Degasser operating pressure range?

<p>Hello, I'm relatively new to UPLC. I've been using this system about 4 months now, and recently I'm having baseline drift problem that I had not seen before. I figured when I degassed the mobile phases manually, the baseline didn't drift. Now, the in-line degasser seems to be working okay. I mean if it's not, I would have gotten some sort of warning message?? We have 3 Acquities in our lab. The degasser pressure reading on each system is:</p><p></p><p>System #1: 0.42 psi</p><p>System #2: 0.49 psi</p><p>System #3: <strong><font color="#ff0000">0.68</font></strong> psi</p><p></p><p>The #3 is the one I've been using. Although not that big difference, I was wondering the somewhat higher pressure than other 2 is an indication of ineffective degassing? I've read thru the Operator's guide and the console help, but I couldn't find any statement about degasser. What is the proper operating pressure range? How would I know if the degasser is not operating properly? Waters team, please let me know... and fellow UPLC users, what is your system's pressure reading??</p><p></p><p>(My mobile phases are water and methanol with 5%IPA, running gradient, if that makes any difference with pressure reading) </p>

Answers

  • Hello:

    Do you have an example of the drift so that we can see it?

    I will get an answer on the values to expect for the pressure.

    Liz

  • Here you go.

  • Here is further information on ACQUITY degasser operation. The error message for the degasser will trip if the pressure goes above 1 psi for 30 seconds.

    Therefore the pressures that you are seeing are normal. The pressure differential are seeing is normal for system to system variation.

    The 0.2 difference he just the normal variance of the transducer.

    We do need to get more information about the problem to properly diagnose your issue.

    First can we get the raw data showing the issue with instrument conditions and method and to find out how you manually degassed the solvents and how you ran them without going through the degasser on the ACQUITY.

    Does the drift follow the gradient and does the drift go away when you stop flow? Letting the instrument set with flow going for a long time will also tell if the drifting is cyclic or random.

    Also can you include the detector conditions such as wavelength, lamp hours and lamp energy.

    This information should at least get us started in determining where to look.

  • This is helpful, but could we have the method info too, please!

    Many TX

    Liz

  • Thank you both for your reply. Unfortunately, I have to proceed with impending analyses, that I don't have time to investigate further. I know I can avoid this problem as long as I degas the mobile phases (with vacuum while stirring, 10 min), so I need to move on. I got the answer I wanted to know (the operating pressure range; it would be nice to have this basic information in the manual), I'm going to close out this thread. Thanks again!

  • One more thought....

    If the vent line from the degasser is restricted, the chamber pressure will increase. when the chamber pressure increases, the partial pressure of the remaining gases in the mobile phases increases. the only degasser chamber failure that i've seen in a BSM has been related to a poorly vented degasser outlet. the user should verify that the vent line is clear and unrestricted.

    if the chamber pressure increases, the dissolved air in the mobile phase will increase. what's interesting is that the event at 20 minutes into this gradient is much larger with the suspect chamber pressure. that event occurs when the organic (is it methanol?) is being jumped high - perhaps 100%. since i don't have all the conditions, this is all speculation but please check if

    1. the vent line isn't restricted (do not put it in solvent waste)

    2. the organic modifier isn't methanol

    3. the wavelength isn't below 260 nm (likely to be 220 - 230nm).

    Just in case!

    Liz

  •    
    michelleaf wrote: "The 0.2 difference he just the normal variance of the transducer. ":
    • Sorry, that statement is incorrect. The transducer is actually far more accurate than that and any variation seen has nothing to do with it.

    I did not see anyone post the correct answer to your initial question about what the normal degasser vac pressure range is. For your system it should be ~ 0.9 psia. It can go as high as 1.5 or as low as 0.4, but should be between 0.4 and 0.9 during normal operation actually, closer to 0.9 is better because too much vacuum on these systems will draw more vapor through the system (increases condensation problem, pervaporation). Variation in the value is NORMAL. It should change anytime you change the flow rate or mobile phase composition as the vac pump must change to adapt to the changing amount of gas in the liquid. Higher flow rates put more stress on the system so degassing efficiency goes down. Depending on the vapor pressure of the liquid, some liquids require more vac "effort" than others.

    Don't forget to have that degasser professionally served EVERY 5 years (or sooner if an error occurs) to maintain operation. Normal lifetime of the parts used is about 5 years and they require regular service to keep running. If you fail to service it, then you end up with contaminated mobile phase in your system and little to no degassing.



  • stevenp said:
       
    michelleaf wrote: "The 0.2 difference he just the normal variance of the transducer. ":
    • Sorry, that statement is incorrect. The transducer is actually far more accurate than that and any variation seen has nothing to do with it.

    I did not see anyone post the correct answer to your initial question about what the normal degasser vac pressure range is. For your system it should be ~ 0.9 psia. It can go as high as 1.5 or as low as 0.4, but should be between 0.4 and 0.9 during normal operation actually, closer to 0.9 is better because too much vacuum on these systems will draw more vapor through the system (increases condensation problem, pervaporation). Variation in the value is NORMAL. It should change anytime you change the flow rate or mobile phase composition as the vac pump must change to adapt to the changing amount of gas in the liquid. Higher flow rates put more stress on the system so degassing efficiency goes down. Depending on the vapor pressure of the liquid, some liquids require more vac "effort" than others.

    Don't forget to have that degasser professionally served EVERY 5 years (or sooner if an error occurs) to maintain operation. Normal lifetime of the parts used is about 5 years and they require regular service to keep running. If you fail to service it, then you end up with contaminated mobile phase in your system and little to no degassing.



    Hello stevenp,

    What kind of tasks does the degasser service consist of?.
    Are there other symptoms, in addition to mobile phase contamination and little vacuum, that indicate that the degaser is not working properly?.
    We have an Alliance 2695 system from 2009.

    Thanks!



  • Gonzalo: Please see this link for more info on diagnosing problems with Waters brand HPLC degasser modules (Alliance or Acquity models): https://www.hplctools.com/waters_acquity_solvent_manager_error_degasser.html

    • The Waters integrated HPLC vacuum degassers require professional service ~ 5 years (that is as long as they last if used on a regular basis). Sounds like your degasser is 11 years old so most likely worn, damaged and/or contaminated, just based on age, but professional diagnostic service is needed to find out exactly what the true condition is. In the USA, Chiralizer Services can professionally clean and  repair most of these units for a fraction of what a replacement module costs.


  • Thank you, stevenp. Yes, it is 11 years old, but not used regularly. The system only registers 225 liters of pumped solvent, and degasser is showing pressure value of 0.5 psia (in the normal range as I know). I asked you about symtomps of a bad functioning degasser, because our LC system is showing high delta psi (about 300-400 psi) and I started wondering if the cause of it could be an improperly degassed mobile phase.
    I think it will be better to open a new post for the delta psi problem.

    Thanks again! 
  • Pressure variation must be put into context to understand if it indicates an abnormal problem. You did not provide what the normal pressure is (300-400 psi is extremely low, most HPLC system can not operate reliably at such low pressures). If instead you meant that the system varies between 300 to 400 psi over a run in total system backpressure (for an isocratic run, that would indicate a serious problem, such as loss of prime. For a gradient run, that may 100% normal).
    We need more info to understand what you question is (ALL normal HPLC method details). Please get some LOCAL help from someone at your school who has HPLC training. They are in a better position to help you onsite. If you do have HPLC questions, then starting a new thread would be the best approach, but please look into local help first.
Sign In or Register to comment.