I recommend PAWS for your cleavage point analysis. Download free from
http://www.proteometrics.com/software/contents.htm
I observed the +136 series myself last year on my LCQ and put out a similar
question. It was suggested (private response) that these were sodium
trifluoracetate clusters. I changed my protocol, to use only TFA solutions
that were made fresh from neat TFA that day and the problem went away. I
suspect that the source was a week old 0.1%TFA solution that had been in a
glass vial.
I should reinforce the request of a few days ago that people reply openly
on the Network and not privately so that we can all see the response. Too
many questions appear unanswered if you search the ABRF archive when in
fact answers were forthcoming. Recipients of private answers don't always
remember to put out a summary on the network (myself included!), so please
reply openly. I suspect the difficulty is that many just hit 'reply' and
that routes the message to the sender rather than the network on most
mailers.
Len
*********************************************************************
Dr Len C. Packman
Assistant Director of Research
Protein and Nucleic Acid Chemistry Facility
Department of Biochemistry
University of Cambridge
80 Tennis Court Road
Old Addenbrookes Site
Cambridge, CB2 1GA, UK
Tel: +44 (1223) 333639
FAX: +44 (1223) 766002
e-mail: lcp2@mole.bio.cam.ac.uk
Visit my WWW page at http://www.bio.cam.ac.uk/proj/adr/PNAC/pnac.html