Determination of 5,7’-Disulfo-3,3’-dioxo-Δ2,2’-biindoline, Disodium Salt, and 5-Sulfo-3,3’-dioxo-Δ2,2’-biindoline, Sodium Salt, in FD&C Blue No. 2

Abstract A partition chromatographic procedure is presented which separates 5,7’-disulfo-3,3’- dioxo-Δ2,2’-biindoline (disodium salt) and 5-sulfo-3,3’-dioxo-Δ2,2’-biindoline (sodium salt) from FD&C Blue No. 2. The separated colors are determined spectrophotometrically. Recoveries of the former, added at 5 to 15%, ranged from 86 t o 101%. Recoveries of the latter, added at 1 to 5%, ranged from 78 to 95%. Commercial samples of FD&C Blue No. 2 analyzed by this procedure contained 0.7–15.6% of the isomer and 0.5–2.4% of the monosulfonated subsidiary color.