A Ca2+ selective membrane electrode based on calcium-imprinted polymeric nanoparticles

Abstract

In this work, a Ca²⁺ selective PVC-membrane electrode, utilizing nano-sized Ca²⁺ imprinted polymers as the ionophore, was introduced. The imprinted polymer was prepared by precipitation polymerization in acetonitrile. Various types of commercially available functional monomers including methacrylic acid, acrylic acid and itaconic acid were tested for the synthesis of Ca²⁺-imprinted polymers. The networked polymers obtained were used as the ionophore of PVC membrane electrodes. The potentiometric responses of the electrodes, prepared using different imprinted polymers, showed that the type of functional monomers used had a crucial effect on the analytical characteristics of the related membrane electrode. The membrane electrode composed of itaconic acid based imprinted polymers showed better Nernstian slope and particularly better selectivity for Ca²⁺ determination. The effectiveness of itaconic acid for complex formation with Ca²⁺, in comparison to two other monomers (methacrylic acid and acrylic acid), was demonstrated by density functional theory-based calculations. The type of cross-linker agent had a definitive role in the performance of the related electrode. Divinyl benzene based imprinted polymers led to an electrode with no significant sensitivity for Ca²⁺; whereas, the utilization of ethylene glycol dimethacrylate led to a sensor with ideally Nernstian response. Other components of the membrane such as the plasticizer and ionic additive as well as the solution pH were evaluated and appropriate conditions were selected. The electrode showed a response time of 10 s with no memory effect. A dynamic linear range of 1 × 10⁻⁶–1 × 10⁻¹ mol L⁻¹, a Nernstian slope of 30.3 (±0.4) mV decade⁻¹ and a detection limit of 7.5 × 10⁻⁷ mol L⁻¹ were obtained for the electrode. The utility of the electrode was checked by its use as an indicator electrode in the determination of Ca²⁺ ions via complexometric titration by EDTA.