Doctor of Philosophy

dissertationRecent literature has increasingly reported on the adverse effects of the worsening air pollution and the resultant demand for distributed air quality monitoring systems. Currently, airborne chemicals measured at the community level fail to account for spatial and individual variability in air pollution exposure. Among various chemical analysis instruments, the gas chromatograph (GC) has regarded as one of the most effective tools because of its wide detection range in gas species. However, in comparison with macro-scale systems, such miniaturization efforts have fundamentally caused a reduction in the detection range of these micro GC systems because of a shorter column length. This shortened column length was mainly imposed by the limitations of existing microfabrication pumps. To address such issues of low detection capacity in current microscale GC systems, one needs to achieve the extended length of the separation column that can operate under the performance limitations of the current micropump technology. One solution would be to achieve an enhanced column length by forming a circulatory path. This dissertation reports the detailed characterization of a miniature closed-loop gas chromatography (MCGC) system that improved the system performance by two 25-cm microcapillary columns with circulation and maintained a working pressure compatible with a microfabrication pump. Three generations of MCGC system has demonstrated (1) first microscale circulatory GC operation, (2) the longest column length iv of 12.5 meters ever reported in micro GC system and (3) the isomer separation with 25 cycles in the MCGC system, which was never achieved in any microscale GC systems up to date