Hand-Held Portable Desorption Atmospheric Pressure Chemical Ionization Ion Source for in Situ Analysis of Nitroaromatic Explosives

Abstract

A novel, lightweight (0.6 kg), solvent- and gas-cylinder-free, hand-held ion source based on desorption atmospheric pressure chemical ionization has been developed and deployed for the analysis of nitroaromatic explosives on surfaces in open air, offering portability for in-field analysis. A small, inexpensive, rechargeable lithium polymer battery was used to power the custom-designed circuitry within the device, which generates up to ±5 kV dc voltage to ignite a corona discharge plasma in air for up to 12 h of continuous operation, and allowing positive- and negative-ion mass spectrometry. The generated plasma is pneumatically transported to the surface to be interrogated by ambient air at a rate of 1-3.5 L/min, compressed using a small on-board diaphragm pump. The plasma source allows liquid or solid samples to be examined almost instantaneously without any sample preparation in the open environment. The advantages of low carrier gas and low power consumption (<6 W), as well as zero solvent usage, have aided in developing the field-ready, hand-held device for trigger-based, "near-real-time" sampling/ionization. Individual nitroaromatic explosives (such as 2,4,6-trinitrotoluene) can be easily detected in amounts as low as 5.8 pg with a linear dynamic range of at least 10 (10-100 pg), a relative standard deviation of ca. 7%, and an R(2) value of 0.9986. Direct detection of several nitroaromatic compounds in a complex mixture without prior sample preparation is demonstrated, and their identities are confirmed by tandem mass spectrometry fragmentation patterns.

A Low-Cost, Simplified Platform of Interchangeable, Ambient Ionization Sources for Rapid, Forensic Evidence Screening on Portable Mass Spectrometric Instrumentation

“…For instance, techniques like desorption atmospheric pressure chemical ionization (DAPCI) [68], LTP [69], atmospheric pressure photoionization (APPI) [70], and easy ambient sonic spray ionization (EASI) [71] could prove adaptable, but may necessitate external compressed gas and power requirements. Simple platforms that are both frugal and expandable, such as that reported herein, could prove to be a catalyst towards full adoption by field practitioner communities.…”

Application of the modified transient plane source technique for early detection of liquid explosives

“…Carbonated liquids cola (16) and ale (18) were indistinguishable from each other, but easily distinguishable from all the hazardous materials. Figure 6.…”

“…It can be seen from Figure 5 that distilled water (3) does not change its thermal conductivity throughout the duration of the test, as expected for a non-carbonated liquid. Ale (18) demonstrates the largest increase in thermal conductivity upon outgassing, followed by cola (16) and sparkling water (17). It is important to note that, while cola (16) and ale (18) have both stabilized in thermal conductivity by 25 minutes open and 50 minutes open, respectively, the sparkling water (17) has failed to stabilize in thermal conductivity by 60 minutes of testing.…”

“…However, this trend changes following outgassing); after 60 minutes of outgassing (Figure 7), ale (18) is no longer distinguishable from nitric acid (13), and cola (16) is now only marginally distinguishable from nitric acid (13). However, sparkling water (17) remains easily distinguishable from all model hazardous materials, and all carbonated liquids remain easily distinguishable from benzene and acrylonitrile (14 and 15).…”

“…14 Spectroscopic technologies employ mass spectrometry or infrared spectrometry to detect illicit or hazardous materials. [15][16][17][18][19][20][21] These techniques are able to detect trace amounts of explosive or illicit material in vapor or as residue collected from swabs taken of luggage or a person's skin. These technologies vary greatly in principle but tend to be spot analyses rather than bulk analysis and are unable to detect materials through a barrier -thus a hermetically sealed can poses an insurmountable barrier to the test.…”