Column flow/pressure drops during desorb

Hi everyone 

I am new in this platform and i am hoping to learn more. 

I recently removed my column and trimed it but when i replaced it back i have experienced the following: immediately after purge and trap desorbs the column flow drops for the set time of desorption. The tune report has passed. I have change the liner, gold seal, and septum but doesn't help the situation. 

I have been doing this same exercise(trimming) before when i was still using the chemstation software. Now the software is changed to mas hunter and since then we have been experiencing problems. Part of the other problem is that the pulsed plit injection doesnt work anymore. 

Could this dropping of column flow be connected to the software upgrade or it is a hardware problem? And what could it be? 

  • Can you share some screen captures from MassHunter Acquisition with your run method loaded of the  Inlets SSL-Front (or whichever one your P&T is connected to), GC Columns window, the Configuration/Columns window, and the Configuration/Modules window?   It could also be an issue inside the P&T. During desorb a valve inside the P&T puts the trap inline with the flow to the inlet while the trap heats up to desorb your compounds. If the valve is not working right, the trap is plugged or leaking, or a few other possibilities, the pressure/flow to the GC inlet won't be present.  

    Does the GC work fine without running the P&T?  If you just setup and start a run by pressing the start button, does it run?  

  • Please see the attached. I however as a routine maintenance of P&T rinse the sample pathway. After that i baked the system. Could i have done something wrong amd if yes how could i rectify. 

  • I have put a beaker with methanol at the end of the transfer line from the P&T and manually desorbs and i could see bubbles in the beaker. Couldn't this mean the p&T desorbs correctly? 

  • I'm in the US and this is the first time I've seen someone using kPa instead of psi.  The parameters look fine. I would recommend a longer Oven Equilibration time, like 1 minute or more.  Maybe increase your Scan threshold from 57, but I'd have to see the data file to know how high to go. The TIC background is not a huge number compared to some, but could be reduced by increasing the threshold.  You could certainly turn off acquiring and looking at the GC detector test signals.  

    Atune.u with tune EM of 2094. That's still usable, for sure. I'd look at the EM age, how long it's been since cleaning, maybe remedial cleaning, but no worries for the moment.

    MIB and Geosmin...I messed with those when I was an intern in like 1980 or so!

  • Yes, probably. But that's with no restrictions on the outlet like the GC inlet, liner, column, column connection, transferline connection, etc.  You can get flow with no outlet back pressure and no flow with it.  What is the carrier supply pressure to the GC and P&T?  The pressure at the transferline outlet must be able to reach at least 63kPa (9.2psi) there.  Any pressure regulation/flow controller needs to be around 140kPa higher than the total of what is downstream of it.  At your final oven temp the inlet is ~164kPa (23.7psi). The trap and plumbing is a restriction, the EPC module, too, so you should have your supply set to at ~482kPa (70psi) or so.  If the gas line filter is plugged up a bit, your trap plugged up a bit, or you have any further restrictions it may required higher pressure than that.

    If this started after you did P&T and column maintenance, I would suggest you go back and do those again to make sure they're as expected. 

  • Hi again. When i start a run by pressing  the start button it doesnt drop down. But when i try with a different sample introduction(G1888) it drops. But the peak shape and background noise is better this time around.

  • Hi Cumysat9552,

    Any update on your problems? If you were able to solve the issue it may help others in the community, if not feel free to post again and the community will continue to work with you.



  • Yes.. Just recently i had checked the purge and trap nut after a water management and it was loose. I guess that's why when at desorbstion stage the pressure would drop.

    Thank you very much 

  • Just before the the line enters the trap

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