MODIFIED FLUORIMETRIC PROCEDURE FOR THE SIMULTANEOUS DETERMINATION OF THIAMIN AND RIBOFLAVIN IN COWPEA

The fluorimetric methods for the assay of thiamin and riboflavin have been modified so that the same sample extract may be used for the simultaneous analysis of the two B vitamins. The procedure eliminates acid hydrolysis and specific pH adjustment for either vitamin; the sample extract is obtained after enzymic hydrolysis only with Clarase and has a pH of 4.5-4.8. A standard additions method for thiamin determination is introduced. A cowpea sample analysed by this procedure gave mean recoveries and standard errors of 103.9 ± 1 and 100.5 ± 2% for added thiamin and riboflavin, respectively; the detection limits for the aqueous solutions taken for fluorescence measurement according to the described procedures for these two vitamins are 0.0025 and 0.0020 μg ml-1, respectively.