Authors Müller, M. ; Wirth, L. ; Urban, B.
Title Determination of the carboxyl dissociation degree and pKa valute of mono and polyacid solutions by FTIR titration
Date 01.02.2021
Number 58903
Abstract Dissociation degree a and pKa of two model carboxylic acid systems are determined by the Fourier transform infrared (FTIR) titration concept and compared to the classical potentiometric (POT) titration concept. pH dependence of poly(acrylic acid) (PAA) is studied in comparison to that of propionic acid (PA) being structurally related to PAA repeating units. Starting with the respective acid forms and increasing the pH value by adding NaOH portions FTIR spectra of PA and PAA show decrease of ·(C·O) band due to carboxyl (COOH) groups and increase of ·a(COO-) band due to carboxylate (COO-) groups. From the integrated band areas A the dissociation degree ···=····-/(······+····-) can be calculated with F taking different absorption coefficients of ·(C·O) and ·a(COO-) into account. pH is plotted versus aIR and this curve fitted by functions related to Henderson–Hasselbalch equation. As fit parameters pKa value for PA and PAA and optionally empirical cooperativity factor B are considered. pKa values found for PA and PAA by FTIR titration are in agreement to respective pKa values found by own and referenced POT titration data. The found pKa deviation between PA and PAA and PAA molecular weight trends are discussed based on the known two–phase–model including Gibbs–Donnan–potential concept.
Publisher Macromolecular Chemistry and Physics
Citation Macromolecular Chemistry and Physics 222 (2021) 2000334

Back to list