High-Performance, Static-Coated Silicon Microfabricated Columns for Gas Chromatography

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Abstract
A procedure is described for the preparation of high-performance etched silicon columns for gas chromatography. Rectangular channels, 150 μm wide by 240 μm deep are fabricated in silicon substrates by gas-phase reactive ion etching. A 0.1−0.2-μm-thick film of dimethyl polysiloxane stationary phase is deposited on the channel walls by filling the channel with a dilute solution in 1:1 n-pentane and dichloromethane and pumping away the solvent. A thermally activated cross-linking agent is used for in situ cross-linking. A 3-m-long microfabricated column generated ∼12 500 theoretical plates at optimal operating conditions using air as carrier gas. A kinetic model for the efficiency of rectangular cross-section columns is used to evaluate column performance. Results indicate an additional source of gas-phase dispersion beyond longitudinal diffusion and nonequilibrium effects, probably resulting from numerous turns in the gas flow path through the channel. The columns are thermally stable to at least 180 °C using air carrier gas. Temperature programming is demonstrated for the boiling point range from n-C5 to n-C12. A 3.0-m-long column heated at 10 °C/min obtains a peak capacity of over 100 peaks with a resolution of 1.18 and a separation time of ∼500 s. With a 0.25-m-long column heated at 30 °C/min, a peak capacity of 28 peaks is obtained with a separation time of 150 s. Applications are shown for the analysis of air-phase petroleum hydrocarbons and the high-speed analysis of chemical warfare agent and explosive markers.

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