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Thanks, Robert.

We are running GC-irMS for dD of n-alkanes. I'd love to see how you go about setting up your sequences, just to get an idea of how others tackle this.

I will look into the references you provided.

Best,

On Fri, Oct 14, 2016 at 2:59 AM, Geldern, Robert <[log in to unmask]> wrote:
Hi,

a couple of years ago, AirrLiquide had a product (called “IsoTop") that at least allowed for a selection of the range of the d2H values (so if the d2H lecture bottle is more to the high or low side). Inside you typically found also a “certificate” that gave you a precise of value of your particular bottle, but as others already pointed out this is not of much use. Not sure if it still available.

With respect to the sequence layout: Yep - correct normalization, linearity, drift and QA/QC need a lot of lines in your sequence. Finally, you have to find a balance between sample throughput and calibration/quality control. Not always an easy task and it also varies from device to device. What analysis are we talking about? I can send you some of our master templates to give you an idea.

But two point reference materials, drift, linearity (if applicable) and unknowns are mandatory on a daily basis. Depending on the device this will reduce, of course, your sample throughput. But: Always decide for better data quality than for more numbers. It is always better to include a standard twice if in doubt than to optimize your sequence for fast analysis.

You also might find some ideas for setting up a sequence in the publications below.

regards,
Robert

Werner and Brand (2001), Referencing strategies and techniques in stable isotope ratio analysis, RCM, 15, 501, 10.1002/rcm.258
Wassenaar et al. (2013), Approaches for Achieving Long-Term Accuracy and Precision of δ18O and δ2H for Waters Analyzed using Laser Absorption Spectrometers, Environ. Sci. Technol. 2014, 48, 1123−1131, dx.doi.org/10.1021/es403354n
van Geldern, R. and Barth, J.A.C. (2012) Optimization of instrument setup and post-run corrections for oxygen and hydrogen stable isotope measurements of water by isotope ratio infrared spectroscopy (IRIS). Limnology and Oceanography: Methods 10, 1024-1036.



Am 14.10.2016 um 02:07 schrieb Jeff Salacup <[log in to unmask]>:

> Thanks everyone for the thoughtful replies. I learn so much important info from this community on a daily basis.
>
> While we are interested in having some H2 of known dD in house, we do not plan to use it for standardization to VSMOW or any other scale. We routinely use two point scale anchors based on standards provided by Arndt et al. And then use this normalized scale to calibrate a third standard from Arndt to see how close we are getting to accepted. We are generally within a few permil, very close to 'within error'.
>
> One question we've been asking ourselves though is how often we need to perform a 2 point anchor... every sequence table (in other words, daily), weekly, every new reactor (3-4 weeks)? If I run 2 anchor standards 3-5 times in every sequence, plus the other 'unknown' standard 3 times, that's 9-13 sequence lines. Then you've got to add in drift standards to make sure the run as a whole stays 'level'. You run out of room for samples! My goodness! So I'd be interested in hearing if there is an accepted protocol, and if not, if folks would be willing to share their experience with balancing the needs of quality assurance with those of the lab (data production).
>
> Thanks again, for any and all info.
>
> Best,
>
> On Thu, Oct 13, 2016 at 4:37 PM, Wolfram Meier-Augenstein (aps) <[log in to unmask]> wrote:
> Even a lecture bottle of H2 with a “calibrated” value represents still only a single point of “reference” and does not do away with the need for proper scale calibration using two scale anchors spanning a d2H value range similar or identical to that covered by VSMOW/SLAP.  Anybody can verify this for themselves quite easily.  Use VSMOW(2) to dial in (aka “calibrate) the d2H value of your H2 cylinder. Once you are happy with the result, use the cylinder gas d2H value thus obtained to run SLAP or even GISP against it and see what the difference is between cylinder gas “calibrated” vs. accepted.
>
>
>
> Besides, it is impossible to correct for scale compression effects using merely 1 single point of scale reference. The need for a 2 point scale calibration, especially for 2H but also for other light element isotopes has covered extensively in the literature and in fact forms part of IUPAC guidelines for stable isotope ratio measurements and reporting results thereof.  Recommended reading on this subject includes Chapter 1 (specifically pages 34 and 35), Chapter 40 and Chapter 41 in Pier de Groot’s Handbook of Stable Isotope Analytical Techniques (Vol. I); Figure 41.2 is reason alone to read Chapter 41.
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>
>
> Another good and instructive read on this subject (using 34S analysis as example) is Appendix B of Zach Sharp’s book Stable Isotope Geochemistry.
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> While of course a convenient way to generate measured (‘raw’) d2H values, as Arndt has already pointed out the use of a cylinder gas to “calibrate” H2 generated from sample conversion that on top has entered the ion source via a separate (different) gas train does not meet the identical treatment requirements.
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>
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> Using a dialled in H2 cylinder to generate measured d2H values has of course its advantages.  It helps writing SOPs with regard to acceptance / rejection criteria for measured d2H values of one to two QC materials on the basis of which one decides whether to continue with or abort a sample batch run sequence.
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>
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> Best,
>
>
>
> Wolfram
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> From: Stable Isotope Geochemistry [mailto:[log in to unmask]edu] On Behalf Of Paul Eby
> Sent: 13 October 2016 20:57
> To: [log in to unmask]
> Subject: Re: [ISOGEOCHEM] Hydrogen Refgas of know value
>
>
>
> You can get this from Oztech (Chuck Douthitt). He has lecture bottles of pure H2, calibrated with a variety of isotopic values. Contact him by email at: [log in to unmask]
>
>
>
> Paul Eby
>
>
>
>
>
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> From: Stable Isotope Geochemistry [mailto:[log in to unmask]EDU] On Behalf Of Jeff Salacup
> Sent: October-13-16 11:36 AM
> To: [log in to unmask]
> Subject: [ISOGEOCHEM] Hydrogen Refgas of know value
>
>
>
> Greetings!
>
>
>
> Can one purchase a bottle of hydrogen gas with a know dD ratio? If so, where, and is it worth the cost?
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>
> Best!!
>
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>
> --
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> Jeff
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> __________________________________________________________________
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> Stable Isotope & Biogeochemistry Lab Manager
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--
PD Dr. Robert van Geldern
Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) | GeoZentrum Nordbayern
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Jeff




Two things are infinite: the universe and human stupidity; and I'm not sure about the universe. - Einstein



__________________________________________________________________
Jeff Salacup, Ph.D.
Stable Isotope & Biogeochemistry Lab Manager
UMass-Amherst