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Chronopotentiometric stripping of sulphated polysaccharides in seawater

Anomalous accumulation of organic matter in a form of macroaggregates (mucilages) under specific climatic and trophic conditions was documented in the Adriatic Sea. The macroaggregates of the northern Adriatic are mostly composed of water-soluble heteropolysaccharides and longer polymethylene chains. The polysaccharides (PS) originate primarily from phytoplankton exudates and structural PS. Acidic (sulphated and carboxyl) PS abiotically form transparent exopolymeric particles (TEP) which have an important role in biogeochemical cycling of trace elements in the seawater. The method of PS analysis in seawater is not straightforward and that is why we have been tried to develop and to apply electrochemical method. By applying chronopotentiometric stripping (CPS), it was proven, that if sulphate groups are attached to a PS chain, a catalytic “peak HPS” in buffered solution (pH 5.2) appears. Peak HPS is a result of catalytic hydrogen evolution on a mercury drop working electrode and it strongly depends on a buffer concentration. In situ obtained peak H may enable a selective detection of nmol concentrations of sulphated PS. But, direct stripping of sulphated PS in seawater (pH 8.2) did not give any peaks. Therefore, adsorptive transfer (AdT) procedure was applied in order to transfer accumulated sulphated PS from seawater into the suitable stripping electrolyte. According to CPS of a model sulphated PS ι-carrageenan, acetate buffered sodium chloride solution (0.55 M) of pH 5.2 was the stripping electrolyte. Results show that AdT CPS enables the analysis of sulphated PS in seawater.

chronopotentimetric stripping; polysaccharides; peak H; seawater

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