ELECTROCHEMICAL REDUCTION OF O-NITROPHENOL AS A TOOL FOR THE ROUGH CHARACTERIZATION OF ORGANIC-MATTER IN SEAWATER SAMPLES

Phase sensitive alternating current (AC) voltammetry with o-nitropheno l (ONP) as a probe is used asa simple nondestructive method for a roug h characterization of organic substances in natural seawater samples. This is based on the measurement of the effects of adsorbed organic su bstances on the peak height and the potential of the ONP reduction pea k. In this work further improvements are presented of the method which is achieved by introducing the measurement of the prepeak of ONP redu ction obtained upon scan reversal. The height of the prepeak is extrem ely sensitive to the type of organic matter adsorbed on the mercury el ectrode at the pH of natural seawater. The ONP prepeak increases in th e presence of adsorbed layers of negatively charged organic substances , such as humic and fulvic acids and proteins. In the presence of adso rbed polysaccharides of dextran type there is no increase of the ONP p repeak height. With increasing concentrations of the polysaccharides a small decrease of the prepeak is observed. The application of the met hod is demonstrated on different seawater samples from the north Adria tic sea.