Using a Phenyl Column When Separation with C18 (ODS) Is Insufficient

The C18 column is an ODS type of column that is marketed by instrument and column manufacturers, in which octadecyl groups are bonded to a silica base to provide wide separation applicability. An appropriate ODS column is typically the first type selected from the various types available at the start of a reverse-phase analysis. However, in the process of investigating the mobile phase conditions, there are cases in which the separation conditions cannot be improved. Selecting a different ODS column or exchanging it with a C8 column to improve separation is also possible, but even then, it may not be possible to achieve sufficient separation.
One possible solution in such a case is to use a phenyl column.