Particle Production in Reflection and Transmission Mode Laser Ablation: Implications for Laserspray Ionization

Particles were ablated from laser desorption and inlet ionization matrix thin films with a UV laser in reflection and transmission geometries. Particle size distributions were measured with a combined scanning mobility particle sizer (SMPS) and aerodynamic particle sizer (APS) system that measured particles in the size range from 10 nm to 20 μm. The matrixes investigated were 2,5-dihydroxybenzoic acid (DHB), α-cyano-4-hydroxycinnamic acid (CHCA), sinapic acid (SA), 2,5-dihydroxy-acetophenone (DHAP), and 2-nitrophloroglucinol (NPG). Nanoparticles with average diameters between 20 and 120 nm were observed in both transmission and reflection geometry. The particle mass distribution was significantly different in reflection and transmission geometry. In reflection geometry, approximately equal mass was distributed between particles in the 20 to 450 nm range of diameters and particles in the 450 nm to 1.5 μm diameter range. In transmission mode, the particle mass distribution was dominated by large particles in the 2 to 20 μm diameter range. Ablation of inlet ionization matrices DHAP and NPG produced particles that were 3 to 4 times smaller compared with the other matrices. The results are consistent with ion formation by nanoparticle melting and breakup or melting and breakup of the large particles through contact with heated inlet surfaces.

Plasma-Spray Ionization (PLASI): A Multimodal Atmospheric Pressure Ion Source for Liquid Stream Analysis

A new ion generation method, named plasma-spray ionization (PLASI) for direct analysis of liquid streams, such as in continuous infusion experiments or liquid chromatography (LC), is reported. PLASI addresses many of the analytical limitations of electrospray ionization (ESI) and has potential for real time process stream analysis and reaction monitoring under atmospheric conditions in non-ESI friendly scenarios. In PLASI-mass spectrometry (MS), the liquid stream is pneumatically nebulized and partially charged at low voltages; the resultant aerosol is thus entrained with a gaseous plasma plume from a distal glow discharge prior to MS detection. PLASI-MS not only overcomes ESI-MS limitations but also generates simpler mass spectra with minimal adduct and cluster formation. PLASI utilizes the atomization capabilities of an ESI sprayer operated below the ESI threshold to generate gas-phase aerosols that are then ionized by the plasma stream. When operated at or above the ESI threshold, ionization by traditional ESI mechanisms is achieved. The multimodal nature of the technique enables readily switching between plasma and ESI operation. It is expected that PLASI will enable analyzing a wide range of analytes in complex matrices and less-restricted solvent systems, providing more flexibility than that achievable by ESI alone. Figure

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激光烧蚀光谱-电感耦合等离子体质谱联用技术应用进展

激光烧蚀光谱（LAS）分析技术具有简便快速的特点,仪器设备简便,但对痕量元素分析能力不足。电感耦合等离子体质谱(ICP-MS)分析技术则具有灵敏度高和多元素及同位素分析能力,但对基体元素分析存在困难。将LAS和ICP-MS分析技术相结合构成LAS-ICP-MS联用分析技术,可相互弥补LAS和ICP-MS技术的缺陷。介绍了近10年来LAS-ICP-MS联用技术的应用进展及发展趋势,并详细阐述了近年来LA-ICP-MS分别在地质、矿冶、材料、环境监测以及其它分析领域的应用。     

C70正负离子的激光引发聚合

Ｃ_（７０）正负离子的激光引发聚合刘朝阳，王春儒，黄荣彬，林逢辰，郑兰荪（固体表面物理化学国家重点实验室，厦门大学化学系，厦门，３６１００５）关键词Ｃ_（７０），聚合，激光等离子体Ｃ６０在激光作用下的进一步聚合是近来在Ｃ６０研究中的又一重要发现，Ｙｅｒ...     

Laser Double Ablation Reactions of Chromium(Iron) and Sulfur Clusters

The sulfides of transitional metals chromium[1-3] and iron[4] are of great importance inmaterial and biology sciences due to their characteristic structures and properties．So the studyon the properties of Cr－S and Fe－S clusters will give many contributions to the understandingof physical and chemical behavior of those compounds．     

激光溅射下原子团簇生长的非平衡动力学

在“半球模型”的基础上,在考虑了因等离子体膨胀和热辐射等引起的温度答体积的变化的情况下,进一步考虑了碳簇的链状、单环、双环、多环及富勒烯等五种结构及中性粒子与中性粒子、中性粒子与离子两种反应,计算了碳簇中性分子和离子的形成动力学及其尺寸分布。     

激光溅射下原子团簇生长的非平衡动力学(I)

以激光溅射的方式,可以产生不同尺寸与组分的原子团簇.但是对这些团簇的生长过程,却一直缺少比较深入和细致的研究.本文结合激光真空溅射石墨的实验条件,考虑了激光能量、体系膨胀、环境压力、热量辐射等诸多因素,建立了在该条件下碳原子团簇生长的物理模型,得出了相应的动力学方程的数值解.计算结果表明:每个激光脉冲溅射出约8×10-9mol(5×1015个)粒子,它们产生时的初始压力约为2×105Pa.由于扩散等因素,团簇的形成反应在7.85μs后已不可能进行,但是各团簇产物的产率在反应开始后0.4μs左右已达到最大值,在约1.5μs内反应即已基本完成,因为此后原子团簇的尺寸分布不再有显著的差异.     

