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From: hmh.vaneijk@AH.UNIMAAS.NL
Date: Wed, 26 Jan 2000 16:26:47 +0100
Subject: lcms determination of FMOC-amino acids
Organization: Universiteit Maastricht

We are currently trying to measure the isotopomeric distribution of fmoc
derivatizated amino acids on a thermoquest LCQ system using ESI ionization.
We observe a severe decrease in mass resolution when measuring these
derivatives as compared to other components.
Does anyone observed the same effect for FMOC derivatives and could a
possible cause be pinpointed?

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From: dana_justin <dana_justin@prodigy.net>
Date: Wed, 26 Jan 2000 18:37:57 -0800
Subject: Re: lcms determination of FMOC-amino acids
Organization: Prodigy Internet http://www.prodigy.com

By coincidence we happen to run similar compounds, namely FMOC-alanine and
FMOC arginine as test compounds for our prep LCMS system, so I can truthfully
say that our single quad in ESI mode sees these two compounds exactly as we
expect to see them and no different to any other test compound.

So no help there, sorry!,

Justin Withers
PE-Sciex (but answering from home)

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From: "M Sweeney - MSMS Consulting" <mattsweeney@earthlink.net>
Date: Thu, 27 Jan 2000 14:50:37 GMT
Subject: Re: lcms determination of FMOC-amino acids
Organization: EarthLink Network, Inc.

dr/mr/ms hmh.vaneijk

The lcq mode best suited to doing this would be zoom scan.  The resolution
in zoom scan mode might be improved be decreasing the target values for this
mode.  The target values are the number of ions which the trap attempts to
accumulate before completing a scan.  I have seen some variation in behavior
of ions within ion traps.  This probably reflects the variation in energetic
requirements for various pathways.  Traps trap - and this means the ions
hang around much longer before they are detected.  This greater "lifetime"
means more things can happen to them.

I can't recall a case where I just could NOT do something on a trap that I
wanted to do however (except parent scans).  If the target adjustment fails
to help (it would reduce the population within the trap and allow fewer
interactions) then you might try either reducing the ion's energy (reduce
cap temp) or making the ion more stable perhaps by using Na+ to ionize it.

 I usually extensively signal average when I measure isotopic abundance  -
one can set the LCQ to avg > 10 scans - I set it to 100.  This may help the
slightly poorer ion statistics  resulting from reducing the target for the
zoom scan mode.  The value usually does not require a very great change. You
might start with a 10% reduction in target value. Observe the resolution and
then reduce by 10% more if required. And so on.

Matt Sweeney
mattsweeney@earthlink.net
Mass Spec Consulting
Training/Operations/Consulting/Method Development
LC/MS Pharmacokinetics, Peptides, Proteins, Metabolism,
Maintenance Classes, Specialist in Finnigan Equipment and Software