Characterization of Alkane Oxidation Products in a Corona-Discharge Reactor Using Ammonia-Doped Ion Mobility-Mass Spectrometry.

This study examines the oxidation of C5-C8 alkanes in an external corona-discharge reactor. Oxidation products were characterized using ion mobility spectrometry (IMS) and tandem IMS-mass spectrometry (IMS-MS) with an internal corona-discharge APCI source. This configuration enables structural isomer resolution and provides deeper insight into the molecular composition of the oxidation products. IMS-MS analysis showed that alkane (M) oxidation produces mainly ketones ([M+O-2H]) and diketones ([M+2O-4H]), with 3-ketone isomers dominating. Under standard APCI conditions, H+(H2O)n reactant ions protonated these products, generating complex IMS spectra for [M+O-2H].H+ and [M+2O-4H].H+. Introducing NH3 as a dopant shifted the primary reactant ion to NH4+(H2O)n, forming [M+O-2H]. NH4+ and [M+2O-4H].NH4+ adducts with similar collision cross sections. This simplified the IMS spectra to a single peak, enhanced sensitivity, and improved suitability for analytical applications. Using this approach, quantitative analysis of selected alkanes yielded detection limits of 0.01-0.1 ppmv.