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Isotachophoresis with counterflow in an open capillary: computer simulation and experimental validation
Bingwen Liu1, Cornelius F Ivory
1The Gene and Linda Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164-2710, USA.
Journal of Separation Science
|April 6, 2013
Summary
Countercurrent flow in isotachophoresis (ITP) can extend separation but causes dispersion. Analyte diffusivity significantly impacts zone broadening, with less diffusive analytes experiencing greater dispersion in stationary counterflow ITP.
Area of Science:
- Analytical Chemistry
- Separation Science
- Biophysics
Background:
- Countercurrent flow enhances separation channel length in isotachophoresis (ITP).
- However, counterflow can induce significant dispersion, potentially limiting ITP efficiency.
- Understanding and mitigating this dispersion is crucial for optimizing ITP applications.
Purpose of the Study:
- To investigate dispersion induced by parabolic counterflow in open-capillary ITP.
- To analyze the relationship between analyte molecular diffusivity and dispersion.
- To evaluate the applicability of the Taylor-Aris dispersion formula in counterflow ITP.
Main Methods:
- Numerical simulations in a 2D axisymmetric domain.
- Generation of stationary ITP zones using back pressure.
- Experimental validation using coated silica capillaries to eliminate electroosmosis.
Main Results:
- Analyte dispersion in stationary counterflow ITP is strongly dependent on molecular diffusivity.
- R-phycoerythrin (low diffusivity) showed a ~20-fold zone width increase, while fluorescein (higher diffusivity) showed only ~10%.
- The Taylor-Aris dispersion formula provided only a rough estimate, often overestimating analyte zone widths.
Conclusions:
- Analyte molecular diffusivity is a critical factor governing dispersion in counterflow ITP.
- Stationary counterflow ITP can significantly increase zone broadening, particularly for low-diffusivity analytes.
- Numerical simulations show good qualitative agreement with experimental results, validating the model.
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