In Our Time - Chromatography

Episode Date: February 4, 2016

Melvyn Bragg and guests discuss the origins, development and uses of chromatography. In its basic form, it is familiar to generations of schoolchildren who put a spot of ink at the bottom of a strip of paper, dip it in water and then watch the pigments spread upwards, revealing their separate colours. Chemists in the 19th Century started to find new ways to separate mixtures and their work was taken further by Mikhail Tsvet, a Russian-Italian scientist who is often credited with inventing chromatography in 1900. The technique has become so widely used, it is now an integral part of testing the quality of air and water, the levels of drugs in athletes, in forensics and in the preparation of pharmaceuticals.WithAndrea Sella Professor of Chemistry at University College LondonApryll Stalcup Professor of Chemical Sciences at Dublin City UniversityAndLeon Barron Senior Lecturer in Forensic Science at King's College London.

Thank you for downloading this episode of In Our Time, for more details about in our time, and for our terms of use, please go to BBC.co.com.uk slash Radio 4. I hope you enjoy the programme. Hello, one of the big ideas in chemistry today is chromatography, a way of separating mixed-up substances to analyse them or extract something useful. In its basic form, it's familiar to generations of school children from when they put a spot of ink at the bottom of a strip of paper, dip it into water, and then watch the pigments spread.

upwards revealing their separate colours. Sometimes, if you are lucky, like feathers on a bird of paradise. With progressive discoveries over 200 years, some fine-tuning and an occasion a Nobel Prize, chemists can now sift out the different molecules in just about any substance. It's a process that has an essential role in many parts of modern life, the cleaning of drinking water, in forensic science, and in medical tests and in making pharmaceuticals. With me to discuss chromatography are Andrea Seller, Professor of Chemist, at University College London, April Stalka, Professor of Chemical Sciences at Dublin City University, and Leon Baron, Senior Lecturer in Forensic Science at King's College London.

Andresella, we've mentioned paper and ink. What's going on there? And can you, is this, can you give us that example of chromatography? Well, this is, this is one of those, those wonderful little experiments or demonstrations, if you will, that everyone should do with their children. I mean, you know, if you've never done this before, then what you really have to do is to get either some kitchen paper or some blotting paper. I must say that, I'm just to explain to the business. Andrea has decided to turn this studio into a mini laboratory. So he's all over the table, which is not very big anyway.

I'll talk while you're cutting the papers into strips or whatever you're doing. We've got stuff, and he's going to tell us how, you're going to tell us what's going on, aren't you? So, absolutely. So what I've done is I've cut a little piece of blotting paper. I'm going to take some water, and I'm going to pour it into a beaker. And then what I'll do is take the blotting. paper and put one spot

of ink about a centimeter from the bottom. And the ink that I'm using is actually a water-soluble ink, so I'm using a magic marker. And now I dip the paper into the water. I'm just reassuring

listeners that this, in fact, is happening. And by capillary action, of course, the water rises up the paper. And what it's really doing is it's setting up a kind of race between the molecules that make up the colors within the magic marker spot, within the ink itself. And so they all start together at the bottom of the paper. And as the water reaches them, what it starts to do is to help them travel up the paper.

So they're carried upwards. Now, the paper is something that we call the stationary phase, because it doesn't move. And on the other hand, the water, which is the moving part, we call the mobile phase. And along the way, the different colors will move up. the paper and they move really to the extent to which they stick to the paper or less. So it's really looking at the, let's call it, the stickiness of the ink itself, right, with respect to the paper. And what this will do is it will ultimately separate things out and allow us to analyze

what this ink is made of. Does anything happen, did you know, Joe? Well, we're only at the beginning. The capillary action is quite small, but of course, as one always says on Blue Peter, here's one I made earlier. So here is a spot that we put a few minutes ago. It was using brown ink, and it separated out into a beautiful sort of bright blue. There's some pink and there's some orange as well.

And what you tend to find is that it brings out the inner child in just about anyone. Right. Well, my inner child has not. Yes, fine, I'll leave it at that. Okay, fine, so we know what's going on. The technique has remained remarkably similar since it evolved from that. that's a simple premise, although the substances, the ways being addressed by different materials, has grown more complicated. Well, the technique actually originated really about 150 years ago,

and in a sense by accident, with a German chemist called... No, I didn't ask that. What do these techniques have in common, the different techniques? Well, the thing that they have in common is really the fact that you're starting everyone off, together and that they travel through a medium at different speeds. And it turns out that there's a plethora of ways in which you can get different molecules to, in a sense, probe their stickiness against different stationary phases. And so one can use paper, when can use all kinds of sort of solid materials like silica, like alumina, like chalk. And on the other hand, you can also use all kinds of

polymers and resins which have charges on them. And what that allows you to do is to see whether the molecules stick through a purely electrostatic. In other words, there's a charge on the molecule and a charge on the stationary phase. That might allow them to stick. In other cases, it might be more subtle forces which actually hold them. But the key point is that some go faster, some go slower. Right.

