Sodium permanganate, sodium picrate (NaPic), Bu
4NPic, Me
4NPic, and Et
4NPic were extracted at an ionic strength of 2 × 10
−5 to 0.08 mol dm
−3 and 25°C from water (w)-phases into the organic (o)-ones, 1,2-dichloroethane (DCE) and nitrobenzene (NB). Thereby, apparent distribution constants (
KD,±) of the anions (A
−) or the cations (M
+) and ion-pair formation ones (
KMAorg) of the univalent salts (MA) in the o-phases were determined at 25°C, where
KD,± = ([A
−]
o[M
+]
o/[A
−][M
+])
1/2 = (
KD,AKD,M)
1/2 and
KMAorg = [MA]
o/[M
+]
o[A
−]
o. Also, the
Kex and
KD,MA values with A
− = Pic
−, MnO
4− were estimated from the relations
Kex (= [MA]
o/[M
+][A
−]) =
KMAorg(
KD,±)
2 and =
KMAKD,MA, respectively. Standard potentials (Δφ
tr0) for ion transfers at the w/DCE and w/NB interfaces were evaluated from the log
KD,A or log
KD,M values by assuming the relations
KD,Pic =
KD,Et4N and =
KD,Me4N, respectively. The thus-obtained Δφ
tr0 values, especially for the w/DCE system, were in good agreement with the values based on the extra-thermodynamic assumption for Ph
4As
+ and BPh
4− transfers at the interfaces. In the present extraction systems, the ion-pair formation of MA in the w- and o-phases was less effective in the determination of their distribution constants into the two o-phases.
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