A Photon Correlation Study of the Concentration Dependence of Macromolecular Diffusion

2000

Biotechnology Progress

Chromatographic data pertaining to the enantioseparation of L- and D-phenylalanine anilide (PA) on a polymeric stationary phase imprinted with L-PA were studied from the viewpoints of phase equilibrium, mass transfer kinetics, and the thermodynamic properties of this enantiomeric separation system. The concentration dependence of the lumped mass transfer rate coefficient (k(m,L)) previously published was analyzed to obtain new information concerning the mass transfer characteristics in this chiral separation system. It was shown that intraparticle diffusion contributed much more to k(m,L) than adsorption/desorption. The positive concentration dependence of k(m,L) seemed to be interpreted by considering that of the surface diffusion coefficient, itself explained by the heterogeneous surface model. The characteristic features of the phase equilibrium, the mass transfer kinetics, and the thermodynamics of the enantiomeric separation system probably result from the adsorption energy distribution on the surface of the imprinted phase having an exponential decay.

Section: Introductionsupporting

confidence: 53%

A Study of Mass Transfer Kinetics in an Enantiomeric Separation System Using a Polymeric Imprinted Stationary Phase

2000

Biotechnology Progress

“…The value of Dm for the two enantiomers was derived from Eq. (16). At the flow rate of 1 ml min -1 , the value of dp/(6kf) was found equal to 1.1 × 10 -2 s for the two enantiomers.…”

Section: Estimation Of Kfmentioning

confidence: 80%

“…10,11 In other previous publications, a concentration dependence was also confirmed for intraparticle diffusivity, 12 for tracer diffusivity, 13 for axial dispersion, 14 for effective diffusivity, 15 and for mutual diffusion coefficients. 16 Concentration dependences of the diffusivities and the mass transfer rate coefficients, km or km,L, seem to be a general conclusion. In previous papers, Knoxville, TN 37996-1600 USA and Division of Chemical and Analytical Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA Kinetic data previously acquired on the enantiomeric separation of L-and D-phenylalanine anilide (PA) on a polymeric stationary phase imprinted with L-PA were reinterpreted.…”

mentioning

confidence: 98%

“…The molecular diffusivity (Dm) was estimated by the Wilke-Chang equation. 6,25,26 Dm,s = 7.4 × 10 -8 (16) where the subscripts s and sv denote acetone and the solvent, respectively, αA is the association coefficient, M the molecular weight, h the viscosity, T the absolute temperature, and Vb the molar volume of the solvent at its normal boiling point. Other parameters in Eq.…”

Section: Estimation Of the Kinetic Parametersmentioning

confidence: 99%

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Kinetic Study of the Concentration Dependence of the Mass Transfer Rate Coefficient in Enantiomeric Separation on a Polymeric Imprinted Stationary Phase

2000

ANAL. SCI.

Molecular imprinting is a most attractive method of preparation of dedicated stationary phases for chromatography. Its use for enantioseparations is attracting considerable interest. 1,2 Imprinted materials can provide a very high selectivity for the objective compound, i.e., the imprinted molecule. [1][2][3][4][5] Although analytical applications are rapidly developing, the situation on the preparative front is less rosy. 1 Columns packed with imprinted stationary phases exhibit a poor efficiency and elution peaks are often unsymmetrical, especially for the more retained enantiomer. Sellergren et al. 1,2 suggested that the nonlinear behavior of the adsorption isotherm was the main cause of the broad and unsymmetrical bands observed for L-phenylalanine anilide (PA) on an L-PA imprinted chiral stationary phase. Although the possibility of a slow mass transfer kinetics was also pointed out, no detailed study supported this assumption. Yet, information on the mass transfer characteristics of imprinted stationary phases is necessary to clarify strategies for the improvement of these materials.Most kinetic studies in chromatography assume that four mass transfer processes are involved in a column, (1) axial dispersion, (2) fluid-to-particle mass transfer, (3) intraparticle diffusion, and (4) adsorption/desorption. 6 The contributions of these four processes to peak spreading are evaluated separately. Axial dispersion and the fluid-to-particle mass transfer resistance are inherent to flow processes through packed beds. They are well understood, relatively easy to control, and their contributions are often small. By contrast, intraparticle diffusion and adsorption/desorption give often larger contributions to the mass transfer resistance in the column. Their properties are intrinsic to each packing material and they are still often poorly understood. In order to evaluate the actual performance of packing materials, the characteristics of the mass transfer kinetics inside stationary phase particles must be clarified.Sajonz et al. 7 measured the adsorption equilibrium isotherm and the mass transfer kinetics of L-and D-PA on a polymeric stationary phase imprinted with L-PA, using a staircase frontal analysis method. The isotherm was well represented by either the Bi-Langmuir or the Freundlich models, but not by the simple Langmuir isotherm. The equilibrium data suggested that the distribution of the adsorption energy on the surface of the imprinted stationary phase is heterogeneous and showed that this phase has a high selectivity for the imprinted L-enantiomer. The lumped mass transfer rate coefficient (km,L) was calculated from each single breakthrough curve by applying the transport model of chromatography. 6 The values of km,L increased with increasing concentration of the enantiomers. The extent of the positive concentration dependence of km,L was larger for L-PA than for D-PA. It is expected that a more detailed analysis of the overall mass transfer rate parameter, km,L, could provide new, useful information and all...

“…The experimental data derived from breakthrough curves are fitted to the proper model of nonlinear chromatography, and a best value of the rate coefficient is identified. A number of recent studies have concluded to a strong positive dependence of this rate coefficient on the solute concentration (Al‐Duri and McKay, 1992; Friedrich et al, 1988; Gallagher and Woodward, 1989; Gibbs et al, 1991; Guan‐Sajonz et al, 1996; Lederer et al, 1990; Marlowe and Jackson, 1990; Rearden et al, 1998; Sajonz et al, 1997; Sajonz et al, 1998; Seidel‐Morgenstern et al, 1993). With relatively small molecules, this was reported for phenol and indole on carbon black (Friedrich et al .…”

Section: Introductionmentioning

confidence: 99%

Kinetic Study of the Concentration Dependence of the Mass Transfer Rate Coefficient in Anion-Exchange Chromatography of Bovine Serum Albumin

1999

Biotechnol. Prog.

The experimental results of a previous study of the mass transfer kinetics of bovine serum albumin (BSA) in ion-exchange chromatography under nonlinear conditions are reevaluated. The analysis of the concentration dependence of the lumped mass-transfer rate coefficient (k(m,L)) provides information on the kinetics of axial dispersion, fluid-to-particle mass transfer, intraparticle mass transfer, and adsorption/desorption. The new analysis shows that the contribution of intraparticle mass transfer is the dominant one. Similar to k(m,L), the surface diffusivity (D(s)) of BSA increases with increasing concentration. The linear concentration dependence of k(m,L) seems to originate in a similar dependence of D(s). The use of an heterogeneous-surface model for the anion-exchange resin provides an explanation of the positive concentration dependence of D(s). This work illustrates how frontal analysis data can be used for a detailed investigation of the kinetics of mass transfer between the phases of a chromatographic column, in addition to its conventional use in the determination of the thermodynamic characteristics of the phase equilibrium.