QC

CO2

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 CO2 measurements

Batch #62 (Bottled on August 21, 2003)

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 these analyses are detailed overleaf.

Salinity 35.224

Total dissolved inorganic carbon 2126.46 ± 0.56 μmol·kg–1 (9;9)

Total alkalinity 2338.20 ± 0.46 μmol·kg–1 (23;10)

Phosphate 0.41 μmol·kg–1

Silicate 2.0 μmol·kg–1

Nitrite 0.00 μmol·kg–1

Nitrate 0.87 μmol·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. CO2 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 2126.46 ± 0.43 μmol·kg–1

Total alkalinity 2338.20 ± 0.20 μmol·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

November 21, 2003
Analytical 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 CO2 evolved is then extracted under vacuum and condensed in a trap cooled

by liquid nitrogen. The water and CO2 are separated from one another by

sublimation and the CO2 is transferred into an electronic constant-volume

manometer [ECM]. There its pressure, volume and temperature are measured

and the amount of CO2 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 CO2 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