The Second Version

29/03/08

The Truth About Analyzers

The sad story of the woman forced to remove her nipple rings at an airpot in Texas by idiotic TSA personnel is all over the web; the comment at Atomic Nerds is probably one of the most interesting.

But no discussion of airport security (and madness thereof) is complete without mentioning analyzers for explosives, and I see there's a lot of misconceptions about these machines:
The sniffers use highly refined gas chromatography, which is the same ballpark as mas spectogrophy (sic)..
No, it is not the same ballpark. In fact, gas chromatography and mass spectrography are based on completely different principles: the former, on the gas-liquid distribution of solutes; the latter on the motion of ions in electrical and magnetic fields.

However, a mass spectrometer is often used as a detector downstream a gas chromatograph, because the two instruments just combine well (no need to go into details) and the MS provides abundant information about the compounds that have been separated passing through the GC.

Moreover, what is "highly refined" supposed to mean? Maybe optimized for instumental compactness, ease of operation and speed of anlaysis. But surely not optimized for high selectivity, linearity of response and all that - those are conflicting priorities. A field instrument of this kind does not even need certain features in fact.

From what I've read on the internet, the typical sensor for these applications is a device called Ion Mobility Spectrometer - a variation on the MS principle, which ionizes the analytes and separates ions by forcing them to move through an inert atmosphere under the influence of an electrical field.

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