A potentiometric titration method using a marker cation and a plasticized poly(vinyl chloride) membrane electrode sensitive to the marker cation is proposed for the determination of cationic polyelectrolytes. A sample solution of cationic polyelectrolyte, such as poly(diallyldimethylammonium) chloride added to a marker cation, such as a cationic surfactant, was titrated with a standard solution of anionic polyelectrolyte, potassium poly(vinyl sulfate) (PVSK). The end-point was detected as a sharp potential change due to an abrupt decrease in the concentration of the marker cation, caused by its association with PVSK. The sharpness of the titration curve at the equivalence point was compared for several marker cations and stearyltrimethylammonium ion was found to be the best, of the marker cations examined in this work.
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