pressure build up over time

[sunnysideup]

after several injections the pressure builds up over time and the system stops. i removed the pre column filter and replaced and restarted the run. but then it happened again! this is a new column. what could be causing the pressure to build up over time? the samples i am injecting are reference materials and blanks... please help..

[tom jupille]

Are you sure that what you are injecting is soluble in the mobile phase? Pay particular attention to things like buffers.

[Consumer Products Guy]

Are you sure that what you are injecting is soluble in the mobile phase? Pay particular attention to things like buffers.

Agree with Tom. Also, make sure your autosampler needle is perfectly aligned with the needle neet, and not scraping a tiny particle off each time. Ask me how I know that.

[Mattias]

Just guessing... Is the pump mixing 100% acetonitrile with 100% phosphate buffer? The only pump I know that can do that for more than a couple of hours is the Alliance pump.

If this is the case, the only way out is to premix the mobile phases (gradient start and end composition in two bottles).

[Peter Apps]

Another possibility is that the pump seals are shedding particles, in which case you will also begin to see pressure and flow problems sooner or later.

Peter

[sunnysideup]

i'm not using any buffers. the mobile phase is composition of acn and water. i have to check about the needle seat.. every time the pressure builds up and the instrument stops, i restart the instrument and then make sure the pressure is low by removing the precolumn filter from the column and then reattaching to the column. which indicates that there is some buildup at that site? samples are all soluble with mobile phases..

[Mattias]

Is the pressure building up also if you don't perform any injections? If that is not the case the problem must be either in the sample (particles) or in the needle seat (as suggested).

[AdrianF]

Have you checked the tubing? Peek tubing can get crimped and then generate a massive back pressure.

[moino]

If this also happens without column(?) - could it be a filter or frit somewhere else in the line, e.g. in the purge valve if you have one (Agilent 1100)?
I often have this problem with the purge frit after running with buffer for longer time. When I change then to 30 % isopropanol in H2O, the small PTFE frit in the purge valve gets blocked, even when I open the valve.
This is easy to check - if the valve is open, the pressure should drop close to 0, otherwise this frit has to be replaced.