Open tubular capillary electrochromatography in etched, chemically modified 20 microns I.D. capillaries

Fused silica capillaries with an I.D. of 20 microns are etched and then chemically modified by the silanization/hydrosilation method to attach an octadecyl moiety for use in electrokinetic chromatography. The etched capillaries after chemical modification are shown to have an anodic electroosmotic flow below pH 4.5. In comparison to bare 20 microns capillaries and unetched but chemically modified 20 microns capillaries, the etched C18 fused silica tubes show better separation of mixtures of lysozymes and cytochrome c's under identical conditions of buffer, pH and applied voltage. It was also demonstrated that this open tubular approach to capillary electrochromatography was amenable to a number of different types of basic compounds ranging in size from typical small amines to biomolecules. As expected, pH is an important variable that must be controlled in order to obtain an optimized separation. Reproducibility studies verify the stability of the silicon-carbon linkage produced in this modification method so that column lifetimes of at least 300 injections can be expected.