Determination of ascorbic acid in vegetables and fruits by differential pulse polarography

Abstract

AbstractA method for the determination of ascorbic acid in vegetables and fruits using differential pulse polarography has been developed. The extraction medium recommended is a mixture of oxalic acid (1%), trichloroacetic acid (2%) and sodium sulphate (1%), and simple filtration is used to remove the residue. An acetate buffer (2M) is recommended to keep the pH at 4.5. The polarograms were recorded using a modulation amplitude of 50mV, a scan rate of 2mVs−1, and a drop time of 1 s. The precision of the procedure was found to be 1.4% at the 1 mg litre−1 level of ascorbic acid. The calibration graph was linear in the range of 0–20 mg litre −1 of ascorbic acid with a slope of 0.48μA mg litre−1. Most common anions and cations did not interfere, however, Fe3+ and EDTA interfered, and Br− and I− seriously interfered with the determination. The method was applied to determine the ascorbic acid content of a number of vegetables and fruits using the standard‐addition calibration.