Mass-transfer properties of insulin on core–shell and fully porous stationary phases

• There is no significant difference between the different columns in respect of the intraparticle diffusion coefficients.
• Surface diffusion has a crucial role in the intraparticle movement of the macromolecules.
• Pore diffusion is at least one order of magnitude slower than surface diffusion.
• The average sojourn times in the stationary phase of the core–shell packed columns are at least the half of those of the fully porous particles.

The mass-transfer properties of three superficially-porous packing materials, with 2.6 and 3.6 μm particle and 1.9, 2.6, and 3.2 μm inner core diameter, respectively, were investigated and compared with those of fully porous packings with similar particle properties. Several sources of band spreading in the chromatographic bed have been identified and studied according to the general rate model of chromatography. Besides the axial dispersion in the stream of the mobile phase, and the external mass transfer resistance, the intraparticle diffusion was studied in depth. The first absolute and the second central moments of the peaks of human insulin, over a wide range of mobile phase velocities were measured and used for the calculation of the mass-transfer coefficients. The experimental data were also analyzed using the stochastic or molecular dynamic model of Giddings and Eyring. The dissimilarities of the mass-transfer observed in the different columns were identified and evaluated.