|DC.description||National Central University||en_US|
|dc.description.abstract||本實驗利用增加靜相體積之概念，以提高分析物的萃取量，自行塗怖PDMS及PDMS/Carboxen高分子薄膜，其成分接近商業化固相微萃取(Solid phase microextraction)的吸附靜相，配合自行研發之進樣裝置，使熱脫附分析物不再侷限氣相層析儀(GC)之注射埠，大幅降低偵測極限。實驗過程中設計組裝一套熱脫附進樣系統，使用benzene、toluene、ethylbenzene、m-xylene、o-xylene (BTEX)純物質全量進樣作為校正曲線(calibration curves)，驗證此系統可達良好線性範圍(R2＞0.99)及再現性(1.07％)。
此外搭配自行設計頂空採樣裝置(headspace sampling device)分析濃度10 µg/L (ppb) BTEX樣品6次，其再現性4~12%。以及連續熱脫附方式，分析之同濃度BTEX，結果顯示分析物在PDMS及PDMS/Carboxen高分子薄膜脫附模式皆呈現指數下降曲線[Q/q0=exp(-aN)]符合典型之擴散行為，其PDMS及PDMS/Carboxen高分子薄膜感度對熱脫附次數存在良好的相關性(R2＞0.99)，並探討動力學常數a值對吸附及脫附效率之影響；且利用動力學常數，求得分析物在基質中的濃度及與靜相的分配常數，以及檢量未知空氣中BTEX的濃度。
|dc.description.abstract||This research is based upon a simple SPME (solid phase micro-extraction) theory, in which the sensitivity of SPME is proportional to the volume of the polymer phase, assuming the volume of the polymer phase is negligible compared to that of an aqueous sample. A thick film of polydimethylsiloxane (PDMS) polymer was coated on a glass rod of 2 mm O.D. x 6.7 cm length to serve as a large volume solid phase extraction medium for increasing sensitivity.
A renovated thermal desorption device was retrofitted from a regular GC injector to accommodate the thick PDMS rod. To cope with peak broadening in chromatography, an in-line micro-sorbent trap packed was installed prior to the capillary column to focus volatile analytes slowly desorbed from the large volume PDMS rod, resulting in highly resolved peaks.
By placing various amounts of high purity benzene, toluene, ethylbenzene, m-xylene, o-xylene (BTEX) into the thermal desorption device the linearity and precision of the injection system were effectively validated with R2 > 0.99 and RSD < 1.07%, which lays a solid ground for the subsequent quantitative and kinetic studies.
Throughout the experiment a headspace device was designed to generate standard gas mixture by equilibrating headspace with a standard aqueous solution containing target compounds of BTEX. The large volume SPME was able to achieve repeatability of 4~12% for BTEX, sufficient for high quality quantitative analysis.
Thermal desorption of the PDMS or PDMS/Carboxen rod showed a rapid exponential decline with the residue which can be described by the first order kinetics [Q/q0=exp(-aN)] and conformed to the diffusion theory. Herein, the kinetic constant can be described as the efficiency of sorption and desorption and has been shown to be temperature dependent but independent of extraction time and sample concentration. The simplified kinetics allows rate constants to be easily determined by arbitrarily loading and successive desorption of the target compounds at arbitrary extraction time. Using rate constants and equilibrium constants the concentrations of volatile analytes in both air and water can be easily calculated avoiding conventional time-consuming calibration procedures.
Both water and air samples were tested by the large volume SPME to show the sensitivity due to volume merit and the overall applicability of this self-developed technique.||en_US|
|DC.subject||large volume solid phase microextraction||en_US|
|DC.title||Large Volume Solid Phase Microextraction for passive air sampling||en_US|
|DC.publisher||National Central University||en_US|