Novel Chemical Surface For Full Control Of Electroosmosis

Electroosmosis is a process used for the movement of fluids through very small channels contained in instrumentation designed on single microchips. Electroosmosis is also useful in capillary electrophoresis, an established small volume, high efficiency separation technique. One limitation of using electroosmosis in these applications is the lack of control and the poor reproducibility of the electroosmotic flow in standard systems. In an effort to provide dynamic manipulation of electroosmosis, and thus fully control and stabilize this flow, a radial voltage field is often applied across the wall of the capillary. This technique provides control, but only with low pH buffers in standard systems, thus limiting the usefulness of the method. To extend this radial voltage flow control technique to higher pH, the surface charge generated at liquid/wall interface must be minimized. In the past, this has been somewhat accomplished through the use of certain types of surface coatings resulting from treatments with organosilanes or certain polymers. However, previous organosilane treatments were not stable and, due to rheological constraints, polymer-coated approaches have proved unacceptable for dynamic flow control by an applied radial field.Researchers at Arizona State University have developed a new coating that results in improved stability and flow control over a large range of pH (2-10). This treatment has also been applied to small-bore capillaries, ranging down to 2-mm internal diameter. The effectiveness of an applied radial voltage field on the control of electroosmosis was demonstrated and this control improved dramatically at high pH (up to pH 10), where no control is possible for uncoated capillaries. The magnitude of the flow control at pH 10 in coated capillaries was equivalent to the most favorable pH conditions (pH 3) in an uncoated capillary.