Coulometric titrations in microscale study of ionic equilibria

Summary Coulometric titration, a well established technique in research and in routine analysis, can successfully be applied to the study of ionic equilibria in solution. Processes, where either lyate or lyonium ions serve as titrants, for determination of acids and bases, respectively, were investigated. Among the systems studied are: autoprotolytic equilibria of various amphiprotic solvents, acid-base equilibria in water, organic and mixed solvents and complexation reactions. In all these examples the titration was followed by a potentiometric pH-indicator electrode. In nonaqueous solvents coulometry overcame the limited solubility of electrolytes, the difficulty of standardization on solutions and the necessity of working in isolated systems to avoid contamination of the sample with water vapour or with carbon dioxide.Because volumes below 1 ml and concentrations in the order of 0.001 mol/l can be used, this technique can be successfully applied to the investigation of micromole amounts of compounds, when protolytic properties of substances available in minute quantities should be evaluated. Furthermore this technique was applied to the evaluation of protonation constants of biologically important buffers and the stability constants of their calcium complexes.