April Stalker, can you explain a bit more detail what's happening in chromatography at a molecular level. So we've had this experiment, as we've seen, didn't work, it's probably working slowly, we'll see it at the end of the program, perhaps. And what's happening in the molecular level, and why is that important? Well, the way I kind of think about it, my first academic position was at the University of Hawaii, and I happened to be stuck in traffic out in front of the international marketplace one day, and noticed a busloaded tourists being dumped out at the front of the marketplace. And if I wanted to characterize, that group of people. How many little boys are in that group? How many senior citizens are in that group?

It's real hard to tell that when they're all clumped together. But if I imagine myself going around to the back of the international marketplace after the people have percolated through that marketplace, they've had different affinities for different sites. The athletes might have been more attracted to the sports paraphernalia stores. The senior citizens might been more attracted to the things selling touristy kinds of things they could bring home to their grandchildren. children. But the fact of the matter is that they all would come out in different clusters that were separated and then it's much easier to characterize the, and that's essentially what's going on in a molecular level. You have things that are more attracted to different

materials like the paper, for instance, in the example that Andrea just gave. And as chemists, we have to understand that on a molecular level and try to exploit it and maximize certain interactions if we want particular separations versus others. Given the simplicity of the experiment, why did it take so long to get around to it? Well, originally, Spett was the one who first did a lot of this kind of stuff and there were two things that had. This was in early 1900s when he first started talking about this. Some of his early papers were published in Russian and they weren't accessible to the general population. Some other colleagues or other scientists in the field used materials that were a lot more aggressive in retaining compounds and so other people couldn't

reproduce it. And so for those reasons, that's a lot of why it didn't get adopted widely. Can you tell us how important the choice of the mobile phase, the water in this case, in Andres case, we put this piece of paper in water? It's critically important. There has to be, it's a balancing between the interactions that the substances and the sample that you're trying to analyze, they have some affinity for both phases. It's just which one dominates. The station phase and the mobile phase. It's a combination.

You can't do it. And molecules are more attracted to one or the other. So they stick or they move on. Yes. And that gives you different definitions. Yes. And of those definitions, you can work out the compound in its individual parts. Yeah.

So that's what's going on. Yeah. Isn't that a wonderful technique? It is. It's great. So where did you go from there? You have to detect it at the end. Now with Svet's case, and in the example given here, you use colors.

What do you mean use colors? You can see the colors on the paper when they're separated out. But a lot of the stuff that we're working with now in chromatography, we're working at very, very small levels. low low concentrations, and we're also working with substances that don't have color. So you have to be separating them is one thing, but you also have to be able to detect them. Okay, Leon Baron, we've got a good idea about how it works now. It isn't all that complicated, but it gets more sophisticated as time goes on because the stationary thing can be gas, can be liquid, not just a piece of solid paper,

and the mobile thing can not only need be water, but there are all sorts of other. So that's the deal. right. Before we go any further, because it's interesting to get into detail, but it'd be useful, I think, for our listeners to know although it began as blue sky thinking, in the great tradition of Royal Society,

of curiosity, it's ended up as a great commercial engine. Where is it working in the practical and commercial world? Okay, I think we could speak for hours about that. It's a very, very exciting topic, but we won't. I think I'll start off by saying that

Almost everybody has had chromatography affect their lives, I would imagine. So here in front of me, I've got a bottle of drinking water. If you look at the label on these drinking water bottles, you generally see a list of compounds in there. I've got things like calcium, magnesium, potassium, sodium and so on. Chromatography was used to find out what was in that drinking water. It's a spring water source. And it also is able to find out how much is there. So it's a delicate balance in drinking water, for example, to find out what's in it

and is it fit for human consumption. The techniques that we described in the initial simple stage, are working there to get that bottle of pure water. What was used here was ion exchange chromatography, and so it exploits a charge on either a metal or its counter-ion here to separate out the molecules from each other and find out how much is there. And what is it doing in forensic science?

It's a very, very active component of most forensic laboratories. It's almost a gold standard in chemical analysis laboratories. Traditionally, people would use it for forensic toxicology, so the study of poisons. Generally, taking a blood sample from somebody, is a very, very complex mixture, and to find out which of the some 2,000 pharmaceutical compounds or illicit drugs might be there.

