A novel ion selective gas sensor based on pulsed atmospheric pressure chemical ionization and ion-ion-recombination

In a former work on the investigation of ion generation and ion-ion recombination kinetics at atmospheric pressure with an ion mobility spectrometer equipped with a pulsable electron emitter, we found that different ion species and concentrations could be distinguished by only considering the specific ion-ion recombination kinetics. In the present work, these findings are utilized for the development of a novel compact and simple gas sensor. In a first step, the gas mixture becomes ionized by atmospheric pressure chemical ionization for a defined ionization time. Subsequently the ionization source is turned off and the ion specific decay of the ion concentration as a function of the recombination time is measured. This decay depends on the generated ion species and the compounds of the gas mixture respectively. For the analysis of these decay curves and visualization of the results, we use discriminant analysis. As an exemplary target analyte, we chose dimethyl-methylphosphonate (DMMP). With the current setup we achieve a limit of detection of 8 ppbv for the detection of DMMP in presence of significant higher ammonia and formaldehyde concentrations by only considering the recombination kinetics.