Tandem Differential Mobility Spectrometry in Purified Air for High-Speed Selective Vapor Detection

Abstract

A tandem ion mobility instrument based on differential mobility spectrometry (DMS) was used to demonstrate selectivity in response through differences in field dependence of mobility for ions in purified air at ambient pressure. The concept of chemical selectivity solely from characteristic dispersion curves or from field dependence of ion mobility was experimentally demonstrated in three steps with mixtures of increasing complexity. In a mixture of four alcohols with carbon numbers four and below, distinct pairs of separation voltage and compensation voltage, applied to the first and second DMS stages, permitted isolation of ions from individual substances without detectable levels of other substances. In a three-component mixture of a ketone, alcohol, and organophosphorus compound, the same level of ion isolation was observed using specific and characteristic separation and compensation voltages on each DMS stage. In the last experiment, the isolation of product ions of individual substances from a mixture of 23 volatile organic compounds from four chemical groups was incomplete though the improvement in the ratio of analyte signal to chemical noise was calculated as 31 for DMMP and 106 for 1-hexanol. These findings demonstrate that chemical information available in dispersion curves can be accessed in response times below 100 ms through a tandem DMS measurement.

Review on Ion Mobility Spectrometry. Part 2: hyphenated methods and effects of experimental parameters

“…Tandem IMS has been studied including combinations with FAIMS or DMS devices: [65][66][67][68] IMS-IMS, DMS-IMS, IMS-DMS and DMS-DMS. Multidimensional IMS Instrumentation has been widely explored by Clemmer's group.…”

Enhanced aerodynamic reach of vapor and aerosol sampling for real-time mass spectrometric detection using Venturi-assisted entrainment and ionization

“…Similarly, the advent of synthetic narcotics has led to a rapidly increasing list of illicit compounds and the subsequent demand on law enforcement and canine units. The detection of vapors and aerosols has been demonstrated with a wide range of analytical methods [1], including colorimetric [2, 3] and fluorescence [4] detection schemes, novel nanomaterial sensors [5, 6], as well as more classical analytical techniques such as Raman spectroscopy [7], ion mobility spectrometry (IMS) and differential mobility spectrometry [8, 9], and mass spectrometry (MS) [10-13]. …”

Tandem differential mobility spectrometry with ion dissociation in air at ambient pressure and temperature

“…A second behaviour for ions in electric fields is decreased mobility when field strengths are increased. The determination of dispersion plots is relatively time-consuming, and a recent embodiment of DMS with tandem stages each with characteristic pairs of compensation and separation voltages (CV and SV) was used to exploit patterns of ion dependence in dispersion plots with response times of 100 ms. 24 Discussions on ion motion in DMS usually presume stability of ions during a measurement, although some substances form ions which can decompose in air at ambient pressure when heated thermally or electrically. This produces a negative alpha function and negative ΔK where the ion peak is displaced from 0 CV, opposite in polarity to ions with the positive ΔK values.…”

“…23 Such dispersion plots provide a measure of the fundamental ion behaviour and can guide the selection of parameters for the best resolving power. The determination of dispersion plots is relatively time-consuming, and a recent embodiment of DMS with tandem stages each with characteristic pairs of compensation and separation voltages (CV and SV) was used to exploit patterns of ion dependence in dispersion plots with response times of 100 ms. 24 Discussions on ion motion in DMS usually presume stability of ions during a measurement, although some substances form ions which can decompose in air at ambient pressure when heated thermally or electrically. A first thorough description of the instability of ions in ion mobility spectrometry (IMS) drift tubes at ambient pressure was given for ions of butyl acetates above 100 °C.…”