A Reflectron Time-of-Flight Mass Spectrometer with a Nano-Electrospray Ionization Source for Study of Metal Cluster Compounds

An experiment facility has been set up for the study of metal cluster compounds in our laboratory, which consists of a nano-electrospray ionization source, an ion transmission and focus system, and a reflectron time-of-fight mass spectrometer. Taking advantage of the nano-electrospray ionization source, polyvalent ions are usually produced in the ＂ionization＂ process and the obtained mass resolution of the equipment is over 8000. The molecular ion peaks of metal cluster compounds [Au20（PPhpy2）10Cl2]（SbF6）4, where PPhpy2=bis（2- pyridyl）phenylphosphine, and [AuaAg2（C）L6]（BF4）4, where L=2-（diphenylphosphino）-5- methylpyridine, are distinguished in the respective mass spectrum, accompanied by some fragment ion peaks. In addition, the mass-to-charge ratios of the parent ions are determi- nated. Preliminary results suggest that the device is a powerful tool for the study of metal cluster compounds. It turns out that the information obtained by the instrumentation serves as an essential supplement to single crystal X-ray diffraction for structure characterization of metal cluster compounds.

Characterization of Organic Aerosols in Beijing Using an Aerodyne High-Resolution Aerosol Mass Spectrometer

Fine particle of organic aerosol （OA）, mostly arising from pollution, are abundant in Beijing. To achieve a better un- derstanding of the difference in OA in summer and autumn, a high-resolution time-of-flight aerosol mass spectrometer （HR- ToF-AMS, Aerodyne Research Inc., USA） was deployed in urban Beijing in August and October 2012. The mean OA mass concentration in autumn was 30 4-30 μg m-3, which was higher than in summer （13 4-6.9 μg m-3）. The elemental anal- ysis found that OA was more aged in summer （oxygen-to-carbon （O/C） ratios were 0.41 and 0.32 for summer and autumn, respectively）. Positive matrix factorization （PMF） analysis identified three and five components in summer and autumn, re- spectively. In summer, an oxygenated OA （OOA）, a cooking-emission-related OA （COA）, and a hydrocarbon-like OA （HOA） were indentified. Meanwhile, the OOA was separated into LV-OOA （low-volatility OOA） and SV-OOA （semi-volatile OOA）; and in autumn, a nitrogen-containing OA （NOA） was also found. The SOA （secondary OA） was always the most important OA component, accounting for 55% of the OA in the two seasons. Back trajectory clustering analysis found that the origin of the air masses was more complex in summer. Southerly air masses in both seasons were associated with the highest OA loading, while northerly air masses were associated with the lowest OA loading. A preliminary study of OA components, especially the POA （primary OA）, in different periods found that the HOA and COA all decreased during the National Day holiday period, and HOA decreased at weekends compared with weekdays.

Modification of Reflectron Time-of-Flight Mass Spectrometer for Photodissociation of Mass-Selected Cluster lons

We introduce a modification of reflectron time-of-flight mass spectrometer for laser photodissociation of mass-selected ions. In our apparatus, the ions of interests were selected by a mass gate near the first space focus point and decelerated right after the mass gate, were then crossed by a laser beam for dissociation. The daughter ions and surviving parent ions were re-accelerated and analyzed by the reflectron time-of-flight mass spectrometer. Compared to the designs reported by other research groups, our selection-deceleration-dissociation-reacceleration approach has better daughter-parent-ions-separation, easier laser timing, and better overlapping between the ion beam and laser beam. We also conducted detailed cal- culations on the parent ion and daughter ion flight times, and provided a simplified formula for the calibration of daughter ion mass.

Mass Spectrometric Studies on Metal-hexafluorobenzene Anionic Complexes(M=Ag, Au, Pd, Pt, Pb and Bi)

The anionic products from the reactions between metal（M=Ag, Au, Pd, Pt, Pb and Bi） vapour produced by laser ablation and hexafluorobenzene seeded in carrier gas（Ar） were studied by means of a homemade reflectron time-of-flight mass spectrometry（RTOF-MS）. Experimental results show that the dominant products were [MmC6F6]^- complexes for the reactions ofAg, Au, Pd and Pt with C6F6, while the dominant products were [MmC6F5]^- complexes for the reactions of Pb and Bi with C6F6. The formation mechanisms of the products, including the adsorption of metal cluster anions on hexafluorobenzene and the C--F cleavage induced by metal cluster anions, were discussed.

