30 psi fluctuation on pressure

schaeferb
schaeferb
in Instrumentation and Mass Spectrometry
<p>Good Morning,</p><p></p><p>I need some advice on how to address a problem when the delta value for equilibration is at ~ 30 psi.  The system was equilibrated using MPA of water and MPB of Methanol at a 90:10 ratio for RP-LCUV.  Our initial pressure has been consistent at 7200 psi, but our noise level has increased.  I would like to reduce the delta to <10 psi, but I am having trouble assigning a cause for this rise in pressure variation.  I've attached a pressure trace, and could use some help in assigning a cause.</p><p></p><p>Thanks,</p><p>Brian </p>

Best Answer

  • Beowulf
    Beowulf
    Answer ✓

    Brian,

    Not to belittle the other responders to your post, but 30psi ripple is far too high for a BSM running 90:10 water:methanol.  UPLC is not HPLC.  The Acquity BSM is capable of <10 psi ripple throughout its pressure envelope with flow rates <1mL/min.  From your trace, I suspect a sticking primary check valve or leaking seal.

    Here are things to check:

    1. Degasser PSI - typically 0.4-0.6 psi.  If you are running higher, then the gas load on your MP might be too high.  If 0.9 or above, your depasser chamber or pump might be bad.  The degasser h/w fault doesn't trigger until above 1.2psi or so.
    2. run each pump individually with 100% methanol at 10,000 psi and see  what the ripple is. If you recently changed pump seals you need to  condition them in methanol for optimal performance.  With both pumps running, you won't be able to tell which pump is causing the ripple.
    3. Then, static leak test at 14,000 psi in 100% methanol.  If this fails, repeat at 10,000 and then at 6000 psi, etc until it passes.  If all fail,  possible bad CV, if the lower pass, possible bad seals/plungers.
    4. What does the primary pressure trace look like?  Does the accumulator spike line up with the primary stroke?

    Also, when you remove the pump head to replace the seal, always inspect the pump head hp seal area for scratches/fissures.  Even the tiniest nick or scratch will cause high ripple and premature seal failure.

    -Ed

Answers

  • Simmelink
    Simmelink

    Hello Brian,

    Well, your pressure variation is not bad, below 0.5%. Some papers recommend use systems with less than 1%, others to use less than 0.5%. When using HPLC with pressures around 3.5 kpsi, the variation must be less than ~ 15 psi.

    Specifically on your system, when using methanol: water, the mixture is subject to bubbles formation. Try to degas solvents sonicating under vacuum. And if the pressure variation still remain over to your taste, try mixing manually, degas and use only one channel.
    What is the ??

    Best regards

    Luis Simmelink

  • rune
    rune

    HI Brian

    I agree with Luis the 30 psi pressure ripple past minute is not critical. Getting below 10 psi in pressure ripple is difficult and normally not needed. Your solvents are degassed by the built in vacuum degasser so air bubles  should not be a problem. I am missing the pressure trace for the primary pump heads since these can tell a lot about how the system is working.

    What about your chromatography ? Do you see stable retention times and baseline ?

    Best regards

  • schaeferb
    schaeferb

    Thanks to everyone who replied.  The pressure fluctuation in moving from <10 psi to 30 psi for our system changed the S/N from 15-20 to <10.  The system was recently requalified, and I'll have a second look at what was performed, who performed it, specifically if the seals were conditioned or not.

    Once the issue is resolved I'll follow up with a summary so we can have some closure on this topic.

    Thanks again.

    Brian

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