I am transferring methods to a colleague's GCFID and trying to align our database, so we can use our retention times to identify analyte peaks on his instrument. Our two instruments have a ~0.3min difference in retention time for all of our analytes and the newer instrument has ~1/4 the area count for each peak compared to my instrument. These area counts are used to calculate PPM for our research and need to be closer.
I have already checked the following:
Septum replaced
Method identical (pressure, temp, ramp time, run time, etc.)
Identical column (My column is a few hundred samples older)
Same gases
Same solvent, injection volume
My hunch is the column should be replaced but it is only about 13 months old so I want to avoid that if there are other possibilities for the differences in area.
13 months on one column? Either the column is not being used that often or your samples are really clean. We go through a column about every month.
Right off the back column age/condition can be an issue for the retention time difference. Has the column been trimmed? That will definitely change the retention times. If the column has not been trimmed then there could be issues with the matrix buildup on the column. This could be the reason for the decrease in the signal. Additionally, if the peaks have not only shifted but are also distorted, the I would be suspicious of matrix build up on the column.
When is the last time the liner was changed and the inlet clean? A dirty liner/inlet can cause decrease in intensity. I would also check for leaks. There can be a small leak that might not affect your pressure, but will affect your chromatography and intensity.
How were the columns conditioned? I have seen where columns were no conditioned long enough which caused issues with retention time and sensitivity.
Were the columns ever removed from the GC and stored? If so, were they conditioned after the reinstall? Have you ran out of carrier gas when the columns were installed? When the tanks run empty then there is a tendency for all the junk at the bottom of the tank to contaminate the system.
This is perfectly normal in GCMS, do not worry about that. When you transfer a method to a new instrument, even if you have the same column, you MUST do a new calibration curve on the new instrument, and you have to assess again the retention times.
As for the old column... 13 months seems quite a lot, maybe you'd better change it regardless the difference with the other instrument. By the way, instead of months, you should better talk about number of injections (most instruments have a count, take a look), and how was the column conditioned and stored.
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