Micelle catalysed methylene blue reduction by ascorbic acid: A procedure for the determination of Vitamin C in pharmaceutical samples

A new spectrophotometric method for ascorbic acid determination has been de scribed. Methylene blue (MB) being a water-soluble, non-toxic, cationic dye (lambda (max) 660 nm), has been observed to be immobilized successfully in the Stern layer of a cationic micelle (cetyl trimethyl ammonium bromide, C TAB) through hydrophobic interaction. The immobilized dye (lambda (max) 660 nm) is quantitatively reduced by ascorbic acid (AA) in the alkaline medium (pH > 8.5). The progress of the reaction and stepwise bleaching of the blu e colour of the dye gives a quantitative measure of ascorbic acid concentra tion. A single aliquot of the micelle stabilized MB could be used for the d etermination of ascorbic acid in the range of 50-400 ppm.