Technique of the Week: Ion Mobility
Nov 5th 2004Wallabynerd alert
The talk itself was fairly routine proteomics stuff for most of it; it’s a very interesting tool, potentially, for studying all sorts of biological and medical problems: how does this bacteria change its enzymes when we warm it up a little? when we add calcium? when we lower the pH? when we give it a different food? But the applications require fairly rapid analysis and high throughput, neither of which is currently possible. At the end, he talked about using gas-phase separations (rather than nano-scale HPLC) with mass spec; it’s a variant on ion mobility spectroscopy, actually. This offers rather less peak capacity than LC — perhaps 50 instead of 200 — but it does so in a very small fraction of the time — seconds, rather than an hour. It’s even possible to use a fast (low resolution) LC step first, followed by the gas-phase separation and then high resolution mass spec. (Actually, the first step is capillary isoele ctric focusing, to give a hundred or so fractions, each of which gets the rest of the process individually.) Of course, it still takes a long time, and requires a couple million bucks’ worth of hardware.
The latest A-page section of Analytical Chemistry has a feature [PDF] on ion mobility spectroscopy, and how it’s used in defense applications. It can be made quite small (a pound or so for the field version), and gives surprisingly good results for nerve agents and explosives. Airports use them to “sniff” baggage and carryon; guards wipe down purses and laptop bags with a cotton pad, which goes into the IMS. Heat and a slight vacuum evaporate anything that was collected from the bag; drugs or explosive residues will show up at characteristic drift times. (At least, that’s the theory; false positives are depressingly easy.)
[This is a draft that had been floating around for a while, probably since January or so .... I think I was planning to add some more to it, but I never got around to it. Clearly. So, to get it out of the way, ta-da.]
