Atmospheric pressure chemical ionization is widely applied in LC/MS. A limitation of APCI coupled to LC is that the mobile phase, chosen for its effect on chromatography, also plays a role in ionization. This limits the choice of chemical ionization (CI) reagents which might be used to optimize a method's selectivity and sensitivity.With APCI for GC/MS, the choice of CI reagent is decoupled from chromatography to a large extent as the gaseous mobile phase is easily reduced or eliminated from the corona discharge region. The result is that CI reagents that promote charge exchange, protonation or real time gas phase chemical reactions such as hydrogen deuterium exchange (HDX) can be applied to adapt analytical conditions for analyses with a variety of purposes. Charge exchange, for instance, may ionize a broader range of compound classes while protonation with a specific reagent may improve sensitivity and reduce fragmentation for a target compound class or analyte. HDX combined with GC APCI on a QTof can be used to contribute knowledge of chemical substructure beyond the knowledge of elemental composition provided by accurate mass measurement. This can allow the distinction between an ether and an alcohol substructure to be made in order to eliminate or include specific proposed structures in identification of unknowns.It has also been found that under some conditions this source is able to create adduct or reaction products not been previously described in literature. Initial investigation indicates that these species have utility for both compound class differentiation and structural elucidation.Data demonstrating HDX APCI GC/MS and the differentiation of compound classes, alkanes v. alkenes, using specific adducts and gas phase chemical reaction products will be presented and discussed.

Ionization combined with gas phase chemical reactions in an atmospheric pressure source for structural elucidation

247th National Meeting (2014)

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