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  • 1 Charles University Faculty of Education 11639 Prague 1 Czech Republic
  • 2 Prague Institute of Chemical Technology Department of Analytical Chemistry 166 28 Prague 6 Czech Republic
  • 3 Kremlickova 964 280 00 Kolín II Czech Republic
  • 4 341 42 Kolinec 250 Czech Republic
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From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium M+(aq)+NaL+(nb)⇄ML+(nb)+Na+(aq) taking place in the two-phase water-nitrobenzene system (M+=Li+, K+, Rb+, Cs+; L=18-crown-6; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. The stability constants of the ML+ complexes in nitrobenzene saturated with water were calculated; they are found to increase in the cation order Cs+Li+Na+Rb+K+. Further, the individual extraction constants for the NaL+, KL+, RbL+ and CsL+ complex species in the wate-nitrobenzene system were determined; their values increase in the series Na+Rb+Cs+K+.