Measurement of effective HCl diffusion coefficients through aqueous and gel films by a pH jump technique

Abstract

Direct measurement of HCl diffusion coefficients in low ionic strength media have not been reported owing to the practical difficulty of controlling pH gradients in two compartments of a diffusion chamber with minimal or no inclusion of buffer. Here we report a single-compartment system in which effective HCl diffusion to a membrane-mounted glass pH electrode can be measured under conditions approaching neutrality. A strong pH-dependent response of the membrane- or gel-mounted pH electrode was observed. Comparison of effective D_HCl values in the presence of a mounted gel and/or membrane showed a clear decrease to that of a liquid film over the pH range studied (3.5–9.5). However, the study also demonstrated effective D_HCl values to be strongly pH dependent with a minimum around neutrality.