Chromatography Practice Test

How can TLC determine purity?

It cannot determine purity. Color intensity indicates purity. Pure compounds usually produce multiple spots. Pure compounds usually produce one spot.

Correct Answer:

Pure compounds usually produce one spot.

Explanation:

In TLC, purity is judged by the number of distinct spots the sample produces on the plate. A pure substance is just one chemical species, so under a given solvent system it should appear as a single spot with a consistent Rf value. If impurities are present, they are other compounds that travel differently, creating additional spots at different positions. Therefore, a single spot strongly suggests purity, while multiple spots indicate impurities. Remember, color alone isn’t a reliable measure—many substances are colorless, and spot intensity reflects concentration rather than purity.

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