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.
Hope this helps.
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
E-mail: [log in to unmask]
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?
Matheus C. Carvalho
Centre for Coastal Biogeochemistry Research, Southern Cross University
Lismore, NSW, Australia
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