Environmental Sensors and Subsystems

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Microfabricated Passive Preconcentrator/Injector for a µGC (µPPI)
Jung Hwan Seo, Jing Liu, Xudong Fan, and Katsuo Kurabayashi
(a) Optical image showing the top layer of the <em>µ</em>PPI with diffusion channel grids and see-through image of Carbopack X beads packed underneath. (b) Optical image of the micro-heater and RTD sensor on the backside of the bottom layer of the <em>µ</em>PPI. (c) Plots of the theoretical and experimental injection peak band profiles of toluene at the heating rate of 90 K/s.
(a) Optical image showing the top layer of the µPPI with diffusion channel grids and see-through image of Carbopack X beads packed underneath. (b) Optical image of the micro-heater and RTD sensor on the backside of the bottom layer of the µPPI. (c) Plots of the theoretical and experimental injection peak band profiles of toluene at the heating rate of 90 K/s.

This project aims to develop an on-chip device named the "microfabricated passive vapor preconcentrator/injector (µPPI)." The µPPI is the first microfabricated VOC preconcentrator that enables both zero-power diffusion-based passive sampling and preconcentration of VOCs (Fig. a) and sample release/injection by controlling the temperature of its integrated on-chip micro-heater (Fig. b). The µPPI achieves a high sampling rate of 9.1 mL/min by diffusion and delivers the sampled vapor to a downstream GC component by thermal desorption at a low power of ~ 1 W. The sample loss is <5 % when a carrier gas flow rate was set at 50 mL/min. To further characterize the thermal desorption/injection performance of the µPPI , we developed an analytical model accounting for heat transfer, temperature dependent desorption kinetics, and peak band broadening. This model well predicts the real-time vapor peak band profiles in good agreement with experiment using an on-column sensor (Fig. c). Thus, we demonstrated the effect of the thermal desorption characteristics of a vapor injection device on injection peak band signal tailings and intensity. With the heating power of 1.1 W, more than 90 % of toluene is released from the adsorbent of the µPPI within 3 s. Ongoing work is focused on in-depth characterization of preconcentration, desorption, and injection performance of the µPPI for moderately complex VOC mixtures. This work was funded by the NIOSH Pilot Project Research Training Program (PPRTP) and the Michigan Center for Wireless Integrated Microsystems by the Engineering Research Centers Program of the National Science Foundation.

Updated 04/06/2012