MASS-TRANSFER IN CHROMATOGRAPHIC COLUMNS STUDIED BY PFG NMR

Pulsed field gradient (PFG) nuclear magnetic resonance (NMR) is applie d to study convective and diffusional transport in chromatographic col umns packed with totally porous support particles, Here stagnant zones exist in the particle pores;, and diffusional mass-transfer limitatio ns between fluid molecules diffusing in the intraparticle pore network and flowing in the interparticle void space are detected quantitative ly, Axial displacement probability distributions were measured for wat er over a range of Peclet numbers and observation times, with diffusio n lengths between 0.15 and 0.91 times the average support particle dia meter. The transition towards complete diffusional exchange is demonst rated, thereby also revealing the development of the classical convect ive dispersion process in a packed bed of (porous) particles. (C) 1998 Elsevier Science Inc.