Atmospheric pressure chemical ionisation study of selected volatile organic compounds (VOCs) by ion mobility spectrometry
coupled with orthogonal accelerated Time Of Flight Mass Spectrometry
離子遷移譜(IMS)和正交加速飛行時間質譜(oaTOF-MS)法對選定的揮發性有機化合物（VOC）進行大氣壓化學電離研究
1Bartosz Michalczuk, 1Ladislav Moravský, 1Jana Hrdá and 1,2Štefan Matej?ík
1Comenius University in Bratislava, Faculty of Mathematics, Physics and Informatics,
Department of Experimental Physics, Mlynská dolina F2 842 48, Bratislava, Slovakia
2National Research Nuclear University MEPhI, Kashirskoe Sh 31, Moscow 115409, Russia
Abstract
In this work, we present an Atmospheric Pressure Chemical Ionisation (APCI) study of several organic solvents relevant to Thin Layer Chromatography (TLC) (methanol, ethanol, propan-2-ol, acetone, ethyl acetate, diethylamine). The solvents were investigated using an Ion Mobility Spectrometry (IMS) combined with orthogonal acceleration Time Of Flight Mass Spectrometry (IMS-oaTOF MS). The solvents were iononised by Reactant Ions (RI – H+.(H2O)3,4 m/z 55 and 73). The ions were analysed using IMS and IMS-oaTOF technique was used to assign the ion mobility peaks to ions according to their m/z. IMS spectra of methanol, ethanol, propan-2-ol and diethylamine exhibited only one peak (reduced ion mobilities of 2.19, 2.07, 1.98, 2.06 cm2.s-1.V-1 respectively) whereas acetone and ethyl acetate were characterised by two peaks (2.15, 1.85 and 1.94, 1.53 cm2.s-1.V-1 respectively). The IMS-oaTOF spectrometry assigned IMS peaks of VOCs to M.H+(H2O)n.n=0,1,2 or M2 .H+ ions, where M represents the solvent molecule.
本文對幾種與薄層色譜(TLC)有關的有機溶劑(甲醇、乙醇、丙醇、丙酮、乙酸乙酯、二乙胺)進行了常壓化學電離(APCI)研究。采用離子遷移譜法(IMS)和正交加速飛行時間質譜法(IMS-oaTOF-MS)對溶劑進行了研究。溶劑被反應離子(RI–H+(H2O)3,4 m/z 55和73)離子化。利用IMS和IMS-oaTOF技術對離子進行了分析，并根據離子的m/z來確定離子遷移率峰，甲醇、乙醇、丙醇和二乙胺的IMS光譜僅顯示了一個峰(離子遷移率分別降低了2.19、2.07、1.98、2.06 cm~2.s-1.V-1)，而丙酮和乙酸乙酯的IMS光譜則顯示了一個有兩個峰(分別為2.15、1.85和1.94、1.53 cm~2.s-1.V-1)。IMS-oaTOF光譜法將VOCs的IMS峰分配給M.H+(H2O)n. n=0,1,2或M2.H+離子，其中M表示溶劑分子。
Introduction
VOCs are widely used in the chemical synthesis and chemical industry. In analytical chemistry, VOCs solvents are used in the processes of sample preparation and in different chromatographic techniques. Traces of the VOCs are thus very often present in the laboratory environment and in the analytical samples. In the case of hyphenated technique, such as thin layer chromatography (TLC) with IMS (TLC-IMS), we deal with the problem of the presence of the solvents VOCs contaminants in the IMS spectra. For this reason, we have carried out a study focused on the identification of the solvents present in the TLC samples. In addition,
we have tried to understand the processes of ion formation from VOCs in IMS as they may interact with the analytes and influence the response of the system1,2,3. In present study we have selected six VOCs – solvents (methanol, ethanol, propan-2-ol, acetone, diethylamine and ethyl acetate) and we have recorded their IMS spectra in positive polarity Atmospheric Pressure Chemical Ionisation Ion Mobility Spectrometry (APCI-IMS) and by the Ion Mobility Spectrometry-orthogonal acceleration Time Of Flight Mass Spectrometry technique (IMS – oaTOF MS). To the selected solvents belong monohydric alcohols - methanol, ethanol, propan-2-ol, which
