Development, evaluation, and application of silicon/glass microfabricated gas chromatography columns.

An investigation of etched-silicon channels as gas chromatographic separation columns for volatile and semi-volatile organic compounds is described. This research was directed toward the ultimate goal of integrating these columns into an autonomous micro gas chromatograph (muGC) capable of comprehensive analysis of complex vapor mixtures covering a broad range of applications. Single- and dual-column configurations were explored using conventional and spectrometric detectors. Keys to achieving high-resolution separations in etched-channel columns are uniformity and thickness of the wall-coated polymeric stationary phase. This work used 3-meter-long, square-spiral channels having rectangular cross sections of 150 x 240 mum. Initial studies employed a dynamic coating method to deposit non-polar (polydimethylsiloxane) and moderately polar (polytrifluoropropylmethylsiloxane) phases within separate channels. The number of theoretical plates ranged from 4600 to 8200 and 3500 to 5500 for non-polar and polar columns, respectively. Pressure tuned separations were performed by connecting two microcolumns in series and periodically actuating a bypass valve between the inlet of the first column and the dual-column junction point. This technique was used to resolve several sets of co-eluting peaks not separated under normal operating conditions, and stands as the first demonstration of pressure-tuned separation enhancement using microfabricated column ensembles. Subsequently, deposition of the non-polar phase using a static method yielded microcolumns with ∼4200 theoretical plates/meter, the highest ever reported. Static coating of the polar phase has been unsuccessful due to solvent limitations. A single, dynamically-coated column was interfaced with a commercial microfabricated differential mobility spectrometer (DMS), which separates ions based on mobility in a high frequency electric field. GC/DMS is demonstrated for the separation of complex mixtures of up to 45 components using two-dimensional analyses. Further DMS work investigated fragmentation patterns with varying detector operating parameters. The nature and relative magnitudes of fragmented species are shown to enhance the analytical information provided by GC/DMS. Additional work was performed on a new generation of PECVD columns. Preliminary investigations indicate significant reductions in power dissipation and improvements in column resolution relative to silicon/glass microcolumns. Also, applications of novel ionic-liquid stationary phases for fused silica columns were explored using dual-column ensembles and spectrometric detection.Ph.D.Analytical chemistryApplied SciencesElectrical engineeringPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/126207/2/3238008.pd