In other retention modes such as ion exchange or HILIC, a high salt concentration may be required. However, these high levels can be detrimental to various aspects of an analysis. In LC-MS, high salt can suppress MS ionization. Even if the mobile doesn’t use high salt concentrations, they can still elute off a column that had previously been used under such conditions.
With Cogent TYPE-C™ Silica HPLC columns in Aqueous Normal Phase (ANP) mode, these high levels are not required; generally no more than 10 mM should be used in any method, whether in LC-MS or regular HPLC. The salts can permanently alter the stationary phase behavior at these high levels and may be virtually impossible to completely remove, even with extensive washing protocols.