Microfabricated integrated sampler-injector (MISI) for micro gas chromatography

We present the design, fabrication, and preliminary performance testing of a microfabricated integrated sampler-injector (MISI) intended for use in a micro gas chromatography (μGC) system for the analysis of volatile organic compounds (VOCs). The MISI comprises a DRIE Si cavity with an integrated heater and temperature sensor that is packed with a graphitized carbon adsorbent and capped with a precision grid-patterned DRIE Si lid. Tapered inlet and outlet ports and fluidic interconnects facilitate pumped transfer of thermally desorbed vapors to downstream components for analysis. The MISI samples the air at a known rate by diffusion without active pumping, it preconcentrates VOCs, and then thermally desorbs the captured VOCs for injection to the separation column. Thus, it consumes no power during sampling. During desorption, the device can be heated from room temperature to 250°C in 230 ms with 1 W. The sampling rate of the device was determined to be 10.5 mL/min by thermal gravimetric analysis, in agreement with theory (Fickian diffusion). Upon exposure to 640 ppb of toluene and subsequent thermal desorption and analysis, the device yielded results within 18% of the predicted value.