Accurate determination of the natural variation in the carbon-13 content of samples has been used in a variety of applications such as geochemistry, forensics, and monitoring the carbon-flux between atmosphere, terrestrial and oceanic environments. Since 1987, this determination is based on the Vienna Pee Dee Belemnite (VPDB) scale which is linked to a Reference Material (RM) such as RM 8543 (carbonatite, δ13CVPDB = -5.01‰) or RM 8544 (limestone, δ13CVPDB = +1.95‰). These RMs are not certified against the SI unit of mass, are limited to a single δ13CVPDB reference value, and are limited for sale (e.g. RM 8544 is currently not for sale). To solve these short comings, it is proposed to gravimetrically prepare a suite of methane (CH4) in nitrogen (N2) balance gas standards where the δ13CVPDB varies from +20‰ to -90‰ in increments of 10‰. This will be achieved by blending a total CH4 concentration of 400 µmol/mol (in line with ambient levels of carbon dioxide) from the purest sources of 12CH4 (C-12 enrichment of 99.999%), 13CH4 (C-13 enrichment of 99.99%), and N2 (purity of 99.9999%, CH4 < 10 nmol/mol). The gravimetric scheme, and expected uncertainty budget will be presented.
I worked for twelve years in the Research and Development department at a private, specialty gas company. My principle areas of activity included: development of cylinder preparation technique; improving blending techniques; and analytical method development. In 2005 I began work at the National Institute of Standards and Technology as a research chemist. My main areas of responsibility include: running the bi-annual US EPA Blind Audit program; SRM / NTRM certification; development of new standards such as ammonia, formaldehyde and methyl mercaptan; development of 13C gravimetric standards.