Analysis and Mechanisms of Cyclotrimethylenetrinitramine Ion Formation in Desorption Electrospray Ionization

Abstract

The general ion chemistry of the explosive molecule cyclotrimethylenetrinitramine (RDX) was studied with an atmospheric pressure ionization mass spectrometer (API-MS) fitted with a desorption electrospray ionization (DESI) source. Explosive molecule chemistry within trace detection techniques such as ion mobility spectrometry (IMS) is an area of intense interest because of the widespread deployment of IMS-based explosive detectors for counterterrorism efforts. As in IMS, the DESI-MS experiments analyze material that starts in the solid phase and is detected in the gas phase. Using the unique chemical characterization inherent in mass spectrometry, information pertinent to the atmospheric ionization of RDX is obtained in order to help explain the behavior of explosive molecule signatures observed within IMS experiments. Qualitative and quantitative information was obtained over 3 orders of magnitude of deposited mass (nanograms to greater than micrograms). A method was developed to use the relative integrated mass spectral peak intensities of RDX monomer and dimer chloride adducts to determine the amount of explosive present on a surface. The ratio of RDX dimer chloride adduct to monomer chloride adduct ranged from 0.1 for 15 ng to 1.0 for 1.5 microg of deposited explosive. The results are explained in terms of mechanisms reported in the literature for electrospray ionization (ESI), as well as by simple solution dynamics and the interaction chemistry between RDX molecules. On the basis of all available data, the RDX dimer chloride adduct becomes disproportionately favored over the monomer chloride adduct at larger amounts of explosive because of effects related to desorbed droplet charge, solvent declustering, and the strong intermolecular forces between RDX molecules in the solid, liquid, and gas phases. Additionally, considerations for optimization of the DESI-MS process are described in order to increase the practicality for this technique as an explosives detection tool in the public domain.

In-source collision induced dissociation of inorganic explosives for mass spectrometric signature detection and chemical imaging

“…These explosives have been detected using a range of analytical techniques, including ion chromatography (IC) [1,2], capillary electrophoresis (CE) [3,4], high performance liquid chromatography (HPLC) [5], and most notably, ion mobility spectrometry (IMS) [6][7][8][9][10][11][12][13] and mass spectrometry (MS) [14][15][16][17][18][19][20][21][22]. The rapid analysis times and cost effectiveness of these field compatible instruments have led to widespread deployment of ion mobility spectrometry.…”

Trace detection and competitive ionization of erythritol tetranitrate in mixtures using direct analysis in real time mass spectrometry

“…Alternative detection schemes such as gas chromatography mass spectrometry (GC/MS) 4,5 or liquid chromatography (LC/MS) 6,7 are hindered by lengthy analysis times. Trace detection of a range of explosive compounds directly from paper, metals, plastics, and human skin has been demonstrated with DESI-MS. [11][12][13] DESI and other liquid dropletbased ambient ionization sources 14 ionize explosive compounds through the traditional mechanisms studied for electrospray ionization (ESI), 15,16 forming adducts with available nitrite (NO 2 À ), nitrate (NO 3 À ), or reactive species added to the spray solvent (Cl À ). 10 These desorption-based ambient ionization methods enable the direct analysis of analytes from a variety of surfaces with no or minimal sample preparation.…”

“…Trace detection of a range of explosive compounds directly from paper, metals, plastics, and human skin has been demonstrated with DESI-MS. [11][12][13] DESI and other liquid dropletbased ambient ionization sources 14 ionize explosive compounds through the traditional mechanisms studied for electrospray ionization (ESI), 15,16 forming adducts with available nitrite (NO 2 À ), nitrate (NO 3 À ), or reactive species added to the spray solvent (Cl À ). 3,9,[11][12][13]18,21 As the threats posed by homemade and improvised explosive devices (HMEs/IEDs) increase, trace detection of primary explosives such as fueloxidizer mixtures and peroxides (triacetone triperoxide, TATP; hexamethylene triperoxide diamine, HMTD; and hexamethylene diperoxide diamine, HMDD) has become a growing area of research in recent years. 4,[17][18][19] Prior investigations have also demonstrated the use of dopants for enhanced ionization and specic adduct formation with DART.…”

Ion spectrometric detection technologies for ultra‐traces of explosives: A review

“…10). Additionally, a method for quantitative analyses based on peak intensities to determine the amount of explosive present on surface was created (Szakal & Brewer, 2009). The principles of and applications of ambient pressure MS-techniques focusing on the DESI method have been reviewed as well as the forensic applications of ambient mass spectrometry (Ifa et al, 2008a).…”