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Victor,

I very recently experienced issues due to the focus quad on a Delta V+: 
the quad was set to -100% by accident, and the slope of my linearity 
test returned a spectacular 3 per mil V-1 or so. It never occurred to me 
that the quad could throw off the linearity that much. People from 
Thermo advised me to set the quad to more or less 0%, and the linearity 
improved right away by an order of magnitude.

Good Luck,

Cedric

*******************************************************
Cedric Magen, Ph.D.
University of Maryland Center for Environmental Science
Chesapeake Biological Laboratory
146 Williams St.
Solomons, MD 20688
Phone: (410)-326-7459
*******************************************************

On 5/9/2016 1:05 PM, Victor Evrard wrote:
> Dear Neighbour,
>
> Thanks for trying to help me again.
> After I recently cleaned the ion source of our IRMS, the focus 
> settings were totally off. I used the AF option with previous settings 
> (before the source cleaning) to tune the source... CO peak shape is 
> good, sensitivity is good, linearity is bad (0.7‰/V). Note that 
> extraction is fixed at 80%.
> So I resorted to starting from scratch, all settings in the middle 
> (except max Emission, max Trap, max eV and 80% extraction) and got 
> more or less to where I was with the previous settings.
> The only thing I haven't touched yet is the Focus Quad settings.
> I just reverted to settings close "factory", which had a ~-28% Focus 
> Quad and AF'd from there. Things seem a little better but definitely 
> not up to specs (the improvement: m/z 29's center now corresponds to 
> m/z 30 plateau while before it was on the edge of the m/z 30 peak). 
> Will keep trying and update here if it's better.
>
> Cheers,
> -- 
> Victor
>
> On Mon, 9 May 2016 at 12:51 Thomas Kuhn <[log in to unmask] 
> <mailto:[log in to unmask]>> wrote:
>
>     Hi Victor,
>
>     optimization of the Focus Quad in the Delta V Plus may improve
>     parameters such as peak shape, sensitivity, and/or linearity. Of
>     course this needs to be done in conjunction with an optimization
>     of extraction, trap, and electron energy, the typical other
>     factors influencing linearity and sensitivity. When I have
>     performed S-isotope analyses, I have seen relatively clear effects
>     of the setting of the Focus Quad on SO2 peak shape and linearity.
>     However, I know that you are not doing SO2-measurements. Do you
>     currently observe any specific issues with linearity and/or
>     sensitivity, which have prompted you to think about changing the
>     Focus Quad setting now? The Focus Quad in our Delta V Plus, which
>     we use for N2O-measurements, is set to –20% and so far it wasn`t
>     necessary for us to change this setting since installation about
>     2.5 years ago.
>
>     There is indeed no Focus Quad option you can tick in the autofocus
>     window, as I think it is considered to be adjusted and optimized
>     only manually. You can try out different Focus Quad values, both
>     within the negative and the positive %-range as well as at 0%.
>     When I try to optimize the Focus Quad I go up or down in either 5%
>     or 10% steps, thereby always checking the effect on peak shape and
>     linearity and sensitivity. So, it can take a little while to find
>     the optimum setting.
>
>     Cheers,
>     Thomas
>     ************************************
>     Dr. Thomas Kuhn
>     Manager of Stable Isotope Laboratory
>
>     Aquatic and Stable Isotope Biogeochemistry
>     University of Basel
>     Bernoullistrasse 30
>     CH-4056 Basel
>     Switzerland
>
>     Phone: +41 61 267 0454
>     Fax:       +41 61 267 0479
>
>     	Email: [log in to unmask] <mailto:[log in to unmask]>
>     https://biogeochem.duw.unibas.ch/
>     ************************************
>
>
>
>     From: Stable Isotope Geochemistry <[log in to unmask]
>     <mailto:[log in to unmask]>> on behalf of Victor Evrard
>     <[log in to unmask] <mailto:[log in to unmask]>>
>     Reply-To: Stable Isotope Geochemistry <[log in to unmask]
>     <mailto:[log in to unmask]>>
>     Date: Montag, 9. Mai 2016 um 12:06
>     To: "[log in to unmask] <mailto:[log in to unmask]>"
>     <[log in to unmask] <mailto:[log in to unmask]>>
>     Subject: [ISOGEOCHEM] Isodat Autofocus Focus Quad
>
>     Hi Everyone,
>
>     I have the feeling that the Isodat autofocus option doesn't do
>     anything to the "Focus Quad" settings. There is no "Focus Quad"
>     option to tick/untick in the autofocus options.
>     Does anyone have some recommendations for the manual focus of the
>     "quadrupole" of our Delta V Plus?
>
>     Thanks
>     Victor
>     -- 
>     Victor Evrard, PhD
>     Lab Manager | BASIEL
>
>     Sustainable Land Use Group | Department of Environmental Sciences
>     University of Basel
>     Schönbeinstrasse 6
>     CH-4056 Basel
>     Switzerland
>
>     http://goo.gl/cl6x97
>     +41 61 267 35 17
>