Aerosol Spray to Identify Bombing Suspects 191
RedHanded writes "Forensic chemists at the Hebrew University of Jerusalem have developed a color-changing spray that can identify people suspected of making or planting bombs. The chemical turns from yellow to bright red when it comes into contact with urea nitrate, an explosive residue that may be left behind on the hands of someone who has handled an improvised device."
Re:First silly string, now spray paint? (Score:2, Informative)
More Griess Test Nonsense (Score:5, Informative)
Re:First silly string, now spray paint? (Score:5, Informative)
Re:bomb makers or... (Score:3, Informative)
Re:ever since oklahoma city anyway (Score:3, Informative)
Re:Basic hygiene (Score:4, Informative)
From what I know of the chemistry of aldehydes (there's a great icebreaker at parties...), this dye should react with any primary or secondary amine- like regular old urea, ammonia, amino acids, etc. What this group claims, however, is that there is a particular color change reaction for this dye which occurs for urea nitrate which does not occur for other amines.
I think what the article's confusing picture of the dye and urea nitrate interacting is suggesting is that the hydrogen bonds between the nitrate and urea moieties remain intact even after the urea has bonded to the dye, so the nitrate moiety affects the dye complex and the color it appears. I'd still be concerned about false positives, personally, particularly from different amine salts. The color produced might be uniquely identifiable to a spectrophotometer, but for a visual test I'd be worried about anything that turns "reddish" enough to produce a false positive.
Re:Basic hygiene (Score:5, Informative)
From the article, the "amazing" new molecule is just commercially available p-dimethylaminocinnamaldehyde. The chemistry involved is already well-known. It is used for, among other things, indirectly detecting biotin (by way of the urea in the molecule). Basically you mix your urea-containing compound with a strong acid (sulfuric acid works), which promotes enol tautomerization and makes the normally unreactive nitrogens of the urea reactive toward electrophiles. One of the nitrogens will react with the aldehyde to form an imine, and due to the availability of a quinoid resonance contributor, turn color (red in the case of dimethylaminocinnamaldehyde and yellow in the case of dimethylaminobenzaldehyde).
What's special here, and why this won't result in a thousand false positives from detection of any urea-containing compound, is that urea nitrate is a stable salt and acidic enough on its own to react with dimethylaminocinnamaldehyde without the addition of acid. So a wipe test, drop it in isopropanol, add some of the aldehyde and see if it changes color. It's a fairly elegant application of old chemistry to forensic analysis.
Re:Basic hygiene (Score:4, Informative)
Having RTFA, I'd worry anyway (Score:3, Informative)
That said, looking at the illustration of the mollecules interacting in TFA, it looks to me like their dye binds to just the nitrate anion, and there is no trace of urea to be seen at all there. I.e., what is so funnily coloured is their mollecule after stealing a nitrate anion from _any_ nitrate whatsoever.
It could be that other mollecules don't give their nitrate as gladly as urea nitrate, or whatever. Again, I don't know enough chemistry to rule that out.
But unless I forgot chemistry completely, _any_ salt will split into a number of ions in a solution. Heck, even water doesn't stay H2O, a number of mollectules split into HO- and H3O+ ions. Ph 7 is basically just the equilibrium point for that mix.
So basically even if you handled potassium nitrate for your orchids, or made a sandwich with ham cured with that (preservative E252 _is_ potassium nitrate), or just are a chain smoker (tobacco is quite commonly treated with it too), or made a model rocket recently, etc, etc, etc... you'll have plenty of nitrate anions on your skin for this thing to bind to. Heck, it's increasingly used in toothpaste too.
And that's just one nitrate. Another common one that comes to mind is ammonium nitrate. Ok, so that one _can_ be used for an ANFO bomb, but is also used by the ton by farmers and even by miners.
So I'm, you know, _curious_ what their miracle aerosol does in the presence of those. Did they spray it on a slice of cured ham and it _didn't_ turn purple, for example? Did they check it on ammonium nitrate too? On a pingpong ball? Basically which nitrates _does_ it react with, and which not? Because again, my uninformed interpretation of their drawing is that it would react with any nitrate whatsoever.