Determination of Saikosaponin Derivatives in Radix bupleuri and in Pharmaceuticals of the Chinese Multiherb Remedy Xiaochaihu-tang Using Liquid Chromatographic Tandem Mass Spectrometry

Saikosaponins are bioactive oleanane saponins derived from the Chinese medicinal herb Radix bupleuri ("chaihu" in Chinese). An LC−MS/MS-based method has been developed for characterization and quantification of 15 saikosaponin derivatives (saikosaponin a, saikosaponin b1, saikosaponin g, saikogenin A, saikogenin H, saikosaponin c, saikosaponin h, saikosaponin i, prosaikogenin C2, prosaikogenin B2, saikogenin C, saikogenin B, saikosaponin d, saikosaponin b2, and saikogenin D) in one chromatographic run. Optimization of the ionization process was performed with electrospray and atmospheric pressure chemical ionization techniques in both positive and negative ion modes. Negative ion ESI was adopted for generation of the precursor deprotonated molecules to achieve the best ionization sensitivity for the analytes. In addition, the most abundant fragment ion was chosen for each analyte to give the best CID sensitivity. Because some of the saponin derivatives are isomeric, complete resolution for the whole analytes was achieved both chromatographically and mass spectroscopically. Furthermore, optimal internal standard was successfully discovered for determination of the analytes by making use of a combinatorial chemistry approach. Good linearity over the range ∼1.65 or 4.98 to 1200 ng/mL for the analytes was observed. The intraday accuracy and precision at nominal low, intermediate, and high concentration varied between 0.8 and 11.8% and between 80 and 116%, respectively, whereas those for interday assay were between 1.1 and 15.5% and between 86 and 119%, respectively. The lower limits of quantitation for the test compounds were ∼16.5 to 49.4 pg on-column. The new method offered higher sensitivity and greater specificity than previously reported LC methods. After the validation, the applicability of the method for determination of these chemicals present in a variety of crude chaihu roots and in different brands of the Chinese multiherb remedy Xiaochaihu-tang (or Shosaiko-to) extract granules has been demonstrated. The sensitivity and specificity of the technique will be the basis of a method for the accurate quantification of the saikosaponin derivatives in biomatrixes.