Electrochemical analysis of natural aqueous media

This thesis focuses on investigations of electroanalytical methods to study natural aqueous media particularly considering analyte quantification with high chloride levels (seawater) or low electrolyte concentrations (drinking water). The two extremes correspond to different voltammetric regimes where high ionic strength suppresses transport via ionic migration and the voltammetry is said to be ‘fully supported’ and mass transport is dominated by diffusion, whilst in the near absence of electrolyte diffusion is strongly coupled with migration. The fundamentals of electrochemistry and the principles of electrochemical methods used in this thesis are introduced in Chapter 1. The chemistry of natural water is discussed in Chapter 2. Experimental methods and non-electrochemical based techniques including simulation software are described in Chapter 3. The investigations of seawater and drinking water each consist of two chapters. In the study of seawater, Chapter 4 suggests the possible toxicity of silver nanoparticles in seawater is assessed in the light of studies of the oxygen reduction reaction on a silver electrode where the toxic superoxide was found to be produced as a reaction intermediate with a lifetime on the voltammetric timescale in seawater media. Chapter 5 builds on the work in Chapter 4 to realise a bespoke chemical sensor for chloride in seawater based on anodic stripping voltammetry of silver chloride in the very high ionic strength seawater medium. On the other hand, the research in drinking water aims to sketch a methodology of chloride quantification to overcome current challenges in performing electrochemical experiments under low ionic strength conditions without the addition of extra electrolytes. Prior to sensor development, some fundamental studies were undertaken to characterise stripping voltammetry under low ionic strength conditions. First, the simulation and experimental investigation of the deposition and stripping voltammetry from ideal fully supported conditions (with a ratio of electrolyte concentration to analyte concentration ~100) to weakly support (electrolyte concentration: analyte concentration <100) and even self-support conditions (in absence of any supporting electrolyte) is discussed in Chapter 6. Then, deposition and stripping voltammetry is used in chloride analysis in self-support mineral water solution without added reagents (Chapter 7)