Things that promote multiple charging are lower (closer to zero) voltages
and lower cap temps. The ideal for your system might be found by spraying a
standard peptide (say MRFA-a Finnigan tune std) in the solution you mention
and then doing a little playing to optimize the system. You want a fairly
hot signal to allow good s/n during signal optimization. There is the
capability of graphing the intensities of ions against time without writing
the data to a file. You can play with the source parameters in TUNE while
graphing them and find the optimal values. I'd graph the intensity of the
+2 ion for your tune peptide and then vary voltages and temps and find the
optimum for production of +2. There is a pop up in TUNE (diagnostics) that
will allow you to graph/optimize almost any LCQ parameter. Then when done
save that tune and (make sure you recheck the ratio of +1/+2 and the general
s/n of the spectra). You can then use that tune for your nano-spray peptide
work. The cap temp might be 150-200C that works best on a classic LCQ.
I think that the +2 for the most part is not "formed" or produced once it
leaves the spray needle. It is only depleted by energetic collisions within
the LCQ. The M+2H ions can lose one proton/charge in a collision(or due to
thermal excitation) in the LCQ and become transformed thru the magic of
charge stripping to M+H. The target then is to deplete this population of
doubly protonated species as little as possible by keeping the
translational/thermal energy low. One can't go too low or then other issues
of clustering and solvent adducts come up. I don't think the std LCQ tune
solution/auto-tune optimizes on any multiply charged species but for the
most part it seems to work pretty well (for prot/pep work). Tweaking the
source parameters can increase the intensity of +2 relative to a "std" tune.
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
-----Original Message-----
From: Len Packman <lcp2@mole.bio.cam.ac.uk>
To: Recipients of ABRF List <abrf@aecom.yu.edu>
Date: Wednesday, December 08, 1999 5:05 AM
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
>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
>
>
>
>