Determination of polyphenols in apple juice and cider by capillary electrophoresis with electrochemical detection

A simultaneous determination of phloridzin, (−)-epicatechin, chlorogenic acid and myricetin in apple juices and ciders by capillary electrophoresis with electrochemical detection (CE-ED) was reported. Effects of several important factors such as the pH and concentration of running buffer, separation voltage, injection time and detection potential were investigated to acquire the optimum conditions. Under the optimum conditions, the analytes could be separated within 20 min in a 75 cm length capillary at a separation voltage of 18 kV in a 50 mmol/l borate buffer (pH 8.7). A 300 μm diameter carbon disk electrode generates good response at +0.90 V (vs. SCE) for all analytes. The relationship between peak currents and analyte concentrations was linear over about three orders of magnitude with detection limits (S/N = 3) ranging from 1 × 10−7 to 5 × 10−7 g/ml for all analytes. This proposed method demonstrated long-term stability and reproducibility with relative standard deviations of less than 4% for both migration time and peak current (n = 7). It has been successively used for the determination of the analytes in apple juices and ciders, and the assay result was satisfactory.