Imagine that you were given a sample of an unknown mixture to analyze by TLC, wi
ID: 568912 • Letter: I
Question
Imagine that you were given a sample of an unknown mixture to analyze by TLC, with pentane and 2-butanone as possible solvents to use. You begin by spotting a plate and developing it using only pentane, but none of the spotted sample has moved after the solvent has traveled up the length of the plate. None of the compounds have separated from each other. You then spot another plate and develop it only using 2-butanone, but all of the compounds in the mixture have moved all the way to the top. Again, none of the compounds have separated from each other. What is wrong in both situations, and what can you do to fix the problem and separate the compounds from each other?
Explanation / Answer
Thin layer chromatography (TLC) is a technique which is used to separate the components of a mixture on a solid support using a mobile phase.
Pentane is a hydrocarbon so it acts as a non-polar solvent. When the mixture is tried to separate using pentane as the solvent then none of the compound in a spotted sample has moved even after the solvent has traveled up the length of the place. This may be because the components in an unknown mixture are polar which are immiscible with the non-polar solvent.
2-butanone is a polar aprotic solvent. When 2-butanone has been used as a solvent then all of the compounds of a mixture have moved all the way to top, this means that components in a mixture have almost the same polarity for the given solvent. That is why they travel up at the same pace with the solvent.
In order to separate such components from a mixture, we should take a polar solvent in which all the components are soluble and they travel at a different rate with solvent.