Abstract
The method is based on the oxidation of
L-ascorbic acid with potassium hexacyanoferrate (III). Excess of oxidant is determined spectrophotometrically by oxidation of phthalophenone to phenolphthalein in alkaline solution. Linear calibration graphs are obtained for 0–7 μg ml
−1 ascorbic acid at 553 nm, with a detection limit of 0.1 μg ml
−1. Sugars and other organic compounds do not interfere when present in moderate amounts.