WEBVTT
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Hi, you already know what a chromatogram is. This is part of a chromatogram and with fractionation
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your goal is to collect or to fractionate as much of one component of a mixture of substances
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as much as possible and also to guarantee a certain purity. So your end product should
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be at least, for example, 90% of a certain component of your mixture since then you can
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make sure that your end product has the properties you want and you can work with it. So assume
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our chromatogram here and we want to fractionate the middle peak and we need to guarantee 95%
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of purity. In that case we can decide where we want to fractionate and mark those times
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with these collectors. For example here, make this green and here. Of course the other peaks
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or the other substances overlap in our fractionation time. So here's a little bit of overlapping
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and here but since we have a purity of 95% this is okay and the exact solution is not
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possible here right now since in that case we would need a computer. So we have optimal
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fractionation times for this chromatogram. However, during a chromatography process there
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can be the temperature in the laboratory is too hot or some parameters are not set exactly.
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So the chromatogram is not this but this and in that case you can see that here there's
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a lot of overlapping and also here it is a huge amount of overlapping. So in that case
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our purity does no longer hold. For that chromatogram the optimal fractionation times would be here,
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let's make it blue and maybe here. So since there is a lot of overlapping on that side
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the fractionation times need to be more narrow here. Alright or something is different in
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the process and the chromatogram looks like that. In that case you can see that here is
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the purity not guaranteed so the overlapping on that side is too much. So we need to stop
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the fractionation maybe here. And on the other side here there are, they cut the component
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very much so for that chromatogram we can start the fractionation already here. Otherwise
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we lose too much of the component. So if you assume that you need to determine when to
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start the fractionation and when to end it and you don't know what chromatogram you will
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get. So you can get one of those three chromatograms. You can't optimize the fractionation time
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for each chromatogram since in that case you have a 33% chance that your end product will
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meet the constraints and a 66% chance that it will not. In that case you need to determine
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the robust solution. A robust solution gives you in that case the fractionation times so
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that the purity is guaranteed no matter which of the three chromatograms you will get in
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the end. And for that you need the interval of fractionation times that is inside the
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fractionation for each chromatogram. So the latest fractionation start and the earliest
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fractionation end. That would be here. So for this chromatogram you are on that side
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your purity is met and on this side your purity of course is met too but you lose a little
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bit of product so the solution could be better. That's the so called price of robustness.
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In order to get the protection and in order to be you can be sure that your end product
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fulfills your purity the productivity might be a little bit less. So it is not the optimal
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solution but it is a good solution that is feasible for all problems. And if we look
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at the next chromatogram here also here you meet your purity and in that case you also
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meet your purity but cut a lot of your peak. Of course it is possible that the robust solution
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is too conservative. This means that in some cases you lose too much mass and your process
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your solution is not productive enough. In that case you have to go back to your processes
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and measure your parameters more exactly or you have to control your settings more so
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your possible chromatograms are not that different. This means that the possible outcomes are
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not so different than before and in that case your robust solution will become better. And
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of course for the last chromatogram you are inside your purity so here and here the purity
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is guaranteed and in this case you lose only a little bit of mass. Alright now to your
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challenge. Now it is your turn to try this on your own and for that we have here three
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chromatograms. You have to try to fractionate this peak that is marked with the arrow and
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for that you can pull your chromatogram in this field. You have to make sure that it
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is exactly inside the orange lines so your axes are not exactly overlapping. Then you
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use your connectors to draw your fractionation times. Then you can determine the inner interval
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so the latest fractionation start, the earliest fractionation end and write those down here.
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Or of course you can read your optimal fractionation times and take the inner interval. Then here
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under this envelope is the optimal solution. You can check your solution and have fun.
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Good luck.