Researchers at Purdue built a miniature mass spectrometer that promises applications in everything from airport security to medical diagnostics. Pictured here is the latest prototype, the Mini 10 portable mass spectrometer, which is roughly the size of a shoebox and can easily be carried with one hand. The instrument measures 13.5 X 8.5 X 7.5 in.

Analytical chemists used prototypes of the handheld instruments to detect minute traces of triacetone triperoxide, or TATP, used by terrorists in last year's London subway bombings.

"It's one thing to detect a substance, but another to be absolutely certain of its composition, which is what you get with mass spectrometry," says R. Graham Cooks, professor of Analytical Chemistry in Purdue's College of Science. Mass spectrometry works by first turning molecules into ions, which can be more easily manipulated, detected, and analyzed based on their mass.

Desorption electrospray ionization (DESI) makes it possible to ionize samples in any ambient environment and not just within the spectrometer's vacuum region. And miniaturization of the vacuum-creating pumps let researchers shrink the device's size. The portable Mini 10 is roughly the size of a shoebox and weighs about 10 kg (22 lb), compared to about 30 times that weight for a conventional mass spectrometer.

Researchers using the Mini 10 have detected one nanogram, or a billionth of a gram, of TATP, which is about one-millionth the mass of a grain of sand. Such a system could alert security personnel to suspicious packages because bomb makers handling explosives are likely to transfer minute chemical traces to the outside of containers.

"TATP is difficult to detect with most other technologies," Cooks says. The portable system has also been used to detect other explosives, including TNT and plastic explosives.