Measurement of intraparticle diffusion in reversed phase liquid chromatography

The intraparticle diffusion coefficient was measured using a method based on the fitting of a set of experimental chromatographic profiles to the lumped pore diffusion model. For this purpose, both the analytical solution of the model in the Laplace domain and a numerical method were used. There was an excellent agreement between the results given by the two methods. These results are compared to those obtained by moment analysis of the same set of chromatographic profiles and by the determination of the intraparticle diffusion coefficient from the second central moment of these bands. Nearly identical results were obtained with these two independent methods. The values of the intraparticle diffusion coefficient, D, for rubrene in pure methanol was found to be 7.89 x 10(-7) cm(2)/s by the modeling method and 7.23 x 10(-7) cm(2)/s by the moment analysis method. These values increase with increasing water concentration, to 1.10 x 10(-6) and 1.24 x 10(-6) cm(2)/s, respectively, in a 96:4 v/v methanol/water solution and to 1.63 x 10(-6) and 2.38 x 10(-6) cm(2)/s, respectively, in a 90:10 v/v solution. These results confirm the validity and the consistency of the lumped pore model and the moment analysis theory. They show that both approaches describe correctly the mass transfer kinetics in the particles of packing material during the chromatographic process. Systematic determinations of the intraparticle diffusion coefficient can now be undertaken and the influence of various experimental parameters on this important property of packing materials can be investigated. (C) 2004 Elsevier Ltd. All rights reserved.