A Comparison of Methods for the Measurement of Dissolved Organic Carbon in Natural Waters

E. T. Peltzer
Marine Chemistry and Geochemistry Department
Woods Hole Oceanographic Institutiton
Woods Hole, MA 02543

B. Fry
Ecosystems Center
Marine Biological Laboratory
Woods Hole, MA 02543

P. H. Doering and J. H. McKenna
Marine Ecosystems Research Laboratory
Graduate School of Oceanography
University of Rhode Island
Narragansett, RI 02882-1197

B. Norrman and U. L. Zweifel
Department of Microbiology
University of Umeå
S-901 87 Umeå
Sweden

Marine Chemistry (1996) 54: 85-96.

Received: 14 December 1995.
Accepted: 10 January 1996.
Published: September 1996.


ABSTRACT

A small suite of natural samples spanning a wide range of DOC concentrations and salinities were analyzed by three high-temperature combustion techniques and persulfate oxidation. One of the high-temperature combustion techniques, sealed-tube combustion, served as a referee method. Using this method, it was possible to obtain absolute DOC concentrations for the natural samples free of any analytical blank offset. Prior to the comparison of samples, an exchange of carbon free water and calibration standards showed that all methods were equally well calibrated. Linear correlation analysis was used to differentiate whether the differences observed between methods was due to variable oxidation yields or to an artifact of the instrument blank. Agreement among the various methods was quite good, but yields for all methods decreased compared to the sealed-tube combustion technique at concentrations above 400 µMC. Persulfate results were found to be very similar to high temperature combustion results. Finally, carbon free distilled water prepared by UV/H2O2 oxidation or Milli-Q systems had near-zero DOC concentrations and was adequate for blank correction of all the various techniques yielding DOC concentrations in excellent agreement with the referee method.


Acknowledgements

This research was supported in part by National Science Foundation grants OCE 91-15201 and OCE 92-03953 with funds provided by the Office of Global Programs, National Oceanic and Atmospheric Administration to ETP; OCE 92-16897 and Department of Energy grant DE-FG-92ER61438 to BF; and financial support from the Swedish Natural Sciences Research Council, project number B-BU9054-306 to BN. Computer support was provided by National Aeronautics and Space Administration grant NAGW-2431 as part of the Earth Observing System Interdisciplinary Science program. This is contribution number 8863 from the Woods Hole Oceanographic Institution and US-JGOFS contribution number 204.


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