Two questions:
1. I too am seeing a large percentage of ions singly charged, even after I
optimize the voltages on a doubly charged peptide standard like angiotensin I.
I am relatively new to the LCQ, but I have been using nanospray on a PE Sciex
API III for 4 years. For the LCQ interface, do you need to have the capillary
heated at all for nanospray? I have run some samples with the capillary set
to 20C. I did start to see ions that were not there at 150C. Why is the
capillary heated for nanospray? I could see the need at higher flowrates for
desolvation. With the capillary heater turned off, would it be like the API
III where the desolvation occurs as the ions are drawn into the vacuum
region?( difference between the orifice and Q0, similar to the LCQ's capillary
voltage and Q1) or do I not understand my ion optics well?
2. I am trying to do MS/MS on an ion and I set the isolation with to 2 amu and
the collision energy to 0 to see if I am trapping the ion well. the MS
spectra shows the ion at 10^7 counts. Hen it is isolated at the above
conditions I get 10^2 counts. If I open the isolation window to 3 amu I get
10^6 counts. Big difference! I went back to an isolation window of 2 amu and
moved the parent mass selection around +/- 2 amu to check if the waveform
generator was out of calibration. still 10^2. Why is such a wide window
needed?
Any help is appreciated.
Mike Knierman
Eli Lilly
Mark E Hail <Mark.Hail@bms.com> on 12/08/99 09:29:07 AM
To: Recipients of ABRF List <abrf@aecom.yu.edu>
cc:
Subject: Re: MassSpec: LCQ
Len
The week doubly charged ions may be more a function of the solvent you are
spraying. You might find that you get more charging by cutting back on the
formic acid concentration. We typically use 0.1-0.2% formic or 1-2% acetic
acid. You will also see less charging out of 0.1% TFA relative to 0.1% formic
or 1% acetic. If you are infusing or nanospraying your sample, a capillary
temperature of 150-200C should be the optimum range. Capillary and tube lens
offset values would probably optimize around zero (plus or minus 10 or 20V)
under these conditions. These conditions are for an LCQ classic, the deca
capillary would probably be run a little hotter (e.g., 250C). Hope that
helps.
Regards,
Mark Hail
Bristol-Myers Squibb
Len Packman wrote:
> 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