Naming convention for adduct ions In order for a compound to be analysed in mass spectrometry it must first be ionised, forming an adduct ion. In many papers (e.g 1 [PDF], 2) these adduct ions are described in the form:


[M+H]+
[M+Na]+
[M-2H]2-


Where M is the analyte, the other content of the square brackets is the ion, and outside the brackets is the resulting charge. The IUPAC Gold Book also mentions this format for protonation without, as far as I can tell, describing it further.

Is there some reference actually describing this convention - ideally encompassing more complex scenarios such as dimerisation or neutral losses as well - around?
Your convention is generally correct; as more complicated adducts and ions are formed (clusters, adducts, neutral losses, etc) things start to become a free for all where the clearest terminology wins.

As of now, just go with (where A means adduct):

$$\ce{[M + nA]^{n+}}\text{ or }\ce{[M - nA]^{n-}}$$

Protonated molecules can be denoted as $\ce{[MH]+}$ (common) or $\ce{[M + H]+}$ (technical). The $\ce{[M + H]+}$ convention is more precise because if you write $\ce{[MH]-}$ for a deprotonated ion the interpretation becomes muddled (i.e is this a hydride adduct or is this a deprotonated ion?).

One important think to keep in mind that is Molecular Ions ($\ce{M^{+.}, M^{-.}}$) are not the same as $\ce{[M + H]+}$ or $\ce{[M - H]-}$ and that the terminology is not interchangable.


$\ce{M^{+.}}$ or $\ce{M^{-.}}$ retains the elemental composition of the ion and is ionized through the removal or addition of an electron.
$\ce{[M + H]+}$ and $\ce{[M - H]-}$ are protonated and deprotonated molecules, respectively. They are not 'pseudomolecular' ions as there are no such thing as pseudo ionized specties.