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Fourier-Transform Infrared Spectroscopy

Meet Dr Andrew Chan who explains how FTIR analysis can identify drugs.
6.6
Hi. Hi Alan. Can I introduce you to Natsumi? Hello, nice to meet you. Hi, nice to meet you. So, Natsumi has a drug sample she’s hoping you can help analyse. OK. So I’ll leave you two together, and hopefully you have some luck. Thank you. So this is the sample. All right. OK, Natsumi, let’s see what FTIR can do for you with this sample. OK. Now here, this is the FTIR spectrometer that we’re going to use. As you can see, this is the area that we’re going to put the sample on in a moment. OK. But for now, before we take a measurement, we need to first measure what we call the background spectrum. OK.
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Now to measure background spectrum, what you need to do is first check all the parametres are set correctly, like in here, and then just press the background button. What the spectrometer is doing right now is measuring the infrared spectrum of the sample, but we have just a clean surface, so we don’t have any sample right now. Later on, we’re going to make another measurement which contains the sample, so that the computer will have both the spectrum of the sample and the spectrum when there’s no sample, so that you can calculate the true spectrum of just the sample without any interference of the environment. I see. OK. So now, the spectrometer has already found its background.
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What we need to do now is to put this sample onto the spectrometer. What I need to do first is to put on the gloves - Ah yes, of course. - because I don’t want to contaminate the tablets, and then what I want you to do is to position the tablets onto this shiny surface, where I said just now where we’re going to have the sample measured. Put it on here. Try to be as accurate as possible. And then we have a press, which allows us to apply some pressure onto the tablet so that we can make sure there’s a good contact between the measuring surface and the tablet to get a good spectrum.
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Now to help us to do that, we can actually monitor the signal as we press down the tablet onto the measuring surface. You can see before we press we have just noise.
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Now I start to bring the tablets to the measurement surface by applying some pressure. You can see as I increase the pressure, the spectrum of the tablets start to come up.
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I think now it looks very good, because we have a very good absorbing signal and very small noise. So, let’s start this measurement by pressing the scan button.
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So what the spectrometer’s doing right now is measuring the infrared spectrum with the sample, with the tablets, so that we can calculate the absorbance profile of the tablet. You can see actually as this measure, it’s already showed the preview of this spectrum that we’re going to see. Now each individual band represents absorption of the infrared light from the sample.
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Depending on the molecule that we are studying - in this case we are trying to see MDMA, so depending on the MDMA molecule, where it absorbs in the infrared spectrum, it should give us a very particular pattern of absorption, and then we can use this pattern of absorption to compare to something that we know for sure is MDMA, which is called a reference sample. If you compare the spectrum, then if they match, then we say, ‘OK, there is MDMA contained in the tablets’. But if there’s not, then we are not so sure. We may need to do more tests. Let’s have a look at the results, shall we? OK.
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So I’ve got a reference spectrum of MDMA here, which looks like this. Let me show it better to you. You see it has a very nice pattern of absorption. Now, if we compare these to the tablets we measured just now, like here, the black spectrum is the spectrum of the tablet that we measured just now. The red one is the spectrum of MDMA. Now you can see the MDMA contained a number of peaks, for example in here, 1491, in here 1248, and in here, 1038. Now the black spectrum may contain some of these peaks that overlap with the peaks of the MDMA, but they are not very clear.
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So what I suspect in this case is the tablet may contain not just MDMA, it actually seems to contain a lot of other ingredients as well. I see. And it is quite common for tablets to contain other ingredients. For example, excipients, where they will use excipient to help in the tablet processing to make a stronger tablet. So I think this is the case that they have added quite a lot of excipients in these tablets. It might contain some MDMA, but it seems like the signal, they overlaps, because FTIR is not a separation technique. Unlike LCMS, where they will first separate the components in the tablet before they make measurement, FTIR just measure the tablets as it is.
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So in this case, I think what you need to do is you need to try other techniques to confirm whether MDMA is really contained in these tablets. OK.
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Let me retrieve the sample for you, and you can see that the tablet is still intact after this measurement. Ah, yes. And it’s ready for you to take it to some other spectrometer or analytical techniques to measure the ingredient. Thank you.
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