Comparison of manual and benzenesulfonyl chloride-semiautomated thiochrome methods for determination of thiamine in foods.

A semiautomated procedure was used to measure the fluorescence of sample extracts before and after the addition of benzenesulfonyl chloride (BSC). Addition of BSC inhibited thiochrome formation and provided a more representative blank based on the fluorescence of all the reactants except thiochrome. Thiamine standard was added to each sample extract so that thiamine concentration could be calculated after correcting for sample matrix effects on thiochrome fluorescence. Twenty food products were analyzed using this method, and the results were compared with those obtained using the manual AOAC method. The mean percent recoveries and standard deviations were 100.2 +/- 5.3 and 101.1 +/- 10.1 for the BSC-semiautomated and the AOAC manual methods, respectively. Replicate analyses using the BSC method gave an average coefficient of variation of 2.8%. Linear regression analysis showed that the BSC method gave higher values, with a mean increase of 14.8%, than those obtained using the manual method. Sixty-four percent of this difference was due to elimination of the column purification step and 36% was due to correcting for sample matrix effects on thiochrome and blank fluorescence. The BSC method provides a rapid, accurate, and reproducible method for thiamine assay in different food products, especially for those foods with low thiamine levels.