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

A novel, lightweight (0.6 kg), solvent and gas-cylinder free, handheld ion source based on desorption atmospheric pressure chemical ionization (DAPCI) 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 hours of continuous operation, and allowing positive and negative ion MS. 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. Advantages of low carrier gas and low power consumption (< 6 W), as well as zero solvent usage have aided in developing the field-ready, handheld device for trigger-based, "near real-time" sampling/ionization. Individual nitroaromatic explosives (such as 2, 4, 6-trinitrotoluene (TNT)) can easily be detected in amounts as low as 5.8 pg with a linear dynamic range of at least 10 (10 to 100 pg), a relative standard deviation (RSD) of ca. 7% and an R2 value of 0.9986. Direct detection of several nitroaromatic compounds in a complex mixture without prior sample preparation is demonstrated and their identities were confirmed by tandem mass spectrometry fragmentation patterns.