RCEES OpenIR  > 大气环境科学实验室
激发态质子转移电离方法的研发与应用
Alternative TitleResearch and application for excited proton transfer ionization
张海旭
Subtype博士
Thesis Advisor束继年 ; 杨波
2018-06
Degree Grantor中国科学院生态环境研究中心
Place of Conferral北京
Degree Name理学博士
Degree Discipline环境科学
Keyword激发态,质子转移,含氧挥发性有机物,胺类,嗅味物质 Excited State, Proton Transfer, Oxygenated Volatile Organic Compounds, Amines, Taste And Odor Compounds
Abstract

    挥发性有机物(VOCs)广泛存在于大气环境中,对人体健康有很大的威胁,目前VOCs已经成为环境检测的重要指标之一。然而,到目前为止,对VOCs的检测大多停留在离线分析,标准的方法仍然多为气相色谱?质谱联用(GC-MS)。由于仪器的检测灵敏度的限制,在很多情况下,样品在分析前需要预富集,大大增加了检测时间。在快速检测的中,光谱的方法应用较多,但这些方法局限性较大,也不能实现高灵敏、高选择性统一。本论文对新开发的电离技术进行了研究和应用,不仅拓展了目前对电离方法的认识,更有助于发掘新技术的应用潜力,具体的研究结果如下:

     (1)在低气压真空紫外光系统中,掺杂二氯甲烷能够显著提高含氧有机化合物的质子化效率,之前的研究一直在氪灯光源的作用下进行。本研究利用氙灯作为光源,其中的所有物质理论上均不能被电离,但是随着二氯甲烷的加入,乙醛、乙醇、丙酮的信号能够提高820---8100倍,最低检测限可达几十pptv。因此,新型的电离技术不受限于光子的能量,其作用原理与普通的光电离不同。由于氙灯条件下的检测灵敏度比氪灯条件低最少两个数量级,因此光子的能量是引发质子转移反应的重要因素。

     (2)本研究利用了氪灯的光源,对新型电离源的质子转移过程进行了机理研究。首先通过控制光通量分别特定总离子量和待测离子的信号强度,确定单个电离过程所需的光子数量为1。其次,通过同位素实验,用CD2Cl2代替CH2Cl2,在检测系统中再掺入额外的D2O,通过质谱的特性,得出CH2Cl2只是质子转移反应的重要参与者,并不是质子的贡献者,H2O是电离反应过程的质子源的结论。结合阴阳离子质谱图,确认电离反应的阳离子和阴离子产物分别为:水分子及其团簇分子的质子化离子、待测挥发性有机物 [M+H]+离子、CH2O、Cl-、HCl·Cl?、CH2Cl2·Cl?。

     (3)质子转移反应的标准摩尔焓变进行计算,可以发现质子转移反应及物质裂解的过程中Δr Hmθ >0,因此在理论上质子转移过程不能分步进行。只有在质子转移反应与产物自由基重组形成分子的过程同时进行时,释放的重组能参与反应才能满足Δr Hmθ < 0。通过对CHCl3、CH2Cl2、CH3Cl、CCl4的质子转移的辅助效果进行对比研究,发现CH2Cl2的作用效果最好,这与其在10 eV 的波长条件下产生离子对态的吸收截面最高相吻合。由此推测离子对的产生是制约此类质子转移反应的关键因素,新型电离源的作用机理也被推测为一种激发态的质子转移反应。由于水分子参与质子转移反应,因此湿度对物质的检测灵敏度具有影响。通过调节系统中的水分子含量,证明H2O在检测过程中不可或缺,但需要量极少。

