Designing working standards for stable H, C, and O isotope measurements in CO2 and H2 O.

The selection of WSs involves a preselection of potentially suitable materials based on initial estimates of their mineralogical, chemical, and isotopic properties and long-term stability, based on literature or previous measurements. Their precise characterization vs international isotopic scales requires a thorough analytical work in a correct sequence. When properly carried out, the proposed protocols should permit WSs to be obtained, defined vs the VSMOW and VPDB scales, with uncertainties comparable with those achieved for the characterization of iRMs.