RP or ANP | Weak Cation Exchange | Undecanoic Acid - Dual Mode Possible
These columns have an 11 carbon, aliphatic linker with a terminal, carboxylic acid group (Undecanoic Acid) bonded to the Silica Hydride surface. This phase is very unique as it has Weak Cation Exchange (wcx) properties in addition to those of Aqueous Normal Phase (ANP) mode. A dual mode is possible with some mobile phases conditions.
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 closely related compounds and LCMS. Precise methods are easily developed even with complex sample matrices as very little desalting is required.