Comparing the oxidation potential of the main peak for the different anions with their standard transfer potentials, ∆ W NOP 𝜙 𝑖 , shows that the transfer of SO4 2-and especially F -are strongly facilitated (Fig. ). Here, the transfer potentials from water to NOP were taken from our previous publication based on the l'Her method for determining Gibbs transfer energies. The value for SO4 2-was extrapolated based on the Born equation with the ion radius taken from Marcus. We also tried to use the parts of the receptor as ionophores at the TPE (Fig. ). Without the crown ether, i.e. for 5FSQB, no ion transfer was seen for SO4 2-, while for F -the slope is only 23 mV per decade. This shows that the electron-withdrawing property of the crown entity is crucial to improving the anion-binding ability of the ionophore (Table Given the importance of the cation binding domain, we also investigated the effect of ions other than potassium (Fig. ). According to the DFT calculations a trend of decreasing oxidation potentials was expected when going down in the periodic table with cations, but also a decreasing affinity to the anion from lithium to sodium and potassium (Table ). However, experimentally, there is very little difference between the peak potentials for SO4 2- with different cations (K + , Na + , NH4 + , Mg 2+ ) and the slopes vs concentrations are also the same. The main difference is that the linear range for K + is slightly wider than for other ions (Fig. ). For F -the situation is different. Here, Li + (not tested for sulphate) is not associated with any anion transfer -the slope of Ep vs 𝑐 F -is zero (Fig. ). This is presumed to be due to weak lithium-crown ether complexation. The ejection of the cation is more beneficial to the system than the transfer of the fluoride ion from the aqueous to the organic phase.