93% and 100% was validated for the applicability of the method for the quantitative determination of ascorbic acid in ginger samples. According to Health Canada dietary reference intakes, the maximum amount of ginger powder recommended intake for adult males in Chilga was 13.1, in Tepi 13.7 and in Dale Sadi 13.8 g/day.