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Towards a Standard Method for the Measurement of Organic Carbon In Sediments

TOWARDS A STANDARD METHOD FOR THE MEASUREMENT OF ORGANIC CARBON IN SEDIMENTS

C.M. Lee and D.L. Macalady

Colorado School of Mines, Golden, Colorado, 80401, U.S.A

The precisions achieved by two different methods for analysis of organic carbon in soils and sediments were determined and compared. The first method is a rapid dichromate oxidation technique (Walkley-Black) that has long been a standard one in soil chemistry. The second is an automated coulometric titration method for which commercial instrumentation is available. The latter method shows relative standard deviations that are six to twenty times smaller than the dichromate oxidation technique. Development of a standardized sediment with a low level of organic carbon is recommended in order to facilitate the evaluation of the precision and accuracy of organic carbon measurement techniques.

KEY WORDS: organic carbon, sediments, coulometric titration, Walkley-Black titration

Hassett et al.10 used the Walkley-Black method to determine the organic carbon content of a group of soils and sediments that have been widely used for environmental studies. The Walkley-Black has long been a standard method for organic carbon determination in the soil sciences. The method uses materials and equipment readily available at reasonable cost. It is simple to use and does not require extensive sample preparation.

The coulometric method we used also involves little sample preparation and is a simple, rapid technique. It does, however, require a substantial initial instrument cost.

The analyses reported herein are presented to provide comparison of the widely-used Walkley-Balck technique to an instrumental method. No such comparisons are available in the literature. Also, the precision of the coulometric method has not been reported for analyses of soils and sediments. We compare the two methods by determinations of the organic carbon content of three sediment samples. Two were collected and characterized by Hassett et al.10 for the U.S. Environmental Protection Agency (EPA) and one was collected by workers from our laboratory.