Methanol peak shape inconsistency on DB-624 column


Instrument: GC 7890A, G1888

I have been running USP 467 as well as Organic Impurities USP <Alcohol> and noticed some inconsistencies in methanol peak shape which elutes very early around RT 2.5 mins on a DB-624 column. Sometimes the peak shape will have a shoulder and looks like it's co-eluting, another time the peak area/size will change even when injecting from the same vial. One method uses headspace, the other direct injection and similar/same issue occurs.

Anyone else experience issues with methanol peak being inconsistent?

I attached a pic below. The two large peaks, blue and purple are the same sample and sample concentration but one experiences a shoulder.


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