Tailoring the surface of a polymeric membrane with a thin-layer Nafion membrane: Construction of an anti-surfactant solid-contact ion-selective electrode

Surfactants are a type of amphiphilic chemicals that comprise both hydrophilic and hydrophobic regions, and the presence of surfactants would bring a detrimental effect on the potential responses of the solid-contact ion-selective electrodes induced by their extraction from the aqueous solution into the polymeric membrane phase. Herein, an anti-surfactant solid-contact Ca 2+ -selective electrode is proposed based on tailoring the surface of the polymeric membrane with the thin-layer Nafion membrane. The extraction of surfactants into the polymeric membrane can be eliminated through using the hydrophobic group of Nafion acting as “a polymer brush”, while the Ca 2+ diffusion from the aqueous solution to the membrane phase is promoted by the hydrophilic group of Nafion based on the electrostatic interaction. The Nafion-functionalized solid-contact Ca 2+ -ISE shows an improved potential stability and an excellent potentiometric performance for detection of Ca 2+ in the presence of cationic and anionic surfactants as compared to the traditional solid-contact Ca 2+ -ISE. Moreover, the anti-surfactant solid-contact ion-selective electrode is feasible for in situ measurement of Ca 2+ at the interface between the seawater and the sediment. This work provides a general and facile strategy to eliminate the interferences of surfactants during the potentiometric measurements, and is favorable for in situ, on-site measurement with high accuracy and precision in the aquatic environment.