Determination of ascorbic acid (Vitamin C) within the citrus juice through the standard addition and calibration curve methods:

Principle:   Ascorbic acid gives a well defined polarographic oxidation wave.

Use freshly prepared diluted juice

Calibration curve method

Prepare a fresh stock solution of 50 cm³ of 0.2% ascorbic acid. Arrange 5 standard solutions of ascorbic acid within volumetric flasks of 25 cm³. To everyone add 0.5 cm³ of 0.5 M acetate buffer and different volumes of 0.2% ascorbic acid, 0, 200, 400, 600 and 800 µdm³. Dilute to the mark along with distilled water. For every solution record polarograms over the potential range -150 to + 200 mV vs Ag/AgCl/1M KCl reference electrode.

Plot i_d vs c of ascorbic acid (calibration curve).