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Separation science: thin layer chromatography

Prepare the tablet found at the crime scene for further analysis with Researcher, Joanna Czerwinska.
So Joanna’s in here, and she’ll be able to help you with some more analysis. Thank you.
Hello, Joanna. Oh, hi. We did have a look at the database and found out this was matching the MDMA - MDMA. OK. - And we need further analysis, please. All right. Excellent. Right, so we’ll prepare the sample for further analysis, and then we’ll also run a very quick experiment that’s called thin layer chromatography. Thin layer chromatography. Yeah. So let me get this vial out of the bag. So we’ve got the tablet in the vial now. So the first step is crush it up. So if I can ask you to put the tablets into here, and then crush it up.
OK. Excellent. So I’m going to go now and weigh out five milligrammes of this sample. In the meantime, if I can ask you to prepare your TLC plate. So if you could take this plate, and using a pencil and a ruler, which are over there, if you could draw two lines - one at the top, one at the bottom - and then we have three samples, so we’ll be running water, our tablet and the reference standards. So if you could just label them up, and I’ll be back in a second.
Excellent. I can see you’re done drawing. So I’ve got five milligrammes of our tablet in this volumetric flask. So, our next step is to add our solvent, which is methanol. So if I can ask you to use this Pasteur pipette and add enough solvents so that it reaches this line over here.
OK. I can do the final bits.
Right. I’m going to put the lid on. I’m just going to give it a bit of a shake.
So, I’m not sure if you can see, but if you look up closely, there are still some undissolved particles in the solution. Normally what we could do, we could sonicate it and then filter it using a syringe and a filter. We won’t sonicate it today, but we’ll filter the solution and get rid of those undissolved particles.
So, I am now going to transfer the solution into a new vial, and I’ll ask you to then filter that solution using a syringe and a filter.
So what you do, you have to draw up the solution, put it on the filter of the device, and if I can ask you now just to slowly press it on the syringe. OK. Like this? Yeah. Keep on going.
So you can see that all the particles that are in soluble methanol are going to stay on the filter - Yes, I can see. - and we should get a transparent clear solution in this vial. OK. Excellent. I’ll do it once more, just to have a little bit more sample.
So, this is now our filtered solution, which shouldn’t have any undissolved particles in it. So now, going back onto our TLC plate, we’ll have to aliquot a tiny amount of this solution, water, which is a negative control, and our reference standard, which contains MDMA, onto the plate. So to do that, you’ll use this capillary needle, and I’ll show you how to do it with our MDMA reference solution, and I’ll ask you to do it with water. So what you want to do, you want to pick up the solutions. So, now you’ve got five microlitres of that solution in your capillary needles, and then you put it on your TLC plate.
You can gently press it down, and slowly you deposit that solution onto your plate. Use this water and aliquot it onto the plate.
Yeah. Perfect. And I’ll just slowly press it down. Like this? Excellent. Yeah, perfect. You can give this back to me. And then the last sample we want to spot on the plate is going to be our unknown. So this is the sample we’ve just filtered. So I’m going to exactly the same thing. I’m going to pick up five microlitres of solvents, put it on the line and gently press it down.
So now this plate needs to go into a TLC tank. So this is a tank that contains a TLC solvent. So I’ll gently put that in, and you can see that the solvent is starting to go up the plate. So the plate needs to sit in the tank until the solvent front reaches that line at the top of the plate. So that’s probably going to take six to seven minutes, so we’ll wait for it. In the meantime, while waiting for this separation to happen, we have to dilute the sample. So this is our filtered sample that we have to dilute down so that it can be analysed by another technique, which you will see later on.
So if I can ask you to dilute this sample into this vial. So this is LCMS vial. If I can ask you to add this solvent, if you could transfer 999 microlitres into this vial.
OK. Excellent, and now we need to add our sample. So this is a very concentrated sample, and the next technique that you will be using to analyse it is very sensitive, so that’s why we’re diluting the sample to make it less concentrated. So if I can ask you to add just 1 microlitre - so it’s going to be a tiny little drop - right into the vial.
OK. Excellent. You can discard the tip. Thank you. So now I’ll just cap the vial and that can go on to the next step of the analysis. So the plate is now done. As you can see, the solvent front has reached that line at the top of the plate. So I’ll take it out, and I’ll just let it dry for 10 seconds, and then we’ll use the UV box to look at this plate under the UV.
So what we can see here is that we’ve got a spot over here next to our - for our reference standard. Then, for the sample, we also have this very faint spot over here, which I will try to draw. So as you can see, they are more or less at the same level, which is indicative of our sample containing MDMA, which has shown up in our reference standard. However, this is not enough to say that the sample only contains MDMA. So now we need to take the sample that has been diluted for analysis for the confirmation.
OK. So we’ve got our results for the TLC.
So now we’ll take this sample to Tom for further analysis.

The tablet found at the crime scene will be prepared for further analysis. An initial identification of the tablet will also be carried out by a technique called thin layer chromatography.

Prepare the tablet found at the crime scene for further analysis with Researcher, Joanna Czerwinska. Carry out an initial identification of the tablet by a technique called thin layer chromatography.

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