Question

How would the following factors affect Rf values in the separation of compounds by Thin-layer chromotrography?

a) Use of filter paper in the solvent chamber while developing a plate.

b) The solvent chamber has been shifted a few times while the plate is being developed.

c) Failed to cover the TLC chamber with a lid/watch glass while running the TLC plate.

d) A student is trying to determind a best solvent systme that would be seperate a three component mixture. After developing the plate, he couldn't detect any spots with the UV visualization. Mention two potential errors that could have goone wrong with his analysis.

Answer 1

1) The use of filter paper in the solvent chamber during the plate development when the chamber is sealed keeps the chamber saturated with the solvent vapours by absorbing the solvent so that the plate does not gets dry at any point of time .This helps in the proper separation of the components on the stationary phase and rf values comes out to be accurate and distinguishable.

2) once the TLC chamber is set up, it should be kept undisturbed untill the development. If it is shifted few times there are chances that solvent can spill on plate and mobile phase will run unevenly , or plate cqn touch the walls of chamber and solvent will move from there to the plate . It will give incorrect value of rf for components.

3) if we do not cover the TLC chamber , all the solvent will evaporate out and the plate become dry, the solvent will stop moving on stationary phase and we get no proper rf values and incomplete saperation of components.

4) the two potential errors could be that the solvent systen has no proper ratio of polar and non- polar solvents. Or the student might have taken impure solvent or solvents which have no property of wetting plate.