Microfabrication of gas chromatographs-on-a-chip Gas chromatography (GC) is commonly used as a method to separate and analyze volatile compounds without thermal decomposition. Compounds are pumped through a long separation column filled with the stationary phase, which is made out of polymers that selectively interact with the analyte of interest. It has been difficult to manufacture the increasingly miniature parts required for micro-gas chromatography systems without resorting to a complex, component-by-component manufacturing process. Standardization of micro-fabrication process would facilitate a much wider acceptance of micro-GC technology. State-of-the-art research suggests that a Knudsen pump, which precisely harnesses the flow of gas molecules under a temperature gradient in a narrow channel, is required for a truly integrated micro-GC system.
A standardized fabrication process of a micro-GC with a Knudsen pump A team of researchers from the University of Michigan has designed a Knudsen pump that utilizes membranes sandwiched between micromachined glass to drive flow throughout the micro-GC. A preconcentrator packed with granules adsorbs vapor-phase analytes and performs thermal injections into the separation column, which is a long channel in a double-spiral pattern coated with the stationary phase that separates gaseous analytes by their retention times. A 3-mask fabrication process is used to deposit the necessary heating and sensing components on glass wafers. The prototype column and preconcentrator has been shown to successfully separate an alkane mixture in 40 seconds, while the prototype Knudsen pump has been shown to deliver 0.42 sccm of air flow rate with a pressure gradient of 329 Pa. Future work involving the integration of the Knudsen pump with other components of the micro-GC subsystem is currently under way.
Applications • Sensors and alarms for volatile organic compounds • Healthcare/diagnostics • Chromatographic separations • Detection of chemical warfare agents • Natural gas pipelines monitoring and control
Advantages • Removes need for complex component-by-component manufacturing