Qualitative and quantitative analysis of iridoid glycosides in the flower buds of Lonicera species by capillary high performance liquid chromatography coupled with mass spectrometric detector

A highly sensitive and specific method, based on capillary high performances liquid chromatography coupled with single quadrupole mass spectrometry using electrospray ionization (capillary HPLC-ESI/MS), is proposed for the identification and quantification of iridoid glycosides in the flower buds of five Lonicera species. A Zorbax SB-C18 (0.3 mm × 150 mm, 5 μm) capillary column and a gradient elution with methanol-acetonitrile-aqueous acetate acid were utilized. The most intensive electrospray ionisation signals were found in the negative ion spectra owing to CH₃COO⁻ adducts. Eight iridoid glycosides derived from the flower buds of Lonicera species were analyzed by mass spectrometry: sweroside (IG1), 7-O-ethyl sweroside (IG2), 7-epi vogeloside (IG3), secoxyloganin (IG4), secoxyloganin 7-butyl ester (IG5), dimethyl-secologanoside (IG6), centauroside (IG7), and loganin (IG8) using combined information on retention time, the molecular ion mass and fragment ion masses. Detection limits were lower than 1.9 ng/mL in selected ion monitoring (SIM) mode and all calibration curves showed good linear regression (r² > 0.9938) within test ranges. The validated method was successfully applied to analyze eight iridoid glycosides in the flower buds of five Lonicera species and provided a new basis of assessment on quality of Flos Lonicerae.