Acetonitrile/aqueous buffer (90/10) is a good starting point for column storage conditions. The mobile phase should be buffered at a pH that puts analytes in their ionic forms, if possible, and within the pH limits of the column (1.5-7.5).

95% ACN can be used to help increase retention and a gradient to lower % ACN may be employed to reduce analyte retention and/or sharpen later eluting peaks, although running a gradient to lower than 50% ACN can significantly add to re-equilibration times in preparation for subsequent injections.