Can you do it in that detail? Yes, you can. Also, it's very, very useful for detecting explosives and arson. In what way? So again, if you go to a scene, it might be a post-blast scene, you might take a sample from that scene,

very complex. A sample of what? It might be soil, it might be a residue on a surface to find out what the explosive might have been. And we were able to separate out all the components and screen it. And I think that's the real advantage of...

So what do we get if we do that? We go to explosive scene, we take a sample, we're looking for. We're looking for characteristic peaks within our chromatogram, so our separate components, that might indicate that that is a particular explosive type. And there could be up to 60 different types, certainly for explosives.

And drugs, there are thousands. And so modern chromatography now is able to separate these things on that scale. So if you know it's a particular sort of explosive, you might think, well, it's come out of that particular area of sale and development, so you're getting towards the culprits all that faster? Yes, so there's two things. first of all, the great wonder about chromatography is it doesn't just isolate what you're looking for. It also separates it from everything else.

And so you can use other things in the sample to help you get more intelligence. So, for example, if you have a TNT explosive, there might be some other impurities there, which might lead you to understand how it might be made, which allows you to get some more intelligence about where it came from, for example. So it tests water, it tests air as well, doesn't it? Air, yes. If you take a city like London, we're all quite concerned about air quality. at the moment. Air is a gas. It might be colourless to you and me, but it's a quite complex mixture of different chemicals. And chromatography is often used in the field even to monitor and in real

time separate the mixtures and relay the information back so we can understand air quality and air pollution in particular. So the pollution figures that we get are the result of chromatology? They can be, yes. There are some other techniques, but chromatography is very strong and underpinning that, yeah. And massively in pharmaceuticals? In pharmaceuticals, yes. So chromatography is used a lot to underpin drug discovery. So by isolating and purifying substances and also to scale it up to manufacture,

it's really important to separate and refine and purify it so that you get your end product that's desirable for human consumption. Is it essential now to pharmaceuticals? You can't put one on the market without having gone through the tests decided by, chromatological examination? As I've said, chromatography is one tool, but yes. Usually we do a lot of impurity analysis using chromatography to see,

rarely it's a case that a chemical reaction will go to completion without some impurities or some original reagents being there. So it's very important to make sure that we've made what we've made and how much of it we've made. And so chromatography really underpins that. Most pharmaceutical laboratories have chromatography as a standard technique.

Thank you. Andrew Seller again. One of the earliest figures associated with this is the German industrial chemist, Friedli Bhrunger. Is it Runger? That's right. Friedli Runger. And what did he do? Well, Rögen was really quite interesting. He was quite a maverick figure. And something that he did sometime around the 1830s was to actually dribble small quantities of chemical reagents onto blotting paper. and what he saw was a spreading out of the colors of the chemicals themselves. And as they reacted, what they did and spread out, he got an incredible kind of pattern with a weird shape to it.

And this struck him as A, very, very beautiful, and secondly, very, very intriguing. And in a way... Why is he doing it as much, Richard? Just for a hide of curiosity. Well, I think one of the ideas was that if you actually could... carried out the reaction in paper. It was known that paper had these very, very narrow gaps between the strands. And in a sense, it was like having an incredibly small test tube. So you were conducting things under kind of capillary conditions. And what does capillary conditions mean?

Under conditions where there are narrow gaps and therefore the liquid will be drawn through by, through its surface tension, by capillary action. And so this resulted in these very strange, rather Rorschach-like blotches on paper. And he was, A, intrigued by the colors, he was kind of amazed by the reactions, but also the fact that he got these patterns. Now, to put this into context, this was in the 1830s,

and this is around or just after the time of Völler and Liebig's great experiments, which are trying to understand where the boundary between the organic, the chemistry of life, and the inorganic, the mineral chemistry, actually less. and people were wondering about the life force, you know, where does life emerge from?

It was clear that chemistry lay at the heart of it. And Rungan became incredibly excited by the patterns that he saw, and he just couldn't explain where they were coming from. And he imagined that what the capillary action was revealing was a life force, a new force, a bit like electricity or magnetism, and he called it Das Ode. And needless to see. Well, I'm not quite sure what it really means. I've looked it up. I've looked it up in my German dictionary at home. It doesn't appear. I think it was an invented word. But the key point there was really this idea that he was trying to get to the heart of what life was. He thought he'd found a secret of life. But in fact, he was completely off base because he'd kind of not really understood the basis of what was going on. But Rogen's experiments actually led on, first of all, to getting lots of schoolchildren to doing it.

