Excretion of Organic Matter during an Experimental Phytoplankton Bloom Followed Using o-Nitrophenol as an Electrochemical Probe

Extracellular excretion of the surface active organic matter during a nutrient enriched phytoplankton culture growth was studied using o-nitrophenol (ONP) as an electrochemical probe. Changes in the hydrophilic and hydrophobic acid fractions, as compared to the unfractionated seawater sample, were followed during the twelve days of the experiment. Diatoms were the dominant phytoplankton species growing during the experiment. It was observed that the enrichment of natural seawater by nutrients caused increased concentrations of both polysaccharides and proteins, in dissolved and particulate phases. At the end of the experiment, polysaccharides were the dominant adsorbable organic matter on the mercury electrode according to the changes of the electrochemical characteristics of the ONP probe. The excreted polysaccharides were weakly acidic. Their estimated concentration was equivalent to 1.2 mg dm-3 as neutral dextran T-500 or 3 mg dm-3 as weakly acidic hyaluronic acid

In-situ electrochemical method for detecting freely dissolved polycyclic aromatic hydrocarbons in waters

A new sensing system for polycyclic aromatic hydrocarbons (PAH) in waters is being developed. The system consists of a wafer based device with chip-based mercury (Hg) on platinum microelectrode as working electrode and platinum auxiliary electrode, incorporated in to a flow cell system with an external reference electrode. Hg microelectrode was coated with a phospholipid/triglyceride mixed layer and interactions between anthracene, phenanthrene, pyrene and fluoranthene and the layer were monitored using rapid cyclic voltammetry (RCV). The layer proved sensitive to interactions with PAHs in “organic matter free” seawater, with the detection limits of 0.33 μg/L for phenanthrene, 0.35 μg/L for pyrene, 0.15 μg/L for anthracene and 0.32 μg/L for fluoranthene. Tested interferences, such as sodium humate, dextran T–500 and bovine serum albumin, representative humic substances, polysaccharides and proteins, did not have an influence on the layer response. The system was also tested with a river water sample where concentrations of PAHs were determined using the standard addition method and compared to the results obtained by using gas chromatography–mass spectrometry (GC–MS). The concentration of total PAH obtained by the standard addition method is about 80% lower compared to the results obtained by GC MS analysis. The difference is explained by the fact that the electrochemical method measures water-soluble and free PAHs while chromatographic methods measures both dissolved and particulate/organic PAH