Tandem Ion Mobility Spectrometry for the Detection of Traces of Explosives in Cargo at Concentrations of Parts Per Quadrillion

Abstract

A tandem ion mobility spectrometer (IMS2) built from two differential mobility analyzers (DMAs) is coupled at ambient pressure with a thermal fragmenter placed in between, such that the precursor ions selected in the first DMA are thermally decomposed at ambient pressure in the fragmenter and the product ions generated are filtered in the second DMA. A thermal desorber and a multicapillary gas chromatography (GC) column are coupled to a secondary electrospray (SESI) ion source, so the adsorption sampling filters are thermally desorbed and the liberated vapors are separated in the GC column, prior to their ionization and mobility/mobility classification. The new fragmenter allows the fragmentation of the five explosives studied: RDX, PETN, NG, EGDN, and TNT. The background of the analyzer is evaluated for the five explosives using air samples of 500 L volume. An atmospheric background of only 2.5 pg (5 ppq) is found for TNT, being somewhat higher for the rest of explosives studied. The architecture GC-IMS2 is compared with GC-IMS obtaining a 100-fold increase of sensitivity in the first configuration, confirming the high selectivity provided by the fragmentation cell and the second IMS stage for the product ion mobility analysis. The analyzer is tested also with real explosives hidden in cargo pallets achieving successful detection of four (EGDN, NG, TNT, and PETN) out of five explosives.

Chemical Fingerprinting of Olive Oils by Electrospray Ionization-Differential Mobility Analysis-Mass Spectrometry: A New Alternative to Food Authenticity Testing

“…In recent years, SEADM has developed an electrospray ionization source, commercially known as D-LFSESI (desolvating low-flow secondary electrospray ionization) . This ionization chamber offers the possibility of ionizing samples, both liquid (ESI) and gaseous (SESI), , which gives it great versatility in addressing the analysis of samples by electrospray.…”

Measuring the Kinetics of Neutral Pair Evaporation from Cluster Ions of Ionic Liquid in the Drift Region of a Differential Mobility Analyzer

“…This method has been successfully implemented in a recent effort to emulate at atmospheric pressure the operation of the triple quadrupole mass spectrometer, with two DMAs placed in series with an oven in between. 25 However, the ion residence time within the oven is difficult to reduce in this configuration to values below several milliseconds. On the other hand, if a cold ion selected by one DMA were injected into a second DMA whose circulating gas was kept at almost uniform temperature and velocity, it would be possible to precisely characterize relatively fast reaction rates taking place over 0.1 ms (k ∼ 10 4 s −1 ).…”

“…Almost instantaneous heating of the cold ions can be achieved by injecting them via an electric field into a heated gas stream held at uniform temperature. This method has been successfully implemented in a recent effort to emulate at atmospheric pressure the operation of the triple quadrupole mass spectrometer, with two DMAs placed in series with an oven in between . However, the ion residence time within the oven is difficult to reduce in this configuration to values below several milliseconds.…”

Instant acquisition of high resolution mobility spectra in a differential mobility analyzer with 100 independent ion collectors: Instrument calibration

“…Parallel plate DMAs have reached an outstanding performance level, with resolving powers in excess of 100 (Amo-Gonz alez and P erez 2018), and high transmissions, even of high mobility ions (Rus et al 2010, Javaheri et al 2008. They are also easily connected in tandem with minimal losses (Amo-Gonz alez and Fernandez de la Mora 2017; Zamora et al 2018;Amo-Gonz alez et al 2018;Amo-Gonz alez et al 2019). However, the flow is neither axisymmetric nor strictly planar, so the relation between the mobility Z, the DMA length L, the voltage difference V and the flow rate of sheath gas Q may not conform to the familiar Knutson-Whitby (1975) form…”