Troubleshooting: n-propanol ISTD response in HS-GC-MS gives two distinct response levels while ethanol remains stable
Hi everyone,
I'm troubleshooting a response issue with an Agilent 7890A/5975C HS-GC-MS method for ethanol quantitation. My analyte of interest is ethanol, internal standard is n-propanol, and my calibrants are all in an aqueous solution.
I'm seeing a very strange (quite interesting actually) pattern with the n-propanol response. Namely that the n-propanol responses appear to form two distinct populations, roughly a high-response state and a low-response state.
Initially I suspected sample preparation, so I prepared a single master mix and aliquoted it into the calibration vials. The problem persisted. Ethanol is quite reproducible while n-propanol continues to show large variability.
My question: what could cause an almost binary change in n-propanol response while ethanol remains relatively stable? Has anyone seen a two-level ISTD response like this before?
EDIT: An inlet sealing issue may have been causing an intermittent leak, which led to the response variability of n-propanol.Thanks everyone for the suggestions!