Over the years, many chromatographers have been given the task to develop HPLC and LCMS methods for highly polar compounds. Those who have chosen HILIC columns have reported gradient methods can be problematic causing frustration, excessive method development time and additional costs. Mostly the issues are the “downtime” between runs that HILIC and all ordinary silica columns struggle with including equilibration of the on-column, silica water layer.
The permanent water layer or “hydration shell” causes difficulty maintaining precision and reproducibility especially after several runs or when laboratory conditions such as temperature changes. It’s also reported that the HILIC column lifetime can be short and the columns can fail without notice during over night runs.
High salt concentrations in the mobile phase (up to 100 mM) is often needed in HILIC to get proper retention times which can be a problem for LCMS instruments and preparative chromatography.
ANP or Aqueous Normal Phase HPLC is similar to HILIC in that polar compounds are retained and separated using high organic content mobile phases as a starting point and running an inverse gradient (high organic to high aqueous). A difference in that Cogent TYPE-C HPLC columns do not retain a water layer , does not have more than 5% residual silanols and utilizes direct silicon carbon bonds for ligands, the problems most often associated with HILIC are eliminated. Low salt concentrations are used in ANP (ie 15mM or less) and no buffering is needed thus avoiding all the problems of high salt concentrations in LCMS and preparative chromatography.