| Summary: | 博士 === 國立中央大學 === 化學學系 === 107 === Compared to conventional one-dimensional gas chromatography, comprehensive two-dimensional chromatography (GCxGC) is inherited with high peak capacity that dramatically improves separation resolution and alleviates the co-elution problem for complicated samples. GCxGC uses two columns of different polarity to provide orthogonal separation on a 2-D surface, it becomes not only a powerful technique to analyze complex chemical compositions but also the mainstream of next-generation chromatography technology.
Modulation plays a central role in GCxGC performance. The high cost in ownership and operation of a commercial GCxGC system equipped with a cryogenic modulation which need of cryogen, such as liquid nitrogen or liquid carbon dioxide, hinders many users from possession due to high expense in purchase and maintenance. In this study, a valve-based modulator based on the Deans switch served as an alternative to the commercial counterpart without the use of cryogen. The novel features with this design is simple structure, ease of use, robust, flexibility and eliminate additional financial burden about cryogen.
Because of the low concentrations of VOCs in ambient air, usually at only sub-ppbv levels, an air sample would require substantial preconcentration before GC analysis. A self-constructed preconcentrator was connected to our GC×GC system. This system was able to analyze atmospheric sample at ambient level. Real ambient air samples collected in a long highway tunnel by canisters and sorption tubes were analyzed for system validation. Furthermore, as the trial studies, PM2.5 aerosol samples collected on filter papers were attempted by thermal desorption of the filter paper. Compound identification was made with GC-MS by analysing parallel samples to reveal the chemical identities of the major constituents of both the air and PM samples. While all the VOCs found in the canisters were non-polar hydrocarbons due to the lack of photochemistry in the tunnel, selected oxygenated VOCs (o-VOCs) were found in the aerosol sample owing to the extended oxidation process in the atmosphere.
Further, we used microchannel device (SilflowTM , provided by SGE) to configure a flow modulator to improve versatility in modulation, such as flow path, flow rate, and sample filling loop length to minimize dead volume. Utilizing standard mixture to verify the performance in gas-separation, and the suitability in ambient sample analysis.
|
|---|
