Simple determination of L-ascorbic acid on TLC by visual detection using autocatalytic reaction.

The L-ascorbic acid concentration in beverages was measured after separation by silica gel thin layer chromatography (TLC) by visually determining the time in autocatalytic reaction for the L-ascorbic acid spot to turn the same yellow color of the background and disappear (the end time of the induction period) after spraying the slide with a 3,6-dihydroxyxanthane solution. There was a good linear relationship between the end time of the induction period and the concentration of L-ascorbic acid for concentrations in the range of 5.0 - 20 mM (r(2) = 0.9944). In addition, there was a good relationship expressed by a quadratic equation in the concentration range of 0.1 - 5.0 mM (r(2) = 0.9975). The relative standard deviations of the L-ascorbic acid values for 3 beverages (2.2 - 8.6 mM) were less than 5% (n = 5), and the recovery of 5.0 mM L-ascorbic acid from 4 beverages (0.7 - 7 mM) was 97 - 110%. A good correlation was also observed between the L-ascorbic acid values of 23 beverages (0 - 86 mM) determined by the proposed TLC method and the colorimetric method contained in a commercially available kit for L-ascorbic acid (r(2) = 0.9945).