And the result was that he had privately published hundreds of copies of books containing these original things. They're absolutely beautiful. They're wonderful. But in a sense, they're kind of meaningless. I mean, you don't learn very much from it. The next major figure, in fact, the major figure, April Star Cup, is the Russian, we can call him. He was Italian-Russian, was he? Mikhail Zvet, for whom I have a great sympathy.

What was he doing? First of all, what was he doing? And then I'd like to know why he thought he was doing it. Well, when he first started out, he actually did a lot of his education in Switzerland. This is late 19th century. Yeah, late 19th century. And he was working on plant pigments.

He was really interested in carotenoids and chlorophylls and all that kind of thing. And the part of it is really instructive because what he knows, when he was trying to extract different things out of these plants was that it depended a lot on the solvents that he was using, which is a lot what we were talking about with the mobile phase. And some of his earliest studies, he thought, a lot of people just said that it was because the solvents were doing something to the plant tissue. And he thought, no, there was more to it than that, that perhaps that the cellulose in the plants was a little bit stickier to these pigments he was trying to extract. And so he used a cellulose column and tried to get things, plant pigments to

move down it during using different solvent systems. And it turned out that that correlated very well with the solvent extraction techniques he was using to get the pigments out. Why was it doing it? What drove him to do this? He just was interested in the pigments. And also, I think some of the, some of it was driven by the fact that so many of the kinds of experiments trying to isolate things back in those days were very, very, you know, and the things. tedious and time-consuming and not very systematic and so he was trying to make it much more systematic. Which he did. Yeah, which he did. And he gave his name to it, didn't he really? Yeah, because... Maybe in both senses of the world. Yeah, well, because chromatography, people think of

that as being color writing, but his name Svet actually means color in Russian as well. So, you know, was he an egotomaniac? Who knows? Maybe a little bit of it. It seems to me to be a man who didn't get his just as earth in his lifetime. Partly because we enter into the bear trap which is in all cultures, in all times, is snobbery. Yeah, there was an element of that. There was also an element later on because of later on, you know, history a lot of times is revisionist. And at the height of the Cold War, there was a lot of things about giving him less than his due because he was Russian. But also the idea that being a technician was of less value than being an abstract, a thinker in science.

and these mere technicians shouldn't win Nobel Prizes and they were doing a lot, in many cases like Faraday, for instance, massively, of the essential work. It's really this snobbery I'd provide. It's usually a sort of mask of ignorance, isn't it? Yeah, he was nominated for Nobel, but it was for his work on carotenoids in chlorophylls,

not on his development of chromatography. I'll come to you in a minute, Andre, but can I just develop, thank you very much, can I develop with Leon, the analysis of chlorophyll, Can you just describe to the listeners exactly what he did and why it shows chlorophyll and what did out of it?

Okay, well chlorophyll as April has said, it's a pigment. And so he did that originally as a botanist. He was interested in these pigments from a botanical point of view. And separating them is not very easy and trying to understand what's there.

So he started by investigating a number of different materials as the stationary phase, so things like calcium carbonate, alumina, I think he worked on about a hundred different sorbents thereabouts. And so, you know, he really did investigate the effect

of these chlorophylls and crotonides on their interaction with the stationary phase. I think you probably would say more. Yeah, I mean, in many ways, you know, what he wanted to do was to tease apart the machinery of photosynthesis. And by then it was recognized that photosynthesis were the basis

of all of life on Earth. And he spotted something kind of amazing when he ground up spinach leaves using petrol and he added calcium carbonate and he added calcium carbonate because it's a base and some of the components when he ground up the cell were acidic, he found that the carotines, which are orange,

actually stayed in the petrol while everything else seemed to stick to the calcium carbonate. And that made him wonder whether if he put the calcium carbonate in a glass pipe and then put the spinach extract at the top and then poured solvent in from the top, what would happen would be that first he could wash off the carotenoids,

and that would allow him to work with that. And then he could change the solvent, and he could run off the next colored band, and that turned out to be yellow, and those were the xanthophils. And suddenly he had a way to progressively separate out each one of the essentially antenna pigments, the light collecting pigments, right, that plants use to do photosynthesis.

And in doing so, he also separated out three different chlorophylls. And so there was chlorophyll A, B, and C. Now, his work was hugely contested. And there were German chemists who were absolutely convinced that what he was doing was getting artifacts. But Svet, what he really identified was something crucial. And that was the fact that some of these pigments stick. and he called this adsorption.

