Old bloodhound gets a sharper nose

Purdue University chemists have developed a fast, efficient means of analysing chemical samples found on surfaces, resulting in a device that could impact everything from airport security to astrobiology to forensic science.

A team, including R. Graham Cooks, has improved the mass spectrometer, a device well known to chemists for its ability to provide information on the composition of unknown substances.

Mass spectrometers, essential tools in any modern chemistry lab, are often used by law enforcement to test suspicious-looking residues that could indicate the presence of explosives or drugs inside packages.

But while most mass spectrometers are unwieldy, cabinet-sized machines that require samples to undergo hours of intensive preparation before testing, Cooks' team has found a way to test untreated samples right where they are found with a mass spectrometer that can fit in a backpack - all by creating a wand that can gather the samples from the environment quickly.

'We've essentially given an old bloodhound a new nose,' said Cooks, who is the Henry Bohn Hass Distinguished Professor of Analytical Chemistry in Purdue's School of Science. 'While mass spectrometry is one of our best ways to determine the makeup of a substance, the time and effort needed to prepare samples for analysis have made it difficult to use them in the field. With luck, this research will change all that.'

The research, which appears in today's (Friday, October 15) issue of the journal Science, was conducted by first author Zoltán Takáts with Justin M. Wiseman, Bogdan Gologan and Cooks, all of Purdue.

Gologan said that the team's innovation was inspired in part by the desire to use one of chemistry's most powerful tools in less limiting environments than the laboratory.

'Testing an unknown sample using standard mass spec can take up to half a day,' said Gologan, a graduate student in Cooks' laboratory. 'You have to dissolve the sample, then dilute the solution, then add additional compounds before you can stick it in the spectrometer. It's a generally effective process, but it's not so attractive in situations where time is of the essence.'

To simplify these preliminary steps in the process, the team developed a technique known as desorption electrospray ionization (DESI) - a mouthful of a name for a method that is relatively simple to conceive.

'Our device sprays a sample with a stream of high-velocity gas that contains some reactive chemicals,' Gologan said.

'Just like a strong wind kicks up dust, the gas breaks off a few small particles of the unknown substance, and these combine with the reactive chemicals to form an ionized compound that a mass spectrometer can analyse right then and there. It can be done anywhere, and because there are fewer intervening steps before the substance is analysed, there's less likelihood that the sample will be accidentally contaminated in the interim.'

Sampling is done with a long, tubelike wand that both delivers the gas and sucks up the resulting ionised compound. It is this wand that the team likens to their bloodhound's new nose. The wand's tip must come within 5 millimetres of the sample to be effective, but the group has also found a way to build a mass spectrometer that weighs about 18 kilograms (40 pounds), which means it can be carried to the sample, rather than forcing investigators to bring the sample to it.

'This backpack-size device will be useful for field analysis of chemicals, filling a need in airport baggage security and drug detection,' said Wiseman, a graduate student working on the project.

'While the technique obviously cannot look inside packages to see what is inside, residue from explosives and drugs often remains on the hands of whoever packed it, and some is transferred during handling to the package's surface. That remaining residue is what this device will be good for detecting.'

While the team is optimistic about the device's potential for application in the lab and on the street, Gologan cautioned that a better understanding of its functioning was still needed.

'One potential criticism of the device is that we haven't yet done an in-depth analysis of the mechanism,' he said. 'We think we know how it works, but haven't yet proven it. That's one of our next research steps.'