are widely used not only as a solvent but also in other applications, e.g., as a fuel additives (methanol, ethanol) or substrates for the synthesis of other compounds (methanol is used to produce formaldehyde)2,4,5,6. Alcohols due to their ubiquity were investigated by IMS with many different ionization sources i.e. UV, 63Ni or corona discharge. Depending on their concentration one or two peaks were observed in IMS spectra corresponding to monomer and dimer formation. From available literature ions like M·H+·(H2O)m or M2·H+·(H2O)m formed in the reaction region of IMS7,8,9. Another important and widespread solvent is acetone, also known as 2-propanone or dimethyl ketone with chemical formula CH3COCH3. It is volatile, flammable, colourless compound miscible in water. Acetone is mainly used as a solvent and as an intermediate in many syntheses of organic compounds1,10 . Regarding acetone’s high volatility and high proton affinity, it is possible to detect it at very low concentration. In most cases, even trace level in a range of ppb is enough to detect acetone by IMS. Vautz et al. has observed in positive polarity and radioactive ion source two peaks in the IMS spectrum and assigned them to MH+ and M2H+11.
VOCs廣泛應用于化學合成和化工行業。在分析化學中，揮發性有機物溶劑用于樣品制備過程和不同的色譜技術。因此，在實驗室環境和分析樣品中，揮發性有機化合物的痕跡經常存在。在聯用技術的情況下，如薄層色譜(TLC)和IMS(TLC-IMS)，我們處理的是IMS光譜中溶劑VOCs污染物的存在問題。為此，我們開展了一項研究，重點是鑒別薄層色譜樣品中的溶劑。此外，我們試圖了解IMS中VOCs的離子形成過程，因為它們可能與分析物相互作用并影響系統1、2、3的響應。在本研究中，我們選擇了六種揮發性有機化合物-溶劑(甲醇、乙醇、丙醇、丙酮、二乙胺和乙酸乙酯)，并在正極性大氣壓化學電離離子遷移譜(APCI-IMS)和離子遷移譜正交加速飛行時間質譜中記錄了它們的IMS譜光譜分析技術(IMS-oaTOF MS)。所選溶劑為一元醇-甲醇、乙醇、丙烷-2-醇，其中不僅廣泛用作溶劑，也廣泛用于其他用途，例如用作燃料添加劑(甲醇、乙醇)或用于合成其他化合物(甲醇用于生產甲醛)2,4,5,6的基質。利用IMS研究了不同電離源(UV、63Ni或電暈放電)對醇類化合物的影響。根據它們的濃度，在IMS光譜中觀察到一個或兩個對應于單體和二聚體形成的峰。從現有文獻來看，IMS7,8,9反應區形成的離子有M·H+·(H2O)M或M2·H+·(H2O)M。另一種重要且廣泛使用的溶劑是丙酮，也稱為2-丙酮或二甲酮，化學式為CH3COCH3。它是易揮發、易燃、無色的化合物，可混溶于水。丙酮在許多有機化合物1，10的合成中主要用作溶劑和中間體。由于丙酮的高揮發性和高質子親和力，可以在很低的濃度下進行檢測。在大多數情況下，即使在ppb范圍內的微量水平也足以通過IMS檢測丙酮。Vautz等人。在正極性和放射性離子源中觀察到IMS光譜中的兩個峰值，并將它們分配給MH+和M2H+11。
Amines are a widespread contaminant in the environment due to their industrial applications or their use as intermediates in chemical and pharmaceutical syntheses12,13,14. The amines are unique as they can form several types of isomers: linear, positional isomers, primary, secondary, and tertiary amines, branched, and cyclic structures and finally, also aromatic isomers15. Due to their odorous and toxic characteristics, these compounds have received much attention as environmental pollutants 16. Some of them are sensitizers and irritants to the skin, mucous membrane and respiratory tract17. The most frequently used techniques for the determination of amines in air and liquid samples are gas chromatography (GC) coupled with different detectors, high-performance liquid chromatography (HPLC) 18 , 19 ion chromatography20, spectrophotometry21 and capillary electrophoresis22. In some cases, for detection of amines in gas and liquid phase ion mobility spectrometry (IMS) has been used23. Due to their high proton affinities, amines protonate readily in the IMS source, and there is usually little doubt about the site of protonation, as the nitrogen electron lone pair is the favoured site. In most cases, the major ionic product is the protonated molecule, although in some cases protonated dimers or molecular or fragment ions are also formed14. One of the most important amines is a secondary amine named diethylamine - (DEA) (Chemical formula - C4H11N) which is a strong base compound miscible with most solvents. It is used as an anti-corrosion agent, as well as in rubber, synthetic resin, paint and drug manufacturing. It is used in the production of certain agrochemicals, such as rice herbicides or insecticides pharmaceuticals, radical scavengers and insect repellents24. In some cases, DEA is frequently used as a chemical reducer25,26.
