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Detection of added L-ascorbic acid in fruit juices by isotope ratio mass spectrometry

Gensler, M., Rossmann, A., Schmidt, H.L.
Journal of agricultural and food chemistry 1995 v.43 no.10 pp. 2662-2666
fruit juices, ascorbic acid, degradation, dehydroascorbic acid, adulterated products, carbon, stable isotopes
A method for the isotope effect free isolation of L-ascorbic acid from fruit juices has been developed. It consists of an anion exchange cleanup procedure and a subsequent liquid chromatography separation on a reversed phase column and implies a preceding reduction of L-dehydroascorbic acid. The recovery of L-ascorbic acid from model mixtures and spiked juices with this method was between 62 and 64%, but the delta13C value difference between the applied and recovered test compound did not exceed 0.2 per thousand. While commercial L-ascorbic acid has in general delta 13C values near -11.3 per thousand, the mean delta13C value of vitamin C from authentic orange juices is -20.7 per thousand, and that of the corresponding sugar is -25.5 per thousand. These differences are the basis for the determination of an addition of synthetic L-ascorbic acid to fruit juices, and it is shown with spiked samples that less than 20% of added commercial product can be identified.