The measurement and meaning of void volumes in reversed-phase liquid chromatography.

Pulsed field gradient nuclear magnetic resonance (PFGNMR) allows the direct determination of the average value of the axial and transverse apparent dispersion coefficient in a packed bed over a certain volume of this bed. From these data, the dependence of the local value of the height equivalent to a theoretical plate (HETP) of a chromatographic column on the fluid velocity can be measured accurately. The results are shown to be exactly accounted for by the Giddings equation. The PFGNMR measurements are made over a very short period of time. Hence they give the value of the HETP averaged over a limited volume of packing and a short time. This value is markedly smaller than the one afforded by the classical methods of chromatography and which is derived from the width of the distribution of the residence time of a small sample. The difference is explained by systematic variations of the local mobile-phase velocity across the column. PFGNMR techniques also allow the determination of the tortuosity of the c...

Study of Dispersion in Packed Chromatographic Columns by Pulsed Field Gradient Nuclear Magnetic Resonance

Measurement and modeling of the equilibrium behavior of the Tröger's base enantiomers on an amylose-based chiral stationary phase.

This work presents a comprehensive insight about simulated moving bed (SMB) technology, from concept to unit operation and process demonstration. A particular relevance is given to SMB nonconventional modes of operation, modeling, and design of SMB-based separations as well as to the construction and operation of SMB units. A conventional separation of a racemic mixture of (S,R)-α-tetralol by means of the FlexSMB-LSRE® unit is addressed to better exemplify a state-of-the-art SMB lab-scale process development and demonstration.

Charles R. Foster

Papers

On the reproducibility of column performance in liquid chromatography and the role of the packing density