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

Abstract A 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.