     (4)在新型电离源的基础上,本研究建立了一种顶空的在线的水体致嗅物质的检测方法,以2?甲基丁醛、甲基叔丁醚(MTBE)、甲基丙烯酸甲酯(MMA)、2?异丁基?3?甲氧基吡嗪(IBMP)、2?异丙基?3?甲氧基吡嗪(IPMP)、β?环柠檬醛、二甲基异莰醇(2-MIB)、土臭素(GSM)为例对检测方法进行了验证和应用。结果表明新型电离源对以上8种物质均有显著的质子化效果,对于2?甲基丁醛、MTBE、MMA、IPMP、IBMP、β–环柠檬醛,检测信号为[M+H]+的质谱峰。对于2-MIB和GSM ,二氯甲烷对其质子化作用也较为显著,但是由于这两种物质的 [M+H]+ 离子十分不稳定,因此,主要检测峰为 [M+H-H2O]+。在二氯甲烷足量的条件下,其他碎片峰在真实样品中无法检出。这种新建立的顶空在线的检测方法与所研究的嗅味物质具有很好的线性相应(R2>0.99),检测灵敏度在9.2±0.4 至 131±3.5 counts per ng L-1范围内,最低检出限为 3.5-50.2 ng L-1,对于2-MIB和GSM ,预测出的最低检出限为 0.25 和 0.77 ng L-1。除此之外,本研究对该检测方法的精确度和准确度进行了测定,结合加标回收的实验方法,验证了新检测方法对浓度为几百 ng L-1的水样的可靠性。通过对自来水和北京的三条河流进行采样和分析,除了IBMP,其他7种嗅味物质均被检出,浓度范围为 0.2 到297 ng L-1。由于顶空蒸汽的湿度趋于饱和,通过测定相同浓度嗅味物质在25℃条件下高纯氮(RH<3%)、RH 20%、40、60、80、100条件下的的信号强度,发现不同物质对相对湿度具有不同的响应,在实际测样中,湿度的轻微改变(<20%)不会对测定结果有显著的影响。

     (5)除了含氧有机物,本研究利用激发态质子转移电离源结合飞行时间质谱仪建立了一种对胺类的在线检测方法,目前涉及了苯甲胺、苯乙胺、苯丙胺、及其同分异构体。结果表明,苯胺是一种芳香胺,其在新型电离源的作用下质子化的离子 [M+H]+ 成为主导信号。苯甲胺、苯丙胺、苯乙胺均为含苯环的脂肪胺,在激发态质子转移电离系统中,三者的质子化效率大大增加,但是由于其不稳定性,[M+H-NH4]+成为主要检测信号。二氯甲烷对含有苯环的胺类物质的信号增益大体相同,约为60-130倍,新型的检测方法在仪器具有狭缝的条件下,对苯胺和苯甲胺线性响应良好,检测灵敏度分别为4.0和2.7 counts·pptv-1,检测限分别为36 和22 pptv。

Other Abstract

     Volatilable organic compounds (VOCs) widely exist in ambient atmosphere, which is a big threat to human’s life. Nowadays, VOCs is an important environmental detec index. However, the exsting methods for VOCs detection mainly reliy on off-line analysis, and the standard method refers to gas chromatography mass spectrometry (GC-MS). In many cases, because of the limit of the detection sensitivities, pre-enrichment is necessary, which makes the analysis time consuming. Optical method is commonly used in rapid detecting, but this method is limited to some specific compounds, and cannot provide high sensitivity and selectivity data. This study investigates the newly-invented ionization technique, which broadens the existing knowledge of ionization mechanism. Besides, this work put this technique into application and reveals its potential. The corresponding results as well as preliminary applications are summarized in the following paragraphs:

     (1) In the low pressure vacuum-ultraviolet (VUV) photoionzation system, dichloromethane doping can enhance the protonation efficiency significantly. Previously, the investigation is performed under Kr lamp. In the current study, acetaldehyde, ethanol, and actone are investigated under Xe lamp. Hence, all the compounds in the system cannot be photo-ionized. The enhancement of acetaldehyde, ethanol, and actone are 820-8100 times after adequate dichloromethane added. Therefore, the newly invented ionization technique is not limited by the photon energy, which indicates that it can not be initiated by a photoionzation process. Because the detection sensitivity under Xe lamp irradiation is at least two magnitudes lower than that under Kr lamp irradiation, the photon energy is proved to be a vital influence factor for the efficiency of the proton transfer reaction.

     (2) The mechanism of the newly invented ionization is investigated under Kr lamp illumination. Firstly, by measuring the total ion flux and the signal intensities of each compound when adjusting the luminous flux, we conform than that the ion formation proceedes via a single-photon process. Secondly, in isotopic experiment, we use CD2Cl2 instead of CH2Cl2, or injecting extra D2O into the system, in order to acquire the characteristics of mass spectra. Accordingly, the results reveals that CH2Cl2 is just a participant in proton transfer reaction, and the only H donator is H2O. Combining the mass spectra of cations and anions, the products in the reaction is: H2O and its clusters, [M+H]+ ions of the investigated compounds, CH2O, Cl-, HCl·Cl?, and CH2Cl2·Cl?.

