Assessing a photocured self-plasticised acrylic membrane recipe for Na + and K + ion selective electrodes

Abstract

A technique for the fabrication of solid-state ion sensors based on self-plasticising poly( n-butyl acrylate) matrix by photocuring is described. The poly( n-butyl acrylate) membrane was prepared by photocuring a mixture of the monomer n-butyl acrylate, cross-linker, 2-hexanedioldiacrylate and photoinitiator, 2,2-dimethoxy-2-phenylacetophenone under UV irradiation. The optimum composition of the membranes is discussed. The photocured films produced were elastic, tough and exhibited excellent adhesion on Ag/AgCl substrates. In the optimum recipe no inherent anionic site response was observed for the blank membrane, but AIBN produced anionic site impurities if used as initiator. By incorporating ionophores and lipophilic anions during photopolymerisation, ion-selective membranes could be formed in situ on Ag/AgCl substrates. Immobilisation of ionophore was also possible if a photopolymerisable ionophore such as 4-acryloylamidobenzo-15-crown-5 was included during the photocuring process. Solid-state potassium ion sensors (based on valinomycin or immobilised 4-acryloylamidobenzo-15-crown-5) and sodium ion sensor (based on bis[(12-crown-4)methyl]dodecylmethylmalonate) were fabricated using this technique. The potentiometric responses of all these solid-state ion sensors were comparable to the corresponding conventional plasticised poly(vinyl chloride) (PVC)-based ion-selective electrodes. The influence of the composition on the lower detection limit was discussed and preliminary studies of these sensors with artificial serum electrolytes indicated that the coextration of counter and interfering ions (rather than analyte buffering effects) predominated, raising the lower detection limit. Long term exposure in a complex media, e.g. real human blood serum resulted in a potential shift indicative of ion transport with full recovery of the sensor after 12 h. The overall manual fabrication reproducibility of the technique was satisfactory with sensors produced from the same batch demonstrated <5% variation in potentiometric performance.