I am operating a GC 6890 with gas sampling valve. The column is a DB-624 UI and I am analyzing alcohols and esters. All of my peaks have a chair shape. How can I fix this?
You have a case of peak tailing starting to split peaks. I recommend trimming your column on the inlet and ensuring it is a horizontal cut. Also check the length of the column into the inlet, this can have these effects also. If this still occurs check the injection into the inlet, you may find a double injection is occurring or a stop in the introduction of your sample. And finally check the sample injection amount, if it's too much the liner will overload.
I have updated the tags on this discussion for better visibility as your example is a good one to help others with maintenance.
I will mark this post as assumed answered due to its age, if that's not the case, feel free to post again or update us with the resolution.
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