Separation and determination of dyes by ion-pair chromatography

A reverse phase ion-pair high performance liquid chromatographic method is presented to determine six food dyes (E-110, E-120, E-122, E-123, E-124 and E-127). The tetrabutylammonium ion (TEA) is used as counter-ion in the mobile phase. The separation was accomplished with a Nova-pack C-18 column using methanol -NaH2PO4/Na2HPO4 pH=7 buffer solution 0.1M containing TBA 0.05 M as mobile phase. The chromatograms were monotorized by measuring the absorbance at 520 nm. The influence of methanol content, counter ion concentration, pH and now-rate of the mobile phase were investigated. In the chromatographic conditions selected, the total chromatogram was obtained in seven minutes. The calibration graphs were established by measuring the peak area in the chromatograms. Determination limits ranging from 1 to 7.8 ng were obtained. Samples containing the six dyes in different proportions were analyzed through the proposed method, obtaining good recoveries in all cases. Finally, the method was successfully applied to the analysis of dyes in several commercial products.