Surface-charge reversed capillary zone electrophoresis of inorganic and organic anions

Anions commonly found in biological fluids such as chloride, citrate, phosphate, bicarbonate, lactate, aspartate and glutamate, were determined within 60 s by means of capillary zone electrophoresis and indirect UV detection using 10 mM of chromate, pH 8.0, as both carrier electrolyte and chromophore. The lower mass detection limit was 0.5 pmol. In order to avoid a gradual shift of the pH and, in consequence, drifting ionic mobilities due to the formation of hydroxyl ions at the cathode, 1 mM of 5,5-diethylbarbiturate was added to the background electrolyte. Moreover, fused silica capillaries were coated with a 0.0003% solution of hexadimethrine bromide for two minutes between runs to reverse electroendosmotic flow which otherwise would counteract the electrophoretic migration of the anions and, hence, increase time of analysis. It is concluded that charge-reversed capillary zone electrophoresis in concert with indirect UV detection is superior to ion chromatography and conductivity detection in the determination of inorganic and organic anions in biological fluids both with regard to selectivity, sensitivity and speed of analysis.