Chromatography Forum

Hi, I am not familiar with GCs at all and am trying to help a fellow colleague figure out the issue on her GC runs. We use a GC to monitor the ratio of a certain compound in a process sample. The method and everything was designed and written before either of us started here. She did some maintenance to the GC and changed the column out, and now the retention times for all compounds have shifted slightly so we have to recalibrate it everytime we run it, which was never needed before. My question is, does anybody know how to make the recalibration save so it no longer needs us to manually recalibrate it to pick up our compounds?

She did some maintenance to the GC and changed the column out, and now the retention times for all compounds have shifted slightly so we have to recalibrate it everytime we run it, which was never needed before.

Did the retention times (1) change just once after the maintenance and column change, or (2) do they jump around day to day or run to run?

If (1), typical and expected. If (2), then likely a leak at the inlet or head of the column, or in the flow plumbing if that was part of the maintenance.

They've just changed the one time and the peaks are at the same RT every run, they are just not being labeled bc the GC is looking for them at the previous retention times for each compound. We just dont know how to update the calibration to the new retention times since neither of us has GC experience and haven't been able to figure it out on our own.

Depends on what software are you using. You should be able to google the manual; if not, someone here might know if you provide more information.

So it is more a lack of knowledge on how to update retention times in the software. Which software are you using???

So it is more a lack of knowledge on how to update retention times in the software. Which software are you using???

Yes, very much so a lack of knowledge. We are using Open lab CDS Chemstation 490. Truly appreciate everyone's time and help:)

If I am not mistaken their is a Compound Table with compound names and retention times, you need to update the retention times in that table, save the method, or master method depending on the version, and the next runs the identification should be OK

They've just changed the one time and the peaks are at the same RT every run, they are just not being labeled bc the GC is looking for them at the previous retention times for each compound. We just dont know how to update the calibration to the new retention times since neither of us has GC experience and haven't been able to figure it out on our own.

If I am not mistaken their is a Compound Table with compound names and retention times, you need to update the retention times in that table, save the method, or master method depending on the version, and the next runs the identification should be OK

In Agilent Chemstation, you can do and should do what varossf states. Go into Data Analysis, open up the Calibration Table, and change the retention times for your peaks of interest. You should be able to set the "width" of the time where software will pick up the largest peak using "From" and "To". If you're not sure what you are doing, Save the Method as a different name and try; of course that Method Name will need to be chosen in the Sequence table.

Thank you! We were updating the method per run, had no idea that would not update the retention times on the master method. I truly appreciate your patience and help!!