Optimization of a liquid chromatography method based on simultaneous electrospray ionization mass spectrometric and ultraviolet photodiode array detection for analysis of flavonoid glycosides

Abstract Different reversed‐phase liquid chromatography (LC) columns of conventional dimensions were coupled to an ultraviolet photodiode array detector (UV‐DAD) and a magnetic sector‐type spectrometer, equipped with an electrospray ionization (ESI) source, by a laboratory‐made flow splitter. A mixture of three flavonoid‐ O ‐glycosides was employed to examine the effects of the solvent composition, the flow rate, the stationary phase, the pH and the organic acid added, on the chromatographic separation, the UV‐DAD detection, the ESI process and the entire LC system with ESI‐MS and UV‐DAD detection. In the positive ion mode, methanol containing 1% acetic acid was by far the most sensitive in ESI‐MS analysis, whereas an acetonitrile/water mobile phase containing 0.5% formic acid was proved to give the best sensitivity in LC/ESI‐MS/UV‐DAD analysis. In the negative ion mode, the highest sensitivity was obtained with a mobile phase containing 0.1% formic acid, while addition of bases decreased the sensititvity. The optimal flow rate was higher in negative ESI (20–50 µL/min) than in positive ESI (5 µL/min), and the percentage of organic phase had an influence on the sensitivity of ESI‐MS detection. With regard to the selection of a suitable C 18 reversed‐phase LC column, a column which is well end‐capped is to be preferred, because residual silanol groups appear to impair the separation of flavonoid glycosides. The optimized LC/ESI‐MS/UV‐DAD method was applied to a commercial Crataegus extract, which is used in phytomedicine to treat cardiovascular problems and is known to be rich in flavonoids. It is demonstrated how UV spectra and first‐order ESI mass spectra allow a fast characterization of flavonoids, even if reference compounds are not available or at hand. Copyright © 2002 John Wiley & Sons, Ltd.