A student spots an unknown sample on a TLC plate. After developing in hexanes/et
ID: 962645 • Letter: A
Question
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 R f 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?Please help and thank you! 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 R f 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 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 R f 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?
Please help and thank you!
Explanation / Answer
The fact that you see only one spot on a TLC plate does not necessarily mean that the solution spotted contains only one component. This is because two compounds can have the same value of R f in a particular eluting system. You must run the sample in a different eluting solvent and see if it again gives only one spot. This is a good indication that the sample is pure. However, you still should verify the purity of the sample by melting point, boiling point, and/or spectroscopic analysis.
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