Analysis of erythromycin by liquid chromatography/mass spectrometry using involatile mobile phases with a novel atmospheric pressure ionization source

A critical limitation of electrospray ionization (ESI) liquid chromatograph y/mass spectrometry (LC/MS) sources is the susceptibility to blockage of in terface orifices due to the deposition of involatile components from the sa mple and/or mobile phase, These components, including salts, buffers, and i on-pairing agents, can be essential to the performance of the chosen analyt ical method. We report here the performance enhancements provided by a nove l atmospheric pressure ionization (API) source in the analysis of erythromy cin A (ERY) using mobile phases that contain involatile components. The enh anced robustness of the new source is derived from the use of a continuous Row of aqueous solvent at the sampling cone orifice that maintains unobstru cted ion transmission. The ESI mass spectral responses measured for ERY, us ing an LC separation that incorporates 10 mM sodium phosphate with and with out 10 mM octane sulfonate, were monitored by repeated injections over 13-1 5 h total analysis time, Minimal effects on ESI mass spectral responses (in tegrated peak area) or chromatographic performance (peak shape, retention t ime) were observed during these studies. In the absence of the aqueous clea ning flow, complete loss of mass spectral responses and total blocking of t he sampling cone was observed in less than 30 min. Responses for ERY spiked into chicken and beef liver, and catfish muscle at or below the regulatory level of interest (100 ppb), were quantified by internal standard calibrat ion using this procedure. These results demonstrate the ability of a novel API-MS ion source to perform analyses that require the use of involatile mo bile phase additives. Copyright (C) 2000 John Wiley & Sons, Ltd.