Negative ESI adducts

[harringg]

Is it possible to get adducts in negative ESI ionization mode, like you can get in ESI +? [M+Na] for example in ESI +. And if so, what would be the likely way for them to form? I think I understand how a sodium displaces a hydrogen in positive mode, but don't understand how a hydrogen is lost and then an adduct is added.

Thank you

[Kostas Petritis]

Yes you can.

Actually there are two different types of adducts the ionic ones like the [M+Na]+ or like [M+H+CH3OH]+.

At the same way you may have [M+Cl]- (actually only in APCI I think) or [M-H+CH3OH]-. Both are possible with MeOH and ACN (I mean that they can give adducts in both positive or negative mode).

TFA, formic and acetic acid give adducts only in the negative mode of the type [M-H+TFA]-.

Kostas

[harringg]

Thank you for your reply Kostas. We are trying to figure out some "what-ifs" in our ESI- work.

Thank you.

[Kostas Petritis]

No problem Harringg,

Keep in mind then that most of the adducts can be broken up by using higher DP values.

Kostas

[MG]

In addition to those already mentioned, it is also possible to have sodium adducts, even in negative ion mode. For example, [M-2H+Na]-. I've seen it happen myself, and it's reported in the literature:

J. Separation Science, 2002, 25(12), 760-766

J Am Soc Mass Spectrom 2002, 13, 1360-1369

J Chromatogr A, 2003, 985, 531-539

Another one I've seen in negative ESI is [M+acetate]-
for compounds that won't readily lose H, with an acetate or acetic acid mobile phase.