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2 University of California, San Diego Scripps Institution of Oceanography Marine Physical Laboratory 9500 Gilman Drive La Jolla, CA 92093-0244 

# Certificate of Analysis

Reference material for oceanic CO 2 

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Batch #69 (Bottled on January 4, 2005)

This reference material consists of natural sea water sterilized by a combination of filtration, ultra-violet radiation and addition of mercuric chloride.

Analysis Results The various procedures used for th ese analyses are detailed overleaf. Salinity 31.569 Total dissolved inorganic carbon 1907.63 ± 0.29 μ mol·kg –1 (12; 12) Total alkalinity 2114.42 ± 0.74 μ mol·kg –1 (16; 8)

Phosphate 0.33 μ mol·kg –1 Silicate 2.6 μ mol·kg –1 Nitrite 0.0 μ mol·kg –1 Nitrate 0.0 μ mol·kg –1 The cited uncertainties represent the standard deviation. Figures in parentheses are the number of analyses made (total number of analyses; number of separate bottles analysed). The nutrient levels may have changed on storage, their stability has not been examined. CO 2 analyses were performed over a period of time to confirm that the batch is stable.
The 95% confidence limits for the certified analyses are thus: Total dissolved inorganic carbon 1907.63 ± 0.18 μ mol·kg –1 Total alkalinity 2114.42 ± 0.62 μ mol·kg –1 STORAGE: The bottles should be stored out of direct sunlight, and preferably at or below room temperature (25 °C). They should not be allowed to freeze!

Andrew G. Dickson July 12, 2005Analytical Methods Used

Salinity The salinity was determined by measuring its conductivity relative to IAPSO Standard Sea Water using a Guildline Autosal Model 8400 conductive salinometer. The procedure is described in an in-house technical manual of the Oceanographic Data Facility (ODF), Scripps Institution of Oceanography,entitled “Autosal Operating Procedures”, dated 10-Dec-1993, revised 10-Jan1994.

Total dissolved inorganic carbon The total dissolved inorganic carbon was assayed in Dr. C. D. Keeling’s laboratory at the Scripps Institution of Oceanography by the vacuum extraction/ manometric procedure. The weighed sample is acidified with phosphoric acid; the CO 2 evolved is then extracted under vacuum and condensed in a trap cooled by liquid nitrogen. The water and CO 2 are separated from one another by sublimation and the CO 2 is transferred into an electronic constant-volume manometer [ECM]. There its pressure, volume and temperat ure are measured and the amount of CO 2 separated is computed from the virial equation of state.

Alkalinity The total alkalinity was assayed by a two-stage, potentiometric, open-cell titration using coulometrically analyzed hydrochloric acid. A weighed sample of reference material is acidified to a pH between 3.5 and 4.0 with an aliquot of titrant. The solution is stirred for a period of time to allow the evolved CO 2 to escape. The titration is then continued to a pH of about 3.0 and the equivalence point evaluated from titration points in the pH region 3.0–3.5 using a modified Gran procedure that corrects for the reactions with sulfate and fluoride ions.

Nutrients
Nutrient levels were determined using a modified 4-channel autoanalyzer. The procedures are similar to those described in Gordon, L.I., J.C. Jennings, A.A. Ross, J.M. Krest (1993) “A Suggested Protocol for Continuous Flow Automated Analysis of Sea Water Nutrients (Phosphate, Nitrate, Nitrite, and Silicic Acid) in the WOCE Hydrographic Program and the Joint Global Ocean Fluxes Study”, WOCE Operations Manual , WHP Office Report WHPO 91-1 (rev. Nov. 1994