全二维气相色谱-飞行时间质谱分析赖百当油的挥发性成分

建立了赖百当油的全二维气相色谱-飞行时间质谱(GC×GC/TOF-MS)指纹图谱,通过质谱库检索、保留指数比对、标准品同时进样验证与文献比较,共鉴定了108个组分,占挥发油总量的94.81%,主要成分为:苯丙酸乙酯(30.92%)、绿花白干层醇(9.85%)、苯丙酸(7.91%)、乙酸龙脑酯(2.87%)、乙酸(2.81%)、杜香醇(2.41%)、喇叭烯(2.14%)等。本实验首次用GC×GC/TOF-MS对赖百当油进行了分析,并初步进行了致香机理的阐释,为该植物的开发、调香应用和品控提供了技术支撑。     

飞行时间质谱峰值的漂移

飞行时间质谱仪(time-of-flight mass spectrometer, TOF-MS)在分子团簇的激光电离/解离动力学研究中广泛使用。文章报道了在用脉冲355 nm的YAG激光进行水/甲醇二元团簇的多光子电离研究中,发现在电离激光相对于脉冲分子束的不同延时下,即激光作用于脉冲束的不同位置,飞行时间质谱仪测得的离子的质谱峰值发生漂移。在激光作用于脉冲束的中段时,离子的信号最强,同时离子的峰值漂移达到最大。分析认为：这种峰值漂移不是因为新质量数谱峰的出现,而是离子在穿越质谱仪的离子引出区和加速区极板时发生部分离子吸附,引起极板间电压的起伏造成的。离子在电场起伏下的数值模拟与实验中观测到的离子峰值漂移规律一致。     

脉冲激光离子源飞行时间质谱计的设计与研制

目前国内外的飞行时间质谱计，大多采用双电场加速的方式改善其质谱分辨率。通过较详尽的计算，讨论了双电场飞行时间质谱计中各参数对质谱分辨率和灵敏度的影响及其选择的方向，并在此基础上选定了仪器的主要参量，为飞行时间质谱计的设计与改进提供了依据。还介绍了在此基础上设计与建立的脉冲激光离子源飞行时间质谱计。     

C60和C60／C70的激光脱附飞行时间质谱分析

采用激光脱附并直接测量离子的方法对实验室提取的C_(60)/C_(70)以及进一步分离得到的纯C_(60)进行了飞行时间质谱分析,并讨论了质谱分析过程中实验条件对结果的影响.     

用飞行时间法研究Si溅射离子簇质谱的结构效应

通过对200kV离子注入机的改造,设计出一台飞行时间(TOF)谱仪,在提高脉冲束时间分辨方面,做了很大努力。测量了单晶、多晶及非晶硅的正、负离子簇飞行谱(质量谱)。比较这三种不同结构Si样品的谱数据,发现溅射离子簇质谱分布与靶物质结构密切相关,这为理论上研究Si离子簇的溅射形成机制提供了实验依据。 关键词：     

脉冲等离子体飞行时间质谱诊断技术

根据脉冲等离子体关键特征参数的特点及相关应用需求,基于垂直引入式有网反射二阶空间聚焦技术,研发了脉冲等离子体飞行时间质谱诊断系统,其质量分辨率约为1690 (FWHM),离子能量诊断范围为3~150 eV,时间分辨率约为0.45 s。通过对典型脉冲等离子体开展飞行时间质谱分析和研究,获得了离子质谱、离子能量分布函数等重要特征参数。等离子体以不同价态的Ti离子为主,Ti+最可几能量约为23 eV,Ti2+最可几能量约为48 eV。     

脉冲等离子体飞行时间质谱诊断技术

根据脉冲等离子体关键特征参数的特点及相关应用需求,基于垂直引入式有网反射二阶空间聚焦技术,研发了脉冲等离子体飞行时间质谱诊断系统,其质量分辨率约为1690(FWHM),离子能量诊断范围为3~150eV,时间分辨率约为0.45μs。通过对典型脉冲等离子体开展飞行时间质谱分析和研究,获得了离子质谱、离子能量分布函数等重要特征参数。等离子体以不同价态的Ti离子为主,Ti+最可几能量约为23eV,Ti 2+最可几能量约为48eV。     

浮地式反射飞行时间质谱计的设计

介绍了国家同步辐射实验室原子分子物理实验站自行研制的小型光电离反射式飞行时间质谱计(RTOFMS-Ⅲ).该仪器为浮地式结构,可用YAG激光器或同步辐射为激发光源.在质量数为107时,其质量分辨本领可达1034.     