不同烟草制品烟气气溶胶的粒径和成分对比研究

该文通过自行设计的在线捕集稀释装置采集烟气气溶胶,采用单颗粒气溶胶质谱仪(SPAMS)测定不同烟草制品主流烟气气溶胶中粒状物的粒径分布和含特定成分的粒状物数浓度随粒径的变化规律。结果表明三种烟草制品烟气气溶胶粒相物粒径的尺寸在0.15μm到0.6μm之间服从正态分布规律,且在0.3~0.45μm范围内分布最为集中。三种烟草制品中含有芳香烃、有机碳和烟碱成分的粒状物占有较高比例,且不同类型的化合物在不同粒径气溶胶中呈现的分布趋势大致相同。含有特征化合物烟碱的粒状物呈现出传统卷烟<电子烟<加热不燃烧卷烟的总体趋势。致癌或促癌的化合物,包括芳香烃和重金属在传统卷烟、电子烟和加热不燃烧卷烟烟气气溶胶中的相对含量呈现逐渐增加的趋势。该文成果有助于研究烟草制品的烟气产生方式和产生条件对烟气气溶胶粒状物粒径和成分的分布规律影响。

在线测量技术在大气有机气溶胶研究中的应用与展望

有机气溶胶作为大气颗粒物的主要组成部分,对气候、空气质量和人体健康造成重要影响。鉴于有机气溶胶在大气中复杂的化学结构及其动态变化,对有机气溶胶进行高时间、高化学分辨率的测量是研究有机气溶胶来源及生成机制的关键。本文综述了多种近期发展的有机气溶胶在线测量仪器的结构、工作原理及应用,介绍的仪器包括在线气溶胶质谱仪、热脱附气溶胶气相色谱仪、气溶胶化学分析入口–质子转移反应飞行时间质谱仪、基于气体和气溶胶的过滤器进样口的化学电离质谱仪和萃取电喷雾电离飞行时间质谱仪等。重点总结了近年来这些技术在大气有机气溶胶外场观测中的应用,以及在有机气溶胶组分表征和来源解析等方面的进展。探讨了目前有机气溶胶在线测量中亟待解决的难点,并对测量技术未来的发展趋势进行了展望。

用于生物气溶胶质谱检测的泵送逆流虚拟切割器研究

单颗粒气溶胶质谱仪(SPAMS)可以提供高时间分辨率和高灵敏度的颗粒物粒径分布和质谱数据组成,广泛应用于大气气溶胶检测和大气科学研究领域。大气环境中的微米级大颗粒数浓度远小于亚微米级小颗粒物,在单颗粒气溶胶质谱的检测中,颗粒经空气动力学加速赋能后,小颗粒物的飞行速度大于大颗粒物,导致生物气溶胶等大颗粒的检测几率大幅度降低。该研究设计了一种泵送逆流虚拟切割器(PCVI),通过3D建模、计算流体动力学(CFD)仿真、实际实验测试以及对实际样品藻类气溶胶的检测,详细介绍了PCVI的实现原理、数据仿真、性能验证与实际应用。PCVI与SPAMS联用,可形成对小颗粒物具有切割能力的PC⁃VI-SPAMS系统,对藻类生物气溶胶的检测证实,所研制的PCVI可以有效去除2μm粒径以下的颗粒,成功对小颗粒背景进行切分,获得了符合预期的效果。

宜兴东南部区域春季大气细颗粒物在线源解析

为探讨宜兴东南部区域春季大气细颗粒物化学特征及来源,利用单颗粒气溶胶飞行时间质谱仪(SPAMS 0515)对其开展为期19天的在线监测。结果显示:主要污染源为扬尘源(39.4%)、二次无机源(25.7%),相较优良时段,污染时段下的二次无机源、扬尘源占比分别上升7.4个百分点和5.0个百分点。监测期间,3次PM_(2.5)浓度升高主要受到扬尘源的排放影响,1次PM_(2.5)浓度升高主要受到二次无机源的影响;早晚交通高峰期的机动车尾气源对PM_(2.5)浓度升高也有一定贡献。

