Chemical apparatus and process disinfecting – deodorizing – preser – Control element responsive to a sensed operating condition
Reexamination Certificate
2000-11-06
2004-05-11
Noguerola, Alex (Department: 1753)
Chemical apparatus and process disinfecting, deodorizing, preser
Control element responsive to a sensed operating condition
C422S070000, C422S129000, C422S050000, C422S081000, C204S601000
Reexamination Certificate
active
06733730
ABSTRACT:
FIELD OF THE INVENTION
Microfiche Appendix
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References
The following publications are cited in this application as superscript numbers:
1
Kopf-Sill, A. R. and J. W. Parce, “Microfluidic Systems Incorporating Varied Channel Dimensions,” U.S. Pat. No. 5,842,787 (1998).
2
Nordman, E. S., “Method and Apparatus for Reducing the Distortion of a Sample Zone Eluting from a Capillary Electrophoresis Capillary,” U.S. patent application Ser. No. 5,833,826 (1998).
3
Culbertson, C. T., Jacobson, S. C., and J. M. Ramsey, “Dispersion Sources for Compact Geometries on Microchips,” Analytical Chemistry, 70 (18) 3781-3789 (1998).
4
Giddings, J. C., “Coiled Columns and Resolution in Gas Chromatography”, Journal of Chromatography 3, 520-533 (1960).
5
Jacobson, S. C., et al., “Effects of Injection Schemes and Column Geometry on the Performance of Microchip Electrophoresis Devices,” Analytical Chemistry 66 (7) 1107-1113 (1994).
6
Kasicka, V., et al., “Contribution of Capillary Coiling to Zone Dispersion in Capillary Zone Electrophoresis,” Electrophoresis 16, 2034-2038 (1995).
7
Nilson, R. H. and S. K. Griffiths, “Wormhole Growth in Soluble Porous Materials,” Physical Review Letters, 65, 1583-1586 (1990).
8
Wilson, R. H. and Y. G. Tseui “Free Boundary Problem of Electrochemical Machining by Alternating Field Technique on Inverted Plane,” Journal of Computer Methods in Applied Mathematics and Engineering, 6 (3), 265-282 (1975).
BACKGROUND OF THE INVENTION
Microchannel devices are finding increased use in the separation, identification and synthesis of a wide range of chemical and biological species. Employing transverse channel dimensions in the range from a few microns to about one millimeter, such systems may permit the miniaturization and large-scale integration of many chemical processes in a manner analogous to that already achieved in microelectronics. Applications for microchannel devices now under development include such diverse processes as DNA sequencing, immunochromatography, the identification of explosives, identification of chemical and biological warfare agents, and the synthesis of chemicals and drugs.
In addition to the potential for large-scale integration, the small physical scales of microchannel devices offer a few inherent advantages over their traditional macro-scale counterparts. Traditional chromatographic separations are usually performed in packed columns. The role of the packing is to provide a stationary phase having a large specific surface area for the adsorption of chemical species. Since various chemical species have different absorption probabilities and residence times on the stationary phase, they move with different speeds through the column and thus exhibit a range of arrival times at the column exit. Although larger surface areas provide better separation between arrival times, the use of packing materials causes nonuniformity of the fluid motion. This results in hydrodynamic dispersion of the solute bands or peaks used to distinguish the species. The benefit of the packing material is thus partially offset by the detriment of increased dispersion. This compromise can be avoided at the smaller scale of microchannel devices. Since the specific surface area of a tube or channel is inversely proportional to its minimum transverse dimension, microchannel columns may provide the required surface area without any need for a packing.
One promising method of microchannel separation is electrochromatography in which electric fields are used to drive electroosmotic fluid motion. Such fluid motion results from the applied electric field acting on charges in the electric Debye layer adjacent to the tube or channel walls, inducing a shear stress very near the boundary of the interior fluid. Electroosmotic flows offer two important benefits over pressure-driven flows for the small physical dimensions characteristic of microchannel devices. First, fluid speeds in electroosmotic flows are independent of the transverse tube or channel dimension over a wide range of conditions, making this technique extensible to extremely small physical scales. In contrast, pressure-driven flows require a pressure gradient that increases inversely with the square of the minimum transverse dimension to maintain a given fluid speed.
The second, more important advantage of electroosmotic flows is that the profile of the fluid velocity across a tube or channel is essentially flat over a very broad range of conditions. All variations in the axial velocity are confined to a small region adjacent to the tube or channel walls. The thickness of this fluid-dynamic boundary layer is comparable to the thickness of the electric Debye layer. The benefit of this flat velocity profile is that samples may be transported over long ranges with very little hydrodynamic dispersion due to nonuniform fluid speeds. Although dispersion in both electroosmotic and pressure-driven flows grows as the square of the Peclet number, the coefficient of dispersion in an electroosmotic flow may be many orders-of-magnitude smaller than that for the parabolic velocity profile of a pressure-driven flow. In addition, this low coefficient of dispersion permits optimum operation of an electroosmotic flow at very high Peclet numbers. This mimizes the role of ordinary diffusion in electroosmotic flows, thus offering the potential for long-range transport in chromatographic columns with little axial spreading of solute peaks due to either dispersion or diffusion. This is critical to chromatographic processes that identify chemical species by distinguishing the arrival times of closely spaced peaks or bands.
Another promising approach to microscale chemical analysis is electrophoretic separation. Here the carrier fluid may be either moving or nearly stationary, and an applied electric field is used to drive ionic species through a gel or liquid. Separation occurs because the ion speeds depend on the unique charge and mobility of each species. Provided that the applied field is uniform across the tube or channel cross-section, all ions of the same charge and mobility move at the same speed and so progress along the column without any induced dispersion. Such motion is analogous to the flat velocity profile of an electroosmotic flow, and the various species thus again exhibit unique arrival times at the column exit. Like electrochromatographic processes, electrophoretic separations may be severely degraded by diffusion or dispersion. ,In the latter case, however, dispersion may arise not only from nonuniformity of the carrier fluid speed but may also arise directly from nonuniformity of the electric field across the column cross-section.
Although species motion in both electrophoretic and electroosmotic transport may be relatively free of both diffusive and dispersive spreading in straight tubes or channels having parallel walls, any local variation in the fluid speed or local field strength introduces dramatic skewing of an otherwise flat interface or species band. Such skewing is known to occur in turns because the fluid moving along the outer radius of a turn must travel further than that moving along the inner radius. This difference in path length is compounded by the electric field gradient which is greater along the shorter inner radius, resulting in a greater fluid speed along the shorter path. Thus, an initially flat interface will be severely skewed in passing through a turn. Moreover, because transverse diffusion quickly redistributes solute concentrations across the channel, such skewing is irreversible, and the net effect of transport through any turn or junction is a large and permanent broadening of any solute peak or interface. Although there have been a number of published studies which demonstrate and quantify the dispersive effects of turns
3,4,5,6
there have been few prior attempts to remedy the problem. As a result, separations are generally performed in straight channels that are limited in length by the maximum substr
Griffiths Stewart K.
Nilson Robert H.
Fliesler Dubb Meyer & Lovejoy LLP
Noguerola Alex
Sandia Corporation
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