Structural Properties Governing Retention Mechanisms on Immobilized Artificial Membrane (IAM) HPLC Columns

The aims of this study were to investigate whether three commercially available immobilized artificial membrane (IAM) HPLC columns yield collinear data for neutral compounds, and whether IAM scales are distinct from the log Poct (partition coefficient in the octanol/H2O system) scale. With these objectives, the retention mechanisms on the IAM HPLC columns were analysed by linear solvation free-energy relationships (LSERs). A set of 68 neutral model compounds with known solvatochromic parameters and log Poct values was investigated, allowing a regular and broad exploration of property space. The resulting solvatochromic equations clearly indicate that the three IAM stationary phases retain small neutral solutes by a balance of intermolecular forces closely resembling those underlying partitioning in octanol/H2O and retention on a reversed-phase LC-ABZ HPLC column. For all systems, the solute's size and hydrogen-bond-acceptor basicity are the two predominant factors, whereas dipolarity/polarisability and hydrogen-bond-donor acidity play only minor roles.