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Aerosol Spray to Identify Bombing Suspects
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."
the silly string hangs of the trip wires, allowing them to bee seen easily without putting nough pressure on the wire to cause it to go off.
In the UK, the Birmingham Six were falsely imprisoned for 16 years (one chap died in prison) largely because of the Griess test. The trouble is, anything nitrated will give a positive. The playing cards the men had been using on the train when they were arrested were probably what set it off. Ping pong balls certainly would. Imagine Forrest Gump in the Twenty First Century, "And then I met the President again, then they tasered me, then I went to prison for life." The Griess test is now completely discredited. Its re-introduction would be on a par with admitting polygraphs, or examining chickens' giblets as evidence, whether it's packaged as an aerosol or anything else.
I believe it is used to detect tripwires. Silly string sprayed ahead of you will drape over tripwires without being heavy enough to trip them. makes sense to me anyway.
man, I feel like mold.
I believe said farmer would have to urinate on their hands after handling fertilizer, not wash, and actually probably need to vigorously rub their hands together until they were hot to generate a positive on this test.
I do not respond to cowards. Especially anonymous ones.
Quote "When was the last time anyone heard about an ANFO bomb going off somewhere anyway?" Depending on the minesite, from once a week to twice a day. Ammonium Nitrate(urea) and Fuel Oil explosives are the backbone of the industrial explosives. There are legitimate uses for explosives, and legitimate uses for ammonium nitrate. A chemical sensor that detects firearm propellants would be more useful for finding criminals - except we are talking about the USA and its miltiary adventures anyway. Just because I work around explosives, and have a beard, does not make me a bomb hurling radical.
Big Brother watching us has got to be better than us having to watch Big Brother
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.
"FDA staff reviewers expressed concern about the number of patients who were left out of the study because they died."
Unless you make it yourself, I think it is unlikely you have urea nitrate in your fertilizer. You probably have urea + potassium nitrate (or ammonium nitrate). To form urea nitrate, you need a strongly acidic conditions.
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.
and catch a lot of farmers.
Now before I get started, bear in mind that not only I'm not a chemist, but Chemistry is one of the things I understand the least. So major talking out the arse follows. If anyone who knows chemistry better wants to correct me, please do, it's very much appreciated.
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.
A polar bear is a cartesian bear after a coordinate transform.