355 nm激光光电离甲醛飞行时间质谱的研究

利用脉宽为5 ns脉冲Nd: YAG 355 nm激光在功率密度为10¹¹–10¹² W/cm²条件下实现了甲醛含水团簇多光子电离, 并用飞行时间质谱对其电离产物和电离过程进行了研究. 实验中观测到了甲醛的质子化团簇系列 (CH₂O)_nH⁺(n=1–4), 甲醛的去质子化团簇系列(CH₂O)_nCHO⁺ (n=1–3), 以及两个起源于H₂CO去质子和质子化的含水团簇系列HCO⁺(H₂O)_n(n=1,3,5)和H₃CO⁺(H₂O)_n(n=1,3,5), 并对其中的一些团簇结构构型进行了猜测. 研究在不同的激光功率密度下甲醛团簇质谱峰的变换情况, 当激光密度达到9.3× 10¹¹ W/cm², 开始出现CH₂O和H₂O本体及其光致碎片的信号, 但对应的各质量峰没有明显地分辨开, 而是以包络的形式出现, 这是激光电离产生高能离子释放的一种表现, 提出认等离子体动力学鞘层加速机制(模型)来解释高能离子形成的物理机制. 关键词： 甲醛 团簇 飞行时间质谱 激光电离     

飞行时间质谱中光发射电子碰撞电离过程

在飞行时间质谱仪中用３０８ｎｍ激光研究ＮＯ／Ａｒ激光多光子电离过程中，发现产生了Ａｒ及ＮＯ的高价离子现象。飞行时间质谱峰宽表明，这种电离过程是在很短的时间内进行的（〈５０ｎｓ）；从离子的质谱峰形分析得到离子产生的空间分布是连续分布在排斥极－拉出极之间的；延时脉冲加速场实验结果表明，当电场落后于激光０．２μｓ时，离子信号消失，综合实验结果，我们提出了拉出极栅网表面光发射电子碰撞电离机理。     

Detection of explosive-related compounds by laser photoionization time-of-flight mass spectrometry

We report studies using laser photoionization and time-of-flight mass spectrometry to detect several explosive-related compounds (ERCs). The ultimate goal of this work is the detection of buried land mines through their chemical signatures. Resonantly enhanced multiphoton ionization using jet expansion cooling, with a nanosecond pulse laser, results in complete photofragmentation of the parent ERC and appearance only of the NO⁺ ion, which forms all of the detected signal. This will also occur for compounds naturally occurring in the environment, such as NO₂ or peroxyacetylnitrate, rendering too many false alarms for this approach to be viable. Therefore, two other techniques were evaluated. Single-photon ionization with nanosecond pulses in the vacuum ultraviolet is shown to produce only the parent ion, and is probably the most suitable choice. For 2,4-dinitrobenzene we find a limit of detection of about 40 ppb, for a signal to noise ratio of 3. This may be sufficient for land-mine detection, but improvement is likely with future work. Nonresonant multiphoton ionization in the ultraviolet with a femtosecond laser produces fragmentation but retains some parent ERC ion signal. The limit of detection is similar to that of single-photon ionization but it is harder to implement with lasers now commercially available. Future directions are outlined. PACS 07.07.Df; 33.80.Rv; 82.80.Ms; 82.80.Rt     

Field ionization mass spectrometry of organic compounds

A review is given on field ionization mass spectrometry of organic compounds. Four different subjects are treated and illustrated by means of significant examples: Experimental techniques, surface reactions induced by high electric fields, the kinetics of fast unimolecular decompositions of ions, and qualitative and quantitative analyses of organic compounds by field desorption methods.     

