SENSITIVE DETERMINATION OF SUGARS BY CAPILLARY ZONE ELECTROPHORESIS WITH INDIRECT UV DETECTION UNDER HIGHLY ALKALINE CONDITIONS

The separation with capillary zone electrophoresis and indirect UV det ection of underivatized sugars was studied. It was found that the high pH of the background electrolyte which was required for the separatio n resulted in a strong increase of the low-frequency noise and baselin e instability with indirect detection. It was shown that the baseline instability is related to the Joule heat production and insufficient t hermostatting of the capillary. Detection could be strongly improved b y using narrow (25 mu m) capillaries and low voltages, and by instrume ntal measures to promote a uniform heat dissipation along the capillar y. The low-frequency noise and baseline disturbances were found also t o depend on the type of monitoring and counterions in the background e lectrolyte. By optimization of the experimental conditions the workabl e pH range for the separation could be extended to 13. After optimizat ion, limits of detection of approximately 0.05 mmol l(-1) were obtaine d. Calibration plots were linear up to concentrations of 5 mmol l(-1). The reproducibility of migration times was within 0.4%; peak areas we re reproducible within 4%. The method developed was applied to the ana lysis of culture medium samples.