Dear Wolfram and others,
I know that EA-IRMS analyses of NO3 salts often yields better results if the oxygen pulse is turned off. Wolfram cites Gentile et al., (2013) on this subject in his book. However, when CaCO3 is analysed (e.g. NBS19 or its replacement IAEA-603) at least in my lab we keep the oxygen pulse on. In fact we also add WO3 (some labs add (V2O3) to the CaCO3 to provide the reaction with further oxygen. During the oxygen pulse the tin cup compusts in a flash and that further increases the temperature to well above 1020 degrees. I seem to remember reading that during the flash temperatures of around 1800 degrees are reached for a very short time, and I think that reaching these temperatures is important to convert the CaCO3 quantitatively to CO2 gas. When we have problems with our EA, e.g. the timing of the oxygen pulse is off, we find that our d13C measurements of CaCO3 are also off. Therefore I would argue that the oxygen pulse during EA-IRMS analyses of carbonates is important. 
In this regard I am currently looking for publications that have described the flash procedure, and the temperatures that are reached during the flash. Maybe someone can point me towards publications if they exists. In the German language literature I have found "Glühfarben" (glow colour) tables that link the colour of steel in steel producing furnaces to its temperature. Does something similar exist for other metals (e.g. Tin for Tin capsules)?

Have a nice weekend,
Heiko

Dr. Heiko Moossen, Dipl.-Chem.

Stable Isotope Laboratory
Max-Planck-Institute for Biogeochemistry
Hans-Knoell-Str. 10
07745 Jena
Germany
Tel: +49-3641-576400 
Fax: +49-3641-577400 
P.O.Box 100164, 07701 Jena, Germany 


From: Stable Isotope Geochemistry <[log in to unmask]> on behalf of Wolfram Meier-Augenstein (pals) <[log in to unmask]>
Sent: 28 November 2018 08:39
To: [log in to unmask]
Subject: Re: [ISOGEOCHEM] preparation of working standards for d13C
 
Dear Mattheus,


The d13C values of the RMs described in Arndt's 2016 paper were scale normalized to the VPDB scale as defined by NBS19 and LSVEC. This does not necessarily mean they were analysed against these RMs although one participating lab did so using optimised EA conditions. Other participating labs used RMs such as USGS40 and USGS41 as scale anchors for scale normalization to VPDB. Internationally accepted RMs such as USGS40, IAEA-CH-6 or IAEA-CH-7 are all anchored on the VPDB/LSVEC scale.

In my book I advised not to use inorganic RMs to scale anchor organic samples as this does not meet with the Identical Treatment principle (due to potential matrix effects).

I also pointed out what the issues are and how to overcome these.

Carbonates do not "burn differently". They do not burn at all. Carbonates represent the highest state of oxidation carbon can assume. It is therefore impossible to burn = oxidise carbonates any further.  What happens in an EA is a thermolytic breakdown of carbonate into carbon dioxide and oxygen. For this to happen in a way to yield "true" d13C values the reactor temperature has to be above 1000C and the oxygen pulse must be switched off. While some EA-IRMS systems can apply individualised run parameters for each samples, others may not offer this option (e.g. O2 pulse active for one sample but not active for the next).

Using organic RMs for organic samples avoids these issues.

BTW, Arndt and I have recently published a paper on the subject of arMs and their use in Isotopes Environ. Health Stud.

https://www.tandfonline.com/doi/full/10.1080/10256016.2018.1538137


Hope this helps.


Best,

Wolfram


******************************************************
Prof. Dr W Meier-Augenstein, CChem, FRSC
Stable Isotope Forensics & Analytical Sciences

Robert Gordon University
School of Pharmacy and Life Sciences
The Ian Wood Building
Garthdee Road
Aberdeen
AB10 7GJ

E-mail:   [log in to unmask]
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From: Stable Isotope Geochemistry <[log in to unmask]> on behalf of Matheus Carvalho <[log in to unmask]>
Sent: 28 November 2018 05:23:43
To: [log in to unmask]
Subject: [ISOGEOCHEM] preparation of working standards for d13C

Dear all, I am a little confused about the use of international reference materials for the preparation of working standards. I read the paper by Schimmelmann et al (2016) Anal. Chem. 88, 4294. If I understood it right, they measured the new standards (all organic substances, like caffeine and glycine) in comparison with international standards like LSVEC and NBS19 for d13C. But I also read in the book Stable Isotope Forensics by our estimated contributor Wolfram Meier-Augenstein (excellent book, by the way) that we should not use these materials for organic sample analyzes because they burn differently in the EA reactor, this being the very reason to use the new standards in the Schimmelman paper. But if the standards in that paper were determined against the inorganic substances, why should I trust them more than an organic standard that I determine myself using LSVEC and NBS19?
Thank you,


Matheus C. Carvalho
Centre for Coastal Biogeochemistry Research, Southern Cross University
Lismore, NSW, Australia
Editor for Plos ONE, Heliyon (Elsevier),HardwareX (Elsevier)

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