A student spots an unknown sample on a TLC plate. After developing in hexanes/ethyl acetate 50:50, he/she saw a single spot with an Rf of 0.55. Does this indicate that the unknown material is a pure compound? What can be done to verify the purity of the sample?

A pure sample is known to give one spot on a chromatogram. This is the first indication that the substance is a pure substance. Since the student saw a single spot, the unknown substance is pure.

Subsequently, the substance can be boiled since it is a liquid. Impure substances boil over a range of temperatures. If the substance is pure, it will have a sharp boiling point which can be compared with boiling points of known substances recorded in literature hence the substance can be correctly identified.

Histrionicus Histrionicus · Answer 2 · 2021-11-29T11:54:24+01:00

The given unknown material or compound is a pure compound - yes, it has only one spot.

In the given TLC plate there is only one single spot found thus we can say it is the pure compound as If an impurity is present along with the major compound then there we could observe more spots other than the major compound.

The verification of the purity of the sample can be tested by a general procedure

conduct the TLC of the given compound and a separate TLC consisting of the pure compound
compare the Rf values of both plates
if it matches with the Rf value of the pure compound then the given compound is confirmed.
the TLC plate has no spots other than the main compound therefore, it is a pure one.

Thus, The given unknown material or compound is a pure compound - yes, it has only one spot.

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