Chromatography Forum

Recently did full maintenance on GC/MS; cleaned the source, replaced the gold seal, inlet liner, septa as well as installed a new column with a new guard column (we were starting to observe lots of ghost peaks and bleed since it had been in use for now a while). I'm observing a contamination peak with 129 and 147 main ions, which seems to correspond to Bis(2-ethylhexyl) adipate - https://imgur.com/us01aBd - both in split and splitless mode. Pretty confident it's from the GC side since if I do a run while keeping the temperatures of the inlet and oven low (50-60), I do not observe this peak.

Interestingly enough, when running a method with a higher starting oven temperature, the abundance of the peak decreases until it pretty much disappears if the starting temperature is above ~175-200 degC. The peak also seems to be absent if I run while heating the oven, but keeping the inlet temperature off. So, thinking this might be an inlet issue, I then replaced the split vent trap, cleaned the inlet itself, as well as cleaned the vent line - also baked out the column some before re-installing. I am still seeing this contamination peak!

At this point, I feel I have replaced everything what am I missing? Anyone know what this peak could be characteristic of?

Have you performed a run without a physical injection, just hitting the start button or with the syringe removed?

That will let you know if it is in the inlet itself or possibly a contamination in the solvent.

Wrap the septum in aluminum foil and try some runs without injections.

Meant to mention that all runs were done without injections. Peak is still there with septa wrapped in foil...