Chromatography Forum

I'm setting up a GCMS method with SIM, and the ISTD is only a few m/z units away from the component of interest and has the same RT (it's a d-labeled variant). When I review the data, the software selects the wrong ion for the ISTD target ion; I'm guessing because the target ion of the unlabeled component is more abundant, and the m/z window is too large.

Where can I narrow the m/z window so that the software selects the correct target and qualifier ions?

We're using ChemStation E.02.02.

I think figured it out.

I opened the Extracted Ion Chromatogram window, and noticed that the amu window values at the bottom of the screen were +/- 4.568 (which happened to be the begin time of data acquisition after the 4.5 min solvent delay). I tried typing in the default values of -0.3 and +0.7 but they didn't change, and remained at 4.568. I tried 0, that didn't work. Then I hit the backspace key so the fields were empty, and presto! After reopening the window, the default values were shown and now used for my data analysis, so all the ions were correctly assigned.