So like I know in atleast American airports you can get randomly selected or if your bag is searched they run a little swab on your hands or stuff. They say it’s for explosives residue which makes sense to check for but how do these tests work?
It seems like explosives could be made out of a huge variety of things that are accessible. Two easy ones that come to mind are gunpowder and gasoline. What test shows all the main potential explosive ingredients? Or do they just only check for a couple?
In: Chemistry
There are a lot of things that can explode, but the vast majority of them do it in the same way. They have a bunch of nitrogen atoms, and when the nitrogen is freed from whatever it’s attached to, they immediately grab onto each other and release a bunch of energy. You can get a very solid first guess by looking to see if the swab has a bunch of nitrogen on it.
many common detectors I have seen at US airports are based upon ion mobility spectrometry (usually using a product under the Smiths brand name).
Wikipedia has a pretty detailed article on the subject, although this kind of analysis could be its own unit of a college course, but trying to summarize: the mobility of an ion in a gas phase moving through an electric field of known strength is can be compared against known values for common targets substances.
I tested positive on one of those swab test at the airport. My hand lotion had glycerin in it. It’s a very common additive in lotions.
Most of those scanners use something call GCMS which stands for gas chromatography / mass spectroscopy. Those are not 5yo friendly words but each part (the CG and the MS) is pretty simple.
For GC they swab your suitcase picking up a bunch of chemicals. The. They blow air across your sample which picks up the chemicals and carries them away in the air. The air flows through a tube filled with a sand like substance which slows the chemicals as they’re carried by the air. It slows different chemicals at different rates so the chemical compounds come out the other end of the tube one at a time. This lets the machine run the MS step on one chemical compound at a time.
Then the gas runs through the MS step. Each chemical has a molecular structure. The MS breaks the molecule up and measures the mass of the different components. So for water (h2o) you could get a fragment weighing 10 (the full h2o since hydrogen weighs 1 and oxygen weighs 8), a fragment weighing 9 (OH), 8 (O), or 1 (H). You could never get a fragment weighing 2 because the two hydrogens are not connected. The machine also measures the ratios of those different mass fragments which results in something like a fingerprint for that substance. It then compares those against fingerprints of known explosives.
Are you trying to get through security after doing shady shit?
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