Subject : Airport Chemistry
Abstract: For all the screening that has become a standard part of air travel, existing methods can't expose every hint of criminal activity ...
Link : http://www.chemistry.org/portal/a/c/s/1/feature_ent.html?id=c373e9079e2c2c0e8f6a17245d830100
has a broken link. I am reproducing the article in its entirety (03 October 2007) until I can find the new link to it, if there is one.
Margaret_Hill
www.chemistry.org
It’s that time of year when thousands of Americans endure long lines at airport security checkpoints as they travel for the holidays. But for all the screening that has become a standard part of air travel, existing methods can’t expose every hint of criminal activity that passes through. Fortunately, chemical detection methods are advancing in ways that should improve the situation.
At Purdue University, for example, R. Graham Cooks’ research group has worked out a rapid and reliable method for detecting trace quantities of compounds lying on surfaces. Its ease of use and quick turnaround time should make it ideal for airport security personnel to scan the exteriors of luggage, packages, and clothing for traces of nefarious chemical compounds such as explosives or drugs.
The method involves mass spectrometry, a chemical identification tool known for its sensitivity and accuracy. Despite these attributes, however, mass spectral methods have not been applied to testing situations such as those needed at airport security sites. A major problem has been the time-consuming sample preparation needed for these techniques. Another factor is the need for vacuum conditions within the ionization chamber of the spectrometer. And finally, to house all of their working parts, mass spectrometers have tended to be quite large instruments not built for portability.
By making several key modifications in instrument design and sampling technique, Cooks’ group has bypassed these limitations. The team adapted electrospray ionization (ESI) technology to engineer a sampling “wand” that dislodges samples from surfaces, ionizes them in the presence of air, and then passes them along to a mass spectrometer for analysis, all within a matter of seconds. Cooks’ group also condensed the equipment down to backpack-size. The method, known as desorption electrospray ionization, or DESI, makes it possible to take mass spectral analyses into totally new environments.
Because the method also can be applied to a broad variety of compounds, it is versatile and has a broad potential of use. When Cooks published this work last year in Science (306, 471–473), he wrote that it “seems particularly promising for forensic and public-safety applications, including analysis of dried blood, detection of explosives, and monitoring of chemical warfare agents.”
Since then, to demonstrate how their technique might be applied to a real-world example, the group evaluated the method’s capability of detecting and identifying a number of explosives. The results were published in the November 5, 2005, issue of Analytical Chemistry (77, 6755N-6764).
Testing their method with four modern explosive compounds, the researchers found limits of detection ranging from 100 picograms down to 0.01 picograms (1 picogram is one-trillionth of a gram), depending on the compound and the surface it was tested on (e.g., metal, paper, glass, plastic, and polymer examples). The picogram capabilities of method produced accurate identification of trace quantities of all four explosives.
The researchers also studied mixtures—military-made plastic mixtures such as Composition C-4 and mixtures put together to simulate post-blast types of situations. Not only did the method sort out and identify the compositions of all of the mixtures, it did so for residue quantities of those mixtures. In one test, for example, an experimenter pressed his thumb to a sample of C-4 and then repeatedly pressed down on a series of glass slides with the same thumb. Even after five sequential transfers, the residue provided sufficient material that could be positively identified.
In addition to its obvious application to security screening and forensic investigations, this method will no doubt have significant impact on environmental testing. It represents a timely and valuable addition to the arsenal of detection methods currently in use.
This article first appeared on November 21, 2005.
Copyright © 2007 American Chemical Society.
All Rights Reserved
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