The application of ac polarography to the determination of surface‐active substances in seawater1

Abstract

An electrochemical method based on the measurement of the capacity current at the hanging mercury drop electrode by alternating‐current polarography was developed and applied to the analysis of surface‐active substances in seawater and in sea‐surface microlayer samples. Surfactant activities of natural samples collected in the Adriatic Sea in 1978–1980 are compared with different model surfactants (Triton‐X‐100, albumin, fatty acid, humic acid, polysaccharide) and with parallel measurements by the polarographic maximum method. The shape of the capacity current‐potential curves of natural samples indicates that the adsorption effect at the electrode is produced predominantly by high molecular weight compounds. The surfactant activity corresponds to about 0.01–0.5 mg·liter −1 for bulk seawater and 0.1–2 mg·liter −1 for sea‐surface microlayer samples, relative to Triton‐X‐100. Seasonal variations in surfactant activity values at offshore stations were related to biological activity.