DETERMINATION OF SUGARS BY CAPILLARY ELECTROPHORESIS WITH ELECTROCHEMICAL DETECTION USING CUPROUS-OXIDE MODIFIED ELECTRODES

The separation by capillary electrophoresis and off-column amperometric detection of underivatized sugars has been studied. A palladium-metal union was used as grounded cathode to decouple the high separation voltage before detection. With a second piece of capillary the field decoupler was connected to a home-made T-shaped detection cell. Cuprous oxide modified microelectrodes were prepared and evaluated. For the detection of sugars they were operated at a constant potential of + 0.60 V. The peak-height reproducibility with these electrodes over a period of 18 h (25 injections) was within 7% absolutely and within 4% when one of the analytes was regarded as internal standard. To preserve the flat electroosmotic flow profile in the separation capillary, pressure compensation was applied. The contribution of various sources to the system zone variance was studied. Under optimized conditions plate numbers of over 100 000 were obtained. For the baseline separation of a mixture of sugars 0.10 mol 1(-1) sodium hydroxide solutions had to be used as background electrolyte. Detection limits of 1-2 mu mol 1(-1) were found for various carbohydrates.