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题名: 高灵敏气相质谱仪的研制与应用
作者: 孙万启
学位类别: 博士
答辩日期: 2016-05
授予单位: 中国科学院研究生院
授予地点: 北京
导师: 束继年
关键词: 高灵敏质谱,单光子电离,挥发性有机物,二噁英,炸药和军事毒剂检测,痕量检测, ; High-sensitive gas mass spectrometer, SPI, VOCs, Dioxin, Explosives and chemical warfare agents detection, Trace detection,
其他题名: Development of a high-sensitive gas mass spectrometer and its application
学位专业: 环境工程
中文摘要:     挥发性有机物(VOCs)广泛存在于自然大气和各类人工环境中,一方面直接危害人体健康,另一方面会促进光化学烟雾、近地臭氧和细颗粒物的生成。其物化性质易变、含量较低,所以发展VOCs的在线检测技术具有重要意义。单光子电离是一种“软”电离,对多数物种可实现无碎片电离,应用在VOCs在线检测中具有优势。本论文介绍了一台自主研发的高灵敏气相质谱仪,并利用此质谱仪对城市空气中的VOCs与焚烧炉模拟烟气中二噁英的前体物进行了在线监测。主要研究成果和创新性如下:
    (1)该高灵敏气相质谱仪是一台真空紫外单光子电离质谱,主要由进样管、射频放电紫外灯、电离器、离子迁移镜、反射式飞行时间质量分析器、数据采集系统和真空系统构成。其进样方式为直接进样,紫外灯输出的光子能量为10.03 eV,质量分析器中离子飞行长度为460 mm,真空系统采用三级差分设计。仪器采用带挡光板的电离器时,最优射频放电功率为50 W,最优前级压力为50 Pa.其噪声水平比仪器装配直通型电离器时降低了88.5%,所以带挡光板的电离器被确定为标配。该仪器的性能指标最终确定为分辨率260(m/△m),灵敏度~1.3 counts/pptv,检测限~3 pptv(S/N = 2)。
    (2)大气中VOCs的平均浓度一般都低于1 ppbv,检测难度较大。利用该高灵敏气相质谱仪对北京城市大气中的VOCs进行了为期6天的在线监测,结果显示:VOCs的质谱峰出现在m/z= 43,47,51,61,69,78,92,106,120和128处,推定m/z= 78,92,106,120和128为苯、甲苯、二甲苯\乙苯、C3-苯的衍生物和萘。苯及其衍生物的浓度变化趋势几乎相同,且都与风速的变化趋势相反,这说明风是去除北京城市大气中VOCs的最有效手段之一。苯的浓度变化范围为0.1-3.2 ppbv。
    (3)利用该高灵敏气相质谱仪对实验室内和实验室外的空气成分进行了测定,结果显示苯及其同系物是室内外空气的主要污染物之一,室内空气成分更复杂,相应污染物含量更高。对油漆门窗后的室内空气的检测发现,其含有大量的苯的同系物。甲苯和二甲苯的含量分别比未油漆的室内空气中相应物质的含量高了15倍和30倍。
    (4)氯苯类物质是一类重要的二噁英前体物,可作为二噁英指示物。利用该高灵敏气相质谱仪对一氯苯、1,2-二氯苯和1,2,4-三氯苯纯物质进行检测,得到其准确、明显的母体信号峰,获得了良好的线性响应。本仪器对三种氯苯的检出限分别低至4.7、8.7和11.9 pptv(S/N=2)。利用本仪器对聚氯乙烯燃烧产生的模拟烟气进行在线监测,一氯苯和三氯苯被检出,二氯苯未被检出,获得了一氯苯的实时监测数据。此实验说明,该高灵敏气相质谱仪具有对燃烧烟气中二噁英前体物在线监测的能力。
    (5)安全类物质的现场检测需要高灵敏的仪器。本仪器用于爆炸类物质和军事毒剂模拟物的在环境条件下的痕量检测研究。在10s检测时间下,2,4-二硝基甲苯, 硝基甲苯, 硝基苯, 和甲基磷酸二甲酯四种物质的灵敏度分别为 30, 0.5, 4, and 1 pptv。与之前真空紫外光电离法用于检测爆炸类物质和军事毒剂模拟物的检测相比, 灵敏度改善了3-4 数量级。实验结果表明该仪器能够用于炸药和军事毒剂类物质的高灵敏检测。
    此高灵敏气相质谱仪提供了一种高灵敏的VOCs检测方法,可以为环境、工业、安全科学中VOCs检测提供快速便捷准确的分析。
英文摘要:     VOCs are universal in the atmosphere and a variety of artificial environments. They can harm human health directly, and are related to the generation of photochemical smog, ground-level ozone and fine particles. Because of the changeable physico-chemical properties and low concentrations, it is of importance that on-line detection techniques are developed. Ionizations with fragment free for the majority of organic compounds are obtained by the single-photon ionization, as a “soft” ionization, so it has more advantages in on-line detection. In this paper, a laboratory-built high-sensitive gas mass spectrometer (HS-G-MS) was developed. Using this HS-G-MS, the VOCs in urban air and precursors of dioxins in the simulated incinerations flue gas were detected on-line. The main results were as follows:
    (1) The HS-G-MS is a vacuum ulta-violet (VUV) single-photon ionization mass spectrometer. It consists of a sampling tube, a radio frequency-powered, a photoionizer, an ion-immigration optics, a reflectron time-of-flight MS, a data acquisition system, and a vacuum pumping system. The direct-inlet was adopted. The photon energy emitted by the VUV lamp is 10.03 eV. The ion flight length is 160 mm. A three-stage differential pumping system was adopted. Via adjusting the sampling pressures and the discharge powers of the VUV lamp, 50 Pa and 50 W is optimal for the HS-G-MS with photoionizer Ⅱ. Further, photoionizer Ⅱ was determined to be the one which assembled to the HS-G-MS finally. The final performance of the HS-G-MS: resolution ratio is 260(m/△m);detection sensitivity is ~1.3 counts/pptv; limit of detection for benzene is ~3 pptv(S/N=2).