胺是一種廣泛存在于環境中的污染物，由于其工業應用或在化學和藥物合成中用作中間體12、13、14。胺是*的，因為它們可以形成幾種異構體：線性、位置異構體、一級、二級和三級胺、支鏈和環狀結構，后還有芳香異構體15。由于它們的氣味和毒性特征，這些化合物作為環境污染物16受到了廣泛關注。其中一些是皮膚、粘膜和呼吸道的致敏劑和刺激物17。用于測定空氣和液體樣品中技術是氣相色譜(GC)與不同檢測器的耦合、高效液相色譜(HPLC)18、19離子色譜20、分光光度計21和毛細管電泳22。在某些情況下，氣相和液相離子遷移率光譜法(IMS)已用于檢測胺類化合物23。由于胺具有很高的質子親和力，因此在IMS源中很容易發生質子化，而且通常對質子化的位置幾乎沒有疑問，因為氮-電子孤對是利的位置。在大多數情況下，主要的離子產物是質子化分子，盡管在某些情況下，質子化二聚體或分子或片段離子也形成14。重要的胺之一是二乙胺(DEA)(化學式-C4H11N)，它是一種強堿性化合物，可與大多數溶劑混溶。用于橡膠、合成樹脂、涂料和藥品制造等領域。它用于生產某些農用化學品，如水稻除草劑或殺蟲劑藥物、自由基清除劑和驅蟲劑24。在某些情況下，DEA經常被用作化學還原劑25，26。
Ethyl acetate is the organic compound (Chemical formula C4H8O2) synthesized in the industry from ethanol and acetic acid. It is widely used as a solvent in the production of pharmaceuticals, essential ingredients in many products and materials, in variety of coating formulations such as epoxies, urethanes, cellulosic, acrylics and vinyls, fragrances in food production and precursors of important chemicals being favoured because of its low cost, low toxicity and agreeable odour27. In high purity, it can be used as a viscosity reducer for resins used in photoresist formulations in the electronics industry. Ethyl acetate is rarely selected as a reactant due to its tendency to hydrolysis and transesterification28,29. Mixtures containing ethyl acetate are commonly used in column-liquid chromatography and extractions. Because of its high polarity index (4.4) ethyl acetate can be used very frequently as a polar-solvent to run TLC (Thin Layer Chromatography)30,31,32,33,34.
乙酸乙酯是工業上由乙醇和乙酸合成的有機化合物(化學式C4H8O2)。它被廣泛用作藥物生產中的溶劑，在許多產品和材料中的基本成分，在各種涂料配方中，如環氧樹脂、聚氨酯、纖維素、丙烯酸和乙烯基酯、食品生產中的香料和重要化學品的前體由于其低成本而受到青睞。毒性低，氣味適中。在高純度的情況下，它可以用作電子工業中用于光刻膠配方的樹脂的降粘劑。乙酸乙酯很少被選作反應物，因為它傾向于水解和酯交換28,29。含有乙酸乙酯的混合物通常用于柱液相色譜和萃取。乙酸乙酯由于其極性指數高(4.4)，可以非常頻繁地用作極性溶劑來運行TLC(薄層色譜法)30、31、32、33、34。