激光溅射下原子团簇生长的非平衡动力学(Ⅱ)

在“半球模型”(即假设激光溅射产生的等离子体向空间均匀膨胀 )的基础上 ,在考虑了因等离子体膨胀和热辐射等引起的温度和体积的变化的情况下 ,进一步考虑了碳簇的链状、单环、双环、多环及富勒烯等五种结构及中性粒子与中性粒子、中性粒子与离子两种反应 ,计算了碳簇中性分子和离子的形成动力学及其尺寸分布.计算结果表明离子的尺寸分布可以近似代表中性粒子的尺寸分布 ,动力学计算所模拟的碳簇的尺寸分布与实验记录的碳簇离子的质谱特征较为相似.     

激光剥蚀电感耦合等离子体质谱(LA-ICP-MS)法测定涂层氧化锆颗粒铌层中24种微量杂质元素

针对涂层氧化锆颗粒涂层分析需求,建立了LA-ICP-MS分析Nb涂层和Zr基质中24种微量杂质元素测定方法,获得了最佳剥蚀条件(激光束斑44μm、能量密度6 J/cm²、剥蚀频率5 Hz),利用NIST610标样作为外标、Nb和Zr作内标分别校正了Nb涂层及Zr基质层。方法检出限1.5μg/g (Fe)、1.16μg/g(Cr)、0.36μg/g(Ni),其他21种元素检出限0.01～695.7μg/g。成功测定了60件Nb涂层和Zr基质样品中24种微量杂质元素,获得了26种元素深度剥蚀信号-时间轮廓图,激光剥蚀涂层时间为16～110 s。建立了涂层厚度测试方法,利用LA-ICP-MS技术结合环境扫描电镜能谱技术测定了球体涂层的厚度,获得了准确的LA深度剥蚀率0.371 4μm/s,并成功测定了60件样品中涂层的厚度(5.942～40.854μm),实现了涂层氧化锆涂层成分定量。     

基于低分散激光剥蚀系统-电感耦合等离子体飞行时间质谱的快速元素成像

微量元素在生物体内含量很低,但发挥着重要的作用。因此,生物体内微量元素原位成像具有重要的意义。本文建立了基于低分散激光剥蚀系统-电感耦合等离子体飞行时间质谱（LA-ICP-TOFMS）的快速生物元素成像方法,采用点扫描模式,得到了尾静脉注射银纳米颗粒的小鼠肾脏切片中19种元素成像图,成像分辨率为20 μm,成像速度为每秒40个像素点,与常规LA-ICP-MS成像速度相比提高了约10倍。成像结果表明,不同元素在小鼠肾脏各分区中具有不同的分布模式。建立的LA-ICP-TOFMS成像方法为原位研究生物体内元素提供了直观可靠的手段,有望在生物医学研究中得到更广泛的应用。     

Direct Analysis of Laminated Dolomite and Zircon by Laser Ablation Inductively Coupled Plasma Mass Spectrometry

Distributions of elements in laminated dolomite and zircon crystal were obtained by laser ablation inductively coupled plasma mass spectrometry. The variation of signal intensity was normalized by an internal standard method using the sum of the signals of Ca and Mg which was assumed to be constant in every position for the dolomite sample and using Zr signal for the zircon sample. The concentrations of elements change correspondingly across the laminated structure of dolomite. U and Th show a zoned distribution in the zircon crystal.     

Studies on Fundamental Processes During Laser Ablation using Time-of-Flight Mass-Spectrometry (TOF-MS)

When a short pulsed, high power laser is focused on any solid target,a portion of the material is instantaneously exploded into its vapor. Laser ablation is a term to describe this explosive laser material interaction. Various processes like ejection of ions,atoms and clusters, thermal evaporation, plasma initiation and expansion, interaction between the plasma and the target, may result.     

