Optimizing the separation of food dyes by capillary electrophoresis

In this work, the separation of eleven food dyes was evaluated by MEKC in electrolytes composed of tetraborate (TBS), Brij 35, and acetonitrile (ACN) using a factorial design at the following levels: TBS concentration (5 and 10 mmol L-1), pH (9.5 and 10.1), Brij concentration (5 and 20 mmo L-1), and ACN (5 and 15%). Several response functions were evaluated and indicated 10 mmol L-1 TBS (pH 10.1), 15% ACN, and 20 mmol L-1 Brij 35 as best values. However, baseline resolution was not achieved (R-cp = 0.76) and the method lacked robustness. New conditions were sought by studying the dye mobility versus Brij concentration (5-20 mmol L-1). A set of well resolved and more uniformly spaced peaks was obtained with an electrolyte consisting of 7.5 mmol L-1 TBS (pH 10.1), 10 mmol L-1 Brij, and 15% ACN. Under these new conditions, complete resolution of the 11 dyes was achieved in less than 9 min. Migration time and peak area repeatabilities were better than 1.6% and 5% CV and the LODs were 0.47 to 2.3 mu g mL(-1). The methodology was applied to fruit juice powders, lollipops, and other hard and soft chewable treats.