Question

Ok, so what would happen if you are working with TLC and have a polar stationary phase (silica) and a mobile phase ( polar eluting solution) and you spot a nonpolar compound? Would the Rf values be greater than in a nonpolar mobile phase?

I know in general if you are using TLC with polar silica and spot a nonpolar compound the nonpolar compound travels further (higher Rf values) because its chemical structure is different than the stationary phase compared if you would spot a polar compound. Yet will a nonpolar compound have higher Rf values in a polar eluting solution or a nonpolar eluting solution if you have a polar stationary phase?

Please help I have been confused about this topic for about a year now.

Answer 1

No the Rf value for polar mobile phase will be less than the non polar spot because the polar eluting solution will interact with the solvent more effectively and hence will travel less distance from the origin. Hence polar solution will have less Rf than non---polar one.

Now when polar eluting solution is used it interacts with the stationary phase more and hence the intreacinte of solute (non polar) component will be less and Rf value will increase

Whereas when non polar eluting solution is used it interacts with the stationary phase with less affinity and hence the solute (non polar) component will have more interaction with the mobile phase and will decrease the Rf value