A modified procedure is proposed for the evaluation of autoprotolysis constants of pure amphiprotic and mixed solvents obtained from electrochemical measurements. The approach described takes into account deviations from the Nernstian glass electrode slope, as well as the diffusion potential arising across the liquid junction. The procedure implies the application of multiple linear regression and is illustrated using Monte Carlo simulation of electrode responses, which is in addition applied to experimental data presented in the bibliography. The strategy followed is based on the previous residual analysis of single linear regression fitted models, in order to check if the junction liquid potential remains constant or not throughout potential measurements in solutions of varying acidity or basicity. The autoprotolysis constants of a number of inert solvents were also recalculated from potentiometric-coulometric titration literature data on the basis of the single linear regression analysis and residual analysis of the fitted models. The liquid junction potential may be considered as negligible in amphiprotic and mixed solvents in which the mobility of proton and hydroxyl ions is much lower than in water. All necessary calculations for performing the treatment of potentiometric or coulometric titration data in aqueous, non aqueous or mixed solvents are accomplished with the aid of a spreadsheet EXCEL.
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