by
lmh » Tue Apr 29, 2014 10:34 am
Hmmm, some confusion I think.
In reverse phase chromatography, the column is non-polar.
Chemicals (analytes) interact with the column by hydrophobic interactions.
Chemicals are retained when the mobile phase (solvent) is hydrophilic.
Chemicals are less retained when the mobile phase is less hydrophilic and more hydrophobic, more like the column.
(i.e. they partition; if a chemical is capable of making hydrophobic interactions, it will do so with the column, but as the solvent becomes more hydrophobic, the chemical has less reason to interact with the column rather than the solvent, so it will partition more into the solvent, and move faster).
To get retention, lower the organic content in the solvent. To get less retention, increase the organic content.
(To others: yes, I'm aware that there are other interactions going on in reverse phase chromatography, maybe with silanols etc., but generally I'd hope that the simple hydrophobic interactions ought to dominate everything when looking for rule-of-thumb explanations about how retention time will vary with choice of solvent strength).