Assay of Citrus Flavonoids, Troxerutin, and Ascorbic Acid in Food Supplements and Pharmaceuticals by Capillary Zone Electrophoresis

Capillary electrophoretic method suitable for the assay of citrus flavonoids (hesperidin, diosmin, and rutin), troxerutin, and ascorbic acid in food supplements and pharmaceutical formulations was devised and validated. The separation was carried out at 25 kV in uncoated fused-silica capillary (50 μm i.d.; total length, 32 cm (21 cm to detector); and spectrophotometric detection at 280 nm) maintained at 25 °C with 40 mM sodium tetraborate buffer of pH 9.5 containing 25 % ( v / v ) of methanol as the background electrolyte. The samples were injected hydrodynamically (50 mbar, 6 s). The calibration curves were linear (correlation coefficients r = 0.9994–0.9998) for 0.05–0.50 mg/mL of hesperidin, diosmin, rutin, and troxerutin and 0.10–1.00 mg/mL of ascorbic acid when using cinnamic acid (0.05 mg/mL) as internal standard (IS). The LOQ values (S/N = 10) ranged between 0.02 and 0.04 mg/mL of an analyte. The intra- and interday repeatability of migration times and corrected peak areas was characterized by RSD ≤ 3.6 %. Single CE analysis of a standard mixture containing all five analytes and the IS took less than 11 min. Accuracy of the method was evaluated by the added/found analyte recovery experiments (recoveries, 95.5–99.8 %). The method was applied to the analysis of five commercially available food supplements and pharmaceuticals.