ORGANIC AMMONIUM ION-SELECTIVE ELECTRODES BASED ON 18-CROWN-6-PHOSPHOTUNGSTIC ACID PRECIPITATES

Organic ammonium(I) ion selective PVC membrane electrodes based on cro wn ether-phosphotungstic acid (PW) precipitates, e.g. 18-crown-6-PW, d ibenzo-18-crown-6-PW, 15-crown-5-PW, monobenzo-15-crown-5-PW and 12-cr own-4-PW, as neutral carriers were developed. Among these crown ether electrodes, the electrodes based on 18-crown-6-PW gave the best perfor mance and exhibited good linear responses with near-Nernstian slopes ( ca. 55-63 mV decade(-1)) for organic ammonium ions, e.g. BuNH(3)(+), C 6H5CH2NH3+, Et(2)NH(2)(+) and Et(3)NH(+), within the concentration ran ge 10(-1)-10(-5) M. The electrodes based on 18-crown-6-PW exhibited go od selectivity for organic ammonium ions relative to ammonium ion (NH4 +); alkali, alkaline earth and some transition metal ions. The electro de performance also depends on the pH of the test solution and the opt imum pH range was about ca. 2-6. The effects of concentrations of inte rnal solutions in the electrodes and the composition of electrode memb ranes were investigated.