Stopped-flow electrospray ionization mass spectrometry: a new method for studying chemical reaction kinetics in solution

In this work a new mass spectrometry based method for monitoring the kineti cs of chemical reactions in solution is described. A stopped-flow mixing in strument is coupled to an electrospray ionization (ESI) mass spectrometer v ia a novel type of interface. Chemical reactions are initiated by rapid mix ing of two reactant solutions, The mixture is instantaneously transferred t o a reaction tube where the kinetics can be monitored in real-time by ESI m ass spectrometry, With the current setup, a time window from 2.5 to 36 seco nds after mixing of the reactants can be monitored. The experimental setup is used to study the kinetics of acetylcholine hydrolysis under alkaline co nditions as a function of pH. The Intensities of reactant (acetylcholine) a nd product (choline) ions are monitored simultaneously as a function of tim e. The reaction is carried out under pseudo-first-order conditions and the intensity-time curves are well described by single exponentials. The rate c onstants determined from these fits compare favorably with previous data fr om the literature. Copyright (C) 2000 John Wiley & Sons, Ltd.