GRAVIMETRIC PREPARATION OF GAS-PHASE WORKING STANDARDS CONTAINING VOLATILE HALOGENATED COMPOUNDS FOR OCEANOGRAPHIC APPLICATIONS

Gas phase standards, containing CCl3F (CFC-11), CCl2F2 (CFC-12), CCl2F CClF2 (CFC-113), CH3CCl3 and CCl4 in the pmol mol(-1) range, were prep ared gravimetrically in dry N-2. The standards were prepared with the relative ratios of the various compounds close to those found in seawa ter, to facilitate calibration of oceanic halocarbon measurements. The standards made in this study were intercalibrated against an atmosphe ric-ratio-based standard that was analyzed at both Scripps Institution of Oceanography (SIG) and NOAA's Climate Monitoring and Diagnostics L aboratory (CMDL). A total of 21 standards was made, with the concentra tions of the above halocarbons reported on both the CMDL and SIO 1993 scales. These standards are currently being used by ten different rese arch groups making oceanic halocarbon measurements. The average system atic deviation of all compounds in our standards was generally +/- 5% or less from the SIO 1993 and CMDL scales. Deviations for CH3CCl3 betw een our standards and the CMDL scale were slightly larger, with our st andards, on average, approximately 10% lower. (C) 1997 Elsevier Scienc e Ltd.