本研究分為「多孔材料性質研究」及「標準氣體製備」兩大部分。 在第一部分中將研究各種孔洞材料對於C2~C10之VOCs（Volatile Organic Compounds）物種的捕捉效率。以商業化碳吸附劑作為比較基礎，評估矽骨幹微孔洞材料ZSM-5和中孔洞材料MCM-41、SBA-1作為吸附材料的可行性。並且藉由增加進樣壓力來改善高揮發性小分子於常溫、常壓下捕捉效率低落的缺陷。 第二部分則針對標準氣體的製備進行探討，其配製方法大致可區分為靜稀釋法（Static Dilution）與動態稀釋法（Dynamic Dilution）兩大類。靜態稀釋法中的重量法是將純物質或原料氣體填入毛細管中秤重，再以線上擊碎並吹入氮氣至高壓鋼瓶中稀釋而成，先前已初步完成21種ppm（v / v）濃度範圍之VOC混合氣體。 由於秤重之初已準確得知鋼瓶中各物種間相對莫耳數比例，但稀釋過程卻存在很大之不確定度，無法準確得知各物種的絕對濃度。因此設計使用一具追溯性之標準品針對選定的物質進行校正，再利用各物種間莫耳數比回推得其他物質之絕對濃度。 本實驗進而利用GC之電子式壓力控制器作為動態稀釋裝置，將此ppmv等級的標準氣體簡易稀釋至ppb（v / v）濃度範圍，以利於空氣中低濃度VOCs的例行性量測。 雖然使用重量法配製標準氣體可得準確度相當高的結果，然而對於某些反應性較大的物種，因易與鋼瓶表面起化學反應而損失，並不適用於靜態稀釋法的製備與儲存。因此本實驗進一步發展動態稀釋法中的滲透管法，使用自行製作的滲透管進行線性與穩定性測試，期望能進一步克服高極性物種無法配製存放於鋼瓶中的缺陷及開發使用自製滲透管進行線上即時分析的技術。 The research includes two parts: the characteristic study on porous materials and the preparation of standard gas mixtures. In the first part, the adsorption efficiency of porous materials for volatile organic compounds (VOCs) was investigated by gas chromatography (GC) with flame ionization detection (FID). Comparison of sorption characteristics was made between self-prepared silicates and commercial carbon adsorbents via trapping a ppm level gas mixture containing compounds from C2-C10. These self-prepared silicates included microporous silicate-ZSM-5, as well as mesoporous silicates-MCM-41 and SBA-1. To quantitatively describe adsorption efficiency, the term “recovery” was defined and assessed for each silicate by referencing to a well-studied multi-carbon sorbent combination. When trapping with silicates at room temperature the recovery was found to be above 90% for compounds heavier than C7, but was poor for higher boiling compounds. It was also noticed that the poor recovery for high boiling compounds can be improved by increasing the sample pressure. The second part describes the preparation of standard gas mixtures. Standard gas mixtures containing 21 VOCs from C2-C12 at low parts per million by volume (ppmv) level was prepared by a gravimetric method developed in-house. Capillary tube containing these compounds were prepared and accurately weighed. These tubes then were crushed and flushed by high purity N2 to a 29.5 L evacuated aluminum cylinder, filling to approximately 1000 psi. Unlike conventional gravimetric method where a large-scale balance is used for weighing filled cylinders to determine final mixing ratios, this study deliberately avoided using the large-scale balance due to its high cost and inaccessibility to average laboratories. Instead, a traceable parts per billion by volume (ppbv) level commercial gas standard was then used to calibrate the concentrations of selected compounds within the self-prepared mixture and to estimate the dilution factor during the dilution process. Because the mole ratios between the 21 compounds were known from weighing, final concentrations of other compounds in the cylinder can then be derived. In this process, GC’s electronic pneumatic controllers (EPCs) were employed as the flow device for diluting the standard mixture from the ppmv to the ppbv level. Although the gravimetric method is suited for preparing standard mixtures with high accuracy for volatile non-polar compounds, it has limitations for polar or unstable compounds due to possible wall effects. As a result, techniques for making permeation tube were also investigated for on-line calibration of ambient VOCs.
