DETERMINATION OF COLORANTS IN BINARY-MIXTURES BY DERIVATIVE SPECTROMETRY USING ZERO-CROSSING AND RATIO SPECTRA

Two methods for the simultaneous determination of Ponceau 4R in the pr esence of Carmoisine and Amaranth dyes in binary mixtures are proposed without any separation step. The classical derivative spectrophotomet ry, on the basis of the zero-crossing measurements in the first deriva tive spectra, is used for the resolution of the binary mixtures, as we ll as the other method based on the use of the first derivative of rat io spectra obtained by dividing the amplitudes, at appropriate wavelen gths, of the absorption spectra of the mixtures by a standard of one f or the components, for determining the other. The binary mixtures stud ied were Ponceau 4R-Carmoisine and Ponceau 4R-Amaranth. The methods pr oposed have been applied to determine those colorants in commercial fo od products containing one of these mixtures.