Organic ammonium ion selective electrodes based on 18-crown-6-phosphotungstic acid precipitates

Organic ammonium(I) ion selective PVC membrane electrodes based on crown ether-phosphotungstic acid (PW) precipitates, e.g. 18-crown-6-PW, dibenzo-18-crown-6-PW, 15-crown-5-PW, monobenzo-15-crown-5-PW and 12-crown-4-PW, as neutral carriers were developed. Among these crown ether electrodes, the electrodes based on 18-crown-6-PW gave the best performance and exhibited good linear responses with near-Nerstian slopes (ca. 55–63 mV decade−1) for organic ammonium ions, e.g. BuNH3+, C6H5CH2NH3+, Et2NH2+ and Et3NH+, within the concentration range 10−1 - 10−5 M. The electrodes based on 18-crown-6-PW exhibited good selectivity for organic ammonium ions relative to ammonium ion (NH4+), alkali, alkaline earth and some transition metal ions. The electrode performance also depends on the pH of the best solution and the optimum pH range was about ca. 2–6. The effects of concentrations of internal solutions in the electrodes and the composition of electrode membranes were investigated.