Dissertation Defense

Monolithic Microscale Gas Chromatographs with Integrated Gas Pumps

Daniel Zhao

Password: DZ221114


The detection and quantification of chemicals at the site of chemical reactions are necessary for applications such as process monitoring and chemical exposure monitoring.  Microscale gas chromatography (μGC) systems provide rapid, in situ testing, which matches the requirements of these applications.  This dissertation investigates the monolithic integration of micro-pumps to form a monolithically integrated μGC chip and the implementation of algorithmic control of the μGC system.

Monolithic integration of the μGC simplifies the assembly process and reduces the size of the system.  A μGC architecture where on-chip Knudsen pumps operate together to generate required gas flows without valves is designed and fabricated.  Knudsen pumps are monolithically integrated with a preconcentrator, separation column, and capacitive detector into a single 15 mm × 15 mm chip.  This work is the first reported case of a fully monolithic gas chromatography system.  In preliminary work, the μGC system has been used to successfully test mixtures of hexene and heptanal along with mixtures of other chemicals with Kovats Retention indices between 600-1000 with high repeatability.  Chromatograms are used to estimate the concentration of chemicals in a mixture with an accuracy of ± 8.5%, making the system suitable for process monitoring applications.

A continuous wavelet transform based algorithm for processing complex chromatograms generated by μGCs is implemented.  This algorithm leverages the inherent and known relationship between the peak locations and peak width to recognize peaks.  As a result, accurate peak recognition, width determination, and baseline compensation of chromatograms is achieved in the presence of non-monotonic baselines and complex peak shapes found in μGC chromatograms.


Chair: Professor Yogesh B. Gianchandani and Dr. Yutao Qin