A bespoke chloride sensor for seawater: Simple and fast with a silver electrode

Chloride quantification in natural seawater is important in both oceanography and corrosion science. A bespoke electrochemical method was developed for a facile and accurate chloride sensor specifically for use for the high chloride levels encountered in seawater (ca 0.5 M). This is based on the voltammetric oxidation of a silver electrode over a well-defined potential range corresponding to AgCl nucleation/formation. The peak current for silver chloride formation varies linearly with chloride concentration in the range 0.484 M–0.624 M provided the electrode is suitably activated. In particular, the reduction of dissolved oxygen was found to clean the surface and also to provide a stable peak potential against which other potentials can be referenced if it is wished to use a quasi-reference electrode. Thus, the overall voltammetric scan embraces first the reduction of oxygen followed by silver chloride formation and stripping. Reliable quantification was achieved in synthetic seawater with this methodology. Furthermore, the chloride anion concentration in three different authentic samples of natural seawater was measured accurately giving excellent agreement with independent analysis. [Display omitted] •A bespoke electrochemical method was developed for chloride detections in seawater.•The method is designed for high chloride levels of 0.484 M–0.624 M.•The method is amperometric and uses the oxidation of a metallic silver.•The oxygen reduction reaction was used to activate the electrode surface prior to silver chloride nucleation/formation.•Analysis of natural seawater gave excellent agreement with independent analysis.