Here, “aq” denotes either the donor (a1) or acceptor (a2) phase, R+ is the quaternary ammonium ion of Aliquat 336, and X− is the counter-transporting anion which is usually Cl− or OH−. If the equilibrium constants on both sides of the organic layer are equal (ignoring any non-ideal behavior and osmosis through the organic phase) and if the concentrations of the complexes at both of the interfaces are identical, i.e., [RX(o1)] = [RX(o2)], [RA(o1)] = [RA(o2)], and [RXHA(o1)] = [RXHA(o2)], where “o1” and “o2” denote the interfacial regions of the organic phase in the donor and acceptor sides, respectively. The concentration ratios of the arsenic compounds are then as follows [37]