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.
Another good and instructive read on this subject (using 34S analysis as example) is Appendix B of Zach Sharp’s book Stable Isotope Geochemistry.
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.
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.
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]
Alberta Innovates - Technology Futures
Vancouver Island Technology Park
3 - 4476 Markham St., Victoria, BC, Canada V8Z 7X8
Phone: 250-483-3290 | Fax: 250-483-1989
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Can one purchase a bottle of hydrogen gas with a know dD ratio? If so, where, and is it worth the cost?
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
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