And adsorption spelt with the D. Ad absorption. And that means a surface effect. It's a little bit like a post-it note which sticks to the surface rather than something that goes into a sponge. It's a surface effect. And that it was absorption

that was the basis of it. Now, because he was from a minor university, first in Kazan on the Volga and then in Warsaw, he was, as you say, poo-pood by the posh German chemists. And his work really wasn't recognized for a good 25, 30 years before people began to come back to it and realize its

generality. Can we come back to you, Leon, for a moment, to end his, to conclude his story? So he worked with that. Did he go and to develop other, more complex systems or work with other substances after working with chlorophyll in that way? I think most of his stuff was with chlorophyll. But he did, he did actually use the same stationary phase material to add to samples of of extracted leaves, for example, to take out each specific component in turn, which actually forms the basis of another modern extraction technique called solid phase micro-extraction

and also solid-phase extracts a different topic. But actually his thought process in doing that actually led to the forerunner to a lot of the extraction and separation techniques we use today based on adsorption. To take up something that Andrea said just then, not being this work, not being accepted for, 25 years. Did he just

lie in and draw somewhere nobody took any notice and life did not go on without it? For the 25 or 30 years between 1906 and 1941 we had obviously a major event as well and we had World War and I think Svet was particularly impacted by that because he had to flee

and so a lot of his work was interrupted Yeah but other people's work was interrupted I mean Einstein's work was interrupted but they still continued with that so why didn't they take it up? I mean, as soon as the First World War, snobbed, people from this country went to corroborate

what Einstein had done and so on. I'm just interested in why this essential work was not taken up for so long. I mean, they can't all have been just merely snobs, or God knows there's enough of them, but still, so what was going on? Well, I think this is a classic example, in a sense of conservatism in science, is

the fact that, you know, when you have a particular way of thinking, a particular paradigm, then that often really quite robust and it will stay in place for a long time. And although Zvet had argued and had really out-argued the great German chemist Wilsstetter, Wilsstetter had such a high position that even though Svet had managed to reject some of Wilsstetter's arguments, nevertheless, that kind of stayed in place. And you have to remember that he was at very minor universities.

He was a, you know, one-man banned, he didn't have lots of students. And so, you know, it's one of those things that before the thinking change changes, sometimes you need a whole generation to go by. I think one more thing to contribute to that. You mentioned Einstein, but Einstein was a theoretician. And it's easier to do that kind of stuff than it is to do the experimental chemistry that's necessary for establishing something like this technique. But didn't they go to Patagonia as not theoreticians as practical scientists,

I think Ten and so on, to prove that there is this theory. You might have me there. I'm sorry. Never mind. Look, can I ask you, so it gets a bump this in the 1940s. I'm going to put this question to you, April,

because you've been out the conversation with Romantor 2. In this country, in Mill Hill, just north of where we're sitting now, the Richard Sting and Archer Martin rather eccentrically moved this on. How did they do it? They basically decided to, they were using a technique called countercurrent chromatography,

which was a particularly cumbersome technique to isolate some materials that they were working with. And the idea here is that they had two solvents, emissible solvents, that were moving past each other in some tubing. And they decided, well, both of those phases don't have to move. One can actually be stationary. And so they coded a material, and I can't remember what it is now, but they put a slight layer of water on it.

Like a film of water. Like a film of water. And it's interesting because that's sort of come back now with a new flavor of chromatography in the last few years called Hillick. So it goes around and comes around again. But they did this and they demonstrated that. They also later on, AJP Martin, well, okay, so they called this partition chromatography, which is different than the absorption that Svet was doing.

And then later on, Martin also developed gas chromatography. And it's one of the reasons why the UK, these two people here from the UK, were some of the earliest inventors. they completely revolutionized chromatography and brought it into the modern era. And then after that, development was relatively rapid, wasn't it? With fits and starts, because it was easier to develop the instrumentation for gas chromatography and to develop stable stationary phases for gas chromatography. It was easier to develop the theoretical models.

Liquid chromatography was their first, but it didn't really start making advances until probably the mid-6-6. because of the lack of equipment, lack of instrumentation. In the mid-sixthes, Leon Barron, we got into liquid chromatography. Is there a sniff in the air then that these men, sometimes extraordinary eccentric men, who had been doing it for the curiosity of doing it, were onto something that was going to enter into the world,

the practical and the commercial and the profit-making world? Is that in the air? Yes, but it's also a more, yeah, a practicality was certainly the driver for liquid chromatography. I think gas chromatography where the mobile phase is a gas and the stationary phase is mainly a liquid really relies on the mixture to be volatile and in the gas phase

and not everything is stable at high temperatures. So for liquids and for things that are not very thermally amenable to changing into the gas phase, liquid chromatography was far more applicable. It was more flexible. It meant that mixtures of liquids could be separated. Can you just explain to the listeners what you mean by liquid chromatography?

