High-performance liquid chromatography of amino acids, peptides and proteins. LXXXVIII. Calculation of the average distance between protein solutes and the stationary phase during isocratic anion-exchange chromatography

This investigation deals with protein retention behaviour in high-performance anion-exchange chromatography in terms of the average distance of approach between the protein solute and the positively charged anion-exchange stationary-phase surface. The theoretical treatment is based on a modified Debye-Hückel theory for spherical impenetrable ions, where the electrostatic potential energy has been related to the chromatographic capacity factor, k′. Results are presented for three globular proteins, eluted isocratically from a Mono-Q strong anion-exchange resin with sodium choride as the displacer salt by a mobile phase with pH in the range 5.50-9.60. Analysis of experimental retention data indicates that topographically predefined, charged regions on the protein surface, called ionotopes, control the orientation and approach distance of the protein solute.