Law enforcement was able to thwart an attempt to set off an explosion in the middle of New York City's Times Square on May 1 thanks to the quick thinking of a T-shirt vendor who noticed smoke coming from a parked SUV. Unfortunately, the signs that a bomb is nearby are often more subtle, detectable only at a microscopic level.

Technology for detecting trace amounts of explosives can be found at high-security locations such as the Statue of Liberty. These ion mobility spectrometry machines—you can recognize them by the puff of air they blow in your direction as you walk by—are good at detecting the presence of chemicals used to make explosives, but they cannot identify which chemicals are present. Austria-based gas-analysis instrument maker Ionicon Analytik Gesellschaft m.b.H. claims to have a solution, from a technology originally used in industrial environments that can easily be adapted to work as a security device.

Ionicon Analytik's Proton-Transfer-Reaction Mass Spectrometry (PTR-MS) technology can distinguish substances that have very similar molecular structures and can correctly identify explosives, chemical warfare agents and chemicals that could be combined to create a bomb, says Kurt Becker, Polytechnic Institute of New York University's associate provost for research and technology initiatives. Becker, who is also a physics professor, serves as a consult to Ionicon Analytik.

PTR-MS does this task by using plasma to generate "protonated" water vapor, so named because an extra proton is added to the water. Most organic compounds—including most explosives and chemical warfare ingredients—have an affinity to grab that extra proton and become themselves positively charged. Determining which compound is present means letting these positive ions drift into a chamber, where they can be extracted and weighed, thus revealing their identity, Becker says. Explosives made from different compounds are set off in different ways, so it is important for security staff and law enforcement to determine as quickly as possible what type of explosive they are dealing with and how it might be detonated, he adds.

PTR-MS technology, invented at Austria's University of Innsbruck and then spun out to form Ionicon Analytik in 1998, has been developed over the past decade to quickly quantify organic compounds in air, including industrial exhaust gases and food flavor chemicals. The instrument, roughly the size and shape of a refrigerator and costing as much as $1 million, can be built for various ranges of sensitivity from parts per billion down to parts per quadrillion, according to Becker.

Within the past four years, the technology has come to the attention of security agencies in the U.K., France, Germany and Austria as a way to potentially detect, identify and quantify minute amounts of explosives and chemical weapons. Recent experiments in Innsbruck demonstrated that after handling explosives and other chemicals, trace quantities left on a person's skin, gloves or clothing, as well as in the surrounding air or on surfaces, can still be identified. Recognition that such leftovers exist led to a beta test of a vehicle-mounted PTR-MS instrument that law enforcement hope can detect facilities being used for the manufacture of improvised explosive devices.

Becker says a demo PTR-MS unit arrived in the U.S. in late March and that Ionicon Analytik has since been offering it to law enforcement and industry for demonstrations.

Image of simulated pipe bomb courtesy of Polytechnic Institute of New York University

Images of Ionicon PTR-MS courtesy of Ionicon Analytik