    (2) The average volume fractions of VOCs, in addition to methane, in the atmosphere are generally less than 1 ppbv, so it is difficult for the detection of them. A 6-days online monitoring for the VOCs in the urban air of Beijing was conducted by using this HS-G-MS. In the mass spectrum, mass peaks at m/z 43, 47, 51, 61, 69, 78, 92, 106, 120, and 128 correspond to the VOCs. The mass peaks observed at m/z 78, 92, 106, 120, and 128 can be attributed to benzene, toluene, xylene/ethylbenzene, C3-alkylated benzene derivatives, and naphthalene, respectively. The concentration variations of benzene and its derivatives have a good simultaneity. However, they show a remarkable opposite trend to the wind speeds. These interesting observation results reveal that the wind can remove effectively the airborne pollutants. The concentrations of benzene were found to range between 0.1 and 3.2 ppbv in the atmosphere.
    (3) Using this HS-G-MS, the VOCs of indoor and outdoor air were analyzed. The result shows that benzene and its derivatives are a kind of main pollutants in the indoor and outdoor air. When comparing the compositions of indoor air with outdoor air, indoor air has more compositions and the VOCs concentrations of indoor air by far higher than that in outdoor air. The spectrum of air in the room with its door newly painted shows that more alkylated derivatives of benzene exist, but benzene don’t. The concentration of toluene and xylene/ethylbenzene in the air of newly painted room are enhanced as high as 15 and 30 folds than that in the ordinary one.
    (4) Chlorobenzenes are important dioxin precursors which have been suggested as indicators for monitoring the dioxins in waste incineration flue gas. In this study, the HS-G-MS was applied to the detection of mono-chlorobenzene, 1,2-dichlorobenzene, and 1,2,4-trichlorobenzene. Accurate and distinct parent molecular ions were observed. The signal intensity of the molecular ion showed a good linear relation with real concentration of the standard gas. The detection limits for the three chlorobenzenesare4.7, 8.7and 11.9 pptv, respectively. The HS-G-MS was also applied to the online measurements of the dioxin precursors in the simulated flue gas from the PVC combustion. The mono-chlorobenzene and 1,2,4-trichlorobenzene were detected, but the 1,2-dichlorobenzene was not. The real-time emission profiles of mono-chlorobenzene in the simulated flue gas was obtained. The experimental results shows that the HS-G-MS has the competence to on-line monitor dioxin precursors.
    (5) On-spot monitoring of threat agents needs high sensitive instrument. In this study, the HS-G-MS was employed to detect trace amounts of vapor-phase explosives and chemical warfare agent mimetics under ambient conditions. Under 10-s detection time, the limits of detection of 2,4-dinitrotoluene, nitro-toluene, nitrobenzene, and dimethyl methyl phosphonate were 30, 0.5, 4, and 1 parts per trillion by volume, respectively. As compared to those obtained previously with PI mass spectrometric techniques, an improvement of 3–4 orders of magnitude was achieved. The experimental results shows that the HS-G-MS has the competence of trace detection of explosives and chemical warfare agents.
    The laboratory-built HS-G-MS has offered an ultra-sensitive analytical method for online real-time VOCs detections. The method may provide a potential tool for a rapid and reliable analysis of the environmental, the industry, and the security sciences.
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/36958
Appears in Collections:大气环境研究室_学位论文

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Recommended Citation:
孙万启. 高灵敏气相质谱仪的研制与应用[D]. 北京. 中国科学院研究生院. 2016.
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