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 degrees 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 mu M. 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. (C) 2006 Elsevier B.V. All rights reserved.