Abstract
A new colorimetric method was devised for determination of L-ascorbic acid with pyrrole as a color developing agent in metaphosphoric acid. The addition of cupric sulfate ensures blue color developing. The method was applied to ascorbic acid preparations snch as injection (I), powder (II), tablets (III), multivitamin solution (IV), and multivitamin tablets (V). The test solution was prepared by dissolving I, IV, or extracting II, III, and V in 5% metaphosphoric acid with iodine-oxidation and with charcoal treatment (VI, V). To 5.0ml of the test solution, 0.05ml of 0.1% solution of cupric sulfate (I, II, III), or 20% solution of cupric sulfate (IV, V) and 0.05ml of 20% pyrrole・ethanol solution were successively added, and the mixture was warmed at 50℃. After cooling to 10℃, the developed color was measured at the absorption maximum of 615mμ, with a reagent blank, which followed the Beer's rule in a concentration range of 100 to 500μg/ml. The optimum heating time for the color development was 20 minutes for I, II, III, and 10 minutes for IV and V. Any vitamin, amino acid did not interfere the coloration.
