陽極氧化鋁靜相之金屬碟式氣相層析管柱研製

Abstract

本研究以金屬加工的方式開發出新型的氣相層析(Gas Chromatography, GC)管柱，在以鋁為底材的微流道中，生長陽極氧化鋁(Anodic Aluminum Oxide , AAO)作為氣相層析的靜相。依照不同的微流道製造方式以及陽極氧化鋁的生長條件，研究分為三大部分。第一部分為在毛細鋁管當中直接生長陽極氧化鋁，第二及第三部分為在沖壓製成的鋁微流道中生長陽極氧化鋁，並封裝製成封閉的流道結構。第一部分在毛細鋁管當中直接生長陽極氧化鋁，毛細鋁管使用抽拉的方式製成，為所有流道結構當中最穩定且截面最接近理想的圓形者。但因為陽極氧化鋁的生長過程受到電流及電解液的限制，而毛細管的截面不足以提供適當的生長條件，因此在數米的尺度上難以製備出均勻的靜相。作為本研究的首次嘗試，這樣的流道製造方式所得到的初步層析表現，對於後續的研究來說是相當重要的參考。由於陽極氧化鋁的生長需要相當的電流以及充分攪拌的電解液，第二部分開始嘗試在平板結構上加工出微流道，在硫酸中生長陽極氧化鋁之後，以封裝的方式來完成整個封閉流道。鋁作為一個相當難以焊接的金屬，再加上應用在氣相層析而不能使用加熱會產生揮發性物質的有機封裝材料，流道封裝技術的開發在本研究當中是相當重要的關鍵。第二部分的研究首次有效地做出以陽極氧化鋁作為靜相的氣相層析管柱，並進行了C1-C15直鏈烷類的分離。由於多孔粉末塗布的條件限制，商用氧化鋁管柱的可操作溫度較為受限，本研究則不受此限制，同時分離如此大沸點範圍的分析物在氧化鋁管柱當中為首見。第三部分則是在第二部分的基礎之上進行管柱結構與陽極氧化鋁表面的優化。第二部分使用的製程雖然能最快速生長最厚的陽極氧化鋁，但其表面極性太強，只能針對烷類化合物進行有效的分離，另外靜相厚度太厚也會對分離的效果造成不利的影響。第三部分研究改為使用草酸二次陽極氧化，使用較薄的靜相，並重新開鋼模，將流道內徑縮小並優化與封裝製程之間的配合。除了在理論板數的表現上有顯著進步之外，能分離的化合物範圍也從只有烷類拓展為烯類、芳香烴以及鹵烷類等化合物，最後再更進一步使用油酸進行表面化學修飾，能夠分離部分含氧及含氮的有機物，在應用上已慢慢接近商用管柱的水準。In this study, a novel gas chromatography (GC) column was developed through metal processing techniques. Anodic aluminum oxide (AAO) was grown as the stationary phase in microchannels fabricated with aluminum as the substrate.The research was divided into three main parts, based on different microchannel fabrication methods and AAO growth conditions. The first part involved the direct growth of AAO within capillary aluminum tubes, which were fabricated through a drawing process and exhibited the most stable and nearly ideal circular cross-section among all channel structures. However, due to the limitations imposed by the current and electrolyte during the growth of AAO, the capillary tubes' cross-section was inadequate to provide suitable growth conditions, resulting in challenges to achieving a uniform stationary phase over meter-scale dimensions. Nevertheless, the initial chromatographic performance obtained from this fabrication method was crucial as a preliminary attempt and a valuable reference for subsequent research. Given that the growth of AAO required significant current and well-agitated electrolytes, the second part of the study explored the fabrication of microchannels on a disk-shaped structure. AAO was grown under appropriate conditions, and the entire enclosed channel was completed through an encapsulating process. Aluminum, being a difficult metal to weld, combined with the requirement of using organic packaging materials that do not generate volatile substances during gas chromatography, made the development of a channel encapsulating technique a crucial key in this study. The second part of the research successfully produced GC columns employing AAO as the stationary phase and achieved the separation of straight-chain hydrocarbons with carbon chain lengths ranging from 1 to 15. Unlike commercially available alumina columns with a limited operating temperature range due to the constraints of porous powder coating, this study overcame such limitations. It demonstrated the separation of such a wide boiling point range of analytes within an alumina column.Building upon the foundation of the second part, the third part focused on optimizing the column structure and the surface of the AAO. While sulfuric acid hard anodization allowed for the fastest growth of the thickest AAO, its highly polar surface only enabled the effective separation of alkanes. Moreover, the excessive thickness of the stationary phase adversely affected separation performance. In the third part, oxalic acid second anodization was employed, which resulted in a thinner and more delicate stationary phase. The steel mold was redesigned to reduce the inner diameter of the microchannels and optimize the coordination with the encapsulating process. Significant improvements were achieved in terms of theoretical plate numbers, and the range of separable compounds expanded from alkanes to olefins, aromatics, and chlorinated hydrocarbons. Finally, further surface chemical modification is carried out using oleic acid to separate parts of oxygen-containing and nitrogen-containing organic compounds, approaching the level of commercial columns in terms of applications.