A Microscale Integrated Sampler-Injector (MISI) for a micro GC

Jung Hwan Seo, Sun Kyu Kim, E T. Zellers, and Katsuo Kurabayashi

Images of (A) top layer and (B) bottom layer of MISI. (C) Toluene mass uptake as a function of sampling time.

This project aims to develop a new MEMS device named the “passive micro integrated sampler-injector (MISI).” The MISI collects, concentrates, and delivers ambient volatile organic vapors (VOCs) on a single chip prior to gas chromatography (GC) analysis. The device structure consists of two layers: the top layer has grids providing sample diffusion channels (Fig. A), and the bottom layer contains a cavity to hold a monolayer of carbon adsorbents (Fig. B). Its diffusion channels and microscale dimensions permit highly effective pumpless sampling at adsorbent surfaces due to passive diffusional effect and rapid, power-efficient thermal sample desorption caused by its low thermal mass. The floor of the cavity is sealed by a membrane with an underlying Ti/Pt meander-line heater and a resistance temperature detector (RTD), which allows rapid heating of the adsorbent materials and measuring of their temporal temperature variations. The silicon diffusion channels and the floor of the cavity are fabricated using DRIE and chemical etching. These two layers are bonded after fabrication and packed with adsorbents under a post-processing. To characterize the sample desorption/injection performance of the µMISI, we measured the injection efficiency of sampled vapors defined as the ratio of the mass of toluene injected to the GC/FID and the total mass of toluene captured by the adsorbents of the device. The injection efficiency of sampled vapors lie in ~95% for the varying sampling time (Fig. C). Ongoing work is focusing on further characterization of the vapor preconcentration and desorption performance for multi-vapor mixture analysis. This work was funded by the Michigan Center for Wireless Integrated Microsystems by the Engineering Research Centers Program of the National Science Foundation.