Redox spectrophotometric method involving electrolytically generated manganese(III) sulphate with diphenylamine for the determination of ascorbic acid present in the samples of various fruits, commercial juices and sprouted food grains.

A spectrophotometric method was developed for ascorbic acid present in various fruits, commercial fruit juices and sprouted food grains. The method involves the oxidation of ascorbic acid with excess manganese(III) following reduction of unreacted manganese(III) with diphenylamine or barium diphenylamine sulphonate forming a product λ(max) 570 nm the system 1 or 540 nm the system 2 and decrease in the colour intensity is proportional to the concentration of vitamin C with quantification range 0.3-3.0 μg ml(-1). The molar absorptivity and Sandell's sensitivity values of the system 1 and the system 2 were 1.829 × 10(4) and 1.813 × 10(4)mol(-1)cm(-1) and 0.0096 and 0.0097 μg cm(-2) respectively. The stoichiometry was 4:1 between manganese(III) and diphenylamine. The ascorbic acid contents of the same samples were determined separately following the procedures of the developed method as well as the reference method and the results were comparable.