Figure 5.

Calculated composition of an ISE membrane based on ionophore 1 and 71 mol % ionic sites when exposed to 2 mM NH₄⁺ and a varying activity of K⁺, corresponding to the K⁺ response in a NH₄⁺ background shown in Figure 2: Membrane concentrations of (a) complexes between ionophore and K⁺ and NH₄⁺, and (b) free ionophore and free K⁺ and NH₄⁺ ions (note the logarithmic scale). All parameters used to calculate these concentrations are the same as for the fit of the EMF in a Cs⁺ background, as shown in Figure 3 (broken line) except for K_ex= 10^−0.55, K_NH4L =10^12.9 and K_NH4L2 = 10^7.0, which are specific to NH₄⁺.