Electrochromatography in chemically modified etched fused-silica capillaries

A new method of electrochromatography is described in which a 50-microns capillary is etched with ammonium hydrogen difluoride, followed by modification of the new surface via a silation reaction with triethoxysilane to produce a hydride intermediate, and then subsequently subjected to hydrosilation using 1-octadecene in the presence of a platinum complex catalyst. The C18 bonded phase is then compared with bare capillaries, etched bare capillaries and the hydride etched capillary to determine if any solute-bonded phase interactions are present. With bradykinin as a test solute, peak efficiencies are quite similar for all capillaries without C18 but become noticeably broader when the organic moiety is attached to the etched capillary wall. A test mixture of peptides and proteins displays shorter retention for some of the components when methanol is added to the mobile phase which is typical of reversed-phase behavior. The same result is also obtained when a mixture of tetracyclines is separated on the C18 capillary with and without methanol as part of the mobile phase. The reproducibility of retention times for two proteins is +/- 1.5%. A few results for several neutral compounds indicate small but measurable k' values.