Silicon Microfabricated Preconcentrator Design and Characterization

Abstract

MEMS fabrication technology has been applied to build micro-GC systems for portable analysis and detection of volatile organic compounds for environmental monitoring, medical diagnostics and food safety and security (1). Pioneering work at Sandia National Laboratories developed - these miniature systems (2). Novel designs for pre-concentrators have been developed to provide efficient sample injection into these systems (3). We have integrated a 6m length micro-GC column with an ion trap mass spectrometer (4). To inject the sample into the column, our initial method was to use a syringe injection into a heated septum with Agilent 6890. However, for automated operation and method of sampling, pre-concentration of the volatile organic compounds is required, followed by rapid heating, for sample injection for analysis. A microfabricated pre-concentrator can fulfill this function by providing a high surface area in a compact platform with reduced thermal mass, compared to commercial desorption tubes. The design has an integrated platinum heater and was fabricated using standard photolithography, deep reactive ion etching and wafer bonding. To evaluate the performance, the pre-concentrator is mounted inside a commercial Agilent 6890 GC system. Liquid injections 0.02uL, using a syringe, with a 100:1 split, at a helium flow rate of 0.005 ml/min. The flow rate was increased during the desorption cycle, and the preconcentrator was heated by electrical current of providing approx. 5W to enable rapid heating to 180°C. This miniature pre-concentrator provides a small thermal mass design and was capable of fast desorption of several analytes with detection by FID.