Optimized gradients for separation

Optimized gradients for separation of dyes are achieved considering the formation of neutral species from the ionized analytes. A gradient elution prepared by a mixture of sodium acetate buffer (0.1 M and pH 7) with acetonitrile was used for the successful separation of 14 synthetic food colorants in standard solutions [26]. At pH 7 all dyes are suitable for reverse phase chromatography since they are neutral. The colorants were eluted from the column according to increasing polarity. The first colorant eluted from the column was the more polar dye tartrazine, while the last was metanil yellow which presents a single sulfonated group and no alcoholic substituents. Quinoline yellow (E104) consists essentially of sodium salts of a mixture of disulfonates (principally),
monosulfonates and trisulfonates [34]. It shows three peaks corresponding to relative isomers. The sum of the three peaks was used for determination of recoveries and precision validation data. Figs. 1e3 show chromatograms related to three samples spiked with red (group AeB together), yellow (group C)and blue dyes (group D).