Effect of hydrophobicity of marker anions on the sensitivity of end-point detection for potentiometric titrations of anionic polyelectrolytes

A potentiometric titration method is described for the determination of anionic polyelectrolytes using a marker anion and a plasticized poly (vinyl chloride) membrane electrode sensitive to this marker anion. A solution of an anionic polyelectrolyte, such as potassium poly (vinyl sulfate) (PVSK) added the marker ion has been titrated with a solution of poly (diallyldimethylammonium chloride) (Cat-floc). The end-point has been detected as a sharp potential change due to the rapid decrease in the concentration of the marker ion caused by its association with the titrant, Cat-floc. The sharpness of the endpoint of the titration curve has been compared for several marker ions and the dodecylbenzenesulfonate ion was found to be the best among the marker anions studied.