Identification of ivermectins by high performance liquid chromatography-electrospray-mass spectrometry-mass spectrometry

8 fractions of commercial ivermectin were isolated and identified by high performance liquid chromatography-electrospray-mass spectrometry-mass spectrometry (HPLC-ESI-MS-MS). The molecular ions themselves were not seen in the ESI-MS spectra, but adduct ions such as [M + Na](+) ions were prominent. The MS-MS data of HPLC fractions were also obtained by the ESI-triple quadrapole mass spectrometer. The charaeteristic daughter ions could be used to distinguish the same molecular weight components. The C-13 nuclear magnetic resonance (NMR) spectrum of ivermectin B-1a was reported and explained with its structure.