Air leak showing in one GC-TQ but not the other (share same gas tank/plumbing)


I am trying to diagnose an air leak in my system.

All three instruments below share the same carrier gas tank:

   Relative abundance                  Abundance
# Intruments Inline filter Water Oxygen Nitrogen PFTBA Water Oxygen Nitrogen
1. New GC-TQ (HES) Yes 1.01% 0.09% 0.35% 41570936 420402 38728 144337
2. Old GC-TQ (HES) No 6.28% 20.81% 77.57% 760063 47728 158190 589573
3. GC-MS (single quad) Yes (H2O saturated) 6.70% 1.00% 40.65% 32344 4839 196224

- System 2. and 3. have air leaks.
- System 2 electron multiplier is aging (max gain factor in autotune report is hovering around 600-900)
- I confirmed the leak is not coming from the MS side of systems 1. and 2. by capping the inlet side of the column and achieving low nitrogen readings.
- Shutting off the gas supply to system 2. and 3. at the EPC resulted in lower nitrogen abundance readings.
- I changed the gas cylinder and the readings are still high
- Used a leak detector to check all swagelok points in the gas lines (there is lot of them) and couldn't find any obvious leaks.

What else can I do to confirm where air leaks are coming from in system 1. and 2.?

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