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Isobaric compounds
Posted: Mon Apr 20, 2015 9:23 pm
by flbak
Hi, new to the site.
How could one- using LCMSMS- differentiate isobaric compounds. Specifically, imipramine and norimipramine?
Re: Isobaric compounds
Posted: Tue Apr 21, 2015 5:51 am
by tom jupille
Are imipramine and norimipramine isobaric?
Re: Isobaric compounds
Posted: Sun May 03, 2015 1:50 pm
by mckrause
Different molecular weight. Also will give different fragmentation pattern.
Re: Isobaric compounds
Posted: Mon May 04, 2015 5:41 pm
by PeterPopoff
As already said these two are not isobaric.
The reason you are seeing two peaks in the Norimipramine MRM window (one at the RT of Norimipramine and the other at the RT of imipramine) is that when the imipramine is first ionized through ESI, a relevant amount of Norimipramine is formed in that first ionization where the M+1 ion is formed. Therefor (in the MRM window for Norimipramine) you see Norimipramine at its normal RT and at the same RT as imipramine.
Its important to note that you are not seeing imipramine and norimipramine in the same MRM window. They have different masses therefore you cannot see them both in an MRM window that only allows you to see one of them. This same thing happens with Nordoxepin and doxepin.
Re: Isobaric compounds
Posted: Fri May 15, 2015 2:31 am
by chemboy831
Peter, would you happen to have a reference for this phenomenon? Mechanism perhaps?
Thanks
Re: Isobaric compounds
Posted: Wed May 20, 2015 3:22 pm
by Klaus I.
This phenomenon is called 'in-source fragmentation' and occurs when source parameters are too harsh for the molecule. The reduction of temperatures and voltages may help to avoid this type of fragmentation.
Edit: Several typos removed, I'm sorry
