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Quantitation of several isotopomers of a compound by a single calibration

Question asked by damatze on Oct 10, 2017
Latest reply on Oct 11, 2017 by damatze

I have a quite specific question:
I want to quantitate nucleosides by an MRM screen on a QQQ. Therefore I do a calibration with synthetic nucleosides (unlabeled) and an internal standard which is heavy isotope labeled.
This internal standard is then added to my samplesas well. That way I'm able to quantitate the nucleosides in my samples. So far, so good.
BUT: I not only have unlabeled nucleosides in my samples, but also heavy isotope labeled isotopomers of the same nucleosides, sometimes several isotopomers in a single sample.
Of course they are still distinguishable from each other and from the internal standard. But the problem ist that I only have a calibration for the unlabeled isotopomers, so the program (MassHunter Quantitative Analysis Software) only is able to quantitate the unlabeled isotopomers but not the heavy isotope labeled ones as I have no calibration for the labeled ones.

The problem is, that I had to enter the different isotopomers as single compounds in the measurment method, otherwise they would only be qualifiers, but I need them to be quantified as well. And for these compounds (which are in fact only isotopomers of the unlabeled nucleosides, just different mass transitions) there is no calibration then of course.
Now my question: Is it somehow possible to tell the program to use the calibration of the unlabeled isotopomers also for the labeled ones?
Perhaps there also is some other way to handle this? For example to seperately quantitate the qualifiers as well? (which sounds kind of wrong already ). Or to circumvent the problem somehow by defining that there are several isotopomers of the same compound which all have to be quantitated.

Hope there is some solution to my problem.

Thank you!


Edit: Of course it would also be of great help if you could just tell me where I could ask this question to get an answer.