Ion Mobility Spectrometer-Fragmenter-Ion Mobility Spectrometer Analogue of a Triple Quadrupole for High-Resolution Ion Analysis at Atmospheric Pressure

Abstract

Two differential mobility analyzers (DMAs) acting as narrow band mobility filters are coupled in series, with a thermal fragmentation cell placed in between, such that parent ions selected in DMA are fragmented in the cell at atmospheric pressure, and their product ions are analyzed on DMA. Additional mass spectrometer analysis is performed for ion identification purposes. A key feature of the tandem DMA is the short residence time (∼0.2 ms) of ions in the analyzer, compared to tens of milliseconds in drift tube ion mobility spectrometers (IMS). Ion fragmentation within the analyzer and associated mobility tails are therefore negligible for a DMA but not necessarily so in conventional IMS. This advantage of the DMA is demonstrated here by sharply defined product ion mobility peaks. Ambient pressure ion fragmentation has been previously demonstrated by both purely thermal means as well as rapidly oscillating intense electric fields. Our purely thermal fragmentation cell here achieves temperatures up to 700 °C measured inside the heating coil of a cylindrical ceramic heater, through whose somewhat colder axis we direct a beam of mobility-selected ions. We investigate tandem separation of chloride adducts from the explosives EGDN, nitroglycerine (NG), PETN, and RDX and from deprotonated TNT. Atmospheric pressure fragmentation of the first three ions yields one or several previously reported fragments, providing highly distinctive tandem DMA channels for explosive identification at 1 atm. RDX ions had not been previously fragmented at ambient pressure, yet [RDX + Cl] converts up to 7% (at 300 °C) into a 166 m/ z product. The known high thermal resilience of TNT is confirmed here by its rather modest conversion, even when the ceramic is heated to 700 °C. At this temperature some previously reported fragments are found, but their mobilities are fairly close to each other and to the one of the far more abundant parent ion, making their identification by mobility alone problematic. We anticipate that moderately higher fragmenter temperatures will produce smaller fragments with mobilities readily separated from that of [TNT - H].

Developments in tandem ion mobility mass spectrometry

“…Tandem DMA [51] and FAIMS instruments can often be used stand-alone coupled to detectors, such as a condensation particle counter [70] (CPC) or a Raman spectroscopy [71]. In 2018 a tandem DMA cell, modified for fragmentation of highly thermally stable volatile compounds, was coupled to a triple-quadrupole, and then faraday cup detector system [45]. These detectors allowed proof-of-concept for the fragmentation and identification of a variety of explosive compounds through the use of IM alone.…”

“…Astrices represent where there were fewer than 10 publications per year (B) Timeline of advances of IM, IM-MS and Tandem-IM, withthe dating from 1960-2020. References, in chronological order:[16,25,27,29,30,32,33,35,[38][39][40][41][42][43][44][45][46][47][48][49].…”

Mechanism of atmospheric pressure chemical ionization of morphine, codeine, and thebaine in corona discharge–ion mobility spectrometry: Protonation, ammonium attachment, and carbocation formation

“…28,29 Furthermore, although ESI and CD are soft ionization methods, sometimes IMS peaks related to smaller fragments are also observed. [30][31][32][33] Hydration of ions and their fragmentation depend on the structure and basicity of the molecule M. 34 In addition, instrumental parameters and existence of modifier gases (dopants) influence the type of produced ions. [35][36][37] Because IMS is used for opiate alkaloids in both the solid and solution phase, hence, in this work, ionization of pure solids and aqueous solutions of morphine, codeine, and thebaine is studied by APCI-CD-IMS.…”

“… 27 However, other ions and larger clusters such as hydrated protonated molecules, MH + (H 2 O) n , and proton‐bound dimers, (M) 2 H + , are also formed 28,29 . Furthermore, although ESI and CD are soft ionization methods, sometimes IMS peaks related to smaller fragments are also observed 30–33 . Hydration of ions and their fragmentation depend on the structure and basicity of the molecule M 34 .…”

Ion Fragmentation and Filtering by Alpha Function in Ion Mobility Spectrometry for Improved Compound Differentiation

“…Thus, two possible routes to fragment ions in IMS can be derived. One is simply increasing the absolute temperature T in a fragmenter region. , Fragmenter setups utilizing temperatures of 700 °C have been demonstrated . The second is an increased effective ion temperature T eff by applying high reduced electrical fields.…”