[mysticalrose]

Hi. I have a question about TLC analysis. I was wondering how to determine the polarity with the sample vs. the eluent system. For example, if the Rf values of a sample with a polar eluent is high, what does that mean in regards of polarity? What if the Rf values came low in a polar eluent system?

I hope this made sense.

Thanks for the help

[dunno260]

A high Rf is going to indicate that the compound in question is relatively non-polar compared to the solvent system while a low Rf is going to indicate that its relatively polar compared to the solvent system in question.

Essentially you can view TLC as a series of interactions between the compound(s) and the solvent.  A tighter interaction (so a more polar compound) is going to result in a compound that has a lower Rf unless the solvent is more polar in which case it binds to the silica gel and the compound travels further up.

Thats a pretty general explanation but normal silica gel can do some unusual things due to its somewhat acidic nature with acidic and basic compounds which tend to streak and so can require more polar solvents than would otherwise be expected (inclusion of an acid with acidic compounds and a base with basic compounds helps alleviate this).