In situ measurement of PM_1 organic aerosol in Beijing winter using a high-resolution aerosol mass spectrometer

Organic aerosol (OA) is a crucial component of atmospheric fine particles. To achieve a better understanding of the chemical characteristics and sources of OA in Beijing, the size-resolved chemical composition of submicron aerosols were measured in-situ using a High-Resolution Time-of-Flight Aerosol Mass Spectrometer in the winter of 2010, with a high time resolution of 5 min. During this study, the mean OA mass concentration was 20.9±25.3 μg/m3, varying between 1.9 and 284.6 μg/m3. Elemental analysis showed that the average H/C, O/C and N/C (molar ratio) were 1.70, 0.17, and 0.005, respectively, corresponding to an OM/OC ratio (mass ratio of organic matter to organic carbon) of 1.37. The average mass-based size distributions of OA present a promi- nent accumulation mode peaking at approximately 450 nm. The prominent presence of ultrafine particles (Dva < 100 nm) was mainly from the fresh emissions of combustion sources. A Positive Matrix Factorisation (PMF) analysis of the organic mass spectral dataset differentiated the OA into three components, including hydrocarbon-like (HOA), cooking-related (COA), and oxygenated (OOA) organic aerosols, which, on average, accounted for 26.9%, 49.7% and 23.4%, respectively, of the total organic mass. The HOA and COA likely corresponded to primary organic aerosol (POA) associated with combustion-related and cooking emissions, respectively, and the OOA components corresponded to aged secondary organic aerosol (SOA).

A collinear tandem time-of-flight mass spectrometer for infrared photodissociation spectroscopy of mass-selected ions

An apparatus based on collinear tandem time-of-flight mass spectrometer has been designed for the measurement of infrared photodissociation spectroscopy of mass-selected ions in the gas phase.The ions from a pulsed laser vaporization supersonic ion source are skimmed and mass separated by a Wiley-McLaren time-of-flight mass spectrometer.The ion of interest is mass selected,decelerated and dissociated by a tunable IR laser.The fragment and parent ions are reaccelerated and mass analyzed by the second time-of-flight mass spectrometer.A simple new assembly integrated with mass gate,deceleration and reacceleration ion optics was designed,which allows us to measure the infrared spectra of mass selected ions with high sensitivity and easy timing synchronization.

Pollutants identification of ambient aerosols by two types of aerosol mass spectrometers over southeast coastal area, China

Two different aerosol mass spectrometers, Aerodyne Aerosol Mass Spectrometer（AMS） and Single Particle Aerosol Mass Spectrometer（SPAMS） were deployed to identify the aerosol pollutants over Xiamen, representing the coastal urban area. Five obvious processes were classified during the whole observation period. Organics and sulfate were the dominant components in ambient aerosols over Xiamen. Most of the particles were in the size range of 0.2–1.0 μm, accounting for over 97% of the total particles measured by both instruments.Organics, as well as sulfate, measured by AMS were in good correlation with measured by SPAMS. However, high concentration of NH4＋was obtained by AMS, while extremely low value of NH4＋was detected by SPAMS. Contrarily, high particle number counts of NO3-and Clwere given by SPAMS while low concentrations of NO3-and Cl-were measured by AMS. The variations of POA and SOA obtained from SPAMS during event 1 and event 2 were in accordance with the analysis of HOA and OOA given by AMS, suggesting that both of AMS and SPAMS can well identify the organic clusters of aerosol particles. Overestimate or underestimate of the aerosol sources and acidity would be present in some circumstances when the measurement results were used to analyze the aerosol properties, because of the detection loss of some species for both instruments.

