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/
************************************

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