SEPARATION OF SYNTHETIC FOOD COLORANTS BY CAPILLARY ZONE ELECTROPHORESIS IN A HYDRODYNAMICALLY CLOSED SEPARATION COMPARTMENT

Separation conditions enabling the complete resolution of eleven permi tted synthetic food colourants and some of their subspecies by capilla ry zone electrophoresis (CZE) were determined. Those conditions involv e combining a suitable pH of the carrier electrolyte (pH 6.8) with hos t-guest complexation effects of beta-cyclodextrin. A 300 mu m I.D. cap illary tube made of fluorinated ethylene-propylene copolymer in a hydr odynamically closed separation compartment was used for the CZE separa tions. The capillary could accommodate 90-nl sample injection volumes, thus providing limits of detection for the dyes of 11-300 ppb using a photometric detector operating at a wavelength of 254 nm. R.S.D.s of 0.4-3.0% were typical for the determinations of the dyes present in sa mples at 16 ppm concentrations. Erythrosine, exhibiting residual adsor ption, gave more-scattered results under identical working conditions (R.S.D. of ca. 9.0%). The utility of this rapid CZE procedure (migrati on times of the dyes were 2.5-10.5 min) is illustrated for several pra ctical samples, including soft drink concentrate and liqueur and monit oring of the stability of aqueous solutions of indigo carmine.