Figure 2.

Experimental estimates of selectivity free energy, $\Delta \Delta G=\Delta G_{\text{K}\to \text{Na}}-\Delta G_{\text{K}\to \text{Na}}^{\text{bulk}},$ for different organic solvents with respect to bulk liquid water (Cox and Parker, 1973; Marcus, 1983; Schmid et al., 2000; Yu et al., 2010a). For these estimates, $G_{\text{X}}={(\partial G/\partial n_{\text{X}})}_{T,P}$ is the partial molar Gibbs free energy for ion X in the specified medium relative to an ideal standard state, so that ΔG vanishes when ion–medium interactions vanish.