Couple things to try:
1) Make sure the concentration of your analyte is not too high. I have
found that lowering the concentration can increase the formation of
multiply charged ions.
2) Put a little water in your spray solvent. I use 80% MeOH, 20% Water 0.1%
formic acid. I don't really know if the water helps that much, but I seem
to be able to get good multiply charged ions using this mixture.
I have rarely seen much difference in changing the voltage and temp on
multiple charges. I have always tuned these parameters for maximum signal
stability and response (with more emphasis on stability than signal
strength). However, incase your starting parameters are way off of what I
use:
Spray Voltage 4.8
Capillary Temp 210
Capillary Volt 40
I have seen times where using a high percentage of acetic acid also can
help with the formation of multiple charges. I have injected samples in
Alex Apffel's TFA fix (75% acetic acid in acetonitrile) without problems,
though that sees a bit extreme.
Good luck.
--tks
Tim Slattery
Berlex Bioscienes
From: lcp2@mole.bio.cam.ac.uk (Len Packman) AT Internet on 12/08/99 07:52
AM EST
To: abrf@aecom.yu.edu AT Internet@WA.CCMAIL
cc: (bcc: Tim Slattery/RM/USR/SHG)
Subject: MassSpec: LCQ
A question for experienced LCQ users:
What's the best combination of parameters (voltages and capillary temp) to
promote formation of doubly charged ions in nanospray MS? I get quite a few
singly charged ions in the 1000-2000 m/z range whose 2+ states can be found
on zoomscan but which are not obvious by inspection of the full scan. What
tricks favour the higher charge state? I'm spraying in 1% formic acid, 70%
MeOH.
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
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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