UPLC PRESSURE ISSUE AGAIN!!

[seamoro]

Hey all,
About two weeks ago i had major problem with uplc. I got it solved by replacing a faulty connection (outlet cable from pda).My system was working fine with good chromatography, low pressure , stable pressure etc then the enginner came back to replace the seal wash housing in the head seals and all the pressure problems have come back!! They seem to be the exactly the same as before. Pressure is very high 0.2ml/min 8000psi when normally i would get 3500 before. takes forever for the pressure to stablise. if i can actually get the system to 0.5ml/min flow rate the pressure will eventually after 30mins will fall from 14600psi to 13600psi and then start building again slowly until it maxs out at 15000psi. I had the engineer in the the whole day yesterday and he is as puzzled as me! He disonnected everything and tryed to work backwards. It disconnected the guard column...the pressure still builded...he attached the column directly to injection valve and therefore bypassed the column housing...the pressure still builded. He used different supplier solvents...the pressure still builded. He connected the column directly to the vent valve where he noticed it seemed to be only happening with pump A where as B remained stable. He also replaced the mixer and also the check valve for A thinking that was the issue but it didnt solve the problem....has anybody any idea what is going on???? Lost and confused!

[seamoro]

Also we have tryed multiple columns the same issue occurs....and all those little things like moblie phase etc all high grade all filtered etc etc

[carls]

what pressure do you get when you replace the column with a union?

[coffee bean]

Has the engineer already checked/replaced the pressure sensor?

[seamoro]

I think its the water!!!!! oh my god....im using hplc grade water filtered through 0.2um filter but i just found this article. http://www.hplc.hu/PDFs/UHPLC_MobilePhasePrep.pdf
What do you goes use hplc grade or UPLC grade water?

[carls]

I have not had any problems related to the HPLC grade water delivered by either a Barnstead or Milli-Q lab DI water system when used for UHPLC. Our water systems are carefully maintained and the water is used on demand, i.e. no large storage reservoirs. "Higher grades" of water are not available or really even possible, except for maybe ultra low organic carbon water.

Filtration can cause as many problems (e.g. ghost peaks) as it "fixes" so only filter when necessary. Filtration of HPLC grade organic solvents or pure water is generally unnecesary.

[seamoro]

Hey carol,
Im pretty sure its the filter we were using is the problem and to a lesser extent the water. I know what filters to get (nylon and ptfe) which will give us stable pressure. What about HPLC grade water....is it sufficient?? when filtered or am i going to have the same or similar issues.

[aceto_81]

We use 0.45um filters for our mobile phases on UPLC, and never had any pressure issues.
Also by using a column prefilter, if the mobile phase is a problem, you can eliminate the column prefilter.

Also, if you are using UPLC Acquity columns, you can try to change the column inlet frit to see if this is blocked.

Ace

[seamoro]

but what type of filters? PTFE?

[richiekichi]

0.22 um PVDF here

[aceto_81]

0.45µm PTFE