Calibration drift issue with a 5975 MSD

I have a 7980/5975 GC/MS that suffers from a significant calibration drift of over 1 amu in a few days.  It affects higher masses more but low mas (O2 at m/z 32) will also drift down to the point it registers as m/z 31. Everything looks good when I perform atune tuning initially, but the draft is affecting results within hours.  Loading different historical atune files and retuning leads to same result (drift in hours to days).

The EM was replaced last year and the instrument met specs during a recent PM, but the drift issue remains,  Last year I reseated the column, and it seemed to help for a while but I never understood why (DB-FFAP 50m x 0.32mm x 0.5 um)

The system is in otherwise good shape but makes it impossible to use MS spectral library matching!  Would also be useful if I could correct calibration in .d files after acquisition as well if anyone knows how to do that!


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