Barbara,
I can't tell you what's going on as far as the HPLC, but if you had a
doubly-charged dimer, the isotope peak spacing would be 0.5. There is no way
I know of that this wouldn't happen, and you would still see it even if it
fell on top of the singly-charged monomer, because some of the dimer peaks
would show up in between the monomer peaks. Of course this assumes that you
can resolve the isotopes at the mass at which you are working. Anyway in
MALDI, it's very unusual to see a doubly-charged peak for something and no
peak for the singly-charged species, especially a peptide.
Arnie Falick
falickam@appliedbiosystems.com
----- Original Message -----
From: Barbara Ciani <barbarac@biols.susx.ac.uk>
To: Recipients of ABRF List <abrf@aecom.yu.edu>
Sent: Friday, October 27, 2000 6:43 AM
Subject: MS intra and inter disulfides
> Dear all,
>
> I am having big troubles during the oxidation of a peptide with one Cys at
> each of the termini.
> The HPLC trace tells me that I have 3 peaks and the Mass-spec says that
> all 3 are the same thing: cyclic monomer disulfide linked (also the
> distance between the C13 and C12 isotopes is +/- 1 Da as it should be).
> My problem is how reliable is the isotope difference rule?
> In relation to the mass-spec:If I have dimers should I see a peak
> of the correspondent single charged
> ion or should I see just the double charged dimer?(that would have the
> same ion mass of the monomer?).
> In relation to the HPLC: why 3 different peaks for the same thing?
>
> Hope someone can help.
>
> Barbara
>
>
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