Method development for the determination of coumarin compounds by capillary electrophoresis with indirect laser-induced fluorescence detection

A capillary zone electrophoresis (CZE) with indirect laser-induced fluorescence detection (ILIFD) method is described for the simultaneous determination of esculin, esculetin, isofraxidin, genistein, naringin and sophoricoside. The baseline separation was achieved within 5 min with running buffer (pH 9.4) composed of 5 mM borate, 20% methanol (v/v) as organic modifier, 10−7 M fluorescein sodium as background fluorophore and 20 kV of applied voltage at 30 °C of cartridge temperature. Good linearity relationships (correlation coefficients >0.9900) between the second-order derivative peak-heights (RFU) and concentrations of the analytes (mol L−1) were obtained. The detection limits for all analytes in second-order derivative electrophoregrams were in the range of 3.8–15 μM. The RSD data of intra-day for migration times and second-order derivative peak-height were less than 0.95 and 5.02%, respectively. This developed method was applied to the analysis of the courmin compounds in herb plants with recoveries in the range of 94.7–102.1%. In this work, although the detection sensitivity was lower than that of direct LIF, yet the method would extend the application range of LIF detection.