title: Modeling pH-zone refining countercurrent chromatography: a dynamic approach.
abstract: A model based on mass transfer resistances and acid-base equilibriums at the liquid-liquid interface was developed for the pH-zone refining mode when it is used in countercurrent chromatography (CCC). The binary separation of catharanthine and vindoline, two alkaloids used as starting material for the semi-synthesis of chemotherapy drugs, was chosen for the model validation. Toluene/CH3CN/water (4/1/5, v/v/v) was selected as biphasic solvent system. First, hydrodynamics and mass transfer were studied by using chemical tracers. Trypan blue only present in the aqueous phase allowed the determination of the parameters τextra and Pe for hydrodynamic characterization whereas acetone, which partitioned between the two phases, allowed the determination of the transfer parameter k0a. It was shown that mass transfer was improved by increasing both flow rate and rotational speed, which is consistent with the observed mobile phase dispersion. Then, the different transfer parameters of the model (i.e. the local transfer coefficient for the different species involved in the process) were determined by fitting experimental concentration profiles. The model accurately predicted both equilibrium and dynamics factors (i.e. local mass transfer coefficients and acid-base equilibrium constant) variation with the CCC operating conditions (cell number, flow rate, rotational speed and thus stationary phase retention). The initial hypotheses (the acid-base reactions occurs instantaneously at the interface and the process is mainly governed by mass transfer) are thus validated. Finally, the model was used as a tool for catharanthine and vindoline separation prediction in the whole experimental domain that corresponded to a flow rate between 20 and 60 mL/min and rotational speeds from 900 and 2100 rotation per minutes.
authors: GEPEA UMR CNRS 6144, 37 boulevard de l'Université, 44602 Saint-Nazaire, France.
authors: Alexis
authors: A
authors: Kotland
authors: ICMR, UMR CNRS 7312, Campus Moulin de la Housse BP 1039, 51687 Reims, France.
authors: Sébastien
authors: S
authors: Chollet
authors: Laboratoires Pierre Fabre, route de Viars, 81600 Gaillac, France.
authors: Jean-Marie
authors: JM
authors: Autret
authors: Laboratoires Pierre Fabre, route de Viars, 81600 Gaillac, France.
authors: Catherine
authors: C
authors: Diard
authors: GEPEA UMR CNRS 6144, 37 boulevard de l'Université, 44602 Saint-Nazaire, France. Electronic address: luc.marchal@univ-nantes.fr.
authors: Luc
authors: L
authors: Marchal
authors: ICMR, UMR CNRS 7312, Campus Moulin de la Housse BP 1039, 51687 Reims, France.
authors: Jean-Hugues
authors: JH
authors: Renault
mesh_terms: D003377:Countercurrent Distribution / Q000379:methods*; D057446:Hydrodynamics; D006863:Hydrogen-Ion Concentration; D012997:Solvents; D014747:Vinblastine / Q000031:analogs & derivatives / Q000302:isolation & purification; D014748:Vinca Alkaloids / Q000302:isolation & purification
chemical_list: D012997:Solvents; D014748:Vinca Alkaloids; C009667:vindoline; D014747:Vinblastine; C017836:catharanthine
keywords: Alkaloids; Displacement chromatography; Hydrodynamics; Hydrostatic countercurrent chromatography; Modeling; pH-zone refining