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
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.
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