Determination of Trace Oxalic Acid in Natural Foodstuffs by Inhibition Kinetic Spectrophotometry

It is well known that hydrogen peroxide in dilute H 2SO 4 solution discolorizes bromocresol purple, while oxalic acid can sensitively inhibit the discoloration reaction or slow the reaction rate. The kinetic beha- vior of the inhibition reaction has been investigated and a kinetic spectrometric method for determination of trace oxalic acid was developed with detection limit 2.8×10 -8 g/mL and the linear range of the determination was 0～8×10 -7 g/mL oxalic acid. e 430=1.50×10 5 L/(mol·cm). The method has been satisfactorily applied to the determination of trace oxalic acid in fruits, greens and cereals.