Enrico,
We had a similar problem previously (+98 to mass). With the help of Sue
Hantman (her message follows) we were able to trace it back to formation of
tetramethylguanidium ions (these show up as +98 for each attached, in
positive ion MS). Turned out it was due to a leaky activator valve in our
synthesizer, I believe. Technical note from Sue is attached.
Randy Wilhelm
Sr. Analytical Research Chemist
Mallinckrodt, Inc
(314)654-3965
(314)654-3355
rrwilhe@mkg.com
Dear Randy,
Sometimes when using uronium salts (HATU, HBTU, TBTU) to do the activation,
you can get a tetramethylguanidinum (+101 actually adds 98 to mass) which
attaches to the peptide.
This is not usually seen unless you either deliver the activator to the
column before activated amino acid, use an excess of activator over amino
acid, or are trying to cyclize a peptide. Maybe this isn't the case for
you, but maybe it is. I have attached a tech note describing this.
Susan Hantman
Technical Support Specialist
Synthesis Products
PE Biosystems
shantman@pbio.com <mailto:shantman@pbio.com>
-----Original Message-----
From: Enrico Millo [mailto:millo@vega.cba.unige.it]
Sent: Friday, April 20, 2001 5:11 AM
To: Recipients of ABRF List
Subject: PEP Syn
Hi all,
I have synthesized a peptide with Fmoc method.In Elettrospray mass
spectrometry result the correct molecular weight (1200 Da) and other weights
1298 , 1396 .What are these + 98 Da and + 196 Da ?Is it perhaps a
modification of side group of ARG (PBF)?
Sequence of the peptide :
GLY-ARG-ARG-ARG-ARG-SER-VAL-GLN-TRP
Mix of cleavage :
TFA,H2O,TIS for 2.30 H
Resin : Rink Am
Thank you
Enrico Millo
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