Insufficient Injection Front Inlet Pressure

Hi everyone, 

I've recently come across an issue with my GCMS system (Agilent 5975MS, 6890N GC, PTV inlet). The system is running at ~14PSI (1.9ml/min) on a new tank of helium when not processing samples. I have recently encountered when running samples the system is unable to achieve the solvent vent flow rate (100ml/min at 2.5PSI) leading to the GC status "Not Ready Waiting for Injection Front Inlet Pressure" and will not inject the sample and start the run. Instead, the syringe stays in the sample vial and does not move until the run times out. I have tried cutting the column and reinstalling to the GC and reinstalling as well as changing the liner but neither seems to have fixed the issue. I have tried changing the inlet liner and cutting the column and reinstalling, and neither has fixed the issue. Any help on fixing the inlet pressure during injection/solvent venting so that I can process samples again would be greatly appreciated. 

Thanks for the help!

  • From a GCMS perspective, 1.9 ml/min into the ion source is not optimal. The MS prefers down around 1.2 ml/min. Sensitivity is better and spectral tilt is more typical.

    Septum head or septumless head?  What is your gas supply pressure?  When was the last time the gas supply traps were replaced?  Is everything completely leak free - nearly zero percent in the tune report?  Will it work at 80 ml/min at 2.5 psi? ... or lower?  When was the last time the split vent line filter was replaced?

    An Electronic Pressure Control (EPC) module only knows pressures, not flows. It sets a pressure against a fixed restriction.  On a 6890 that is a sintered metal calibrated frit, and the resultant flow is calculated.  As the frit ages the tiny channels get clogged with microparticulates mostly from itself. At some point, the frit is much more restrictive than it was at the beginning and higher flow rates become problematic. If that's the culprit, the fix is to replace the EPC module as the frit is inaccessible.

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