Simultaneous ESI‐APCI(+) ionization and fragmentation pathways for nine benzodiazepines and zolpidem using single quadrupole LC‐MS

Nine important 1,4‐benzodiazepines and zolpidem were characterized by liquid chromatography‐mass spectrometry using a multimode ionization source able to generate ions using both electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI), and a single quadrupole mass analyzer. An optimum chromatographic separation was applied for all target compounds in less than 8 minutes using a Zorbax Eclipse Plus column (100 x 4.6 mm, 3.5 µm) kept at 35°C and a 0.3% HCOOH/ACN/IPA (61:34:5) mobile phase pumped at 1 ml/min. Optimization of LC‐MS method generated low limit of quantitation (LOQ) values situated in the range 0.3–20.5 ng/ml. Comparison between differences in method sensitivity, under specified chromatographic conditions, when using ESI‐only, APCI‐only, and simultaneous ESI‐APCI ionization with such a multimode source was discussed. Mixed ESI‐APCI(+) mode proved to be the most sensitive ionization generating an average 35% detector response increase compared to ESI‐only ionization and 350% detector response increase with respect to APCI‐only ionization. Characterization of the nine benzodiazepines and zolpidem concerning their MS fragmentation pathway following ‘in‐source’ collision‐induced dissociation is discussed in detail and some general trends regarding these fragmentations are set. Copyright © 2013 John Wiley & Sons, Ltd.