Development and fundamental investigation of Laser Ablation Glow Discharge Time-Of-Flight Mass Spectrometry (LA-GD-TOFMS)

Glow Discharge (GD) spectroscopy is a well known and accepted technique for the bulk and surface composition analysis, while laser ablation (LA) provides analysis with high spatial-resolution analysis in LIBS (laser-induced breakdown spectroscopy) or when coupled to inductively coupled plasma spectrometry (ICP-OES or ICP-MS). This work concerns the construction of a Laser Ablation Glow Discharge Time-Of-Flight Mass Spectrometry (LA-GD-TOFMS) instrument to study the analytical capabilities resulting from the interaction of a laser-generated sample plume with a pulsed glow discharge. Two ablation configurations were studied in detail. In a first approach, the laser-generated plume was introduced directly into the GD, while the second approach generated the plume inside the GD. The ablated material was introduced at different times with respect to the discharge pulse in order to exploit the efficient ionization in the GD plasma. For both LA-GD configurations, direct ablation into the afterglow of the pulsed glow discharge leads to an ion signal enhancement of up to a factor of 7, as compared to the ablation process alone under the same experimental conditions. The LA-GD enhancement was found to occur exclusively in the GD afterglow, with a maximum ablation S/N occurring in a few hundred microseconds after the termination of the glow discharge. The duration of the enhanced signal is about two milliseconds. Both the laser pulse energy and the position of the ablation plume (with respect to the sampling orifice) were found to affect the amount of mass entering the afterglow region and consequently, the enhancement factor of ionization.     

In Situ Explosive Detection Using a Miniature Plasma Ion Source and a Portable Mass Spectrometer

A small low-temperature plasma (LTP) ionization probe was coupled to a portable mass spectrometer for the rapid detection of trace explosives on surfaces. Using only a small diaphragm pump to supply ambient air to the LTP source, 100 ng each of pentaerythritol tetranitrate (PETN), 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), and 2,4,6-trinitrophenylmethylnitramine (Tetryl) were detectable on glass in under 1 minute. The main ion signal from these molecules (M) is the [M + NO₃]^? species. While much optimization remains, it is believed that this miniature LTP source will remove the need for external gas cylinders and additional heating for in situ explosives detection using portable mass spectrometers.     

Analytical Analysis of Different Karats of Gold Using Laser Induced Breakdown Spectroscopy (LIBS) and Laser Ablation Time of Flight Mass Spectrometer (LA-TOF-MS)

Laser induced breakdown spectroscopy (LIBS) coupled with a laser ablation time of flight mass spectrometer (LA-TOF-MS) has been developed for discrimination/analysis of the precious gold alloys cartage. Five gold alloys of Karats 18K, 19K, 20K, 22K and 24K having certified composition of gold as 75, 79, 85, 93 and 99.99% were tested and their precise elemental compositions were determined using the laser produced plasma technique. The plasma was generated by focusing beam of a Nd:YAG laser on the target in air and its time integrated emission spectra were registered in the range 250–870 nm. The calibration free LIBS technique (CF-LIBS) was used for the quantitative determination of the constituent elements present in different Karats of gold. Elemental compositions of these gold alloys were also determined using a Laser Ablation time of flight mass spectrometer (LA-TOF-MS). The LIBS limit of detection was calculated from the calibration curves for copper, silver and gold. Results of CF-LIBS and LA-TOF-MS are in excellent agreement with the certified values. It is demonstrated that LIBS coupled with LA-TOF-MS is an efficient technique that can be used to analyze any precious alloys in a fraction of a second.     

双电离源(辉光放电/激光溅射电离)四极杆质谱仪的研制

本研究将辉光电离源与激光溅射电离源巧妙地结合在同一台仪器中,使固体样品在离子源腔体中既能辉光电离,也能激光电离;并且使用同一质量分析器,两种离子源的结果可以相互比对,进而得到更为准确的分析结果.此仪器主要由真空系统、离子源、离子传输系统、四极杆质量分析器及检测与数据采集系统等组成.实验中分别用两种离子源测试了标准样品SRM 1262b,并获得了半定量结果.结果表明,仪器具有定性能力强,分析速度快,检测灵敏度高等优点,对固体样品元素分析的检出限可达μg/g量级.实验表明,激光溅射电离质谱的性能优于辉光放电质谱.     

Laser Based Optical Emission Studies of Zinc Oxide (ZnO) Plasma

We present the optical emission characteristics of the zinc oxide (ZnO) plasma produced by the first (1,064 nm) and second (532 nm) harmonics of a Q switched Nd: YAG laser. The target material was placed in front of laser beam in air (at atmospheric pressure).The experimentally observed line profiles of neutral zinc (Zn I) have been used to extract the electron temperature using the Boltzmann plot method, whereas, the electron number density has been determined from the Stark broadening. The electron temperature is calculated by varying distance from the target surface along the line of propagation of plasma plume and also by varying the laser irradiance. Beside we have studied the variation of number density as a function of laser irradiance as well as its variation with distance from the target surface. It is observed that electron temperature and electron number density increases as laser energy is increased.