Identifying Explosives and Residues Quickly with TOF Mass Spectrometery

Law enforcement organizations require equipment for the safe and efficient characterization of residues and explosives. An example of these compounds is the explosive triacetone triperoxide (TATP), which has been utilized in many prominent terrorist attacks and is of particular interest to law enforcement services.

​​​​​​​​​​​​​​​​​​Image Credit: TOFWERK

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Chemical ionization mass spectrometry (CI-MS) is a real-time, sensitive gas-phase analysis method that is highly capable of identifying a range of explosives at trace amounts.

When performed with the TOFWERK Vocus TOF mass spectrometer, CI-MS can quantify molecules with a broad range of vapor pressures and chemical characteristics.

Ambient air is directly included in the chemical ionization area of the Vocus. The ions produced are robustly identified by the TOF mass analyzer resulting in highly efficient response times with no preparation of samples.  

Realtime detection of trace triacetone triperoxide (TATP)

Sensitivity and time response are crucial for high-speed screening in close proximity sampling. The Vocus TOF mass spectrometer can perform analyses several times each second and has response times of fractions of a second for a number of organic compounds.

Figure 1 presents the efficient, real-time identification of TATP. A person carried a canine training aid (a highly diluted, small sample of TATP) while walking multiple times in front of the Vocus detector at a proximity of 2 meters.

Reliable detection was ensured by the direction of the plume towards the inlet. Every passage is instantly seen in the observed, TATP-specific ion as a sharp spike with a width of several seconds.

The efficient, sensitive response measurement of TATP in plumes is achieved even with only trace TATP emissions, meaning this detector is ideal for mobile platforms.

Figure 1. Fast, real-time detection of TATP. A human subject carrying a small amount of TATP walked several times in front of the Vocus detector. Ventilation directed the low-concentration plumes of TATP to the detector inlet. Each detection of the TATP “threat” is visible as a sharp spike.

Image Credit: TOFWERK.

Figure 2. Detection of residual TATP inside a contaminated package. A cardboard box was briefly exposed to TATP, then left unsealed for 20 hours. The air inside the box was periodically sampled with the Vocus CI-TOF. The measured concentration of TATP decreases over time but remains well above the instrument detection limit.

Image Credit: TOFWERK.

Residues are left behind on packaging, clothing, and additional surfaces by explosives. The high selectivity and sensitivity of Vocus TOF mass spectrometer enables real time evaluation of residual explosive vapor.

Figure 2 outlines the quantification of residual TATP on the interior of a cardboard box over a duration of almost one day. The cardboard box was subjected to the canine training aid for 45 seconds. Less than 50 µg of vapor was exposed to the inside surface of the box.

The box remained unsealed and was regularly measured with the Vocus TOF Mass spectrometer utilizing a flexible inlet line. After almost 20 hours, TATP can be identified at approximately 100 times the detection limit of the instrument.  

Sensitive detection of low-volatility explosives

The Vocus TOF mass spectrometer can additionally be employed to identify explosives containing vapor pressures that are even lower. The vapor pressure of the explosive is very important because it establishes the gas-phase concentration above the liquid or solid.

The detection limits of the Vocus TOF mass spectrometer are in the range of parts-per-quadrillion (ppqv) and parts-per-trillion (pptv) for widespread explosives. Hexamethylene triperoxide diamine (HMTD) is an organic compound that is highly explosive and has a low vapor pressure.

This means that isobars and alternative compounds found in air are more likely to influence the detection. Identification after significant dilution is much more difficult. Exceptional sensitivity is required for a low vapor pressure explosive like HMTD to identify it at all.

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Figure 3. Detection of HMTD vapors from a canine training aid. The room-temperature sample was opened and held near the Vocus CI-TOF inlet. HTMD is immediately observed.

Image Credit: TOFWERK.

The Vocus TOF mass spectrometer was used to quantify HTMD vapors released at room temperature from a canine training aid. Figure 3 demonstrates that HMTD is instantly detected in room air when the sample is positioned close to the inlet.

A quantitative evaluation of the ion-molecule reaction chemistry enables the identification of the vapor concentration of HMTD at a few tens of pptv. The use of thermal desorption and swab samples could enable the identification of explosives with an even lower volatility.  

Acknowledgments

Produced from materials originally authored by Felipe Lopez-Hilfiker from TOFWERK.

About TOFWERK​​​​​​​

TOFWERK is a global leader in time-of-flight mass spectrometry, delivering sensitive instruments for laboratory, industrial, and field analyses. Our customers’ interests range from materials science and geochemistry to metabolomics and trace-gas​​​​​​​
measurements.

TOFWERK engineers and scientists collaborate with research laboratories and OEM customers to develop custom MS solutions based on our modular design platform. This platform enables rapid design and manufacturing of novel instrumentation for research laboratories and OEM customers.

Our end-user product line includes the icpTOF, Vocus PTR-TOF, IMS-TOF, and EI-TOF for GC. These mass spectrometers bring the speed and sensitivity of TOFMS to many disciplines and sample types.


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