While many people searched at airports merely have their personal items strewn on a table, some get more thorough treatment–a cotton swab wiped across their belongings and placed in a machine that identifies suspicious chemicals like explosives.
Many of these machines use a technology known as “ion mobility spectrometry” (IMS), an analytical technique not widely used when it was first developed in the early 80’s, according to Herb Hill, professor of chemistry at Washington State University since 1976.
But things have changed since September 11. Last year, the Transportation and Security Administration contracted Boeing to install 4,800 to 6,000 explosives trace detection machines, which use ion mobility technology, in airports across America.
Hill, an expert in detecting trace amounts of chemically and biologically important compounds, describes IMS as a way to separate and identify molecules of different structures. This is important, because two compounds made up of the same atoms can act very differently depending on the structure–one may be harmless, while the other is a great security risk.
IMS works by electrically charging the questionable sample and sending those charged particles, called ions, through a gas-filled tube. Different chemicals travel through the tube at different speeds, depending on their size and shape, so materials can be identified by their signature speed.
Hill has improved the technology to reduce the number of false positives, in which harmless substances appear as a potential risk. “False positives are expensive, because they lead to shutting down airports and interrogations,” says Hill. Wes Erron Steiner, a graduate student in Hill’s lab, combined IMS with mass spectrometry (MS), a process that separates compounds based on molecular mass, in one machine. This “two-dimensional” system is more precise than using IMS alone, says Hill.
Besides being accurate, the system is also versatile. Ion mobility technology is most often used for detecting explosives, drugs, and chemical warfare agents, according to the Idaho National Engineering and Environmental Laboratory, an organization Hill collaborates with. But the potential applications are much broader. Pesticides, pollutants, and even large molecules like proteins can be detected. Next year, Hill’s group will take its system to an Army facility where it will test actual nerve agents, instead of the simulations it currently works with.
“By choosing the right ionization and separation conditions,” says Hill, “you can detect a lot of different compounds.”
Finding trace amounts of hazardous materials is even tougher when they’re hidden in complex matrices like river water. With minimal filtering, Hill’s IMS-MS system can detect up to 10 different compounds in one sample of air or water. The system as a whole can detect about 60,000 different chemicals. “We’re still the only people who can do liquids well,” Hill says.
Despite the value of IMS-MS technology, adapting new developments in the lab to use in rugged, field-portable instruments around the world is a slow, expensive process, according to a 2002 International Union of Pure and Applied Chemistry (IUPAC) report.
“Everybody wants it cheap and portable, while keeping the integrity of the system high,” Hill says, jokingly adding that what people really want is a “tricorder,” a hand-held, futuristic–and entirely fictional–machine from Star Trek that gives the complete chemical make-up of any object it zaps.
Hill was surprised to learn at an IUPAC workshop that current weapons inspectors do not use analytical techniques to find chemical weapons, because the machines are not available at the investigation sites. He imagines that an airplane with a lab equipped for chemical analysis should be flown around the world to give inspectors an analytical tool, but acknowledges that it’s an unlikely prospect any time soon.
Within a year, Hill plans to make a desktop-sized system, but envisions a more portable briefcase type in the future. One of his students, Maggie Tam, is taking “portable” to a new level by working on an IMS approach that would fit on a chip.
Since September 11, research activity surrounding detection of explosives and chemical weapons has increased, but Hill’s interest in the subject originated long before. The “challenge of seeing things at very low levels” has always motivated his work. In the future, he plans to investigate the use of IMS to detect carbohydrates in mammals, including some that could indicate the presence of cancer.
“Most people focus on a system and use different tools to study it. We’ve chosen the tool as our focus,” says Hill. “Without new measurements, you can’t make new discoveries.”