AbstractGinsenosides Rb1, Rb2, Rc, Rd, Re, Rf, Rg1, Rg2 and F11 were studied systematically by electrospray ionization mass spectrometry in positive‐ and negative‐ion modes with a mobile‐phase additive, ammonium acetate. In general, ion sensitivities for the ginsenosides were greater in the negative‐ion mode, but more structural information on the ginsenosides was obtained in the positive‐ion mode. [M + H]+, [M + NH4]+, [M + Na]+ and [M + K]+ ions were observed for all of the ginsenosides studied, with the exception of Rf and F11, for which [M + NH4]+ ions were not observed. The signal intensities of [M + H]+, [M + NH4]+, [M + Na]+ and [M + K]+ ions varied with the cone voltage. The highest signal intensities for [M + H]+ and [M + NH4]+ ions were obtained at low cone voltage (15–30 V), whereas those for [M + Na]+ and [M + K]+ ions were obtained at relatively high cone voltage (70–90 V). Collision‐induced dissociation yielded characteristic positively charged fragment ions at m/z 407, 425 and 443 for (20S)‐protopanaxadiol, m/z 405, 423 and 441 for (20S)‐protopanaxatriol and m/z 421, 439, 457 and 475 for (24R)‐pseudoginsenoside F11. Ginsenoside types were identified by these characteristic ions and the charged saccharide groups. Glycosidic bond cleavage and elimination of H2O were the two major fragmentation pathways observed in the product ion mass spectra of [M + H]+ and [M + NH4]+. In the product ion mass spectra of [M − H]−, the major fragmentation route observed was glycosidic bond cleavage. Adduct ions [M + 2AcO + Na]−, [M + AcO]−, [M − CH2O + AcO]−, [M + 2AcO]2−, [M − H + AcO]2− and [M − 2H]2− were observed at low cone voltage (15–30 V) only. Copyright © 2002 John Wiley & Sons, Ltd.