I will not answer the first question. Many of the ABRF recipients have more
experience at nanospray than I.
However, on question 2:
The isolation process applies a resonance waveform to excite ions outside of
the isolation width. In a simple but functional view, with a narrow
isolation width some of this energy is absorbed by the ion of interest.
This ion may then be either ejected or fragmented before the activation RF
is applied. This sensitivity is a function of the isolation width, ion mass
and bond strengths. Few ions will survive a 1 amu isolation.
A common procedure with small molecule analysis is to apply zero collision
energy and observe peak heights as you have described as the isolation width
is stepped down; 10, 5, 3, 2, 1.
Peptides usually work well with isolation widths of 3 amu if the instrument
is well calibrated. Poor calibration may decrease resolution which may then
cause poor isolation efficiency at 3 amu.
Bill Mahn
TMQ Technical Support
bmahn@thermoquest.com
----- Original Message -----
From: Michael D Knierman <KNIERMAN_MICHAEL_D@Lilly.Com>
To: Recipients of ABRF List <abrf@aecom.yu.edu>
Sent: Thursday, December 09, 1999 9:21 AM
Subject: Re: MassSpec: LCQ
>
>
>
> Fellow nanospray users,
>
> 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
>
>
>
>
>