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
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On 5/9/2016 1:05 PM, Victor Evrard wrote:
[log in to unmask]" type="cite">
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]> 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]
https://biogeochem.duw.unibas.ch/
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From: Stable Isotope Geochemistry <[log in to unmask]> on behalf of Victor Evrard <[log in to unmask]>
Reply-To: Stable Isotope Geochemistry <[log in to unmask]>
Date: Montag, 9. Mai 2016 um 12:06
To: "[log in to unmask]" <[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