Silicon micromachined gas chromatographic system (SMGCS) for directly separating binary fugitive emissions of ammonia (NH 3 ) and nitrigen dioxide (NO 2 )

Abstract

A miniature gas chromatography (GC) system has been designed and fabricated using silicon micromachining and integrated circuit (IC) processing techniques. The silicon micromachined gas chromatography system (SMGCS) is composed of a miniature sample injector that incorporates a 10 (mu) l sample loop; a 0.9-m long, rectangular-shaped capillary column coated with a 0.2-micrometers thick copper phthalocyanine (CuPc) stationary-phase; and a dual- detector scheme based upon a CuPc-coated chemiresistor and a commercially available, 125- micrometers diameter thermal conductivity detector bead. Silicon micromachining was employed to fabricate the interface between the sample injector and the GC column, the column itself, and the dual-detector cavity. A novel IC thin-film processing technique was developed to sublime the CuPc stationary-phase coating on the column walls that were micromachined in the host silicon wafer substrate and Pyrex cover plate, which were then electrostatically bonded together. The SMGCS can separate binary gas mixtures composed of parts-per-million (ppm) concentrations of ammonia and nitrogen dioxide when isothermally operated (55-80 degrees C). With a helium carrier gas and nitrogen diluent, a 10 (mu) l sample volume containing ammonia and nitrogen dioxide injected at 40 psi (2.8 X 10 5 Pa) can be separated in less than 30 minutes.