Conservation of dimer peak intensity in ion mobility spectrometers with ketone-doped carrier gas

• We conduct the quantitative analysis with ion mobility spectrometry.
• Measurements are performed for mixtures containing analyte and dopant.
• Dimer ion peak intensity is nearly independent of dopant presence.
• Conservation of dimer ion peak intensity results from reaction kinetics.

Doping of gases in ion mobility spectrometry (IMS) is a well-known method for improvement of detection selectivity. Ionization of analyte molecules in doped carrier gas occurs as a result of reactions with so-called alternative reactant ions containing molecules of dopant. Properties of these ions are different from those of the reactant ions found in pure carrier gas. Therefore, the dopant may influence the quantitative characteristics of detection in IMS. In this work, we present the results of studying the detection of two organophosphorus compounds, dimethyl methylphosphonate (DMMP) and triethyl phosphate (TEP), conducted in the presence of ketones containing 3–9 atoms of carbon in the molecule. Experiments were carried out with a generator of gas mixtures that allowed for simultaneous introduction of two substances into the carrier gas. Our investigations indicated that for the studied analyte/dopant systems, the presence of dopant does not influence the intensity of the signal generated by dimer analyte ions. This effect was observed for IMS instruments of different construction. Dimer ions peak intensity conservation is explained based on the ion–molecule reaction kinetics and the balance of ions in the reaction sections of IMS instruments.

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