A comparison of methods for the determination of dissolved oxygen in seawater

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1991-08Author
Culberson, Charles H.
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Knapp, George P.
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Stalcup, Marvel C.
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Williams, Robert T.
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Zemlyak, Frank
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https://hdl.handle.net/1912/243DOI
10.1575/1912/243Abstract
An intercalibration of dissolved oxygen methods was conducted at 2 stations
in the Sargasso Sea between April 28 and May 3, 1990. The experiment compared
three techniques using automated endpoint detection with the manual Winkler method using a starch endpoint. Institutions participating in the
intercomparison were the Bedford Institute of Oceanography (automated photometric
titration), the University of Delaware (automated amperometric titration), the
Scripps Institution of Oceanography (manual titration), and the Woods Hole
Oceanographic Institution (automated amperometric titration).
Differences in measured oxygen concentrations between institutions were
encouragingly small. However, small, systematic differences in dissolved oxygen
between institutions did exist. The range between the highest and lowest oxygen
values reported by the 4 institutions never exceeded 0.6% over the entire
concentration range studied (3.4 to 6.2 mlj1). The good agreement is probably
due to the use of the essentials of Carpenter's (1965) modification of the
Winkler method by all institutions.
The intercalibration revealed several aspects of dissolved oxygen
measurements that require further research: (1) the intercalibration should be
extended to very low oxygen concentrations; (2) procedures for measur ing and
applying corrections for the seawater blank need to be formalized; (3) a simple
procedure to measure the temperature of seawater at the time of sampling needs
to be developed; and (4) the solubility of atmospheric oxygen in the Winkler
reagents must be measured as a function of temperature.
The intercalibration also revealed that analytical techniques required for
precise and accurate volumetric measurements were often not applied, even by
experienced analysts. It was found that uncalibrated pipets were used to
dispense standards, that the volumes of oxygen flasks were not corrected for
buoyancy, and that corrections for the thermal expansion of aqueous solutions were often not applied.
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Working Paper: Culberson, Charles H., Knapp, George P., Stalcup, Marvel C., Williams, Robert T., Zemlyak, Frank, "A comparison of methods for the determination of dissolved oxygen in seawater", 1991-08, DOI:10.1575/1912/243, https://hdl.handle.net/1912/243Related items
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