All results lower than expected.

HI everyone, I am new to the community and new to working with GC instruments. 

The annual maintenance was performed on my GC 7890A two weeks, quality control at that time was perfect and running as expected. Last week and this week all of my quality control levels on every volatile tested have shifted downward, all running lower than expected.  I have recalibrated the instrument, however results are the same.   Any advice and help are greatly appreciated. Slight smile

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