Hi all, 

After recently changing to a split/splitless inlet and capillary column on our 7890B GC we've found ourselves changing out the bead more than usual. When starting up our machine we recently got a noisy flat line, as pictured.  I know that this can happen if the there is not enough sample drawn into the system, but the syringe in this scenario was freshly changed. We ended up changing out the bead to resolve the issue, but still aren't certain as to root cause. Has anyone experienced this issue and is familiar with what may cause it?

Additionally, any experiences with why changing to a capillary column from a purged packed inlet/glass column that might put more strain on the bead? 


  • Hello  

    I’m sorry for the delayed reply to your message.  Do you still need assistance with this? If you do, please take into consideration the notes below. However, if the issue was resolved, could you please share what the resolution was?

    I am not sure if this is something on my end or not, but I cannot see the attached photo.

    What type of bead are you using (BLOS or ceramic), and does your NPD have its dedicated air supply?

    If you are using beads faster than usual, do consider the steps recommended in the 7890B Advanced Operation Manual (publicly available on our website). Pages 199-200 go over good practices for extending the bead life. Here is an screenshot containing that section from the manual:


    Noise issues could be caused by a plethora of things, a non-exhaustive list being: contamination from the Make Up Gas tank/line, contamination in the inlet/column and electronic issues. For contamination issues, running  a bakeout on the system, as well as performing inlet/column/NPD maintenance can improve the situation. Leak checking (inlet, column connections on the inlet and detector sides) is always a good practice too. The good news is that on you can also find the 7890 Maintenance Manual, where you can find all maintenance procedures relating to any inlet/detector, as well as column maintenance/installation topics.

    For the last question, I would like to say that I don't see any issues with it. But, to be certain, I would like to know what inlet you are using now, and the gas flows for both cases.

    Let me know if you have further questions on this.

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