Radiofrequency field enhanced chemical ionization with vacuum ultraviolet lamp for miniature time-of-flight mass spectrometer

It is difficult to rapidly and on-line detect trace volatile organic compounds for miniature massspectrometry due to its limited sampling volume at slow pumping speed. In this paper, we developed anew radiofrequency field enhanced chemical ionization source （RF-ECI） with vacuum ultraviolet （VUV）lamp by coupling radiofrequency electric field and direct-current field together. The experiment resultsshowed that the sensitivity of benzene, toluene, hydrogen sulfide and other compounds increased by 2-3orders of magnitude under the introduction of RF-ECI comparing to traditional single photon ionization（SPI）. At the same time, the reagent ion of O2＋ realized the charge transfer reaction chemical ionization,and the RF-ECI effectively expanded the detection range of the VUV lamp based SPI. The VUV lamp hasinherent advantages in the on-site analytical instrument for its small size and low power consumption,and the VUV lamp based RF-ECI miniature time-of-flight mass spectrometer （TOFMS） has a limit-of-detection for H2S as low as 0.0571 mg/m3, and it is expected to be used widely in the field of on-site rapidanalvsis.

Chemical composition and size distribution of secondary organic aerosol formed from the photooxidation of isoprene

Photooxidation of isoprene leads to the formation of secondary organic aerosol （SOA）. In this study, the chemical composition of SOA formed from OH-initiated photooxidation of isoprene has been investigated with gas chromatography/mass spectrometry （GC/MS） and a home-made aerosol time-of-fiight mass spectrometer. Sampling particles generated in a home-made smog chamber. The size distribution of SOA particles was detected by a TSI 3321 aerodynamic particle size spectrometer in real time. Results showed that SOA created by isoprene photooxidation was predominantly in the form of fine particles, which have diameters less than 2.5 μm. The obtained mass spectra of individual particles show that products of the OH-initiated oxidation of isoprene contain methyl vinyl ketone, methacrolein, formaldehyde, and some other hydroxycarbonyls. The possible reaction mechanisms leading to these products were also discussed.

气溶胶单粒子化学成分的实时测量

自行设计了国内第一台可实时测量气溶胶单粒子化学成分的气溶胶飞行时间质谱仪 ,并用该仪器对两类燃烧过程产生的气溶胶粒子进行了实时测量。实验结果展示了本仪器能够同时实现实时在线测量和单粒子检测 ,从而克服了传统的离线检测方法如色谱法、化学方法的局限性。

运用单颗粒气溶胶质谱技术初步研究广州大气矿尘污染

自主研发的单颗粒气溶胶飞行时间质谱仪(Single Particle Aerosol Mass Spectrometer,SPAMS)采用空气动力学透镜、双激光测径系统以及双极飞行时间质量分析器,并用其对广州市大气细颗粒物进行在线分析,实现了矿尘颗粒物的空气动力学直径和化学组成的同时检测.在连续4 d的采样中,共采集到249 057个粒径在0.2～1.2μm且同时含有正负质谱信息的颗粒物,其中矿尘颗粒物占7.9%.结果表明:矿尘颗粒物的正离子成分以Ca2+,K+,Fe2+和Na+为主,同时还含有Li+,Mg2+,V5+,Ba2+和Ti4+等;负离子成分以NO3-和NO2-为主,另外还含有HSO4-,SiO3-和PO3-等.在广州市大气细颗粒物中,矿尘贡献不如含碳颗粒物和生物质燃烧颗粒物,且在矿尘颗粒物中贡献较大的几类(如含钙、含铁、含钠钾颗粒物等)大多是老化的成分.

单颗粒气溶胶质谱仪研究进展

大气气溶胶因其对气候和公众健康的影响而成为当今环境研究领域的中心课题.单颗粒分析是目前国际上大气气溶胶研究的一个前沿领域,该方法具有高的时间和空间分辨率,能够提供全颗粒物分析所无法提供的大量信息.利用自主研制的单颗粒气溶胶质谱仪(single particle aerosol mass spectrometer,SPAMS),对广东鹤山地区气溶胶进行在线分析.重点分析含金属颗粒的相关性、数浓度和可能的来源,并简单介绍该仪器的产业化情况.

