Characterization and detection of polyanions by direct polyelectrolyte titration

Abstract

Abstract A novel technique is described for the investigation of polyanions by direct polyelectrolyte titration. In connection with a specially developed phototitrator, an extremely high sensitivity can be reached using 3,6‐ionene bromide as cationic titrant and eriochrome black T as metachromatic indicator for end‐point detection. This enables both the determination of charge densities for polymer characterization as well as the detection of polymers in aqueous solution down to trace concentrations of 10 μg/L. Monovalent salt ions do not interfere with the titration up to concentrations of about 0,1 mol/L. Potential interference of divalent metal ions can be prevented by adding ethylenediaminetetraacetic acid (EDTA) as chelating agent. The applicability of the method was proved by measuring charge densities of poly(sodium acrylate) (NaPAA) in the concentration range of 0,01 to 10 mg/L and of poly(potassium vinyl sulfate) (KPVS). As expected, the charge density of NaPAA decreases with a pH decrease from 11 to 7, whereas the charge density of KPVS is independent of pH.