Theoretical studies in high-performance liquid chromatography

Abstract

The various modes of chromatography, particularly liquid chromatography are discussed. Various theories of band broadening in chromatography are described, and equationssuitable for testing against experimental data are devised. In order to facilitate the interpretation of experimental data, diffusion coefficients for a number of solute /eluent pairswere measured directly by the chromatographic broadening technique using glass capillary tubing and HPLC detection technology.

Band broadening by axial diffusion was examined by the interrupted flow technique This enabled determination of the obstructive factor for both excluded and retained solutes. The relative rate of diffusion in the stationary phase was also obtained frc these experiments.

Band broadening by slow mass transfer was examined by determining plate heights using large (50 - 540um) particles and high reduced velocities. Although it was not possible to ignore flow effects in this experiment, reasonable assumptions bring the experimental data into the range predicted by the non -equilibrium theory. The retention dependence of the data was also in agreement with this theory.

In a completely different vein, a computer model was developed to investigate the mechanism of size -exclusion chromatography. This model consisted of randoe, -sized touching non -overlapping spheres. Although the model did not adequately fit the results, this was probably due to differences in porosity and pore-size distribution than to any effect of pore shape. Pore shape was not found to be critical in these studies.

An alternative model consisted of cylindrical pores whose radii were determined by the pore-size distribution of the material in question. Initial results were encouraging, and better data may lead to a good model for SEC.