engleski

The potential of electrochemical methods in analysis of natural polysaccharides

Natural polysaccharides (PSs) constitute a major part of organic matter present in the hydrosphere where they are involved in the carbon cycle, speciation of trace metal ions, aggregation and sedimentation processes, etc. From electroanalytical point of the view, PSs are electroinactive molecules that could not be oxidized nor reduced. But, recently it was reported that PSs carrying sulfate groups such as carrageenans or amino groups such as chitosan produce in buffered solution well-developed “peak H” using chronopotentiometric stripping (CPS) method. Peak H is due to the catalytic hydrogen evolution reaction at hanging mercury drop electrode (HMDE). Concerning PSs detection in seawater where they are naturally present, peak H was observed only if an ex situ procedure of adsorptive transfer (AdT) is performed. Here we report about detection of amino PS chitosan in seawater applying AdT procedure as direct CPS in seawater gave no peak H even for 100 mg/L of chitosan. AdT included adsorption of chitosan in seawater onto the HMDE surface, transfer of the modified HMDE into the buffer (without PS) followed by CPS detection of peak H. The layer of adsorbed chitosan on the HMDE surface was very stable even 20 min after the transfer. An increase of the peak H height at higher buffer concentration (0.01-0.10 M) and at lower pH (5-8) confirmed faradaic catalytic nature of the electrode process. The effect of CPS parameters (accumulation potential, accumulation time and stripping current) as well as other experimental conditions (type and concentration of the buffer, pH, and ionic strength) on the peak H height and peak potential of chitosan were evaluated and defined. Nanomolar concentrations of chitosan in seawater was determined at moderate accumulation times and/or stripping currents. Accordingly, our results highlight the capacity of electrochemical CPS technique for characterisation of natural polysaccharides carrying sulfate and/or amino groups in the structure, not only in the medium where they are naturally present (such as seawater), but in any buffered electrolyte using HMDE that are suitable for detection of catalytic peak H.

Adsorptive transfer ; polysaccharides ; chronopotentiometric stripping analysis ; peak H ; seawater

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