Dear All,Back to the Top
1.We would like to know about the MS/MS of isomeric compounds. Is the
MS/MS
pattern is similar for isomeric compounds or different?.
2.In the case of Quantification of Drug by LC-MS/MS, by MRM mode as per
theory onely one peak detection is possible (based on parent mass and
fragment mass), suppose I get more than one peak is it means that it is
due
to Isomers or something else?
(we confirmed that the extra peak is not eluting from column at that
particular RT).
Expecting your suggestion.
Advance thanks
Thanks & Regards,
Dr.B.Sivakumar
Dear collegue,Back to the Top
It is possible to have several peaks in a MRM transition, since
metabolites
can be submitted to a fragmentation into the source going back to the
parent
compound. The Rt of these additionnal peaks will be those of the
metabolites
involved.
Hope this help
Henri BENECH, PhD
CEA
Service de Pharmacologie et d'Immunologie
DSV/DRM/SPI/LEMM
F-91191 Gif-Sur-Yvette Cedex, FRANCE
Dear Sivakumar,Back to the Top
"1.We would like to know about the MS/MS of isomeric compounds. Is the
MS/MS pattern is similar for isomeric compounds or different?."
Theoretically isomers of a compound should give rise to similar
fragmentation pattern.
"2.In the case of Quantification of Drug by LC-MS/MS, by MRM mode as per
theory onely one peak detection is possible (based on parent mass and
fragment mass), suppose I get more than one peak is it means that it is
due to Isomers or something else? (we confirmed that the extra peak is not eluting from column at that particular RT).
"
What I understand from your question is that in a particular MRM scan
you are seeing two peaks and that they are eluting at different retentions times (of course if they co-elute you wont even know that there are two peaks).
If I understand it correctly - YES, that's possible. Because you can always
have a metabolite with same mass as that of parent. Since the chances of matching precursor mass and fragment mass for an extraneous/endogenous compound are fairly low, it could most probably be a metabolite with same mass as parent and giving rise to similar fragment.
Then why didn't you see in your HPLC run. There could be two possible
reasons for that - It could be that metabolite had poor UV absorption at the wavelength you've used (I Imagine you've monitored using UV detector) or It could be that metabolite levels are low and UV detector could not pick.
Is that second peak eluting at solvent front. As run times are short
(in MRM mode) your metabolite might elute in solvent front and you may not have noticed in UV trace.
Hope this helps.
Good luck,
Kasiram.
Dear Dr Sivakumar,Back to the Top
I think you could find different MS/MS pattern for two isomer of the
same
coumpound only if it is two positional isomers.
But you could have two different peaks responding to the same MRM
transition
for other isomeric forms such as cis/trans isomers (diastereoisomers).
In other words the fact you have two peaks could be due to isomers but
it
could be due to many other things :
- Is your coumpound subject to instability that could lead to a
rearrengement of its structure ?
- Is your coumpound a pure coumpounds ? You could have two product with
the
same m/z ratio and fragments ? You may study the product ion scan and
check
if the relative abundance of the fragments ions is the same for the two
peaks.
- ...
Regards.
Nicolas Picard
DEXO Limoges France
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