(1). It's very common to see Na and K adduct ions in ES.
(2). I don't think the group 2 are the Na adduct ions based on the info you
provided.The m/z difference between (M+H) and (M+Na) is 22, not 20 unless
your instrument is REALLY off calibration.
(3) Group 3 looks like K adduct ions. (m/z differences are 38).
(4) The isotopic pattern (or peak ratios) of the three group ions will be
needed to make a conclusion.
BTW, it may help if we know what kind of accuracy your mass spec has.
Ping
> ----------
> From: Leo Kei Iwai[SMTP:leo.biof@infar.epm.br]
> Sent: Friday, October 22, 1999 10:37 AM
> To: Recipients of ABRF List
> Subject: MS: MM + Na + K
>
> Dear ABRFers,
>
> I'm used to use Maldi-tof as a MW quality control of the peptides I
> synthesize. A couple of weeks ago, I synthesized an GM(O)G wich
> MW=278. As I could not detect low MW in the Maldi I use, I asked a
> friend to do it in a Electron Spray, and it showed the following
> results:
> 1) 278.45; 279.09; 280.12
> 2) 298.75; 300.82; 301.04
> 3) 316.28; 317.03; 318.06
>
> It looks for me that group 1 correspond to Na+ and group 2 =
> K+. I'm used to see Na+ and K+ when I analyse Maldi spectra. Is it
> common also to see them in ES?
> Can I realy attribute the difference, I would say 298.75-
> 278.45=20.3 as the Sodium or I have to use the higher value of the
> isotopes of group 2 minus the lower value of group 1 (301.04-
> 278.45=23.3)? Wich peak do I have to use to calculate the "real"
> MW? (same question for the possible K+ peaks).
> Thanks in advance,
>
> Leo
>
> ----------------------------------------------------------
> Leo Kei Iwai - Chemist
> Dept of Biophysics
> Escola Paulista de Medicina - EPM - UNIFESP
> Lab of Transplantation Immunology
> Instituto do Coracao - Incor - FMUSP
> ----------------------------------------------------------
>