Lost sensitivity in 5973 MSD but only in one group

[Meggie1983]

Recently lost sensitivity in PAH analysis but only in group 5 which looks for m/z 228, 226 and 240. Other groups are not affected. Nothing was changed in the method.
Trying to identify cause of the problem.
Any help is much appreciated.

Meggie

[Rndirk]

What do you mean with reduced sensitivity? Higher baseline in those regions? Extra peaks? Worse QC's for those compounds?

Generally an MS in SIM mode is good at hiding contaminations. MS/MS even better. It is normal that contamination manifests itself in regions where you look for target ions that just happen to also be stuff that you're not looking after.

It can be column bleed, septum bleed, contaminated syringe/solvent vials, dirty liner,...

You can try to isolate the problem by running in full scan mode. Run a method with manual injection (don't inject anything) and check for peaks. Then compare it to an injection with a solvent blank.

[James_Ball]

Do you have your resolution set to Low or High in your SIM setup window?

If set to High, and your mass axis in that mass range has shifted, then you may be losing sensitivity on some masses, if so adjust mass assignment in the tune and see if it fixes it, or switch to Low resolution.