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 #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 these analyses are detailed overleaf. 

Salinity 31.569 

Total dissolved inorganic carbon 1907.63 ± 0.29 μmol·kg–1 (12; 12)

Total alkalinity 2114.42 ± 0.74 μmol·kg–1 (16; 8) 

Phosphate 0.33 μmol·kg–1 

Silicate 2.6 μmol·kg–1

Nitrite 0.0 μmol·kg–1

Nitrate 0.0 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 1907.63 ± 0.18 μmol·kg–1 

Total alkalinity 2114.42 ± 0.62 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 

July 12, 2005 
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