| 摘要: | 左旋葡萄醣(levoglucosan)與低分子量二元酸(low-molecular weight dicarboxylic acids)是大氣氣膠中常見且含量較高的水溶性有機碳化合物(water soluble organic carbons, WSOCs)，本研究將以不同衍生化方法搭配氣相層析質譜儀(GC/MS)對這兩類分析物進行衍生化方法之研究與偵測方法之開發。 本研究之第一目標，是以矽烷化衍生法將大氣氣膠中常見的三種複羥基類化合物，左旋葡萄醣、甘露聚醣、半乳聚醣衍生為低極性高揮發度的衍生物，同時搭配具有高靈敏度和良好分離效果的氣相層析質譜儀來對大氣環境進行分析檢測。衍生化研究以添加不同比例的促進劑(TMCS)至衍生化試劑(BSTFA, MSTFA)中，來探討不同配方衍生化試劑對最終衍生化產物的影響。研究結果顯示三個分析物無法完全衍生的主因乃是因為分子中具有三個相鄰的羥基(OH)所帶來的立體障礙而影響，然而隨著促進劑比例、衍生反應之溫度與時間的增加亦可使分析物增加完全衍生化之比例。最佳衍生化條件：溫度80℃，反應時間60分鐘，衍生化試劑BSTFA添加1% TMCS，未完全衍生化產物(bis-O-TMS)比例分別是半乳聚醣23%，甘露聚醣29%，左旋葡萄醣10%。在檢測上主要是偵測分析物完全衍生化之產物(tris-O-TMS)為主，而在上述衍生反應研究中可知未完全衍生化之產物仍佔有相當大的比例，本研究在定量檢測上將未完全衍生化產物加入計算，其結果與完全衍生化產物的定量比較皆小於11%。 本研究的第二目標，是以離子對試劑直接高溫衍生法對低分子量二元酸進行衍生化研究與偵測方法之開發，並觀察衍生化產物在質譜儀產生的斷裂情形。衍生化研究是以不同長度之碳鏈與陰離子的四烷基銨鹽類離子對試劑，來比較不同離子對試劑對分析物衍生化效果之影響，結果顯示以含氫氧根之四丁基銨鹽(TBA-OH)對於二元酸分析物的衍生化效果最佳，而最佳線上衍生化條件：注射埠溫度300℃，離子對試劑濃度為20 mM溶於甲醇中。在前處理步驟上，本實驗採用固相萃取法來取代減壓溶縮法，結果在固相萃取中真實樣品的添加回收率介在67-86%，精密度(RSD)為6-13%，說明本實驗的偵測方法具有良好的回收率與再現性，而本實驗所開發的偵測方法與傳統方法(Kawamura’s method)以Student’s t-test程序來比較實驗結果之差異，計算所得tcalculated為1.4498，小於95%的信心區間(confidence level)五自由度(degrees of freedom)下ttable值2.571，說明此二種方法用於檢測低分子量二元酸在95%的信心區間無明顯差異亦證明本實驗所開發之偵測方法的可行性。 Recent investigations on aerosol water-soluble organic compounds (WSOCs) formed by burning biomass have become increasingly concerned with the role of these compounds in atmospheric chemistry and their effect on climate, cloud formation and precipitation. Mono- saccharide anhydrides and low-molecular weight dicarboxylic acids are the two most important groups of WSOCs. The first part of this study is determination the three most commonly monosaccharide anhydrides (levoglucosan, mannosan and galactosan) in atmospheric aerosols using gas chromatography-mass spectrometry (GC-MS). Various silylating agents, mainly trimethylsilylating agents (TMS), were compared, and the effects of various contents of trimethyl- chlorosilane (TMCS, as a stimulator) were evaluated to optimize the conditions for detecting these compounds in aerosol samples. Differe- nces among the abundances of the derivatives were caused by the sterical hindrance of three hydroxyl groups in the structures of monosaccharide anhydrides. The effects of the reaction time and temperature were also examined. The optimal reaction time and temperature were 60 min and 80?C with 1% TMCS. Under these conditions, the percentages of formation of bis-O-TMS derivatives (as by-products) were 23%, 29% and 10% for galactosan, mannosan and levoglucosan, respectively. The concentrations of galactosan, mannosan and levoglucosan in particles of smoke samples ranged from 29 to 88 ng/m3, 23 to 69 ng/m3 and 77 to 380 ng/m3, respectively; and in particles of atmospheric aerosols ranged from 0.06 to 0.75 ng/m3, n.d. to 0.49 ng/m3 and 1.6 to 132 ng/m3, respectively. Levoglucosan was the dominant MAs detected in both type of samples. Less than 10% quantitation difference was obtained when bis-O-TMS derivatives were included in the calculation. The second part of this study is application of on-line derivatization technique to determine low-molecular weight dicarboxylic acids (from C2 to C10) in atmospheric aerosol samples. The technique involves direct derivatization in the GC injector using a large-volume sample device with tetrabutylammonium hydroxide as the derivatization agent. The butylated dicarboxylic acids were then separated and identified by ion- trap GC-MS with electron impact ionization. Solid-phase extraction method instead of rotary evaporation method was used to concentrate analytes from filter extracts. The recovery from filter extracts ranged from 67 to 86% with RSD less than 13%. The concentrations of dicarboxylated C2, C3, C4, C5 and C6-C10 in atmospheric aerosols ranged from 91-240 ng/m3, 11-56 ng/m3, 12-49 ng/m3, 8-35 ng/m3 and n.d. to 17 ng/m3, respectively. Comparison with off-line butylated method, compatible results were obtained by using on-line derivatization with shorter derivatization time and a small quantity of solvent consumed. |
