To improve the quantification sensitivity of large molecular weight compounds--with ginsenosides as example

High cone voltage was used to improve the quantification sensitivity of large molecular weight compounds in high-performance liquid chromatography electrospray ionization mass spectrometry (HPLC/ESI-MS), with ginsenosides as example. Investigations on the effect of cone voltage showed that within a voltage range of 30-130 V, for all the ginsenosides tested, i.e., Rb(1), Rb(2), Rc, Rd, Re, R(f) and R(g1), an increase in the applied cone voltage can significantly increase the sensitivity of the method. The maximum sensitivity in the determination decreases with the decreasing molecular weight of the ginsenosides in the order of Rb(1) > Rb(2) > Rc > Re > Rd > R(g1) > R(f). At the high cone voltage of 130 V, both molecular weight and structural information was obtained from a single mass spectrum. It can also be used for isomer differentiation and determination of O-glycosidic linkages in ginsenosides. Linear relationships between the peak area response and concentration were observed in the range of 50-2 x 10(5) ng/mL, with the correlation coefficients >0.99. The limits of detection reached down to pg for ginsenosides. The method was successfully applied to the determination of ginsenosides in commercial ginseng samples.