| Summary: | 碩士 === 國立臺灣師範大學 === 化學系 === 102 === The object of this study is to design, fabricate and characterize a multi-stage μ-preconcentrator, which is an important component in micro-gas chromatograph. It uses adsorbents to concentrate volatile organic compounds before thermal desorption to improve the detection limit of instrument, therefore detecting the low concentration of VOCs even SVOCs in the atmosphere is more convenient. It also can help analyzing low concentration gas mixture in human breath in a non-invasive way.
In this study, we use high temperature to form carbon molecular sieve and carbon base adsorbent by saran and cellulose, which combine with a commercial adsorbent Tenax TA, and then inject into a pre-sealed, anodic bonded multi-stage μ-preconcentrator. During the sampling, carbon molecular sieve, carbon base adsorbent and Tenax TA are in series. The surface area of the adsorbents are 899 m2/g, 308 m2/g and 35 m2/g accordingly. It is arranged by strength of adsorption from strong to weak with sampling capacity, but gas flow is reversed during desorption. It can prevent signal tailing and memory effect in the preconcentrator. We applied Wheeler model to access the thermodynamic capacity of our carbon molecular sieve and found the value is 0.482 mg/g.
Finally, we use multi-stage μ-preconcentrator to concentrate 12 VOCs for capacity testing, the carbon numbers are from 2 to 14, boiling points are from 56℃ to 253.5℃, and all of the concentration are in 100 ppb. This multi-stage preconcentrator can concentrate ethanol up to 0.8 L, and concentrate others up to 1.2 L.
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