     (3) According to the calculations of standard molar enthalpies of reactions, ionization process without reorganization of OH and CH2Cl raidcals can not realized (Δr Hmθ >0). Only when the reorganization enegy of OH and CH2Cl raidcals to form HCl and CH2O is involved, the proton transfer reaction can occur (Δr Hmθ < 0). By comparing the proton effect of CHCl3, CH2Cl2, CH3Cl, and CCl4, with the formation cross-section of ion pairs, the ion-pair state is recognized as an important state for ionization. Besides, the ionization is classified into an excited proton transfer process. Considering the participation of H2O, humidity might influence the detection sensitivity. By adjusting the water content in the system, H2O is proved necessary but the demand is weak.

     (4) Based on the newly-invented ionization source, we develop a headspace detection method for taste and odor (T&O) compounds in water. 2-Methylbutyraldehyde, methyl tertiary butyl ether (MTBE), methyl methacrylate (MMA), 2-isobutyl-3-methyoxypyrazine (IBMP), 2-isopropyl-3-methoxypyrazine (IPMP), β-cyclocitral, 2-methylisoborneol (2-MIB), and geosmin (GSM) are investigated. The results show than the new ionization technique has significant protonation effects on the eight compounds. For 2-methylbutyraldehyde, MTBE, MMA, IPMP, IBMP, and β-cyclocitral, the detection signals are mass peaks of [M+H]+ ions. For 2-MIB and GSM, protonation effects are significant as well, but the [M+H]+ ions are unstable. Therefore, detection signals are mass peaks of [M+H-H2O]+ ions. All the fragment ions are negligible when dichloromethane is adequate when analyzing real samples. Besides, the instrument shows good linearty (R2>0.99) accoding to the linear calibration curve. For 2-Methylbutyraldehyde, MTBE, MMA, IBMP, IPMP, and β-cyclocitral, the detection sensitivities range from 9.2±0.4 to 131±3.5 counts per ng L-1, with the limits of detection (LODs) calculated to be 3.5-50.2 ng L-1. The LODs of 2-MIB and GSM are predicted in high purity nitrogen, and the datas are 0.25 and 0.77 ng L-1, respectively. The experiments for accuracy, precision, and recovery verifies that the detection method are reliable in several hundreds ng L-1 level. Besides, water samples from city tap water and three rivers in Beijing are sampled and assessed using this technique, and the investigated T&O compounds are detected with 0.2-297 ng L-1. Because the humidity of the headspace vapor is close to saturation, humidity influence are investigated under 25 °C. By comparing the signal intensity of the T&O compounds in high purity nitrogen (RH<3%), RH 20%, 40, 60, 80, and100, the influces are determined, which are different between differeny compounds. In real sample analysis, silght changes in humidity (<20%) will not make differences in the results.

     (5) This study also establishes an online analysis method for amine detection based on the excited pronton transfer ionization source combined with a time of flight mass spectrometry (TOF-MS), referring to aniline, benzylamine, phenylethylamine, amphetamine, and their structural isomers. The results shows that aniline, as a kind of aromatic amine, has a detction signal resulting from [M+H]+ion. Benzylamine, phenylethylamine, and amphetamine are aliphatic amine containing a benzene ring, which also can be greatly pronated in the new ionization system. However, because the [M+H]+ ions are unstable, [M+H-NH4]+ ions becomes the major signal for detection. The enhancement performances for the amines containing a benzene ring by dichloromethane are similar, which are about 60-130 times. In the study, a slit is placed at the entry orifice of the TOF cavity, reducing the ion transmission efficiency to ~10%. The current dection sensitivities are 4.0 and 2.7 counts·pptv-1, and the LODs are 36 and 22 pptv, respectively.

Pages147
Language中文
Document Type学位论文
Identifierhttp://ir.rcees.ac.cn/handle/311016/41578
Collection大气环境科学实验室
Recommended Citation
GB/T 7714
张海旭. 激发态质子转移电离方法的研发与应用[D]. 北京. 中国科学院生态环境研究中心,2018.
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