Analysis of a commercial preparation of erythromycin estolates by tandem mass spectrometry and high performance liquid chromatography/electrospray ionization tandem mass spectrometry using an ion trap mass spectrometer.

Because of the lack of a UV chromophore and their much smaller abundances in comparison with the major component, the minor components in erythromycin estolate preparations are difficult to analyze by high performance liquid chromatography ultraviolet (HPLC-UV). Tentative assignment of the major and minor components can be achieved with the combination of full scan and ZoomScan using an ion trap mass spectrometer. Tandem mass spectrometry (MS/MS) provided an effective method to quickly identify most components without chromatographic separation, and all the related compounds, except the isobaric pair ECE and PdMeEA, could be identified in this way. The best result was obtained by using liquid chromatography/tandem mass spectrometry (LC/MS/MS) operated in selected reaction monitoring mode. The major compound, the estolate of erythromycin A (EAE), and seven other minor components, could be separated and identified, with semiquantitative estimates of relative concentrations.