Doctor of Philosophy (PhD)
Rapid and comprehensive on-site analysis of chemicals in applications ranging from industrial process control to homeland security is of significant importance to improve the environment and save human life. The need for sensors that are fast, reliable, and portable has never been greater. For the challenging task of on-site instrumentation, where power sources can be limited, shrinking the size of the device is the most effective way to conserve power. Although gas chromatography is a mature technique well suited for these applications, current instrumentation has deficiencies that limit its usage. Speed of analysis and non portability are severe hindrances to using the bench top and portable instruments for on-site applications. This focus of this research is to provide a transition from a portable gas chromatograph (GC) instrument to a handheld GC sensor. The significant issues for realizing a handheld GC sensor were addressed. One important design criterion was that the sensors have the same analytical capability as a commercial GC instrument. Of the many components of a GC, the separation column primarily defines the resolution and the analysis time. Thorough theoretical analysis led to the conclusion that high aspect ratio, rectangular cross-section columns have a distinct advantage over capillary columns. A column including an on-chip sample loop and a makeup gas manifold were designed. Previously reported attempts to fabricate rectangular columns have focused on low aspect ratio or square cross-section columns. Contrasting all prior efforts, significant strides in process development were made to realize nickel GC columns using the LiGA technology with aspect ratios as high as 20. Through process control, a device yield of over 90% was achieved. Tests on these columns yielded more than 20,000 plates for unretained species. Four hydrocarbons were separated in less than 2 s at 100 °C on a 50 μm wide by 600 μm tall by 0.5 m long coated LiGA column. For the first time reported, 2-D GC was implemented using MEMS columns.
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Bhushan, Abhinav, "System optimization for realizing a miniaturized gas chromatograph sensor for rapid chemical analysis" (2006). LSU Doctoral Dissertations. 3168.