It depends on the type of samples you are working with…
The purpose of cleaning the column while in use or after use, is to remove contaminants that build up on the column’s stationary phase or on the frits from your samples. As such, injecting clean samples such as standards mean that the column will rarely need cleaning. On the other hand, biological, physiological or many real life samples have very complex matrices and adsorbed compounds can build up on the column more frequently.
A rule of thumb is to wash the column with 50:50 methanol / DI water every 10 injections for these types of samples then reqilibrate the column with your starting mobile phase. You can tell when the column needs cleaning by when the run-to-run retention time repeatability begins to be affected.
There are several things you can do to help keep the column clean, including use of guard columns and also having 50% methanol or isopropanol in the mobile phase A solvent for Aqueous Normal Phase ANP methods. It is also highly recommended to use a Cogent Column Filter to be sure that large, undissolved particles do not make their way onto the column. Every Cogent HPLC column is supplied with a free Cogent Column Filter. Click HERE for information on these economical filters.