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Sensitivity issues in "He" mode. Agilent 7850 ICP-MS

Volodymyr Sirous

Hello. Dear colleagues, may I seek your advice about my problem?

I have sensitivity issues with Agilent 7850 ICP-MS in "He" mode. Usually, I carry out measurements a couple times a week. And before every measurement I have to purge the cell with helium at 12 ml/min via MassHunter settings (Cell maintenance) or by unscrewing the relief valve manually. If I don`t do that, signal intensities in "He" mode are very low, sometimes the instrument can`t even perform the tune in this mode because "Sensitivity is too low". Is it normal that I need to purge the cell every time or I have some malfunction in my instrument?

Also, recently we`ve installed Hydrogen line. And when working in two modes ("H2" and "He"), again, the sensitivity in "He" mode is quite low compared to some our previously obtained data, despite purging the cell with H2 (10 ml/min) and He (12 ml/min) simultaneously beforehand. So, I have the same question - what is the problem with sensitivity? In Element Selection settings we had Stabilization time 10 sec for He after H2, is it enough?

I should note, that for the Tune before acquisition in Startup configuration I always check only Torch Axis and Plasma Correction. Other Tunes I check from time to time. Is it OK, or I should check all Tunes (maybe except P/A factor) each time when I ignite the plasma? 

Thank you in advance for your ideas!

Parents
  • +1

    Hi,

    1. It is not normal, that you have to purge the cell gas lines every time

    2. Ou should perform at least following "Tests" during Plasma ignition: Torch Axis - EM - Resolution/Axis. But a performance report every day would be nice (and therefore you should select "lenses tune" as well)

    3. I think you are having a leak in the gas line. Are you closing the gas bottles every time? i would recommend not doing this. 

    You should check the Cell Gas Lines for leaks. to do so, do the following:

    Close the pressure regulators at the gas cylinders. with the instrument in standby, open the maintenance dialog from the "Cell/Raktion Gas Tab".

    Now you can set up a gas flow (12 ml/min for He and 10ml/min fpr H2). Leave this running over night (as it takes quite a loing time). If your gas lines are sealed correctly the meter readings should show a measured flow >0.2ml/min. If not, there this a leak. 

    Good luck

    Chris

Reply
  • +1

    Hi,

    1. It is not normal, that you have to purge the cell gas lines every time

    2. Ou should perform at least following "Tests" during Plasma ignition: Torch Axis - EM - Resolution/Axis. But a performance report every day would be nice (and therefore you should select "lenses tune" as well)

    3. I think you are having a leak in the gas line. Are you closing the gas bottles every time? i would recommend not doing this. 

    You should check the Cell Gas Lines for leaks. to do so, do the following:

    Close the pressure regulators at the gas cylinders. with the instrument in standby, open the maintenance dialog from the "Cell/Raktion Gas Tab".

    Now you can set up a gas flow (12 ml/min for He and 10ml/min fpr H2). Leave this running over night (as it takes quite a loing time). If your gas lines are sealed correctly the meter readings should show a measured flow >0.2ml/min. If not, there this a leak. 

    Good luck

    Chris

Children
  • 0 in reply to cschulz

    Dear Chris,

    Thank you for your valuable advice. 

    We performed the leak test as you suggested. Also, we consulted the "Troubleshooting tool for low sensitivity" and got a bit confused with the criteria. After 17 hours the He flow still was 12 mL/min. Does it mean that there is no leak or otherwise? Because according to "Troubleshooting tool" the He flow should be less than 0.1 mL/min if no leakage is present in the system which sounds a bit illogical to me. Below, there is the screenshot of our MassHunter window after 17 h of the leak test ant the "Troubleshooting tool" page.

    Another problem emerged - lately we have very high CPS RSDs - they can reach more than 100%. We`ve already cleaned the nebulizer, spray chamber, torch and cones; changed all sample uptake tubing. But we`ve never cleaned the lenses (since 2022). Can this cause our problems?

    Best regards,

    Volodymyr

  • +1 in reply to Volodymyr Sirous

    Hi Volodymyr,

    If you still have a flow reading of 12L/min you have a „massive“ leak. I’m wondering, if your helium bottle drains quite fast. 
    I would fix this problem first before thinking about anything else. 
    Use a wrench and retighten every connection in the Cell Gas line. 
    Good Luck 

    Chris

  • 0 in reply to Volodymyr Sirous

    Hi. As Chris says, if the flow is 12 ml/min means you have a massive leak.

    But, just in case, did you close the Helium cylinder, right? That's a part of the procedure.

    Also, I think that 2 years without cleaning the lenses is quite a lot of time. In our case, each time we clean them, the doubly charged go down. I don't know if it would improve your RSD, but I'll definitively do it. But again, as Chris said, your biggest issue now seems to be that Helium problem.

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