Mikrochimica Acta [Wien] 1975II, 699--704 9 by Springer-Verlag 1975 Contribution from Pakistan Council of Scientific and Industrial Research Laboratories, Lahore-16, Pakistan Modified Method for the Estimation of Ascorbic Acid from Preserved Juices and Squashes By M. Sarwar, Zafar Iqbal* and Shaheen Zaidi (Received July 24, 1973. Revised May 7, i974) Introduction The common method for the estimation of vitamin C is with 2,6-dichlorophenolindophenol. This method is only useful for pure solution. Serious difficulties arise when it is applied to biological samples, where other substances like glucose, fructose, urea, esters, alcohols and iron salts are present 1. To overcome this difficulty, Barakat et al. 2 used N-bromosuccinimide for the selective oxida- tion of ascorbic acid where other reducing substances did not inter- fere. However, this method did not give satisfactory results when it was tested on preserved juices and squashes which contain meta- bisulfite as preservative. Because the oxidation potential of sulfite is 0.17 volts in acid medium, which is less than that of ascorbic (0.33 voltsS), sulfite will be oxidized first as compared to ascorbic acid, thus causing erraneous results. Nazar and co-workers4 have proposed to complex bisulfite by using formaldehyde, but the meth- od was found by us to be irreproducible. We attribute the reasons for this behaviour that excess of formaldehyde also reacts with N-bromosuccinimide. It has been found that formaldehyde combines with ascorbic acid 5. As estimation of vitamin C from juices and squashes is of importance, we have modified the method by using acetone as the complexing agent. Acetone has marked advantage over formal- * Institute of Chemistry, University of the Panjab, Lahore, Pakistan.