Optimization of a quadrupole ion storage trap as a source for time-of-flight mass spectrometry

Designs of a quadrupole ion trap (QIT) as a source for time-of-flight (TOF) mass spectrometry are evaluated for mass resolution, ion trapping, and laser activation of trapped ions. Comparisons are made with the standard hyperbolic electrode ion trap geometry for TOF mass analysis in both linear and reflectron modes. A parallel-plate design for the QIT is found to give significantly improved TOF mass spectrometer performance. Effects of ion temperature, trapped ion cloud size, mass, and extraction field on mass resolution are investigated in detail by simulation of the TOF peak profiles. Mass resolution (m/Δm) values of several thousand are predicted even at room temperature with moderate extraction fields for the optimized design. The optimized design also allows larger radial ion collection size compared with the hyperbolic ion trap, without compromising the mass resolution. The proposed design of the QIT also improves the ion-laser interaction volume and photon collection efficiency for fluorescence measurements on trapped ions.     

An analysis of absorption-desorption of volatile organic compounds by molecularly imprinted polymer films

A theoretical analysis of the experimental data on absorption (desorption) of volatile organic compounds by (from) molecularly imprinted polymer films was performed. The theoretical time dependences of the amount of absorbed analyte in a film were calculated using a system of equations with four kinetic parameters (Γ, K, K _sur , and C _eq ), which were determined by theoretically approximating the experimental data. The special features of the absorption-desorption process in a polymer film were suggested to be described using a parameter called the specificity coefficient. Specificity coefficients were determined for all the polymers and analytes studied. The specificity coefficients obtained from the chromatographing data were compared with the imprinting factors of chromatograms calculated from the experimental retention time values. An empirical linear dependence of specificity coefficients on imprinting factor values was obtained.     

Laser ablation of lithium and lithium/cadmium alloy studied by time-of-flight mass spectrometry

Ablation of solid lithium and lithium/cadmium alloy was performed by a 308-nm, nanosecond excimer laser. Analysis of the atomic and molecular composition of the plume in vacuum and in nitrogen atmosphere was performed by means of a linear time-of-flight mass spectrometer. Several ionic masses were observed and systematically studied with respect to the laser fluence, laser beam spot size, background pressure, and target composition. PACS 52.38.Mf; 52.50.Jm; 82.80.Rt     

Temporal evolution of laser-ablated Co ions probed by time-of-flight mass spectrometry

A pulsed-field time-of-flight mass spectrometric (TOFMS) technique was used to investigate the expansion dynamics of the ionic species ejected from the visible (λ=532 nm) laser ablation of cobalt target at low laser fluence less than 1 J/cm². The temporal evolution of Co⁺ ions was studied by varying the delay time of the ion repelling pulse with respect to the laser irradiation, which provides significant information on the ablated plume characterization. The obtained TOF mass spectra were well fitted by shifted Maxwell–Boltzmann distributions on a stream velocity, commonly used to describe the measured velocity distributions. The TOF distribution of Co⁺ ions showed a bimodal distribution with fast and slow velocities. These velocities show a decreasing tendency with delay time, which is attributed to the gas collisions between the plume ejecta and to the related gas dynamics. The present results suggest that the in situ measurements of the most probable velocity of ablated ions along the normal to the solid target can be accomplished by the simple technique of a laser ablation/TOFMS.     

痕量挥发性有机物的高场不对称波形离子迁移谱研究

高场不对称波形离子迁移谱(high-field asymmetric waveform ion mobility spectrometry,FAIMS)技术是一种快速、高灵敏的痕量物质检测技术.利用自制的高场不对称波形离子迁移谱仪分别对丙酮、苯和甲苯样品进行了检测,结果表明三种挥发性物质在谱图中的分离效果优于传统离子迁...     

挥发性有机物同分异构体光电离-离子迁移谱检测研究

自行研制的紫外光电离-离子迁移谱装置,对碳链异构、官能团异构和官能团位置异构的11种同分异构体挥发性有机物进行了实验研究,结果表明,这些有机同分异构体能够在离子迁移谱中实现分离。得到了11种挥发性有机物离子的约化迁移率,对实验所研究的同分异构体而言,迁移率大小符合以下规律:直链<分支<环状,一级<二级<三级,对位<间位<邻位,醇类<酮类<芳香类。实验中用指数稀释法对11种样品进行了定量分析,利用该方法得到装置检测限达到ppb～ppm量级。其中对丙醛、叔丁醇、乙苯、乙醚等同分异构体的光电离离子迁移谱研究均为首次报道。