5973 AMU +/- for 13C-Dieldrin versus Diel. SIM ions

[Pelgy2]

I am trying to choose the best SIM ions for 13C-Dieldrin and Dieldrin. There aren't any dieldrin ions with a decent abundance that do not also occur in 13C-Dieldrin.
Can a 5973 discriminate between ion 262.85 (in dieldrin) and 262.95 (in 13C-dieldrin)? I am guessing not but I would like confirmation.
If I can narrow down the +/-amu that the SIM looks for, what consequence would that have for my multiresidue method other than a sensitivity drop?
How would I go about narrowing the amu if it is possible.
Thanks!
Peg

[carras]

For starters you cannot achieve 0.1 amus resolution with a quadrupole. But if want to try here's how I would go about it.
To narrow your amu window go to the SIM parameters in your method, in the window were the ion groups are you should find a low/high resolution option. Just select high resolution and you are done. A word of caution, to check if the method has really switched to high resolution open the file "acq.ms" in your method folder (use Windows Notebook). Scroll the file until you see the ion group you have modified, the line "resolution" should read "Resolution=0". If that is not the case just modify it and save the file.
(My chemstation version has a bug and you need to go to the acq file to change resolution.)
Hope it hepls

[Pelgy2]

And I think that would change the resolution for the whole method to high? I'd love to do that but I don't think I can. The other twenty pesticides I'm looking for would be affected. Thanks for the reply! Nice to know I wasn't shouting out to emptiness. :0)

[lmh]

am I missing something here? The only change you should expect to see by adding 13C is addition of 1amu to any fragment that contains the 13C (or more than 1 if there are multiple 13C atoms present in the fragment). Minor differences of 0.1amu are probably just run-to-run variation in an imprecise MS. If your 13C-labelled version is labelled in a position that is not retained in any fragment, it isn't suitable as an internal standard when using an instrument that cannot isolate the isotopically-labelled parent. In the case of Dieldrin the huge amount of chlorine presumably makes isotopic labelling a bit harder to interpret in any case?

[mckrause]

You should see the C13 labeling shift for the lower mass ions (70 instead of 69, for example). Also, with C13 labeled dieldrin you should be able to chromatographically separate it from unlabeled dieldrin.

SIM work with isotopes should always be run using the High resolution option - this narrows the window. Also, tune to a 0.4 amu peak width - it'll cost you some EM voltage to keep your sensitivity but it's worth it. You may have problems getting 502 to set and hold at 0.4. I'd switch my tune ion set to 69, 131 and 219 - you'll be setting your mass resolution precisely where you most need it, rather than across an amu range that you don't need.