Jim Roach and colleagues, Weill Cornell Medical College, Qatar, have studied the performance of poly(4-vinylpyridine) (P4VP) in the polyelectrolyte-enhanced ultrafiltration of perchlorates.
Polyelectrolyte-enhanced ultrafiltration employs polyelectrolytes, such as P4VP, to electrostatically bind anionic contaminants in water. The colloid and contaminant are then filtered with an ultrafilter.

By using potentiometric titration data, the team showed that P4VP provided up to 95.8 % retention of perchlorate due to the greater affinity of perchlorate over chloride of its protonated pyridine residues. The ionization properties of P4VP were shown to depend on the titrant used, the degree of protonation, and concentration of counterion in the aqueous solution.

• Comparative study of the uses of poly(4-vinylpyridine) and poly(diallyldimethylammonium) chloride for the removal of perchlorate from aqueous solution by polyelectrolyte-enhanced ultrafiltration
  J. D. Roach, R. F. Lane, Y. Hussain,
  Water Res. 2010, 44.
  DOI: 10.1016/j.watres.2010.10.027