What could affect one compound out of many in GCMS


We have a method to analyze 27 organic compounds in our GCMS 8860/5977B.

Our method works had been working fine, but yesterday I ran a new calibration and for most compounds it was really good, but for hexane I got this (the peak to the right)

Calibration was run with 7 levels in triplicate. As you can see the left peak looks fine, 7 distinct levels with good repeatability, but for hexane I basically have 2 levels.

If it had happened to all compounds I would assume some injections problem. But what could affect a specific compound that had been working fine with previous  calibrations?

Thank you in advance 

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