1. Why is it necessary to run TLC in a closed container and to have the interior

Question

1. Why is it necessary to run TLC in a closed container and to have the interior vapor saturated with the solvent?

2. You want to know the detergent composition of an extract of a shampoo. You spot the sample on a TLC plate and develop it in dichloromethane and observe a single spot at Rf 0.95. Does this verify that only a single detergent compound is in the extract? What specifically can you do to gain more information about the composition of the shampoo extract?

3. What will be the appearance of a TLC plate if a solvent of too low polarity is used for the development? too high polarity?

Explanation / Answer

1) The one of the major reason necessary to run TLC in a closed container and to have the interior vapor saturated with the solvent since otherwise the solvent will be evaporated in the atmosphere through the TLC plate leaving less amount of solvent in the TLC plate which will in turn lead to slower migration of the solvent in comparison with the value with which it should have been migrated

2) The value of Rf = 0.95(close to 1) implies that there is only one single detergent compound since there is only one spot, but we cannot guarantee that there exists another detergent compound having value very close to 0.95 which will mix with the solvent and shown as one spot

3) Low Polarity - Solvent sweeps through the sample being less polar than the sample

High Polarity - If the solvent is high polar, then it will move the sample out of the TLC plate

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