You are asked to rapidly assay the purity of a sample, but do not have access to

Question

You are asked to rapidly assay the purity of a sample, but do not have access to instrumentation. You decide to use TLC and melting point to check its purity. With 10:1 hexanes:ethyl acetate solvent, the sample gives one spot by TLC (Rf = 0.15) and has a melting point range of 115–125°C. (a) Do you think the sample is pure? Why or why not? (b) Using the tools you have at hand (a melting point apparatus and TLC setup), what other data could you collect to test your hypothesis from part a? Give two possibilities.

Explanation / Answer

Solution:- (a) The sample is not pure. The reason is, a pure sample has lower range of melting point. Lowest is the melting point range, higher is the purity. Here the melting point range is given as 115 - 125 degere C which is high and indicates the sample is impure.

(b) Using TLC, we can opt for solvent of higher polarity like 5:2 or 5:3 hexane:ethyl acetate that increases the Rf value of the spot.

If the polarity is increases then there would be a possibility to separate the second or third spot that might have overlapped with the first spot that we got when hexane:ethyl acetate was 10:1.

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