Science Interviews


Thu, 26th Mar 2015

What's your poison?

Dr Sarah Hall, Anglia Ruskin University

Listen Now    Download as mp3 from the show Whodunnit? Fascinating Forensics

There a many things that are toxic to humans and can cause death if we ingest Drug Testthem in high quantities. But these might not cause visible signs that show up in a post mortem. So how do we detect them? To find out what tests can be carried out Chris Smith spoke to Sarah Hall from Anglia Ruskin University...

Chris - So, what sorts of chemicals can you detect?

Sarah - All kinds of things Ė natural products, obviously, more synthetic drugs, all kinds, yeah.

Chris - And how do you go about doing that normally?

Sarah - Well, we first do preliminary tests which tend to be colour tests that give you a positive ID, more about the class of the drug rather than a specific drug.

Chris - So, when you say a colour test, are you saying you literally take a sample from a person and you mix it with something and if a chemical is there, a drug is there, it will produce a colour that you can see?

Sarah - Yes, it will, yeah.

Chris - How does that work?

Sarah - There's different reactions. There's lots of different tests, but it involves a fair amount of sort of complex chemistry. But the idea of them is they work quite fast. You can do it at a scene in situ and they give a bright colour very quickly. So, itís very obvious if you get positive.

Chris - So, what sorts of specimens you can test?

Sarah - We can test urine, we can test blood, we can even test hair. Hair is quite good because it gives us a sort of longer timeframe to looking at maybe the victim themselves or maybe abuse of drugs, etc.

Chris - How does that work? How does the hair end up being useful?

Sarah - There are certain chemicals in your hair that allow things to be trapped in it and they sort of bond quite tightly. So, they remain in your hair for a long time.

Chris - The chemical would therefore go around in your bloodstream and because the hair is growing inside your body and then coming out, the drug in your bloodstream gets incorporated inside the hair. Is that what you're saying and you can pick that up?

Sarah - Yeah, thatís correct, Chris. Yes, we can.

Chris - Can you tell roughly how much someone has been using a drug?

Sarah - Yes, we can. We can quantify it, yeah.

Chris - Wow! Shall we have a go? Have you got anything you can show us?

Sarah - I've got some little coloured tests to have a look and if somebody wants to come and have a look at it, they are most welcome.

Chris - What's your name?

Milly - Milly.

Chris - While Milly gets her gloves on, just talk us through please Sarah what weíve got here. So, you have got a little china plate with lots of little indentations in it, little wells and a big box with Ė it says there's some dangerous drugs in here. So, what are we going to do?

Sarah - Well, the first test is a test that can be used in a crime scene straightway. So, you donít need to be a chemist to do this sort of thing. itís just a glass ampoule thatís got a specific reagent in that reacts to certain classes of drugs.

Chris - Which drugs are you going to look for?

Sarah - Weíre looking for opiates. So, I've got an opiate with me. So, letís see if we get a nice colour change.

Chris - Do you want to test any of the audience?

Sarah - No, I better not.

Chris - Sure, you would find nothing. So, you are taking out from the box, youíve got a little ampoule there. This is the reagents, the thing thatís going to react with the drug molecules if they're there.

Sarah - I'm just going to find myself a pipette.

Chris - There's a little glass pipette to draw up.

Sarah - And a little spatula because you donít need much. A really small amount gives you a really good colour change which is why they're very good tests.

Chris - Okay, so weíre going to mix some of Ė youíve brought along obviously some opiate chemicals to show us that this actually works.

Sarah - So, weíve got a glass ampoule and you see itís got reagents. Can you see the solid in it, Milly?

Milly - Yeah.

Sarah - So, what you do is you break the top off, put a small amount of powder but you could also put a liquid in. Put the top on, give it a shake and you should get a nice purple colour.

Chris - Okay, letís have a go. So, at the moment, this ampoule has just got clear colourless fluid in it. Thatís the top coming off the glass ampoule and youíve got your pot of opiate and there's a policeman. Do you know there's a policeman here?

Sarah - I do. I'm keeping quiet.

Chris - Wow! That really is a very tiny amount youíve put in. Literally, a couple of grains of the agent.

Sarah - Yeah, milligrams. You hardly need any.

Chris - So, weíre going to shake that up.

Sarah - You should start seeing a purple colour coming through..

Chris - Tell us what youíre seeing, Milly.

Milly - At the bottom the bubbles are turning purple.

Sarah - Yeah, good.

Chris - A very bright purple.

Sarah - So, itís a very bright purple. So, that tells me there's an opiate there.

Chris - How sensitive is this? How much can you pick up?

Sarah - They are quite sensitive but the actual instrument techniques that we use are very sensitive too. But they have to be sensitive because most street drugs are very dilute. They're diluted with some really nasty dilutants and all kinds of things. so yeah, they have to be quite sensitive.

Chris - Thank you very much, Milly. Do have a seat. If you used that at the scene of the crime, that would give you an indication of what was going on. But it obviously wouldnít tell you exactly what the agent was. It would tell you it was just a class of agent like an opiate or something. But you'd like to probably know more accurately what it was. So, what can you do to get a more accurate chemical diagnosis of what's going on?

Sarah - Well, so we do analytical tests. So, the most techniques that we use in forensic science tend to be chromatography techniques because most drugs are fairly complex. There's a lot of things in street drugs. So, you try and separate everything out. So weíre able to just look at the thing you're interested in which is what the chromatography does.

Chris - How does that work? what is chromatography?

Sarah - Well, itís just separation. So, I've got some pictures to show you actually if you want to see them.

Chris - That will be good for the radio.

Sarah - What we call a chromatogram because itís chromatography.

Chris - It looks like a graph effectively. There are lots of little peaks, like little teeth in a sharkís mouth actually. So, what are those little peaks?

Sarah - Well these, this is a chromatogram of petrol. There's over 200 components in petrol so we need to separate them all out before we can identify all the individual components.

Chris - I see. So, you would feed a sample into the machine and it breaks it up into all of the individual components so you can see when someone has been exposed to something, you won't just say, ďItís opiates.Ē You'll know all the different chemicals that are in there.

Sarah - Yes and we have a detector on it which is a really good detector. Itís called mass spectrometry but basically, how I understand it, itís like getting a hammer and smashing a molecule apart. And how the molecule breaks apart is indicative to that molecule. Only certain molecules break in certain ways. If we know that, we can then do a positive identification.

Chris - Does that mean you could for instance, if you had a sample of some drugs in an environment and you had a sample from the person, you'd be able to marry up almost the chemical profile in the drugs and environment with the chemical profile from the person and  prove that one led to the other.

Sarah - Yes. We donít just look for the drug. We look for everything else thatís there too and it enables you to do that through chromatography.

Chris - What sorts of things can one probe? Itís not just illegal drugs you could look for. What else could you look for with these sorts of techniques?

Sarah - The fair amount of ignitable liquid. So, accelerant analysis is a good one, fire debris analysis.

Chris - So, if it wasnít something that was routine chemical that had killed our victim but it was something a little bit  more unusual, you could still find the molecule.

Sarah - We could. It would take a bit longer because it would be like looking for a needle in a haystack a little bit, but yeah, we could.

Chris - Because it would stand out as one of those peaks because it wouldnít normally be in the body and you'd see something that was there that shouldnít be.

Sarah - Yeah.


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