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Exploitation of a simple redox reaction between manganese(III) and o-tolidine for a highly sensitive spectrophotometric determination of ascorbic acid

Mahadevaiah, Mansour S.Abdul Galil, M.S.Yogendra Kumar, M.A.Sathisha, M.S.Suresh, M.D.Gowtham, C.Vijaya Bhaskar, G.Nagendrappa

A simple and highly sensitive spectrophotometric method for the determination of ascorbic acid is described. The developed method is based on a redox reaction in thatMn(III) generated electrolytically is taken in excess, which is oxidizing a known but a less quantity of vitaminCand the unreacted oxidantwill oxidize further o-tolidine to produce a orange yellowquinonedi imine absorbing cation(max. 455nm). Therefore, in principle, the decrease in colour intensity of the absorbing system is proportional to the concentration of vitaminC. The stoichiometry betweenMn(III) and o-tolidine and stability of the complex were determined by Job’smethod, the corresponding values obtainedwere 2:1 and 1.58105 lmol-1. The systemwas found to be obeying Lambert-Beer’s lawin the range, 0.08-0.8mg l-1 of ascorbic acid. Molar absorbtivity, correlation coefficient, and Sandell’s sensitivity valueswere also calculated and found to be 4.4359103, 0.9987 and 0.0397g/ cm-2 respectively. The reliability of the new method was tested by parallel determination of ascorbic acid in standard, pharmaceutical and fruit samples using a standard method. The results of vitamin C obtained from both the methods were comparable with one another and the reliability and reproducibility of the newmethod were concluded by F and t test values. Therefore, the newmethod could be employed effectively for the determination of ascorbic acid in standard and other samples either as an independent high sensitive spectrophotometric method or a complimentary method to officialmethod.