Electrochemistry of solutions in liquid ammonia. Part VII. The use of glass electrodes for ammonium and sodium cations as ion-selective sensors at −40 °C

The behavior of Li/La glass electrodes as specific ion sensors for NH ₄ ⁺ and Na⁺ cations in liquid ammonia solutions at –40°C has been assessed using concentration cells with transference. The measurement of emf's of cells with very high resistances due to glass at –40°C has been overcome partly by the use of thinly blown Li/La glass and mainly through the design and use of a floating shield emf measuring system. For solutions of NH₄NO₃, NH₄I, NH₄BF₄, and NH₄Cl almost linear pNH₄ vs. emf responses were observed between pNH₄ 0 and 5; for NH₄NO₃ solutions the slope (40±1 mV/pNH₄) was invariant for substantial increases in Na⁺ concentrations. Solutions of NaNO₃, NaCN, NaClO₄, NaNCS, NaN₃, and NaNO₂ gave almost linear pNa vs. emf responses but the slopes were markedly dependent upon the NH ₄ ⁺ concentration. Estimates of the mean molal ion activity coefficients for nitrate solutions were obtained from earlier transference data: ±(NaNO₃)=0.14±0.02 and ±(NH₄NO₃)=0.30±0.03 at 10^– molal concentration in fair agreement with earlier data.