Fluorescence Detection and Identification of Tagging Agents and Impurities Found in Explosives

Abstract

The detection and identification of 2,4,6-trinitrotoluene (TNT), 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX), and pentaerythritol tetranitrate (PETN) vapors have proven to be difficult and challenging due to the low vapor pressures of these high explosives. Detecting higher vapor pressure impurity compounds found in TNT and possible tagging agents mandated to be added to plastic explosives (RDX and PETN) would allow for easier vapor detection. The higher vapor pressure nitro compounds of interest are considered to be non-fluorescent; however, once reduced to their amino analogs, they have relatively high quantum yields. The standard reduction products, the reduction products obtained in solution, and the reduction products obtained in vapor phase were analyzed by conventional fluorescence, synchronous luminescence, and derivative spectroscopy. The nitro analogs of the isomers 1,3-diaminobenzene, 1,2-diaminobenzene, and 1,4-diaminobenzene are found as impurities in TNT. We provide for the first time the synchronous luminescence derivative spectra of these isomers; including their individual spectra and a spectrum of an isomeric mixture of the three. Using the standard reduction products associated with these isomers and other aromatic amines, our data suggest that the vapors of two signature impurities, 1,3-dinitrobenzene and 2,4-dinitrotoluene (2,4-DNT), minor impurity compounds, and two possible tagging agents, 2-nitrotoluene (2-NT) and 4-nitrotoluene (4-NT), can be detected and selectively identified using our fluorescence approach. To prove our methodology, we show that we were able to generate, collect, and reduce 2-NT, 4-NT, and 2,4-DNT vapors to their amino analogs. Using our fluorescence approach, these vapors could be detected and selectively identified both individually and in a mixture. Collectively, our data indicate that our method of detecting and identifying higher vapor pressure explosive-like compounds could potentially be used to detect and identify low vapor pressure explosives such as TNT, RDX, and PETN.

Supramolecular Luminescent Sensors

“…Examples of detection systems that fit into this category include the detection of TNT based on analyte-induced amplified quenching of a conjugated fluorescent polymer reported by Swager and co-workers, ,− as well as the detection of TNT using conjugated polymer nanoparticles and conjugated organosilole polymers . Challenges in the practical detection of TNT relate to its low vapor pressure which complicates vapor-phase detection, although methods to address this issue through the detection of commonly coexisting and higher vapor pressure impurities have been reported. , …”

“…The detection of TNT and other small molecule explosives has significant relevance for national security applications, as such explosives are used in the fabrication of improvised explosive devices (IEDs) and in terror attacks, such as in the case of the “Underwear Bomber” in 2009 and the “Shoe Bomber” in 2001. , Challenges in the detection of TNT in military settings include its extremely low vapor pressure, which make the detection of buried explosives by monitoring the air above the explosive site particularly challenging . Selectivity for TNT relative to other nitroaromatics with higher vapor pressures is also challenging, although many of these nitroaromatics are found in such explosives as well and can serve as reasonable proxies for TNT detection.…”

“…840 Challenges in the practical detection of TNT relate to its low vapor pressure which complicates vapor-phase detection, 841 although methods to address this issue through the detection of commonly coexisting and higher vapor pressure impurities have been reported. 842,843 The detection of nonaromatic explosives can be more challenging due to a lack of a clear spectroscopic signature for many of these compounds. 844,845 Cyclotrimethylenetrinitramine (commonly known as RDX) and pentaerythritol tetranitrate (PETN), for example, are often detected through monitoring the products of reactions that these analytes induce, including analyte-promoted reductions.…”

A Rapid and Sensitive Quantitative Analysis Method for TNT using Raman Spectroscopy

“…It is usually synthesized by the nitration of toluene, in which the byproducts such as [a] F. Gao 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 2,4-dinitrotoluence (DNT) and 2,6-DNT would be produced. In general, the purity of explosives has a great influence on their detonation and power [20,2]. Liquid chromatography is a common approach for components analysis; nevertheless, it is very time-consuming and captious to separation conditions.…”