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.

Simultaneous determination of carminic acid, riboflavine, curcumin and erythrosine by derivative spectrophotometry and ratio spectra derivative.

A quaternary mixture of carminic acid, riboflavine, curcumin and erythrosine can be resolved with a previous extraction step into metyl-isobutyl ketone and, resolving the binary mixtures obtained in the aqueous phase and organic phase, using derivative spectrophotometry on the basis of the zero-crossing measurements in the first derivative spectra as well as the first derivative of ratio spectra. The conditions of extraction established and the proposed methods have been tested to determine these colorants in several synthetic mixtures of four dyes, obtaining good recoveries. The methods have been applied in yoghurt samples spiked with the dyes.