[Rosalind Franklin]

Hey guys!

How does one choose the best mobile phase while doing TLC? My stationary phase is silica gel and my analyte contains salicylaldehyde and diethylmalonate. Few papers suggested benzene:acetone( in 1:1 ratio) but this did not work. I want to understand the logic behind choosing the best mobile phase and ratio. Is it just trial and error, or is there something more to it that I am missing?

[MOTOBALL]

On no account should you use benzene——-KNOWN CARCINOGEN.
Always substitute toluene for benzene.

The rationale for the mobile phase is that the solvents should be miscible in all proportions; one relatively polar and one relatively non-polar.

I would use hexane/ethyl acetate at 3:1 v/v as a starting point.
Adjust ratio as necessary to achieve resolution.

Regards,
Motoball

[wildfyr]

Its a case of experience and guess and check until the ratio gives good separation. And agreed, benzene is a poor choice. For a reason beyond health ones, toluene and benzene are both bad because they absorb well in the UV and make it harder to read your plate by UV light. The most common combination is ethyl acetate/hexane. Starting with 1:3 EtOAc/Hexane is pretty standard as motoball said.