Chemical reduction of FD&C yellow No. 5 to determine combined benzidine

Data are presented suggesting the presence of the aromatic amine benzidine as a combined impurity in the regulated color additive FD&C Yellow No. 5. The benzidine exists as an azo-dye constituent that forms from free benzidine impurities introduced during the manufacture of the color additive. The presence of combined benzidine is ascertained by sodium dithionite reduction of the azo bonds in the commercial color additive. The resulting reduction products are extracted with chloroform, and the liberated benzidine is determined by high-performance liquid chromatography (HPLC). The levels of benzidine determined by HPLC exceed those levels of benzidine accounted for by direct determination of free aromatic amines in the unreduced color.