Determination of electrokinetic charge with a particle-charge detector, and its relationship to the total charge

The main features of polyelectrolyte titrations with end-point indication by means of a particle-charge detector (PCD) were investigated. Because of their well-defined character, the charges of different synthetic polyelectrolytes and of latex samples with different functional groups were measured at different pH and ionic strength. The results show that PCD is a valuable tool for detecting effective or dissociated counterion charge without additional model assumptions. For negatively charged samples with exclusively strong acid functional groups, an excellent agreement was obtained between cation-exchange capacity and the charge measured by PCD over a wide pH range. For samples with additional carboxyl groups, the PCD charge was significantly lower than the total charge calculated from cation-exchange results. It can be concluded that counterion immobilization by a Stern layer-type arrangement is responsible for this effect.