Sol-Gel-Derived Materials for Analytical Separations

Abstract

The use of fused silica capillary columns (<500 μrn i.d.) to perform liquid phase analytical separations the offers numerous and very attractive features.^1–4 These include an increased mass sensitivity, high efficiency, short analysis times, low solvent consumption, low operational cost, and the capability of handling extremely low volume samples (<1μL). Open tubes and packed capillaries are the typical columns used to separate the solutes in a sample. The open tubular format is used in capillary electrophoresis (CE),⁵ capillary electrochromatography (CEC),⁶ and open tubular liquid chromatography (OTLC).¹ In the case of CE, analytes are separated based on their differential migration under an applied electric field; in most cases, a net solvent flow is also generated due to electroosmosis. In OTLC, separation is based on distribution ratios between two phases (mobile and stationary phase). The mobile phase is pumped through the column while the stationary phase is fixed at the walls of the capillary. Open tubular capillary electrochromatography (OT-CEC), however, is a relatively new technique that combines CE and OTLC. In this technique, an electric field is applied across a capillary column which contains a stationary phase at the inner walls. The electric field generates an electroosmotic flow (EOF), which possesses unique properties, to drive the solvent and solutes through the column. CE is the most commonly practiced of these techniques.