An NO+ reactant ion source for ion mobility spectrometry

Abstract

The major reactant ion in conventional ion mobility spectrometry (IMS) is the hydronium ion, H3O+ which is produced in the usual ionization sources such as corona discharge or radioactive sources. Using the hydronium reactant ion, mostly the analytes with proton affinity higher than that of water are ionized. A broader range of compounds can be detected by IMS if other alternative ionization channels, such as charge transfer from NO+, are employed. In this work we introduce a simple and novel method for producing NO+ as the major reactant ion in IMS. This was achieved by adding neutral NO to the corona discharge ionization source. The neutral NO was prepared via an additional discharge in an air stream, flowing into the corona discharge source. A curtain plate was mounted in front of the corona discharge to prevent the influence of the analyte on the production of NO+. Using this technique, the reactant ion could easily and quickly switch between the H3O+ and NO+. The performance of the new source was evaluated by recording ion mobility spectra of test compounds with both H3O+ and NO+ reactant ions.