Mass difference of 22

[jan]

I got a few masses with difference of 22. For the first two, I could assume they are protonated species and sodium addicts. But what about the followings? It can not be 2 Na's since it will be doubly charged. Any comments. Thank you in advance.

[MG]

So you are seeing "X", "X+22", "X+44", "X+66", etc?

If that is the case, I don't have an answer for you, but just wanted to clarify.

[jan]

Actually I only observed X, X+22, X+44. Any explaination? Thanks.

[MG]

If the molecule has an acidic group, I suppose it could lose a proton and gain an additional sodium. So the X+44 would be (M+2Na-H)+.

I have seen sodium adduct to dicarboxylic acids in negative mode (minus 2H, plus Na), but I don't recall if I've ever seen the above phenomenon.

Alternately, if you think they could be separate compounds, this paper has an explanation for a mass difference of 22:

Kalgutkar and Nguyen
Drug Metabolism and Disposition, 2004, 32(9), 943-952
http://dmd.aspetjournals.org/cgi/content/full/32/9/943
http://dmd.aspetjournals.org/cgi/conten ... t/32/9/943

[Basil]

First of all we are suposing that you are using an ESI positive mode to ionize the sample, no ?

I agree with MG opinions.

Another way to be sure that is Na+ aducts is to try to find 2X+22 and also 2X+44 then it will confirm the presence of Na+ in a dicarboxylic acid.

It also will be interesting to know if you see anything in negative mode

[jan]

Thanks, MG and Basil. Actually I did ESI- scan and found same mass difference. Any comments?

[MG]

In negative mode, it depends on how many protons your molecule could reasonably lose. So you could see:

(M-H)- = X
(M-2H+Na)- = X+22
(M-3H+2Na)- = X+44

if it seems reasonable that your molecule could lose three protons based on its chemistry.