Simultaneous spectrophotometric determination of three food dyes by using the first derivative of ratio spectra.

Ternary mixtures of colorants E-123 (Amaranth), E-124 (Ponceau 4R) and E-120 (Carminic acid) are resolved by using the first derivative ratio spectrum-zero crossing method without the need for any separation step. Calibration graphs were linear up to 64 mg l(-1) of carminic acid, 32 mg l(-1) of Amaranth and 32 mg l(-1) of Ponceau 4R. The method was applied to different commercial food products and results concordant with high performance liquid chromatography were obtained.