So liquid chromatography is very similar to what we described earlier on, where we've got a liquid mobile phase, and usually it's a solid stationary phase. And in the mid-60s, we move from the kind of gravity-fed mobile phase to a more technological advance in pumping the mobile phase through a packed column. And so that advance, coupled with the stationary phase, advanced with the particle technology to make that material, led to high-performance liquid chromatography.

And this is where it started to be used really in its own right as a much more commercial piece of instrumentation. How was it taken up first of all? What was the first crossover, as it were? The first use of high-performance liquid chromatography was in what we call now normal phase chromatography, which is a tube packed with silica.

The mobile phase is generally non-polar, so something like hexane, for example. and it separated components based on their increasing non-polarity. Right? Non-polarity. I always get it mixed up. I'm glad you're not looking at me. So polar

compounds tend to retain more. Sorry, it's the other way around. Polar compounds tend to retain more than non-polar ones. And that led on then to the development of the opposite. Could we reverse that polarity and do it the other way around? And it was actually AJP Martin who figured that out or who was the first one to do reverse phase chromatography. We've been concentrating on this, Andrea, other than chromatography, looking back, were there other efficient ways of separating substances? Yes, I mean, chromatography is kind of a late bloomer in a way, but there were all kinds of classical methods, let's say, for separating things.

The most important of these was crystallization, the idea that you might dissolve something up in a hot solvent, and then you let it cool down very slowly and outcome crystals. And you might be able to get pure crystals that way. Now, that works fine if you have a large amount of material. And if the differences in the solubilities are quite big, but it starts getting quite difficult if, for example, you're dealing with the pigments of a plant, which just don't work very well that way. The other possibility is to use two solvents. And this is in a way related to this idea of liquid chromatography. We know that petrol and water don't mix. So what you get are two layers. And so if, for example, you were to take a plant leaf, grind it up, and you mix it with the petrol, the solution will turn green, but if you now add water, you'll also get some color, a different color, in the water part. In other words, you're able to put, the kind of partition, let's say, have a ratio of the pigment across the two phases in the water and in the hexane. Again, this is a process which turns out to be relatively inefficient. And the really fantastic thing about chromatography was the chromatography, particularly the liquid chromatography,

essentially allowed you to do that partitioning between the oil and the petrol and the water. many, many times over and over again, thousands of times as you go through this long pipe, which is where the chromatography takes place. So in a sense, chromatography is in part a development of that very classical technique of separating a kind of petrol phase from a water phase. It began very, I'm reading at the moment about the 7th century, and a man who's got 90 colors, 90 different colors to illuminate a man. script out of six plants

and a few minerals. So he's been doing, he's been separating, hasn't he somewhere or not? He's had ways of doing it. Just linked up with this program curiously. Well, unquestionably, and one of the things that the science writer Philip Ball has argued for a very long

time is that actually the development of art and the development of chemistry really go very much hand in hand. And so the ability to, first of all, identify pigments, but also manipulate the colors, transform them, and separate them, is really part and parcel art and science going hand in hand. Very good. April, chromatology is now enormous.

We're told, we were, in the producer of this program, Simon, was authoritatively informed, the biggest conferences in the world are now chromatological conferences. How come? Because it's such a useful technique. It's used all over. We mentioned before about pharmaceuticals, for instance, I will tell you that I make the best pancakes in the world, okay, but one of my son's best friends won't eat my pancakes anymore

because he got a mouthful of baking soda. And in the pharmaceutical industries, they use a lot of the same kinds of things that they use in bakeries to mix all the powders and all the active pharmaceutical ingredients together. Okay. I'm lost with the pancakes. I'm awfully sorry. I don't know whether they did you make a mistake with baking the pancakes?

No, they didn't get mixed. It didn't get mixed adequately. And when you put all these powders in, to mixers that they use in the pharmaceutical industry, it's quite possible that the active pharmaceutical ingredient, suppose you're making a lot of a thousand tablets and all of the API ends up in a handful of those tablets, you can't release those to the market.

The way you tell that is you do chromatography on a subset of those tablets to make sure that it's uniformly distributed. Did you do chromatography in your pancakes? No, I don't. I don't. Sorry, it's trivial, trivial, please forgive me. That's okay. been talking really hardcore science now for a while. It's time to lighten it up a little bit. Okay, we're going to go back to supercritical fluids, Leon Barron, just to put me in my place.

