TLC-thin layer chromatography

[datdat]

when the stationary phase or absorbant is silica gel which is very polar, the non-polar sample will move quickly than the polar one.

but i don't understand why the the polar solvent make the smple to migrate faster?(KBB p.429)
(the more polar the solvent, the fster the smaple will migrate)

can anyone help me with this?

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[stiney44]

If the solvent is really polar both the non-polar and more polar compound will go more quickly or further up the plate, but what to know is their relative position does not change. The more polar compound will still have the smaller Rf factor they both just "hold" onto the solvent longer.

 

[uncbestyet]

The more polar solvent will compete better with the polar silica gel when attracting X (X = polar substance in question).

The more polar the solvent, the better it pulls X off of the silica gel and carries it with the solvent front.

If the solvent were not polar at all, the polar substance in question would remain adhered to the silica gel and not move up with the (non-polar) solvent front. (competes ineffectively in attracting X)

If you use a solvent that is too polar, all blots (x,y,z) will move all the way to the top (giving no resolution (or separation) between substances in question. The purpose of this test, most of the time, is to separate substances based on polarity.