The use of capillary electrophoresis with contactless conductivity detection for sensitive determination of stevioside and rebaudioside A in foods and beverages

•Capillary electrophoresis facilitates the determination of rebaudioside A and stevioside.•Low LOD is achieved by contactless conductivity detection.•Coated capillary with narrow inner diameter provides an efficient separation.•Sample preparation is based only on its dilution and filtration.

Two electrophoretic methods with contactless conductivity detection have been developed for determination of the content of rebaudioside A and stevioside in samples of sweeteners and beverages prepared from extracts of the plant Stevia rebaudiana Bertoni. The total content of rebaudioside A and stevioside can be determined in a fused silica capillary with an inner diameter of 10 μm and total length of 31.5 cm in optimised background electrolyte with the composition 170 mM H3BO3/LiOH (pH 9.0). The combined peak of the two glucosides is characterised by a migration time of 54 s, which completely separates it from EOF. INST coating solution in an amount of 0.5% v/v, which effectively suppresses the electroosmotic flow, was added to the background electrolyte for mutual separation of rebaudioside A and stevioside. The CE method with suppression of EOF is characterised by complete separation of rebaudioside A and stevioside, LOD is 0.3 mg/L (0.1 μM).