The carboxylic acid group contributes some additional Selectivity to the phase. When the mobile phase is above pH 5.9 the acid group becomes 90% negatively charged and at pH 6.9 it becomes 99% charged and may act as a Cation Exchanger.
Below pH 4.9, the group does not have significant ion exchange properties and should be used primarily for ANP. Recommendation: to use the cation exchange function with this column, use a mobile phase around pH 6 or higher if possible.
The Cogent UDA column is a good choice for LCMS and precise methods are easily developed even with complex sample matrices as very little desalting is required.