Indirect potentiometric determination of polyquaternium polymer concentrations by equilibrium binding to 1-dodecyl sulfate

Polyquaternium polymers are polycationic polymers that are contained in many hair shampoos and conditioners and are also often added to water to remove organic and inorganic anions by floc formation. While polyquaternium analysis is not trivial, electroanalytical methods have been proposed for their detection using either irreversible emf responses or reversible potential-driven extraction into and out of polymeric sensing membranes. We present here an alternative technique for the determination of a representative polyquaternium polymer, poly(dimethylamine-co-epichlorohydrin) chloride, by equilibrium binding with a singly charged anionic surfactant, 1-dodecyl sulfate. Binding of an anionic surfactant to the polyquaternium polymer simplifies electrochemical detection as the concentration of unbound surfactant can be monitored using the equilibrium Nernstian emf response of ion-exchanger membranes. The latter can be used to determine the nature of the binding interaction and allows for the straightforward determination of polyquaternium polymer concentrations by titration.