What kind of detector you are using? Sounds like a detector problem.
Dear JI2002
my detector is FID.
now I change The carreir gas (helium instead of nitrogen) and base line at high sensitivity is better but upward drift changes to up and down drift.
thanks
I don't think your column is bleeding. The up and down drift usually indicates that there are something that "hugs" your system, and it lets itself go slowly to have this kind of drift.
Usually, i would consider the analytes you are analyzing, is it because...
1. the analytes stick to the glass insert? Use deactivated glass insert, could be base deactivated if your analytes are basic.
2. the analytes stick to the septum? means your analyte sticks to the needle tips, and the injection is not complete. Maybe consider the new injection method.... For example, in your syringe, you have a fraction of solvent, gap of air, then your analyte, then the gap of air, then the solvent again; and you inject it all in one shot. This works like a charm for some pharmaceutical samples.
3. the analytes stick to the detector? This is a big problem. I usually change the detector type for better detection.
Just out of curiosity, what is your CV between your first three sets and the last three sets of your calibrtaion samples? Also, does the recoveries changes dramatically between the begining and the end?
Or, even better. Post a problematic chromatogram at
http://www.imageshack.us/ .