Determination of the unsulfonated color concentration from D&C Yellow No. 10 by the derivative spectrophotometry

Abstract

The method that we used is based on the measurement of the first derivative of the mixture of the two colorants at the wavelength for which one of them has the first derivative equal to zero.The Code of Federal Regulations (21 CFR 74.1710) specifies for D&C Yellow No. 10 the maximum permitted levels of an unsulfonated subsidiary color and of diethyl ether-soluble matter other than that specified.In the proposed method a color additive sample is dissolved in water and the unsulfonated subsidiary color are extracted from this solution with dichloromethane. The analysts in dichloromethane solution are determined by spectrophotometry.The unsulfonated subsidiary colors determined are:– D&C Yellow No. 11 [2-(2-Quinolinyl)-1H-indene-1,3(2H)-dione] (Y11), from which D&C Yellow No. 10 is manufactured by sulfonating and– 1,5-Naphthyridinequinophthalone (1,5-NQ).Another compound soluble in water and dichloromethane (which I called S) is present in dichloromethane solution after extraction together with the other two colors and can affect the correct determination of the concentrations. The dichloromethane-soluble matter other than specified is a mixture consisting mostly of chlorinated derivatives of the unsulfonated subsidiary color. Because the S color is present both in aqueous and in dichloromethane solutions, the spectra of calibration solutions should be corrected. The applied correction does not affect the determination of the unsulfonated subsidiary colors concentrations.D&C Yellow No. 11 and 1,5-NQ are used as standard for unsulfonated subsidiary colors.