Unknown peak co-eluting with MeOH on DB-624 GC-FID



I am injecting ethanol samples by direct injection which contain trace amounts of methanol and notice the methanol peak varies injection to injection on the same sample. I also injected pure air (empty vial injection) to find out if there is something eluting from the system and notice there is a peak with the same RT of methanol at the that varies by injection to injection.

I am wondering where this unknown peak is coming from, since it is interfering with my ability to quantitate trace levels of methanol.

I changed the liner, septum, o-ring, gold seal, column, syringe and the issue reappears.

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