Quenching effect of electrolytes on the fluorescence intensity of riboflavin and thiochrome

After the discovery of riboflavin, and its identifica- tion as vitaminr B,, assay methods based on the measurement of its fluorescence intensity were de- scribed (v. Euler & Adler, 1934; Cohen, 1934; Josephy, 1934). Similar methods of assay were developed for vitamin B1 after Jansen (1936) had shown that thiochrome, the fluorescent oxidation product of thiamin, could be used as the basis for the fluorimetric estimation of this vitamin. These