Characterization of organic matter in fractionated seawater samples using o-nitrophenol as an electrochemical probe

In the presence of adsorbed layers of organic matter on the mercury electrode, the electrochemical characteristics of o-nitrophenol (ONP) change in significantly different ways, depending on the different properties of organic substances like hydrophobicity, acidity, molecular weight, etc. Based on this phenomenon, a method was developed to roughly characterize surface active organic matter in seawater samples by measuring the changes in ONP peak and prepeak heights, and shifts of peak potential. The method was improved by fractionation of seawater samples on the XAD-8 resin in hydrophobic basic and neutral, hydrophobic acid and hydrophilic organic fractions. To better understand the behaviour of natural seawater samples, sorption properties of different model substances on the XAD-8 resin, particularly those of acidic polysaccharide hyaluronic acid and protein albumin have been investigated. The obtained results have shown that hyaluronic acid is distributed between the hydrophilic and hydrophobic acid fractions in the ratio of ca. 80 and 20%, respectively. Albumin is going almost completely into the hydrophobic acid fraction. The results on the sorption properties of other model surface active substances, representatives of other major groups of organic substances in marine samples, were published earlier [1]. The advantages of the fractionation are the separation of hydrophobic acid from hydrophilic organic material, which enables distinguishing between adsorption effects of acidic polysaccharides and fulvic acids, and obtaining better distinction of proteins from other organic compounds. Three seawater samples from the Adriatic Sea were used to demonstrate the applicability of the method. All the samples and fractions were compared to dissolved organic carbon (DOC) values.