what effect pH has on RP separation?

[yangz00g]

For example, separate an amino acid methionine (-CH2CH2SCH3) on a C-18 column without derivatization, will there be a noticable difference on its retention between pH=pI (Zwitterion) and pH>or < pI by 2 units (99% in anion or cation form)? Just curious anyone has done the study practically or theroretically?

Thanks a lot

[Uwe Neue]

We have done a lot of these things. I can send you one or two publications that contain such information, if you contact me at me e-mail address.

Yes, the difference in retention is substantial.