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A reverse phase liquid chromatographic (LC) method is presented for determining intermediates, subsidiary colors, and 2 reaction by-products in FD&C Yellow No. 6. Gradient elution from 0.02M ammonium acetate to 60% methanol in 0.02M ammonium acetate is performed on a C-8 column. Recoveries of the analytes from samples of FD&C Yellow No. 6 were as follows: 82 to 129% for the intermediate sulfanilic acid added at levels ranging from 0.04 to 0.2%; 85 to 107% for the intermediate Schaeffer's salt added at levels ranging from 0.03 to 0.3%; 91 to 107% for the reaction by-product 4,4'-(diazoamino)-dibenzenesulfonic acid added at levels ranging from 0.01 to 0.1%; 67 to 108% for the reaction by-product 6,6'-oxybis(2-naphthalenesulfonic acid) added at levels ranging from 0.1 to 1%; 88 to 100% for the subsidiary color 3-hydroxy-4-[(4-sulfophenyl)azo]-2,7-naphthaIenedisulfonic acid added at levels ranging from 0.7 to 5%; and 43 to 106% for the subsidiary color 6-hydroxy-5-(phenyIazo)-2-naphthalenesulfonic acid added at levels ranging from 0.1 to 1 %. To further demonstrate the capabilities of the method, results of multiple analyses of several FD&C Yellow No. 6 samples are presented, and results from corresponding analyses by an AOAC ion exchange LC method and by a thin layer chromatographic method are compared with results found with the new reverse phase LC method.