- The auto detector check fails
- Poor mass accuracy on DRE data
- MassLynx 4.1
- SYNAPT G2-Si
The reference sample is required for a lockmass peak, but it is also used for the auto detector check (which ensures that the correct detector is used for the acquisition). You must use leucine enkephalin for the auto detector check, and it must be of the correct intensity (2 IPP is required). An intensity that is too weak does not provide a stable signal; an intensity that is too strong is out of the DRE operating range.
[Glu1]-fibrinopeptide B is the preferred reference sample for proteomic applications. When using both samples, you must consider the ratio of the peaks—the optimal ratio is 1:1. The incorrect peak intensities of leucine enkephalin and [Glu1]-fibrinopeptide B can cause these errors.
FIX or WORKAROUND
The recommended sample concentrations are 100 fmol/μL [Glu1]-fibrinopeptide B and 100 pg/μL leucine enkephalin (50/50 ratio).
Ensure that the [Glu1]-fibrinopeptide B sample quantity/concentration is intense enough for a stable lockmass signal.
Ensure that the leucine enkephalin sample is not too intense for the detector setup.
You can adjust the sample as required, because it is not being used for sensitivity specifications.
Also see the article How to make leucine enkephalin.