Explosives vapour detection technology: the new “sniff test”

A quick, accurate and highly sensitive process to reliably detect minute traces of explosives on luggage, cargo or travelling passengers has been demonstrated by scientists at the Department of Energy's Pacific Northwest National Laboratory.

The vapour detection technology accurately detects and identifies the vapors of even very low-volatility explosives in real time at ambient temperature and without sample pre-concentration. Details are outlined in a recent issue of Analytical Chemistry.

Rather than searching for particle residue using a typical method like surface swipes or using pulses of air to dislodge particles for analysis, the system 'sniffs' directly for explosives vapors, much the way bomb-sniffing canines do.

"We have demonstrated direct, real-time vapour detection for the low-volatility explosive compound RDX, which is used in many types of explosives," said David Atkinson, senior research scientist at PNNL. Low-volatility compounds are those which release very small amounts of the explosive vapour typically at parts per trillion levels or lower, making it extremely difficult to detect. The PNNL system easily detects vapors from a fingerprint-sized sample of RDX at levels below 25 parts per quadrillion.

"The system correctly identified the RDX vapour using selective atmospheric pressure chemical ionization with mass spectrometry," explained Atkinson. The approach involves pulling an air sample stream and ionizing it within a reaction region in an atmospheric flow tube. The ionized sample moves to a mass spectrometer for ion detection and identification. These air samples need no heating or pre-concentrating.  Analysis happens in about one second.

"The key part is ionisation," said Atkinson. "We tailored the chemistry to greatly enhance both ionisation efficiency and selectivity, which results in the best possible detection."