Hi Michael,

Did you clean things good with the supplied sandpaper before installing the plates? That was the most tedious part of the retrofit that I remember, and the concern of any residue falling into the cups.

Ben

-----Original Message-----
From: Stable Isotope Geochemistry <[log in to unmask]> On Behalf Of Michael Nathaniel Dyonisius
Sent: Monday, July 05, 2021 11:08 AM
To: [log in to unmask]
Subject: [ISOGEOCHEM] Delta V Plus losing precision and bad peak alignment after moving building

Dear Isogeochem,

We at Copenhagen ice core lab have been struggling with an old Delta V Plus. The instrument used to be able to achieve precision of 0.005 permil for d15N of atmospheric N2 and 0.010 permil for atmospheric O2 (1sigma) on dual inlet mode, at least back in 2016. 

Then we had to move our lab to a new building, and we've been working to bring the lab up and running for the last 2 years. On "plug and play" at the new place the Delta V Plus was doing 100% worse precision, 0.01 permil for d15N of N2 and 0.02 permil for d18O of O2. After significant troubleshooting, we managed to diagnose (in part) the symptom of our problem, which is - the peak alignment. When "Extraction %" - which is one of the focus setting is 80% (as per recommended by the manual), the alignment was horrible - we got really narrow peak shapes. The imgur link below contains the peak shapes for N2 configuration (m28, m29, m30) but it is also the same for air (O2/N2/Ar) configuration. 

https://urldefense.com/v3/__https://imgur.com/a/CprcVpE__;!!JmPEgBY0HMszNaDT!_xInxdC92YaKy1IeDoj4wpfp-3k9nE2P1FIYgqBah1Jr0GWrpsM_jGPG-av21rc$ 

We tried the usual stuff. Changing filament, baking capilaries, adjusting crimps, cleaning the source, nothing helps. We even chuck in a source from our other Delta V into this machine and got the same terrible peak shape. 

The only thing that helped was to change the "Extraction %" parameter. At 20% extraction we managed to get an acceptable flat top peak shape and alignment (peak shapes at various extraction % are attached in imgur link). This represents 50% improvement as now our internal precision on zero enrichment run is 0.008 permil for d15N and 0.015 permil for atmospheric O2, but it is still 50% worse than what the instrument is capable before moving building (depends whether you are a glass half full or half empty person). Also running more cycles, more idle time, changing integration time, increasing sample size does not help. 

In consultation with our Thermo representative, they recommend us to install these stainless steel shims as upgrade package for an old Delta V Plus. We took out the magnet, open the flight tube, and install the shims on the flight tube. To our surprise it does fix the problem, but only for 1-2 weeks as the precision got gradually worse again, the peak shape got gradually worse, and now we are back to where we were when the shims are not on. It is as if the shims fell out, but it is obviously impossible because there is only one way the shim could go into the flight tube and it was very secure. 

Any tips and recommendation, or just thoughts & comments on what the problem could possibly be would be greatly appreciated

Best regards

Michael N. Dyonisius
Postdoctoral Researcher
University of Copenhagen
Tagensvej 16, Copenhagen DK
2100