Elimination of NO+ from the Reactant Ions in Ion Mobility Spectrometry

Ionization of analytes in ion mobility spectrometry (IMS) happens through reaction of reactant ions (RI) with the analyte molecules in gas phase. The usual reactant ions produced in corona discharge in air are H3O+, NO+ and NH4+ as shown in Fig.1 [1].H3O+, and NH3 + reacts with the analyte via proton transfer reaction while NO+ react via charge transfer reaction. The product ions are usually heavier than the reactant ions so that their peak appears in longer drift times. Some compounds such as nitro-compounds, possess low proton affinity so that proton transfer does not happen easily. However, these compounds produce NO+ in the discharge. Theproblem is that the background NO+ peak prevents a true measurement of the NO+ ions produced by the analyte. The aim of this work is to reduce or eliminate the background NO+ peak in ion mobility spectrum.