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 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:
[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.


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.  

Dr. Thomas Kuhn
Manager of Stable Isotope Laboratory

Aquatic and Stable Isotope Biogeochemistry
University of Basel
Bernoullistrasse 30
CH-4056 Basel

Phone: +41 61 267 0454
Fax:       +41 61 267 0479

Email: [log in to unmask]

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?

Victor Evrard, PhD
Lab Manager | BASIEL

Sustainable Land Use Group | Department of Environmental Sciences
University of Basel
Schönbeinstrasse 6
CH-4056 Basel
+41 61 267 35 17