Abstract
S-Benzoylthiamine monophosphate and S-benzoylthiamine were detected on filter paper by thiochrome reaction after reduction with cysteine into thiochrome positive form. In contrast to aqueous solution, the thiochrome formation on the paper was strongly hindered by the presence of cysteine, thus giving only very weak fluorescence. However, the increase of the intensity of the fluorescence was observed by spraying of mercuric chloride before the formation of thiochrome, as excess SH group of cysteine was oxidized. The procedure was as follows : after spraying of 1% cysteine solution (pH 6.5) and heating for 30 minutes in a fume chamber, the paper was sprayed with 5% HgCl_2 and finally with a mixture of 2 parts of 96% ethanol, 1 part of 10% NaOH and 0.05 parts of 2.5% K_3Fe (CN)_6. This method would be applicable for detection on filter paper of other thiamine derivatives with open thiazole ring.
