Biomedical subjects

David T Leighton

Publications and source records attributed to David T Leighton.

3 recordsLinked to original sources

PubMed2003

Dispersion reduction in open-channel liquid electrochromatographic columns via pressure-driven back flow.

Application of electrokinetic forces to drive the mobile phase diminishes analyte dispersion in open-channel liquid chromatographic columns due to minimization of shear in the flow field. However, the retentive layer coating the inner walls of such devices slows down the average convective velocity of solute molecules in its vicinity, inherently causing dispersion of analyte bands. In this article, we explore the possibility of reducing such dispersion in electrochromatographic columns by imposing a pressure-driven back flow in the system. Analysis shows that although such a strategy introduces shear in the flow field, the overall dispersion in the mobile phase is reduced. This occurs as the streamline velocity in such a system is greater near the channel walls than that in the center of the conduit, thereby allowing fluid dispersion to counteract wall retention effects. For an optimally chosen magnitude of the back flow, hydrodynamic dispersion of any target species in the mobile phase may be shown to diminish by a factor of 3 and 10/3 in a circular tube and a parallel-plate geometry, respectively. A similar reduction in slug dispersion is also realized in rectangular conduits for all aspect ratios. In trapezoidal geometries with large wedge angles or isotropically etched profiles, this reduction factor may attain values of 10 or greater.

Algorithms↗

PubMed2003

Dispersion in large aspect ratio microchannels for open-channel liquid chromatography.

Solute dispersion in open-channel liquid chromatography is often dominated by transverse diffusion limitations in the mobile phase (Martin, M.; Guiochon, G. Anal. Chem. 1984, 56, 614-620) convecting the solute species. While such dispersion is known to scale with the square of the Peclet number based on the narrower dimension of the conduit, the proportionality constant may significantly vary with the aspect ratio of the channel geometry. In this article, we investigate the effect of channel sidewalls on axial dispersion in electrokinetically and pressure-driven chromatographic systems. The analysis presented here clearly identifies the contribution from flow, wall retention, and the interaction between the two to the overall slug dispersion in the mobile phase for any arbitrary channel geometry. The particular geometries that have been investigated in this work, however, are the rectangular and the isotropically etched profiles often employed in microanalysis systems. Further, the effectiveness of simple double-etched profiles proposed elsewhere (Dutta, D.; Leighton, D. T. Anal. Chem. 2001, 73, 504-513) to diminish the effect of channel sidewalls on Taylor-Aris dispersion has also been examined. Analysis shows that dispersion arising due to shear and wall retention, as well as the interaction between the two, may be significantly reduced in large aspect ratio microchannels for optimized channel geometries.

Journal Article↗

PubMed2002

A low dispersion geometry for microchip separation devices.

Curved channel geometries introduced on microchip separation devices to achieve greater separation distances often lead to large analyte dispersion, degrading the performance of these systems. While such electrokinetic dispersion may be minimized by reducing the channel width around the curved region, alternative strategies involving larger channel curvatures may be promising as well, depending on the application. For example, Culbertson et al. (Anal. Chem. 2000, 72, 5814-5819) recently demonstrated the effectiveness of gentle spiral geometries in carrying out separations of small molecules. For moderate and large Peclet number systems, however, larger spiral geometries are necessary to diminish electrokinetic dispersion of solute slugs which may not conform to the needs of the microchip format. In this work, we investigate a modified spiral geometry with a wavy wall along the inner track of the channel. Analysis shows that such width profiling may significantly improve the performance of the spiral geometry, making the design effective for larger Peclet number or smaller radii systems. Numerical simulations performed to optimize these modified spirals suggest equating transit times along the inner and the outer track of the channel as a useful design criterion for minimizing electrokinetic dispersion. An analytical model has been formulated to derive the optimal channel parameters based on this criteria which compares well with the simulation results.

Journal Article↗