One of the primary causes of slowly increasing pump pressure is the buildup of material on a filter or frit surface, forcing the pump to work harder to achieve the same flow rate. This build up is usually caused by particulate contamination in the mobile phase, solid particles from the sample being introduced into the system, or breakdown particles from seal surfaces, primarily the pump seal. Another source of increased pressure can be the slow deposit of impurities or other sample components that permanently bond with the stationary phase within the column. As this deposit increases, it takes more effort from the pump to push the sample and mobile phase through in order to maintain the set flow rate. In order to solve this problem, it is best to go through your system and change – one at a time – the filters and frits, and maybe even the column, until the pressure goes back to normal. Keep in mind that if you make a change on your system and the changed part does not improve your system’s performance, it is usually safe to put the original part back in and save your new part for a future necessary use.