High pressure is often caused by system clogging. To identify the part that is the problem, remove each flow line at the connection fitting from downstream to upstream and monitor the pressure. You will find the point of clogging due to a drastic lowering of pressure when that connection is removed or bypassed. Once the source of clogging is identified, please see additional info below:
To determine the quality of the precolumn, disassemble the precolumn and ensure the packing material is white in color. The precolumn is used to filter out contaminants before they enter the column. The precolumn should be changed every month during normal use. In the case of tissue, plasma or urine samples, change the packing materials at least every 100 samples.
Separation Column Clogging
Separation columns can also become clogged after many uses. It may be necessary to clean the column. To clean any column follow the procedure outlined in the manual. Please note that it may take several hours or even overnight of running mobile phase for the column to equilibrate after washing. If washing the column doesn’t solve the problem, the lifetime of the column may be expired and it might be time to buy a new column.
If the tubing is clogged, buildup typically occurs on the inlet side of a connection fitting due to the narrower diameter. Once you find the location of the clogged tubing, cut the 1 cm (half inch) of the tubing at the inlet with a tubing cutter to ensure a straight cut. If you do not have a tubing cutter, make knife score around the tubing and bend and crack the tubing. Do not push the knife into the tubing.
If you find that the injector is clogged, the most likely spot is the sample loop, which would need to be replaced altogether, because its volume is important. Second most commonly, the clogged part is at port #5 or #4. In such case, remove the stator and sonicate in methanol.