Ion-Transfer Polarographic Study on the Lithium Ion Selectivity against Sodium Ion of Bis(8-quinolyloxy)propane Derivatives and Dibenzyl-14-crown-4 at Aqueous/Nitrobenzene Solution Interface

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Lithium and sodium ion transfers from water (w) to nitrobenzene (NB) phase containing Li⁺-selective neutral carriers (L), three bis(8-quinolyloxy)propane derivatives and dibenzyl-14-crown-4 (DBz14C4), were studied by ion-transfer polarograph at 25°C. The logarithmic values of potentiometric selectivity coefficients were obtained by the relation log k^pot_LiNa=(F/2.3RT)(Δφ^o_Li/LiL-Δφ^o_Na/NaL), where Δφ^o_Ma/ML (M=Li and Na) denotes the formal potential of the process M⁺(w-phase)+L(NB-phase)_ML⁺(NB-phase). They were -2.1 for DBz14C4 and -1.₆-1.₂ for bis(8-quinolyloxy)propane derivatives. The stability constants (mol^-1 dm³) of the 1:1 complexes for Li⁺ and Na⁺ in the NB-phase were also obtained from the metal ion-concentration dependence of the half-wave potentials. The Li⁺ selectivity of each carrier L against Na⁺ was discussed in terms of the values of Δφ^oo′_Li/LiL and Δφ^oo′_Na/NaL.