Question

If we have lipid standards like Phosphatidylinositol (PI), Phosphatidylethanolamine (PE), Cardiolipin (CL), Cholesterol (CH), Fatty acids (FA), Phosphatidylcholine (PC) and have been developed using a Basic solvent system (chloroform: methanol: ammonia 65:35:5) and an Acidic solvent system of (chloroform: acetone: methanol: acetic acid: water 10:4: 2: 2: 1) in a 2D-TLC plate, why would the basic solvent system have the higher Rf values for each lipid, when compared to the acidic solvent Rf?

Answer 1

The difference in Rf value is due to polarity of the lipid. The higher the polarity of the lipid, the less it will travel on the plate which means a low Rf value for that lipid. For example, in the basic solvent system the solvent makes a dipole in the molecule by removing a hydrogen which leads to negative charge on the molecule, this is called a polar molecule. When a molecule is polar, it binds more to the silica gel in the stationary phase and less in the mobile phase; travelling slow on the plate. The standard lipids in order of increasing (lowest to highest) polarity in basic and acidic condition are as follow: Basic CH, CL, FA, PE, PC, PI Acidic CH, FA, CL, PE, PC, PI.