Species discrimination of Radix Bupleuri through the simultaneous determination of ten saikosaponins by high performance liquid chromatography with evaporative light scattering detection and electrospray ionization mass spectrometry

Abstract

A simple, rapid and robust high performance liquid chromatography-evaporative light scattering detection (HPLC-ELSD) method was established for the species discrimination and quality evaluation of Radix Bupleuri through the simultaneous determination of ten saikosaponins, namely saikosaponin-a, -b 1, -b 2, -b 3, -b 4, -c, -d, -g, -h, and -i. These compounds were chromatographed on an Ascentis ® Express C18 column with a gradient elution of acetonitrile and water containing 0.1% acetic acid at a flow rate of 1.0 mL/min. Saikosaponins were monitored by ELSD, which was operated at a 50 °C drift tube temperature and 3.0 bar nebulizer gas (N 2) pressure. The developed method was validated with respect to linearity, intra- and inter-day accuracy and precision, limit of quantification (LOQ), recovery, robustness and stability, thereby showing good precision and accuracy, with intra- and inter-assay coefficients of variation less than 15% at all concentrations. Furthermore, a high performance liquid chromatography–electrospray ionization mass spectrometry (HPLC–ESI-MS) method was developed to certify the existence of ten saikosaponins, as well as to confirm the reliability of ELSD. The extraction conditions of saikosaponins from Radix Bupleuri were also optimized by investigating the effect of extraction methods (sonication, reflux and maceration) and various solvents on the extraction efficiencies for saikosaponins. Sonication with 70% methanol for 40 min was found to be simple and effective for extraction of major saikosaponins. This analytical method was applied to determine saikosaponin profiles in 20 real samples consisting of four Bupleurum species, namely B. falcatum, B. chinense, B. sibiricum and the poisonous B. longiradiatum. It was found that three major saikosaponin-a, -c and -d were the major constituents in B. falcatum, B. chinense, and B. longiradiatum, while one major saikosaponin (saikosaponin-c) was not identified from B. sibiricum. In addition, no saikosaponin-b 3 was detected in B. longiradiatum samples, indicating that the toxic B. longiradiatum may be tentatively distinguished from officially listed Bupleurum species ( B. falcatum and B. chinense) based on their saikosaponin profiles. Overall the simultaneous determination of ten saikosaponins in Radix Bupleuri was shown to be a promising tool to adopt for the discrimination and quality control of closely related Bupleurum species.