Quantitative Response of IMS Detector for Mixtures Containing Two Active Components

Abstract

This study describes the relationship between the output signal of the ion mobility spectrometry (IMS) detector and the concentrations of two compounds being simultaneously introduced into the reaction section. Investigations were performed for three pairs of compounds, that is, dimethyl methylphosphonate (DMMP) and acetone, methyl tert-butyl ether (MTBE), and acetone, as well as trimethylamine (TMA) and n-nonylamine (NA). Vapors of the investigated compounds were produced in a two-channel generator with permeation sources and a dilution system based on mass-flow controllers. The generator design and the method of concentration determination are discussed in this paper. It was found that admixture can differently influence detection of an analyte. The presence of acetone does not effect the signal corresponding to dimer ions of DMMP. For pairs MTBE + acetone and TMA + NA characteristic peaks of analyte ions diminish with growing concentration of admixture, however, the detection based on the peak of the asymmetric dimer containing proton-bound molecules of both compounds is effective. For the detection of TMA in the presence of NA, the signal generated by the asymmetric dimer ions is meaningfully higher than the signals of monomer or dimer TMA ions measured without the NA admixture. The course of calibration dependencies was analyzed on the basis of a simple mathematical model of the reaction region. This model provided an estimation of the intensity of the signal for a given ionic species for definite concentration of analyte.

A sensitive gas chromatography detector based on atmospheric pressure chemical ionization by a dielectric barrier discharge

“…If the depletion of the reactant ions is the limiting factor for the response, it is most likely that the acetone peak is still not separated well enough from the reactant ion peak, leading to a smaller difference current even though most reactant ions are already depleted. In this case, the increasing sensitivity at high concentrations could be attributed to the formation of a so-called dimer ion [32] containing two acetone molecules. As such an ion is significantly slower, it would be separated better, leading to an increase in sensitivity.…”

Separation of different ion structures in atmospheric pressure photoionization-ion mobility spectrometry-mass spectrometry (APPI-IMS-MS)

“…We believe that the change could be due to sample solvent somehow "overloading" the drift tube on this one day, since the next day's measurement of the mobility of the first peak was as expected. It has been reported that mobility of monomers can be more dependent on measuring conditions than dimers [57]. Interestingly, when hexane:toluene (9:1) is used, a new peak with a lower mobility, K 0 ϭ 1.63 cm 2 /Vs, appears while measuring mass-selected mobility of the ion m/z 80 (Figure 3b).…”

Dopants and gas modifiers in ion mobility spectrometry

“…Analysis of the quantitative aspects of the application of dopants was presented in [86]. The use of acetone as a dopant can reduce the analytical signal when the analyte and the dopant PA are similar.…”

“…Therefore, in many analytical applications, it is necessary to ensure the stability of the concentration of the admixture. Permeation standards constructed from vials covered by membranes are often used as sources of dopants [79,86].…”