So when we say chromatography, we're going to say that this is a technique that involves a separation of components, mainly solids and liquids within a mixture because of a difference in molecular attractions. We're going to say in the procedure a mixture is spotted on a silica plate and the progress of the components on that plate is based on their affinity to the solvent or the plate itself.
Now with this process we have two phases. 1 represents the silica plate which doesn't move and it holds the mixture. Because it doesn't move, we call it the stationary phase. The other phase represents the solvent, the portion that's moving, the liquid portion. So we call it the mobile phase. So it moves up the silica plate and it moves by capillary action.
So here I have a TLC plate. I draw a line. I have a mixture and I take a sample of this mixture and I spot the TLC plate. I place it within my mobile phase, which is my solvent, and here let's say that the solvent is 50% ethanol, which is C2H5OH. C2H5OH ethanol is slightly polar and then we have 50% hexanes which is C6H14. It's a hydrocarbon, so it's non polar. Now the dots can start to separate and move up.
So here as the solvent phase is moving up the TLC plate, we can see that this dot which is made-up of a mixture of two different compounds part starts to split. It splits into red dots and green dots to show the separation of the mixture that that I originally took from my sample. Now, if the dots themselves, if the the attraction to the plate is greater than the attraction to the solvent, then the dots are not going to move very far up the plate, so the plate. So there's going to be low movement.
Now let's say that the dots have a greater affinity for the solvent than the plate. So since they have a greater affinity or attraction to the solvent, the mobile phase, they're going to move with it. So there's going to be high movement or higher movement. Looking at this, we can see that at the end the solvent is reached up this high. In terms of the plate, I take it out, we can see that the green dots have moved up higher than the red dot. So the green dots had a higher affinity for the solvent, they moved up with it. The red dots had less of an affinity for the solvent, so they don't move up as high.
Here I marked 123 and four, one being the original position the starting starting line. Two is the position where the red dot stopped, three is the position where the green dot stopped, and four is my mobile front. That's where my solvent stopped where I took it took the paper out. From these numbers I can determine my RF value. So the distance traveled by the component is a method we use to we use we can use to find the RF value. This helps us in the identification of the compound.
Your RF value equals distance traveled by compound divided by distance traveled by solvent. So how would I do this? Well, if we're looking at the red dots here, we'd say the red dots traveled to and the solvent traveled for. So the RF value of red is 0.50 or green. It traveled 3, solvent traveled 4, so that's 0.75. So these are the RF values of the red dot and the green dot. Usually you'd have a manual and associated with these numbers. You'd have themes of actual compounds with RF values and you choose which compound from that list matches closely with 50 and 75. And in that way you'd identify what is the red dot represent, what compound and what is the green dot represent.
So that's how we can use basically TLC plates and spotting mobile phases and stationary phases to determine the identity of these two different spots, OK, And we incorporate the RF value to do so.
