Chromatography Forum

Perfect match right? Not any more. This method used to be rock solid, we could even detect 5 ppb easily on our old 5972.

I had posted this in the GC section since I suspected an inlet issue. But after connecting the 5977 to a better, less used 7890 GC and seeing the same problems, I doubt it.

We are losing the following compounds from the 16 EPA list: ACE, ANT, PYR, BAA,BAP. It's odd that PHE is strong, but ANT is greatly reduced.
I don’t see why certain PAHs would drop out entirely while others would not.
The source has been cleaned. Changed the column, liner, septa, syringe, gold seal, cleaned the inlet, tried a different GC
Tune seems ok, not great.
Anyone had issues like this before?

Are you quanting SIM or SCAN? Are masses identified correctly; anthracene for instance, quant ion 178, what does the TIC show, 178? or 177.7? I have seen weird behavior if the quant ion and actual ion m/z were off by more than 0.3 amu.

As CJM said, definitely make sure the mass assignment is correct.

If using SIM, you can set it to lower resolution and it will ignore some variations in the exact mass assignment.

Also, are you using the larger diameter drawout lens? The PAH seem to do better when using the 6mm one than the standard 3mm.

Have you tested a brand new standard from an unopened ampule? Many of those PAHs are ones that I'd see trending low when an LCS or a standard wasn't protected from light/stored in an amber vial.