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From: ui22273@sunmail.lrz-muenchen.de
Subject: FAB-HR?
Date: Sat, 2 Dec 1995 16:51:42 +0100
Organization: Leibniz-Rechenzentrum, Muenchen (Germany)

Hi everybody,

I`m working at the University of Munich and am currently experimenting with 
FAB-HR on a MAT95Q. As our samples work mainly in m-NBA as matrix I use PEG as 
reference. Does anyone has a exact mass list of the signals, as these are not 
only PEG Fragments but others with strange differences of 6 or 13 amu? 
Has someone experiences with PEG as reference? What mmu difference do you 
think is ok for the confirmation of a sample?  

 Werner Spahl (ui22273@sun1.lrz-muenchen.de)
"The meaning of my life is to make me crazy!"

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Date: Wed, 06 Dec 95 09:46:37 -0500
From: Chip Cody <cody@titian.jeol.com>
Subject: Re: FAB-HR?

Dear Werner, 

We have a mass listing for PEG on our web page at 

http://www.jeol.com

along with FAB matrix spectra and other reference masses.  PEG is generally a 
very good reference standard for use with NBA as a matrix.  You will often see
cation adducts (M+Na or M+K) as well as the protonated species.  The cations
are omnipresent, and probably come from solvents stored in glass, etc.  You may
see dehydrated species, particularly at low mass.  However, I'm not sure about 
the strange mass differences that you report.  There may be impurities 
present.  

The mmu difference required to confirm a sample depends a lot on the molecular
weight and other information available to you about the sample (isotope 
ratios, other chemical information, sample history).  The higher the
mass, the less you can trust the mass measurement to PROVE a composition.
However, an accurate mass measurement is always a valuable piece of 
confirming evidence, and a check against errors in interpretation.  For
what it's worth, there's an essay on interpreting exact masses on our
website.  Good luck!


					Chip Cody
					Applications Manager
					Mass Spectrometry
					JEOL USA, Inc.



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From: jwindak@umich.edu (Jim Windak)
Subject: Re: FAB-HR?
Followup-To: sci.techniques.mass-spec
Date: 7 Dec 1995 12:35:26 GMT
Organization: University of Michigan


The main peaks in the PEG spectrum are the protonated oligimers of PEG. 
They are of the general form (C2.H4.O)nH3O+ , and they differ by 44 amu
(the mass of the repeat unit C2.H4.O).  I've also observed smaller
intensity peaks due to sodium or potassium adducts of the PEG oligimers. 
These are of the form (C2.H4.O)H2O.Na+ and (C2.H4.O)H2O.K+ .  

I've never observed peaks that differ by 13 amu, but the 6 amu difference
which you observe might possibly be explained by the presence of lithium
ion.  At times I've observed lithium ion adducts of the form
(C2.H4.O)H2O.Li+ .  These would differ by 6 amu from the corresponding
protonated oligimers. (Subtract 7 amu for Li and add 1 amu for the proton).

 PEG produces higher intensity peaks if it is run in a 4:1 mixture of
dithiothreitol / dithioerythritol which has been melted to form a viscous
liquid, rather than running it in m-NBA.  Also, the PEG should be diluted
about 20:1 with methanol before adding it to the target.  If it is too
concentrated, the signals will be suppressed.

Jim Windak
University of Michigan 
Chemistry Dept.
jwindak@umich.edu