Perfusive flow and intraparticle distribution of a neutral analyte in capillary electrochromatography

Abstract

The relevance and magnitude of an electroosmotic perfusion mechanism in electrochromatography is analyzed. To systemize our studies we first considered the transport of an electroneutral and nonadsorbing tracer. Based on the refractive index matching in a microfluidic setup containing fixed spherical porous particles, we conducted a quantitative analysis in real time of the spatio-temporal distribution of fluorescent tracer molecules during their uptake by (and a release from) single particles using confocal laser scanning microscopy. Even under conditions of a significant electrical double layer overlap the intraparticle electroosmotic flow produces due to its unidirectional nature and in striking contrast to the symmetric (spherical) distributions typical for purely diffusive transport strongly asymmetric concentration profiles inside spherical particles as the locally charged pore liquid begins to respond to the externally applied electrical field. The profiles retain an axisymmetric nature, i.e., rotational symmetry with respect to the field direction. Results of our measurements could be successfully interpreted and further analyzed by a compact mathematical model. Intraparticle Peclet numbers of up to 150 have been realized and found to significantly enhance the mass transport on particle scale towards the convection-dominated regime when compared to a conventional (diffusion-limited) kinetics.

Protein Mass Transfer Kinetics in Ion Exchange Media: Measurements and Interpretations

“…For example, the model of Dziennik et al [51], while producing a slight overshoot in the pore fluid protein concentration, did not yield an overshoot in the adsorbed concentration, which would by far dominate the observable behavior. The model of Liapis et al [52] resulted in adsorbed concentration overshoots. However, as pointed out by Dziennik et al, this model was based on diffusivity and isotherm parameters that were unrealistic for the experimental system for which overshoots have been observed.…”

“…Other authors [48±51] have extended the technique to different proteins and to multicomponent systems. While these measurements have generally been limited to optically transparent particles, extensions to opaque matrices may be possible by refractive index matching of mobile and stationary phases following the work of Tallarek et al [52]. In general, CLSM can provide optical sections of fluorescence intensity in real time.…”

Dynamics of Capillary Electrochromatography: Experimental Study of Flow and Transport in Particulate Beds

“…In this respect, selective techniques like spectroscopic imaging methods, which allow for a focus on particular mechanical or nonmechanical contributions to dispersion, are promising approaches in resolving combined kinetics and thermodynamics [55,80,117± 120]. For example, by using quantitative confocal laser scanning microscopy in combination with a microfluidic device it has been visualized that electrokinetic species transport through a fixed bed of spheres produces, in striking contrast to the symmetric-spherical distributions observed for diffusion-limited operations, pronounced asymmetric intraparticle concentration profiles caused by the unidirectional nature of electroosmosis and electrophoresis [119,120]. Quantitative image analysis permitted a direct determination of the velocities of intraparticle EOF and electrophoretic migration.…”

Protein adsorption‐dependent electro‐kinetic pore flow: Modeling of ion‐exchange electrochromatography with an oscillatory transverse electric field

“…Figure 2 illustrates the coordinates for a single bead in the pIEEC in the Cartesian coordinates. The three-dimensional problem for the particle can be simplified to a twodimensional form because protein concentration is rotationally symmetric to the x-axis (EF direction) [13]. So, for any fixed position in the column, the partial differential equation for protein distribution in a particle can be deduced by mass conservation as (all symbols are listed in the Appendix),…”

“…The retention difference of solutes in SEC processes was considered due to EP, EOF and concentration polarization (CP) [1]. Tallarek et al [12,13] quantitatively studied the electro-kinetic transport in single porous media (no solute binding) by confocal laser scanning microscopy. They showed pictures of intraparticle excursion profiles of protein in the presence of EF, and obtained consistent modeling results for neutral analyte intraparticle distribution with those with perfusive flow driven by pressure [14].…”