How do you identify a poison?

09 January 2018

Interview with 

Dr Lorna Nisbet, Anglia Ruskin University

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In this programme so far, we've looked at historical poisoning cases. But how are poisons detected today? Lorna Nisbet is one of the many forensic scientists who identifies poisons, sometimes in deadly cases. Katie Haylor met Lorna at her lab in Anglia Ruskin University, to find out more...

Lorna - This machine here is a gas chromatography-mass spectrometer, and it’s actually two instruments that have been coupled together. You have the gas chromatography (GC) side and then you’ve got the mass spectrometer side. Your sample, your poison, will go into the vial and the instrument will take it in a syringe and it will inject it into the GC. At that point it will become a gas and that will separate out all the different components that would be in that sample. Because, unfortunately, when people do pass away or they have got an acute reaction to a drug or another poison, they might not have just taken one. So we need to separate out all those different components to see what is in that sample.

Katie - Are we putting blood or some sort of bodily fluid in here?

Lorna - You don’t put the bodily fluid in (directly), you do some cleanup beforehand but it would be like that. Then it will travel through the GC, and the GC is made up of a column that’s that’s 30 metres long.

Katie - It doesn’t look like it’s 30 metres long.

Lorna - And it is extremely thin and all coiled round and round and round, so it’s quite compact. Then it will travel through to the mass spectrometer and here it gets bombarded by electrons so it goes past something that looks like a filament in a lamp effectively. It goes into what’s called the mass spectrometry source and, from that point, because it’s getting bombarded by these electrons it causes your compound to fragment. The idea is that every compound has a different fragmentation pattern so it’s like a fingerprint.

Katie - So if you know the fingerprint you can tell what it is?

Lorna - Yes, exactly. If you have something, once you’ve identified what it is, you can put down something that you think is the same and if it’s got the same fingerprint you can confirm that that’s what it is.

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