Exploiting adduct formation through an auxiliary spray in liquid chromatography-electrospray ionization mass spectrometry to improve charge-carrier identification.

We describe a simple and effective approach to probe adduct formation in liquid chromatography - electrospray ionization mass spectrometry (LC-ESI-MS) and help designate and/or confirm which particular analyte is leading to which particular charged species that is detected. A compound tends to form similar adducts with adduct-forming analogs, at various abundance levels, of course. It is based on this understanding that in this work we probed adduct formation by modulating the adduct-forming analogs and observing the adducts formed with these analogs to lend experimental evidence to adduct annotation. The approach was implemented through an auxiliary spray and made possible thanks to the interaction between the plumes of the sample spray or main spray and the auxiliary spray. Changing adduct-forming analogs by switching the auxiliary spray solution, or simply turning on and off the auxiliary spray facilitated the observation of the adducts corresponding to these analogs or lack thereof, giving rise to a simple and effective approach to probe adduct formation and thus help annotate the analyte ions.