Mass transfer in chromatographic columns studied by PFG NMR

Pulsed field gradient (PFG) nuclear magnetic resonance (NMR) is applied to study convective and diffusional transport in chromatographic columns packed with totally porous support particles. Here stagnant zones exist in the particle pores, and diffusional mass-transfer limitations between fluid molecules diffusing in the intraparticle pore network and flowing in the interparticle void space are detected quantitatively. Axial displacement probability distributions were measured for water over a range of Peclet numbers and observation times, with diffusion lengths between 0.15 and 0.91 times the average support particle diameter. The transition towards complete diffusional exchange is demonstrated, thereby also revealing the development of the classical convective dispersion process in a packed bed of (porous) particles.