单颗粒气溶胶飞行时间质谱仪在细颗粒物研究中的应用和进展

单颗粒气溶胶质谱技术起源于20世纪70年代,在近二十年得到了快速的发展。单颗粒气溶胶飞行时间质谱仪具有高时间分辨率,且同时测量大气中单个细颗粒物粒径、多种化学组分和混合状态的特点,在大气细颗粒物监测和科学研究中逐渐得到了广泛应用。本文对单颗粒气溶胶飞行时间质谱仪的发展历程进行了介绍,对目前已商品化的单颗粒气溶胶飞行时间质谱仪ATOFMS和SPAMS的原理、数据分析方法、结果输出方式以及在环境监测和研究中的主要应用进行了总结,并指出单颗粒气溶胶飞行时间质谱仪的发展方向。

单颗粒气溶胶飞行时间质谱仪分析香烟烟气气溶胶

单颗粒气溶胶飞行时间质谱可同时对气溶胶单颗粒的粒径大小、化学成分进行实时、在线检测。本研究介绍了新近研制的单颗粒质谱仪的原理、结构、主要技术指标及对香烟烟气气溶胶的应用研究。仪器采用空气动力学透镜聚焦,双光束粒径测量系统确定颗粒物的空气动力学直径,激光电离系统实现颗粒物精确电离,通过双极有网反射飞行时间质量分析器实现正负离子同时检测。香烟检测结果表明,在颗粒物粒径分布上,新鲜香烟烟气颗粒范围较老化烟气宽。在气溶胶化学成分上,老化烟气颗粒物与新鲜烟气相比,尼古丁,氰酸盐,硝酸盐,硫酸盐及铵盐5种成分的数浓度百分比都有所增加,而含Cl-的数浓度百分比减少。原因可能是由于烟气由气相到粒相之间的转化,及颗粒物与空气中的气体发生了非均相反应;Cl-老化之后的减少是因为HNO3与Cl-之间的非均相反应。

基于单颗粒质谱信息气溶胶分类方法的研究进展

气溶胶质谱仪在对气溶胶颗粒的监测过程中会产生大量单颗粒的化学成分和粒径信息,基于这些质谱数据能够推测颗粒的来源。而对气溶胶来源的分析,很大程度上是由颗粒的种类决定的,故对海量数据的分类就成为不可忽略的步骤。针对气溶胶质谱仪采集到的数据,概述了用于气溶胶分类的多种方法的理论核心、分类步骤及各自的优缺点等。据此可为今后气溶胶分类方法的研究提供建设性意见。

单颗粒气溶胶质谱仪串联热稀释器在线测量单个气溶胶颗粒的挥发性

颗粒挥发性可以影响颗粒在大气中的寿命,对大气颗粒物中二次气溶胶的形成机制研究有一定的参考价值。以往研究测量颗粒挥发性采用的是热熔蚀器,其活性炭吸附器一旦老化后,在较高温度下可能会释放出活性炭,造成测量失真。本研究针对热熔蚀器的上述缺点,以稀释器替代活性炭吸附器部分,与单颗粒气溶胶质谱仪(SPAMS)连接,建立了一种在线分析单个气溶胶颗粒挥发性的测量方法。气溶胶颗粒分别通过两个通道进入SPAMS分析颗粒信息。通道1,气溶胶颗粒由管路进入加热器,被加热至不同的温度,颗粒挥发产生的气体和挥发后的颗粒内核进入稀释器部分,利用干净干燥冷的稀释气对加热挥发后的气体和颗粒进行稀释,使颗粒温度降低并短时间内不与气体发生冷凝,最后进入SPAMS进行检测。通道2为单独硅胶管,其长度与通道1相同,气溶胶颗粒通过通道2直接进入SPAMS检测。通过对比通道1和通道2获得的颗粒信息(粒径、数目和质谱信息等),得到气溶胶颗粒在不同温度下的挥发性。实验室用标准物质进行评估测试,结果表明,采用稀释器可以避免活性炭吸附器使用时间变长而失效,防止挥发性物质冷凝回到颗粒中。应用本方法初步测定了广州市春季气溶胶的挥发性,表明春季气溶胶多为高度挥发性和中度挥发性物质。