which functional groups give rise to which adducts in ESI?

[lmh]

Like, I suspect, many users of this forum, I get used to seeing hydrogen, sodium, and ammonium adducts in electrospray, and notice that certain functional groups favour certain adducts (in our instrument).

I was wondering if anyone could help me find a reference that explains the chemistry behind this a little more? I've found a few comments about how addition of heavier group 1 metals can discourage the formation of Na and K adducts that can be confused as +/- an oxygen atom, but haven't had much luck in finding a more global discussion. Perhaps it depends too strongly on instrument design.

It's also a subject where I'm struggling to find a useful set of terms for a Google search.

Thanks!

[Kostas Petritis]

Adduct formation will indeed depend on a lot of things, among other the composition of your diluent (if you do infusion) and mobile phase (if you do chromatography). Most positive chargable compounds in electrospray will just pick a proton (in positive ion mode) if you have enough available. If you do not include any, then they can start forming adducts with other cations...

I do not know of which publication you speak about and I do not quite see how formation of Na and K adducts can be confused as addition or substraction of oxygen atoms...

[lmh]

Oh, sorry, the Na/K thing: It's merely that the mass difference between a K+ adduct (39) and sodium adduct (23), is 16, which can easily be confused with an extra oxygen atom. I've seen this mentioned in various places, e.g. a review of MS of carbohydrates someone showed me, that came from Ch. 6 of Vol 4 of encyclopedia of mass spectrometry Gross and Caprioli (but I have to admit I've never done anything about it).

Thanks for the reply. It sounds like adduct formation is something I'll have to accept on trust rather than trying to understand.

[sindhu]

When doing Electrospray on neutral organic molecules, we will often dope the sample with NaCl, and will then see a significant [M + Na]+ ion, although you will sometimes see an [M + H]+ ion as well.

By Electrospray, you will sometimes see solvent adducts, such as an [M + Na + MeOH]+ ion. Small molecules tend to cluster when run by Electrospray, particularly if the sample concentration is high.

The best way to get out of adduct formation is to avoid using the metal salts during our sample preparation it self. Off course I do accept that it is a cumbersome as we have to do method development , validate the method etc. Probably if you do once then you are sure of no adducts at a later stage