A hydrogen ion-selective sensor based on non-plasticised methacrylic-acrylic membranes

A methacrylic-acrylic polymer was synthesised for use as a non-plasticised membrane for hydrogen ion-selective sensor incorporating tridodecylamine as an ionophore. The copolymer consisted of methyl methacrylate and n-butyl acrylate monomers in a ratio of 2:8. Characterisation of the copolymer using FTNMR demonstrated that the amount of each monomer incorporated during solution polymerisation was found to be similar to the amount used in the feed before polymerisation. The glass transition temperature of the copolymer determined by differential scanning calorimetry was -30.9degreesC. Potentiometric measurements conducted showed a linear pH response range of 4.3 - 9.6 with the response slope of 56.7 mV/decade. The selectivity of the sensors towards hydrogen ions was similar to other plasticiser based membrane electrodes and the logarithmic selectivity coefficients for discrimination against interference cations is close to -9.7. However, the incorporation of a lipophilic anion as membrane additive is essential in ensuring optimum performance of the hydrogen ion sensor.