mrm of an adduct

[mardexis]

I read in a textbook that you should never quantitate in an MRM
method of an adduct but there was no explanation. Can anyone
offer one to me? I'm doing it anyway so what should I be on the
lookout for?

Thanks,
Marc

[lmh]

I can't honestly see how anyone could disagree with quantifying from a straightforward adduct such as a hydrogen or sodium adduct in ESI, but the book has a point for some adducts:

If a system is much used with formic acid, you may find that the majority of analytes in a negative mode run will be formate adducts. They will all fragment by loss of formic acid (46), so SRM becomes entirely pointless. It offers no advantage over SIM.

In positive mode, ammonium adducts may be a very bad choice, particularly in ion traps. They frequently fragment by loss of ammonia (uninformative and not very specific), and in my hands they trap badly.

[sassman]

Most likely because if you do MRM of an adduct, there will be more noise than with true MRM. This is because there will be many other compounds that form an adduct which will have the same fragmentation pattern (loss of adduct). If you have the proper control samples in place and are getting results that make sense, I see nothing wrong with using MRM of an adduct.

[dr_Pyrex]

About adducts with formic and acetic acid: in some cases you can obtain much better sensitivity when you monitored MRM with adducts. Good example is determination of corticosteroids by LC-ESI-MS/MS in negative ionisation.