Observations on the estimation of ascorbic acid by titration

THE work of Tillmans et al. [1932], of Harris and Ray [1933] and of others on the estimation of vitamin C by titration against phenolindophenol has offered an opportunity to investigate quickly the antiscorbutic activity of foodstuffs.Since no information in this respect was available regarding Canadian foods, it seemed advisable to make a series of measurements.It was soon found that several modifications in the available procedures could be made to render the estimation more convenient and more accurate.We have employed the procedure of Harris and Ray [1933] with the following modifications.(a) The indicator, 2:6-dichlorophenolindophenol, was made up in a phosphate buffer solution, PH 7-2.In this solution the indicator was found to be fairly stable, but daily standardisation is essential.(b) The indicator was standardised against ferrous ammonium sulphate according to the method of Tillmans, Hirsch and Hirsch [1932].Since both ferrous ammonium sulphate and ascorbic acid reduce the indophenol indicator, it was possible, through the medium of the indicator, to standardise the sulphate solution against pure ascorbic acid crystals.The slightly acidified solution of ferrous ammonium sulphate when kept under an atmosphere of nitrogen in an auto- matic burette showed no.deterioration in 6 months.