ELECTROCHEMICAL ESTIMATION OF THE DOMINANT TYPE OF SURFACE-ACTIVE SUBSTANCES IN SEAWATER SAMPLES USING O-NITROPHENOL AS A PROBE

A simple electrochemical method is developed for direct estimation of the concentration and nature of the dominant type of surface active substances (SAS) in natural waters using o-nitrophenol (ONP) as a probe. It was noticed from studies of model systems of selected adsorbable organic substances (humic and fulvic acids, carbohydrates, proteins and lipids), representative of the chemical composition of organic matter in natural waters, that different surface active molecules influence the polarographic oxidation-reduction processes of ONP in very specific ways. This is indicated by different shapes and peak potentials as well as by the change of the peak height of the ONP reduction peak in the presence of different SAS. The application of the method is demonstrated on a number of seawater samples collected at different locations, depths and seasons in the Adriatic sea. Results were compared with the measurements of surfactant activity values by alternating current voltammetry and discussed on the basis of the DOC values of the samples.