When a system is constantly run in Reversed-Phase (RP) HPLC, many Contaminants are retained, coat Seals, Frits, Check Valves and many other parts of an HPLC System. When these Contaminants build up, often it is time to replace them during a PM (Preventative Maintenance).
It is important to note that when a system is used for RP HPLC then abruptly is used in Aqueous Normal Phase (ANP) or HILIC, the change in Solvent Composition and perhaps the presence of Acids or Bases could force Contaminants to “elute” off the System and into the Cogent TYPE-C or other type of Column such as HILIC or Mixed Mode. Depending on what these Contaminants are (can be sample, impurities, unknowns, dust etc.), they could cause damage to the Column Frits, the Column Stationary Phase and ultimately, you may see Peaks or problems with your data that may seem very puzzling.