Chemical Trace Screening Technology

Found this at Schneier.

The research from Purdue, led by analytical chemistry professor Graham Cooks, developed a technique called desorption electrospray ionization, or DESI, that eliminates a part of the mass spectrometry process, and thus speeds up the detection of substances to less than 10 seconds, said Williams.

To use it, law enforcement officials and security screeners will spray methanol or a water and salt mixture on the surface of an object, or a person's clothing or skin, and test immediately for microscopic traces of chemical compounds.

In the lab, DESI has tested for chemicals at the picogram level -- or trillionths of a gram. This is about 1,000 times less than the minimum amount of material previously required for detection.

Cooks also hopes to commercialize a rugged DESI sensor that would weigh as little as 25 pounds and fit into a knapsack.

"We have tested it for a wide variety of explosives and the experiments represent several practical conditions such as using mixtures using different surfaces (skin, paper, luggage)," says Nari Talaty, a graduate student on Cooks' team at Purdue.

Now there is a brilliant piece of work that is just going to fail miserably.
Examples? Hmmm, what explosives would they be checking for? Would they look for things like gunpowder residue per chance? Go to the range on Saturday, get arrested on your Monday flight for work.

How about other chemicals that are common, such as fertilizers or nitro-cellulose?

What about cross contamination issues? Will the people doing the sceenings wear gloves and change them after each sample? Will they handle equipment and sampling devices without cross-contaminating? I doubt it. Don't believe me? Watch your dentist or the hygienist next time you're in. The tools are nice and laid out, they put on their gloves, then they adjust the light. Was that light sterilized since the last patient? How about that pencil that they annotate their records with? I've never seen any dental type not cross contaminate during work.

Schneier worries about false positives, and rightly so. Since the people doing the work won't be taking their time and carefully watching their actions. The more sensitive the device the more likely the possibility of poor sampling methods causing false indications. And the more likely you'll be missing that flight.