A new way of making ions could revolutionize the venerable practice of mass spectrometry, in which ionized molecules are identified by their weight. The new method works without cumbersome vacuum chambers and specially prepared samples, and experts say it could be used in airports to "sniff" luggage for traces of explosives, in orchards to test fruit for pesticide residues, and in many other venues outside the laboratory.
"It's the greatest thing since night baseball," says John Fenn, a chemist at Virginia Commonwealth University in Richmond. Fenn won a share of the 2002 Nobel Prize in chemistry for developing a technique on which the new method is based. That approach--known as electrospray ionization--ionizes large molecules by dissolving them in a solvent and using an intense electric field to pull tiny charged droplets of solution from the end of a needle. The new technique uses an electrospray jet differently, to shoot ionized droplets of solvent at a sample.
Zoltán Takáts, R. Graham Cooks, and colleagues at Purdue University in West Lafayette, Indiana, describe the new method, dubbed desorption electrospray ionization (DESI), in the 15 October issue of Science. DESI resembles techniques in which beams of ions or laser light blast ions from a sample for analysis. However, the ion beam technique works only in a vacuum chamber, and laser samples usually must be specially prepared and must fit into the laser rig. DESI works with everyday surfaces, liberating ions that flow into the spectrometer through a sampling tube. Using the method, Takáts and Cooks have detected traces of the explosive RDX on a leather surface and residue of the chemical weapon DMMP on a rubber glove; tracked organic compounds in seeds and stems of plants; and even sniffed out an antihistamine on the skin of a person who had taken the drug 40 minutes earlier. The team has patented the technique, and a start-up company will try to commercialize it.
Some researchers predict that DESI will prove most useful for analyzing laboratory samples. But Albert Heck, a mass spectrometrist at Utrecht University in the Netherlands, says the technique opens the way for taking mass spectrometers out into the world and analyzing surfaces wherever they may be found. As they travel down life's road, mass spectrometrists can now stop and ionize the roses.