Extremely uniform packing of colloidal silica in capillaries is shown. Reversed-phase electrochromatograms of DiI-C12 exhibit plate heights as low as 0.13 µm and a reduced plate height as low as 0.4, using 75 µm i.d. capillaries packed with 330 nm silica particles. The contribution from the A term is 0±20 nm in electrochromatography. The particles are shown to form colloidal crystals inside the capillaries. Optical images show Bragg diffraction, indicative of crystallinity; SEM images show face-centered cubic crystallinity; and the porosity is 0.25±0.01, which is in agreement with that for face-centered cubic crystals. The capillaries are fritless, and 100 µm i.d. capillaries packed with silica colloidal crystals withstand pressures of at least 12,400 psi.

Silica colloidal crystals formed from 330 nm nonporous silica spheres inside of 75-μm i.d. fused silica capillaries were evaluated for the efficiency of capillary electrochromatography of proteins. Three proteins, ribonuclease A, cytochrome C and lysozyme, each covalently labeled with fluorophor, were well separated over a distance of 1 cm by isocratic electromigration, using 40:60 acetonitrile:water with 0.1% formic acid. A van Deemter plot showed that the plate height for lysozyme, which was the purest of the three proteins, was diffusion-limited for electric fields ranging from 400 to 1400 V/cm. The plate height for lysozyme was below 50 nm at almost all of the migration velocities, and it approached 10 nm at the highest velocity. Eddy diffusion was negligible. Lysozyme migrated over a 12 mm separation length with more than 10 6 plates in 1.5 minutes. These results indicate that silica colloidal crystals are well suited for electrically driven separations of large, highly charged analytes such as proteins. The 10 6 plates observed for a separation length of barely more than a cm means they are potentially valuable for miniaturized separations in microchip and μTAS devices.

Glycosaminoglycans (GAGs) are important in a number of biological processes and are structurally altered in many pathological conditions. The complete determination of GAG primary structures has been hampered by the lack of sensitive and specific analytical techniques. Nuclear magnetic resonance spectroscopy (NMR) is a powerful tool for GAG structure elucidation despite its relatively poor limits of detection. Solenoidal microcoils have greatly enhanced the mass limits of detection of NMR, enabling the on-line coupling of microseparation and concentration techniques such as capillary isotachophoresis (cITP), which can separate and concentrate analytes by 2-3 orders of magnitude. We have successfully used cITP coupled with on-line NMR detection to separate and concentrate nanomole quantities of heparin oligosaccharides. This sensitive on-line measurement approach has the potential to provide new insights into the relationships between biological function and GAG microstructures.

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