Determination of flavonoids and ascorbic acid in grapefruit peel and juice by capillary electrophoresis with electrochemical detection

Grapefruit (Citrus paradisi Mact. (Rutaceae)) has been known for its accumulation of flavonoids and ascorbic acid. These contents are important because of their nutritional and antioxidant properties. Five flavonoids (hesperidin, naringin, hesperedin, narigenin and rutin) and ascorbic acid were separated and determined in grapefruit juice by capillary electrophoresis with electrochemistry detection (CE-ED). Two flavonoids (hesperidin, naringin) and ascorbic acid were found in extract of grapefruit peel with the same method. And the distribution comparision of the ingredients between juice and peel was discussed. The effects of several CE parameters on the resolution were studied systematically. Under the optimum conditions, the analytes could be well separated within 25 min in a 60 mmol L−1 borate buffer (pH 9.0). The response was linear over four orders of magnitude with detection limits (S/N = 3) ranging from 1.4 × 10−7 to 1.0 × 10−6 g ml−1 for the analytes. The method has been successfully applied for the analysis of grapefruit with satisfactory results.