Invited Paper MN-MoA3
An Integrated Passive µPreconcentrator with Progressively-Heated µInjector for µGC

Monday, October 21, 2019, 2:20 pm, Room A210

We report on a new device designed to serve as a universal ‘front-end’ for gas chromatographic microsystems (µGC) for remote, long-term monitoring of vapor-phase chemical threats or environmental pollution. This small, low-power, Si/glass-micromachined device, dubbed a micro-collector/injector (µCOIN), combines a passive micro-preconcentrator (µPP) with a progressively heated micro-injector (µPHI). The µPP samples vapors at known rates by molecular diffusion and transfers them under active flow via thermal desorption to the µPHI, which, in turn, injects them to a downstream (µGC) separation column via progressive (sequential) heating. Most testing to date was performed with discrete devices, both of which contain tandem cavities packed with granular carbon-based adsorbents of different specific surface areas. Carbopack B (CB, 100 m²/g) and Carbopack X (CX, 240 m²/g) were used for most compounds. But CX was used with Carboxen 1003 (C3, 1000 m²/g) for more volatile compounds. Using a conventional GC for downstream analyses, we have found that the µPP (CX/CB) can collect vapors of widely different volatility at a nearly constant effective sampling rate for up to 24 hrs (low concentrations) and over a 2,500-fold concentration range (0.25-hr samples). Effective (compound-specific) sampling rates ranged from ~0.25 to 0.69 mL/min, most of which agreed with theoretical predictions. Desorption/transfer efficiencies from the µPP were > 87% (most > 94%) at 5 mL/min and 250 °C for 60 sec. For the µPHI (CX/CB) bolus challenges of compounds at 5mL/min, mimicking transfer from the µPP, resulted in > 90% capture efficiency for up to 3.6 µg of lower volatility compounds. More volatile or highly polar compounds required the CX/C3-loaded device. Back-flushed progressive heating of the µPHI produced injection bands < 250 ms wide at flow rates < 0.5 mL/min. In separate tests, remarkable selectivity for polar compounds was achieved by applying an ionic-liquid surface modifier to the carbon adsorbents (tests in the µPP and µPHI are pending). The monolithically integrated µCOIN (0.23 cm³) has not yet been tested. But, a hybrid-integrated µCOIN (capillary connections) provided good preliminary performance, including efficient sampling, transfer, and injection of multi-component mixtures. Valveless flow modulation was implemented to avoid backflow to the µPP. Using typical power levels for each device, two valves, a pump, an interconnect heater, and supporting electronics, the energy consumption was only 320 J per cycle for the hybrid µCOIN. Thus, the µCOIN shows promise as a component in future ultra-low-power µGC systems for analyzing complex vapor mixtures.