Sample pressure errors

<p>Hello</p><p style="height: 8pt"/><p>We have a UPLC/TQD that I keep getting sample pressure low errors. It will pick up the sample but soon as it gets to that tower thing it stops and gives me that error. The needle looks perfectly fine. The solvent and sample syringes are full, no bubbles. No bubbles in the lines. I've done the characterize needle and loop volumes and needle seal. Leak test for the sample syringe, wash syringe and needle seal all pass. Service has been here two times and it works just fine when they are here. After they leave it comes back. Yesterday it came back and I had to shut down for the day getting nothing done. Then this morning no sample errors.</p><p style="height: 8pt"/><p>Anyway I'm getting really frustrated and seek ideas on what to do next.</p><p style="height: 8pt"/><p>It doesn't seem to matter what the method is but yesterday it was for a Pentobarbital method that is isocratic 30:70 ammonium acetate:ACN moble phase. 10 uL full loop.</p><p style="height: 8pt"/><p>TIA</p>


  • lizh

    It would be great to get a copy of the Service profile from your machine, but "Sample fluidics pressure low ({###})" message is associated with an issue with the wash solvents. Basically, please contact the FSE.

    The "error message" generated in the ACQUITY Console occurs when pressure drops below 100psi during the injection sequence. Therefore, this message is subject that accompanies not only a leaking or faulty sample syringe 3-port valve as well as an obvious leak. Please examine the entire Fluidics Drawer lines for leaks during leak tests and syringe priming function. Look for bubbles etc.

    If there is no leak you have to apply a more subjective evaluation of the Autosampler fluidics.

    When does the error occur? Sounds like during the injection sequence? Have the wash syringes been tightened? What is the weak wash solvent used? Is it highly compressible? Is there a leak at the Degasser fittings for the washes? Are the Needle Seal loose or needs to be replaced?

    Please contact Technical Support or your FSE.


  • lizh

    I was just checking in again to see how you are doing and I asked our RandD engineers for further details. Again, the test performed that outputs this message is a test that checks all the seals are sealing and there are no leaks in the wash needle system in the sample manager. This test is run at the following times:

    (1) During a Partial Loop Injection at the pressurization step of the injection process.

    (2) During PLNO Mode the Sample Manager will attempt to pressurize the system to be sure the customer has wash fluid. (in this case. the test is only used to keep consistency between injection modes and alert the customer to a situation where they may be out of wash solvent. Since this is not critical to the operation of the instrument in PLUNO Mode and PLNO Mode is the Default injection Mode, and it does not use the regulator or the seal).

    (3) Any characterization or Seal Diagnostic.

    If you wish you can also follow the sequence of events that is displayed in the console during the seal test. During cases 1 and 2 above a slightly modified sequence of events is used in order to save injection overhead time. You will see that there are multiple places a leak could occur. Below is a complete list of the most probable causes to a failure of this test:

    • (a) No Wash Fluid

    • (b) Air Bubble in Line from the Wash Syringe to the Regulator

    • (c) Perfuse Leak or loose fitting in any part of the system

    • (d) Bad or Improperly Adjusted Injection Seal

    • (e) Bad or Loose Pressure regulator

    • (f) If the needle has been changed particularly from a PEEK to a SS full or tipped needle it is possible that the Outer Diameter of the needles are difference. Normal Tolerance Allow for +/-0.001" Diametrically on the Outer Diameter of the Needle. If the Seal was adjusted for a large Outer Diameter needle and a low Outer Diameter needle was installed this could show up as a failure during this test. This might also show up as an intermittent failure. (If you think there are no leaks please talk to your FSE becasue this last issue may fit these circumstances and I did not list in my earlier reply).

    Let us know if we can assist further.

    Edited by: Elizabeth Hodgdon on Oct 22, 2008

  • I've had the FSE out here twice but everytime they come the problem disappears and all pressure/leak tests pass.

    I'm afraid this instrument is rather daunting for me. I am a long time GC man. GC is a lot more straight foward for me. A long time ago I did cyclosporins on an HP1090 and as simple as that instrument was compared to the UPLC it was still a mystery for me.

    The first time the error came up was when I was developing a method for phosphatidylglycerol which I was doing a partial loop with overfill. I thought it was odd that my other method which uses a full loop would work just find but nobody (at waters) thought anything about it.

    The FSE thought it could be the firmware so he updated the firmware but soon as he left the error returned. Eventually I just changed the injection to full loop and diluted my sample with more aqueas phase. The method has been on hiatus of late though and I haven't been working on it.

    Everything had been going along fine with just running one test (Pentobarbital) until I tried developing a method for ethylene glycol. I never could get it to ionize (subject for another discussion) so I gave up to study the matter later but when I tried doing a Pentobarbital the error returned. This time sample mode has nothing to do with it since I'm doing full loop. So I tried all the before performed troubleshooting steps all of which passed. Since I'm on the left side of the country I don't get phone help after 2 PM so I just shut everything down and went home. Of course the next day I start up the instrument and the error does not present inself.

    The only thing really different I did that day was use MEOH and 0.1% FA for the mobile phase while the Pentobarbital is ACN and ammonium acetate. I left the weak and strong wash in the ammonium acetate and ACN, maybe it didn't like that combination.

    The needle always look fine. I never see any bubbles in the syringes or evidence of leaking anywhere.


  • lizh

    Here is a list of ways to avoid SAMPLE MANAGER LOW PRESSURE ERRORS

    During the transfer of sample from the sample needle to the sample loop, the Sample Manager pressurizes the flow path to 100 PSI. If the pressure does not reach 100 PSI, this error will display.

    Some common points to consider:

    • - Rogue air bubbles in flow path - Ensure ACQUITY Quick Reference Card details are being followed daily or in Sample Set.

    • - Out of wash solvents or wash solvents are not primed sufficiently - Check Wash Solvents, refill as needed, prime solvent lines.

    • - Leaky syringes or fluidic line - Run Sample Manager Syringe leak diagnostics to determine leak point. Inspect fluidic lines

    • - Damaged or marginal needle - Run Change Needle Seal Diagnostic to view and check for performance.

    • - Damaged or marginal O-ring - Run Change Needle Seal Diagnostic to view and check for performance.