IEX and ACN question

[pph31]

Adding ACN can reduce the hydrophobic interaction in IEX. What's the mechanism? ACN interacts with the hydrophobic chain?

In typical RP-HPLC, ACN is used as mobile phase. Analytes interacts with the Carbon chain of the stationary phase. I never think about the ACN-reducing-the-hydrophobic-interaction story.

Is it contradictory?

Thanks

[HW Mueller]

The ACN is in competition with the hydrophobic analyte, in other words, the more ACN, the more the equilibrium of the analyte is shifted toward the mobile phase.