What are they, Leon, and why are they important? Okay, supercritical fluids kind of came along in the 60s as an alternative use for a mobile phase in comparison to liquids and gases. And so supercritical fluid is essentially has the properties of both a liquid and a gas by heating it, and also by applying high pressure. So the advantage of that is that you get the efficiency of mass transfer or separation combined with it being very flexible to solubilize a sample and all of its components, which a gas can't do on its own. So it sort of offers a middle ground between gas chromatography and liquid chromatography.

Its value really is that it can be used with a lot of different stationary phases. I think stationary phase materials for liquid chromatography tend to be a lot more diverse than gas chromatography. So being able to apply that same kind of theory in gas chromatography to a lot of different materials really allows us to do an awful lot more. What sort of things more that we would recognise? So, for example, there's a type of molecule called a chiral molecule that's particularly used for that type of separation,

which is, I suppose, a simple way to describe a chiral molecule is if you look at your two hands, they're opposite mirror images of each other. It's the very same thing with molecules. They don't superimpose no matter what way you turn them. They're different. And they're so chemically similar that GC and LC sometimes really struggle to separate the two from each other.

And what's important is that one form of the other, for example, could be more toxic than the other. And so the separation becomes very, very difficult. And supercritical fluid chromatography is a really useful way to really, really combine the best of both worlds. I suppose to just draw on what April said earlier on, chromatography is a really nice example of a science that constantly reinvents itself.

And SFC is a really good example of that in the sense that it was invented in the 60s, there were some problems with the technology, and recently in the last five or ten years it started to re-emerge again now that the technology is caught up. It's the very same with liquid chromatography. It went away for a while, gas chromatography came in,

and then in the 60s was really nailed down. And it's also, just one thing more is that it's used on a preparative scale and it becomes a green technology because then your carrier is a gas that you don't have to dispose of. It just can go out into the air. You know, it's a constituent of air anyway. Andrea, Andrew Seller, can you, does iron exchange chromatography? Is that taking further along the iron? Are you more precise able to do more things? Well, ion exchange chromatography is a marvelous technique which allows you,

essentially to separate molecules according to their charge. And it involves essentially making a resin, which is studded with charges. And you can choose whether to put positive charges or negative charges. And it was invented here in Britain in the 1930s by a couple of chemists in Teddington just up the road from here. And they made a resin which essentially allows you to pour, for example, tap water in at the top, and essentially separate out all of the ions that are

present in the water. So, for example, in London, we know there's a lot of limestone. If you want to find out how much magnesium, how much calcium, and of course, sodium, potassium, all the other ions, then you can use this ion exchange chromatography to essentially separate them out. But there's more to it than that. In fact, something very similar to ion exchange chromatography is present in all of our dishwashers. And of course if you have a water softener at home, the same kind of resin is in there. Because what it's able to do is to exploit

this stickiness, the fact that the resin is charged, that the ions have the opposite charge, and so they can stick. And that allows you to essentially eliminate Lime Scale, A, from your dishwasher, and B, from your tap water. April, what happens when you build these

things, these chromatography tests to other equipment such as mass spectrometers. What's happening there? Actually, that makes it an incredibly powerful tool. And Leon's work with forensics, they use it an awful lot. It's been a tremendously powerful tool. He can probably speak to that better than I can about the hyphenation of liquid chromatography and mass spectrometry or gas chromatography. You're on, Leon. Yeah, so we can separate things with the chromatography, but also the mass spectrometry gives us structural information. So briefly we can tell straight

away what something is by its chemical structure in the mass spectrometer. That's the advantage of it. There's breaking news. Andrew is waving his piece of paper across the is determined yes and you've got a bloodstain. No, it doesn't it's a colour? There you are. What have you got? So what we've done

is we've taken the brown pigment and we've really separated it out into a beautiful sort of turquoise blue, some red and some orange. Now, what does that tell you? You've got that. Okay, so what? So what it's telling us is that, of course, the brown pigment is not a unitary substance, that it's actually a complex mixture, which has been optimized by the marker manufactured. But in very much the same way, in which you might use this for forensic purposes,

then what you're able to do is to separate it out into its components. And these hyphenated techniques that we've just been talking about, what they're doing is they're giving you a detector at the end. And it's the detection. What comes off our column? What comes off the separation? What is it? And that's what those tools allow you to do. Briefly.

Briefly. I visited an elementary school classroom where the class mouse had been kidnapped. And the kidnapper had left a ransom note. And everybody's favorite villain came in. The vice principal, he had a pen. They analyzed the pen and were able to establish that it was the vice principal who had kidnapped the mouse. Has it in any way peaked this Or is there? Oh, I've got to go.

