Influence of hydrophobicity on the ion exchange selectivity coefficients for aromatic amines

Hydrophobic effects could play an important role in determining the selectivity of organic ions for ion‐exchange resins in aqueous solutions. We used the octanol–water partition coefficient (P) and the chromatographic capacity factor (k′) as indices of hydrophobicity of a series of primary and secondary amines, and examined their relationships with the amine selectivity coefficient (K) in binding to the Amberlite IRP‐69 ion‐exchange resin. Good correlations were found between log K versus log P and log K versus log k′, but the relationship appears to be dependent on the degree of substitution at the amino nitrogen. These relationships may be useful for the estimation of selectivity coefficients of various amine drug candidates when they are considered for incorporation with ion‐exchange resins in potential controlled‐release systems.