KWRRI Research Reports


The objective of this study was to obtain a better understanding of the behavior of surfactants in aqueous solutions at electrodes. With this understanding it should be possible to design electrochemical methods for the detection, identification, and quantitative determination of such substances. This study was concerned primarily with the influence of extraneous salts on the behavior of surface active agents when these are examined by the electrochemical technique known as tensammetry.

The tensammetric method consists essentially of the measurement of the electrical impedance of an electrochemical cell. This impedance is characteristically increased in the presence of surfactants at those potentials where the surfactants are absorbed on the electrode. At sufficiently negative and at sufficiently positive polarization, surfactants are absorbed, and at these absorption potentials, the impedance of the cell is decreased. Curves of admittance as a function of polarization of the electrode therefore usually sh.ow two tensammetric waves. The extent of surface activity is proportional to the separation between the two tensammetric waves, to the heights of these waves, and to the degree to which the impedance is increased at polarizations between the two waves.

Since tensammetric measurements can be made only in solutions of sufficiently high conductivity, the nature and effects of added salts on the result obtained is a considerable importance. In this study it was found that the salt effect is relatively unimportant when the salt concentration is not greater than approximately 0.1 m. This concentration might then be used as a standard condition for making measurements of the surfactant concentration in aqueous solution.

The applicability of the technique to the analysis of surface active agents under actual field conditions was not attempted.

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The work on which this report is based was supported in part by funds provided by the United States Department of the Interior, Office of Water Resources Research, as authorized under the Water Resources Research Act of 1964.

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