DETERMINATION OF CARBOHYDRATES IN FRUIT JUICES BY CAPILLARY ELECTROPHORESIS AND HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

A capillary zone electrophoresis (CZE) method with indirect UV detecti on was adapted for the routine determination of carbohydrates in a var iety of fruit juices. The method was optimized with respect to the eff ect of buffer pH, temperature and capillary length. Potassium sorbate was chosen as the background electrolyte and chromophore for UV detect ion at 256 nm. Optimum separation conditions were found with a buffer of a pH of 12.2-12.3 and a subambient temperature of 15 degrees C. The optimized CZE method was compared with a routine method for the deter mination of sugars in fruit juices, a high-performance anion-exchange chromatographic method with pulsed amperometric detection (HPAEC-PAD), with respect to separation efficiency, sensitivity, linearity and rep eatability. The CZE method showed a 10-20-fold increase in separation efficiency compared with the HPAEC-PAD method, but the amperometric de tection in the latter proved to result in detection limits of 2-3 orde rs of magnitude lower than those obtained by indirect UV detection. Bo th methods showed good linearity in the investigated concentration ran ges and good repeatability for migration times and peak areas. CZE wit h commercial instrumentation was applied to the routine determination of carbohydrates in fruit juices such as orange, apple and grape juice . The quantitative CZE results with internal calibration showed no sig nificant differences from those for the HPAEC-PAD reference method. It was demonstrated that capillary electrophoresis (CE) can be applied i n a routine food testing laboratory. The method is simple, inexpensive and easy to implement and will further broaden the application range of CE in food analysis.