The alleged antithiamine activity of o-diphenols: an artefact of oxygen in the thiochrome method?

1H-n. m. r. and t. l. c. measurements show that ortho-diphenols induced little or no chemical change in thiamine when co-dissolved in aqueous solution at pH 7.8. Thiamine determinations on the same solutions by the classical thiochrome method are critically susceptible to the amount of dissolved oxygen. An oxygen saturated equimolar solution of thiamine and pyrocatechol (0.03 mM), after 24 hours at pH 7.8 and at 37 degree, gives almost no thiochrome fluorescence response unless the solution is first degassed to remove all traces of oxygen. It is suggested that earlier literature reports of the pronounced anti thiamine effect of o-diphenols were erroneously based on this apparent disappearance of thiamine when oxygen is not excluded.