Determining pKa and a New Total Diffusion Coefficient for Weak Acids via the Electrochemical Acid–Base Transport Limitation Method

This study presents the determination of the dissociation constant (pKa) and diffusion coefficient (D) for 21 weak acids (WAs) using the electrochemical acid–base transport limitation (eABTL) method. The measurements are straightforward and based on the mathematical relationships of the eATBL response, with the merits of saving time and eliminating the need for complex instruments and algorithms. The measurements of the pKa values demonstrated high repeatability with most relative standard derivation (RSD) values below 1%. The determined D values exhibited a reasonable magnitude order of 10–10 m2/s, considering the influence of the ionic strength. For the WAs that did not meet the application prerequisites of the eABTL method well, their pKa and D values could still be measured, and the results were apt for describing acid–base transport processes. Notably, the observed D values using this approach were of a new form, representing the average of the conjugate acid–base pair. Its independence from the dissociation degree and analyte concentration makes it a valuable and versatile parameter in various applications.