Thin Layer Chromatographic analysis of drug components
Thin layer chromatography is a procedure that gives a chemist a kick answer to how many components are in a mixture and therefor it may help him identify the nature of the mixture. In fact TLC is used to separate mixtures of substances into their different components.
Chromatography works this way: there is a stationary phase, the silica gel (the stationary phase also contains a substance which fluoresces) and a mobile phase, which is a suitable solvent. The mobile phase is a solvent flowing through the stationary phase while carrying the different components of the mixture studied. The different components of the mixture travel at different rates according to the solvent used.
In fact during TLC the determination of the solvent is really important. The more you increase the polarity of the solvent, the more all the components of the mixture will move faster (and vice versa with lowering the polarity). Therefor the ideal solvent is simply the one that gives the best separation so, to find it some trial and errors are required.
In this experiment, we used TLC to identify the components of an unknown drug that has been assigned to us.
We already had three known solutions, the first one was caffeine the second one was aspirin and the third one was acetophenol.
After we’ve prepared the solution composed of our unknown drug, we started spotting.
Spotting a TLC consists of: first of all, dissolving the material that will be studied in a solvent to make a solution.
During the experiment we dissolved a portion of our unknown drug in 2,5 ml of ethanol/dichloromethane 1:1.
Then, took some of the solution prepared into a microcapillary, and gently pressed (touch) the microcapillary onto the TLC.
The TLC is properly prepared before the spotting.
If the spotting is done correctly, the solutions should all drain onto the TLC, creating a wet circular spot. The solvent in the spotted solutions, are then allowed to evaporate leaving behind only material that we want to study, before placing the TLC plate into the developing solvent.
Spotting has to be done correctly and carefully to have a good result during the “developing” phase, we don’t want our spots to be too big and not enough concentrated (the spot diameter should be around 0.7 to 1mm).
So, during our experiment we spotted our unknown solution called the “U” spot then we spotted the “1” spot with the caffeine solution, the “2” spot with the aspirin solution and finally the “3” sport with the acetophenol solution that was already gave to us.
After preparing the TLC plate with the spots on it, we’ve placed it in the developing beaker, containing the developing solvent, which is, for our experiment: ethyl acetate/acetic acid (200:1). We covered the beaker, and left it.
After that, comes the Developing phase with the UV light: we saw that ou U spot and the second spot (aspirin) are in the same height.
Afterward we calculated the Rf values, Rf value is defined as the distance traveled by the compound divided by the distance traveled by the solvent.
In our experiment the Rf values are:
As we can see the Rf value of aspirin (2) is the same Rf value of our drug preparation (u), so we can conclude that our unknown drug is composed of