Abstract: In accordance with the present invention, stable electroosmotic flow systems and methods for designing the same are disclosed. The invention provides electroosmotic flow systems comprising electroosmotic flow elements, including bridge elements, that have matching flux ratios, i.e., when two or more elements of an electroosmotic flow system are in fluidic and electrical communication at a junction, the flux ratio for each of the elements is selected so that the difference in flux ratios system adjacent two elements is less than a target value. The invention also provides methods for designing such systems.

Abstract: A chromatography system having continuously variable sources of fluid pressure and a controller to control the flow rates of one or more carrier fluids during an HPLC separation, the controller being responsive to the rate of analyte elution from a sample.

Abstract: An electrokinetic pump achieves high and low flow rates without producing significant gaseous byproducts and without significant evolution of the pump fluid. A first feature of the pump is that the electrodes in the pump are capacitive with a capacitance of at least 10?4 Farads/cm2. A second feature of the pump is that it is configured to maximize the potential across the porous dielectric material. The pump can have either or both features.

Abstract: A liquid sample is prepared at a preparation site and then processed, e.g. in an HPLC column. The sample is prepared and conveyed to the device at a flow rate which is substantially less than the flow rate through the device. The different flow rates are preferably provided by variable rate working fluid supplies which drive the sample from the preparation site and through the device.

Abstract: Liquid flow devices, particularly microfluidic devices, containing solid porous materials. Flow in the devices can be pressure-driven flow and/or electroosmotic flow. The porous materials are preferably pre-shaped, for example divided from a sheet of porous material, so that they can be assembled with liquid-impermeable barrier materials around them. The devices can for example be prepared by lamination. A wide variety of devices, including mixing devices, is disclosed. A mixing device is illustrated in FIG. 23.

Abstract: A method of pumping fluid including the steps of providing an electrokinetic pump comprising a pair of double-layer capacitive electrodes having a capacitance of at least 10?2 Farads/cm2 and being connectable to a power source, a porous dielectric material disposed between the electrodes and a reservoir containing pump fluid; connecting the electrodes to a power source; and moving pump fluid out of the reservoir substantially without the occurrence of Faradaic processes in the pump. The invention also includes an electrokinetic pump system having a pair of double-layer capacitive electrodes having a capacitance of at least 10?2 Farads/cm2; a porous dielectric material disposed between the electrodes; a reservoir containing pump fluid; and a power source connected to the electrodes; the electrodes, dielectric material and power source being adapted to move the pump fluid out of the reservoir substantially without the occurrence of Faradaic processes in the pump.

Abstract: A variable flow rate injector provides accurate, precise, and reproducible injection volumes that have low dispersion. The invention is particularly well-suited for HPLC injection volumes <500 nL but can be used to inject larger volumes and in different applications as well. Injections are performed at a first flow rate and separations are performed at a second flow rate. For improved HPLC system performance, the first flow rate is less than the second flow rate. The injector uses a variable flow rate fluid supply that allows rapid switching between flow rates desired for injection and flow rates desired for separations.

Abstract: Electroosmotic flow systems containing two or more electroosmotic flow elements which meet at a junction, at least one of the electroosmotic flow elements having a substantial charge ratio. The electroosmotic flow elements have matching flux ratios. The electroosmotic flow elements may contain porous materials whose terminal portions are shaped to increase the surface area exposed to the fluid at the junction. Examples of such terminals are illustrated in the figure.

Abstract: In accordance with the present invention, stable electroosmotic flow systems and methods for designing the same are disclosed. The invention provides electroosmotic flow systems comprising electroosmotic flow elements, including bridge elements, that have matching flux ratios, i.e., when two or more elements of an electroosmotic flow system are in fluidic and electrical communication at a junction, the flux ratio for each of the elements is selected so that the difference in flux ratios system adjacent two elements is less than a target value. The invention also provides methods for designing such systems.