Gravimetric preparation of gas phase working standards containing volatile halogenated compounds for oceanographic applications

Gas phase standards, containing CCl3F (CFC-11), CCl2F2 (CFC-12), CCl2FCClF2 (CFC-113), CH3CCl3 and CCl4 in the pmol mol−1 range, were prepared gravimetrically in dry N2. The standards were prepared with the relative ratios of the various compounds close to those found in seawater, to facilitate calibration of oceanic halocarbon measurements. The standards made in this study were intercalibrated against an atmospheric-ratio-based standard that was analyzed at both Scripps Institution of Oceanography (SIO) and NOAAʹs Climate Monitoring and Diagnostics Laboratory (CMDL). A total of 21 standards was made, with the concentrations of the above halocarbons reported on both the CMDL and SIO 1993 scales. These standards are currently being used by ten different research groups making oceanic halocarbon measurements. The average systematic deviation of all compounds in our standards was generally ± 5% or less from the SIO 1993 and CMDL scales. Deviations for CH3CCl3 between our standards and the CMDL scale were slightly larger, with our standards, on average, approximately 10% lower.