[Barney]

I have been asked which component will come off the column first and last from a mixture of octane, acetic acid and methyl chloride using a non stationary phase and a polar aqueous buffer as the mobile phase.

I have been reading around the subject all day and believe I have switched my own brain off

Could anyone give me any reasoning?

[Train]

You should put your components in order of polarity and then ask yourself whether they would spend more time in the stationary phase as they get more polar or less polar.  Remember the rule that like dissolves like.

[Barney]

Thanks for the reply. I have been looking at the structures of the three which helped me alot. Would I be right in saying that methyl chloride would normally be polar due to the electronegativity of the Cl ion but this is cancelled out by the symmetry of the molecule. Acetic acid is polar due to the O and OH groups meaning that in a polar aqueous buffer it would be the first elute. In a non-polar stationary phase, hydrophobic interactions are relied upon and due to the size and number of methyl groups on the octane, this would be the last elute.

I don't have much confidence when it comes to chemistry and I'm trying to excorcise my demons!!!!!! Does what I have said make sense?