Researchers with the U.S. Naval Research Laboratory have just made it easier and safer to detect explosives and illegal drugs with a small footprint, second-generation vapor generator that can be used in the field.
The Trace Vapor Generator for Explosives and Narcotics (TV-Gen) can accurately generate trace vapors of low vapor pressure compounds and produce vapors in complex backgrounds.
"We can use the TV-Gen in the early stages of sensor development, where the developer is just determining if their proposed sensing material responds to a target analyte, all the way to determining instrument and assay limits of detection for hand-held trace detectors and hyphenated instrumentation," said Braden Giordano, author of the study recently published in AIP.
The main advantage of the TV-Gen is its single sample port, which allows it to deliver trace vapor concentrations continuously without the need for clean air generation systems. It can provide a stable vapor for several hours, rapidly switching between a clean vapor stream and an analyte vapor stream.
The TV-Gen device comprises three main components: the manifold, the oven, and the instrument control box. Explosives and narcotics are introduced through the control box, nebulized, then sent through the manifold to a vapor output port, which extends from the oven. The manifold is contained within the oven and has two isolated flow paths for the clean and analyte vapor streams. The control box contains all the hardware necessary for the operation of two nebulizers: one for the clean side of the manifold, and one for the analyte side.
The device was developed to work with a broad range of analytes, detection systems, materials, and sensors. Analytically, it was evaluated for the generation of a number of vapors of explosives and drugs. Total evaporation efficiency for the tested explosives and narcotics are described below:
- TNT- >82%
- RDX- >85%
- PETN- Ranged from 48% at 20 L min−1 to 78% at 5 L min−1
- NM- 50%, which was expected as nitromethane has a much higher volatility than any of the explosives evaluated on the first-generation model
- EGDN- 60%
- NG- 86%
- Methamphetamines including MDMA- 90%
- Cocaine, THC, heroine- 50%
The bottom research line? The lower the vapor pressure, the lower the measured vaporization efficiency, ensuring the system can reproducibly and accurately generate trace vapors (ppqv to ppmv) of low vapor pressure compounds, i.e. explosives and narcotics.
The TV-Gen is a follow up to the previously developed Trace Explosives Sensor Testbed (TESTbed), which can also generate and deliver trace vapors of explosives to detectors, sensors and/or materials. However, the design of the TV-Gen—namely its two pneumatically modulated liquid delivery systems (PMLDS)—gives it an advantage over its predecessor. The separate but identical PLMDS-nebulizers is what gives the TV-Gen the ability to rapidly switch between a clean vapor stream and an analyte vapor stream.
"The TV-Gen is significantly smaller than the TESTbed, and while providing only a single sample port for device evaluation, it maintains or improves upon the older systems' performance metrics," said Giordano. "It can fit on a small cart, so you can bring the vapor source to your technology, not the technology to the vapor source."
Giordano and team intend to continue their line of research, hoping to expand the library of vapors and explore methods to maximize vapor generation efficacy at lower operating temperatures.
In the immediate-term, they are working with bomb-sniffing canines to get a better idea of detection limitations.
“[We are] testing detector canines to get quantitative measurements of olfactory detection threshold and, potentially in the future, be able to compare canines directly to instrument for the first time," said Giordano.
Photo: Diagram illustrating the flow path of the analyte in an aqueous solution as it moves from the sample introduction vessels on the Trace Vapor Generator for Explosives and Narcotics (TV-Gen) control box, through the nebulizer interface, where the analyte is vaporized and continues through the TV-Gen oven, dual manifold system. Credit: Diagram provided by U.S. Naval Research Laboratory