How to perform a TLC?

Why saturate the elution chamber?

To achieve a reproducible TLC, the chamber must first be saturated with the vapor of the chosen eluent.

Indeed, it can be considered that the execution of a TLC actually involves three phases: the mobile phase, the stationary phase, and also the atmosphere (air) present around the TLC in the chamber.

Illustration of a closed container seen from the side. At the bottom is the eluent. Above, arrows indicate its evaporation. The TLC plate is placed on the bottom and partially soaked in the eluent. Arrows symbolize the evaporation in the center of the TLC plate. At the top of the TLC plate: the front of the eluent. Finally, at the top of the container, blue clouds symbolize the vapor.

Migration of the eluent on the TLC plate is accompanied by its partial evaporation into the chamber’s atmosphere. The prior saturation of the latter ensures that it is at equilibrium and that the eluent velocity is established and reproducible. The determination of the Rf of the sampled substance will then be established and reproducible.

On the contrary, if the chamber is not saturated beforehand, the elution rate of the eluent is slowed down and varies according to the nature of the atmosphere in the chamber. Then the Rf value of the sampled substance will not be reproducible.