Sorry, time's up. Has it peaked? Quickly, yes or no, this? No, no. Not at all. Well, you've got a certain interest. And thank you very much. It was difficult. You made it comprehensible to one non-chemist at least. Thank you very much, Andrew Seller, April Stalkap and Leon Baron.

Next week we'll be talking about the poems of Rumi, the 13th century Persian scholar and mystic. Thanks for listening. And the In Our Time podcast gets some extra time now with a few minutes of bonus material from Melvin and his guests. It usually begins by me saying, what did I crucially and culpably miss out? I can start with that one.

I think it's important to remember that chromatography is not the only way to separate things in much the same way. And a good example of that is electrophoresis. And electrophreis doesn't have a stationary phase. We have an applied potential across a tube. and it separates things on their size and their charge. And why that's important is that it's primary use, certainly in forensic sciences, in DNA profiling.

And so it's the preferred technique for DNA profiling because it's such a large molecule, it's quite complex, it's much better at doing that. You can do it by chromatography, but the preferred technique is electrophoresis. So it's a similar concept, but there's different physics to it. I'd go along with that.

And then also it could be argued that mass spectrometry is also a separation technique because you are separating things based on the ratio of their mass to charge, very similar to what you're doing in electrophoresis, except you're doing it in a vacuum. I'd just explain, if I may, for a moment I do it, what I literally said in the program, but I'm doing something about the 7th, anyway, I'm reading about the 7th century, and about the illuminated manuscripts. And this man called Iyidfries, who was the bishop of Lindisfarne, for about 20 years, let's leave it at that

in that century. And he alone did the Lindisfan Gospels. They're usually teams working on it. It's extraordinary. You must have seen them. It's extraordinary. And there are over 90 different colours and they're all vibrant, dynamic colours. And he had six plants

and a few minerals to get those colours. And he just seemed to me to fit in with this discussion. I couldn't make it fit in properly. It did. So what do you say to that? I think that was a great example. Because in fact, a lot of what drove the chromatography development was industrial applications. The gas chromatography, a lot of that development was driven by the petroleum industries

as they were trying to characterize the different petroleum that they were getting out of the ground. And so, yeah, and when you were talking about the ion exchange and that being used in water softeners, a lot of the techniques that we use in chromatography are also the basis for cleaning up drinking water. use the same kinds of resins to pull things out. So, yeah. To industry and development of instrumentation and techniques go very much hand in hand. They're the ones with the deep pockets and also with the interesting problems that need to be solved. Are they directing the way research goes now?

Are people like you going to them and saying, look, I've had a terrific idea. I've been fiddling around with it for five years. I think there's a really important point that comes out of this. And that is that, to me, chromatography is one of those. great examples of the importance of allowing the curious scientists to go off and have a play. I'm certainly saying that, yes. You know, the interesting thing is that, you know, here is a man who is asking a very profound question of no industrial relevance. You know, when Svet actually starts taking apart plant cells, and he finds a way to separate them out,

and his work is contested, and it lies fallow for about 30 years. I mean, in the current environment, there is absolutely no way that someone like that would get ahead. Now, it's true that he didn't get very far ahead. He didn't become famous and so on. But, you know, he sort of had his career. But today, I think, you know, there's a very good chance he wouldn't have got tenure that he would have been sort of hived off quite quickly because he wasn't publishing in the high-profile journals. And yet out of this has come not simply an industry that is worth a huge amount to us, but actually which underpins all of the quality control that runs our lives. I mean, whether it be in pharmaceuticals, whether it be in our foods, if we want to know if food is counterfeit or contaminated, right? You know, chromatography really

kind of rules our lives in all kinds of ways. And so the idea that we should always turn to the industrialists and solve their problems, they're looking at problems on a three-year time scale, especially the way shareholders want to do. This idea that you might explore weird things on long timescales doesn't exist. That's a great loss. Archers are the same, isn't it? I mean, Matt Archer up in Mill Hill with his hosepipes and all the rest of it. I mean, he published casually any papers nowadays. He'd have been kicked out. He was fired from his, well, he was asked to leave the University of Houston because he wasn't publishing enough.

He only published 90 papers in his career. It was the ninth one for which he got the Nobel. We should all be so lucky. Thank you very much. Thank you. Here's Simon coming in with the great BBC offer. Tea, coffee or a glass of water with a piece of paper in it. I'd love a cup of tea. There are many more science and discussion programs from Radio 4 to download for free. Find these on the website at BBC.co.com.uket slash Radio 4.