XeCl激光诱导的CS_2多光子电离质谱

本文报道了CS_2在XeCl准分子激光(波长为308nm)诱导下的多光子电离质谱实验.我们测量了各种离子(S~ 、CS~ S_2~ 和CS_2~ )强度相对激光强度和样品气量的变化规律,根据这些结果和一些相应的计算确立了CS_2多光子电离的动力学模型和每一种离子的具体生成过程.     

CH_3I分子多光子电离和碎裂的机理

本文报道了CH_3I分子在308nm激光作用下多光子电离质谱,测量了I~ 和CH_3I~ 离子产率对样品气体压强和激光脉冲能量的依赖关系,指出在308nm处,CH_3I分子同时存在两种碎裂通道的碎裂机理.     

XeCl准分子激光诱导的氮分子多光子电离

本文采用分子束和改装过的质谱装置,进行了氯化氙准分子激光诱导的氨分子紫外光电离的研究。我们不仅在(m/e)=16,17处分别观察到NH_2~+和NH_3~+离子峰,而且还在(m/e)=18处观察到NH_4~+离子峰。为搞清各种离子特别是NH_4~+离子的产生机理,测量了各种离子产率与样品压强和激光功率的依赖关系。     

激光诱导击穿光谱机理及爆炸物研究

激光诱导击穿光谱(LIBS)技术是基于激光诱导等离子体发光探测物质成分的方法。激光诱导等离子体的发射谱线由两部分组成:一部分是电子-离子复合及自由电子相互作用辐射的宽带连续谱;另一部分是原子和离子发射的特征谱线。对这些谱线进行识别并测量其强度,给出物质成分的定性和定量信息。分别讨论了样品所附着的基质为金属和电介质的两种情况,并对ns和fs级激光脉宽的影响作了介绍。     

大气压基体辅助激光解析离子源发展及其应用

介绍了国际上新出现的一种离子源——大气压基体辅助激光解析离子源(atmospheric pressure matrix-assisted laser desorption/ionization,AP-MALDI)。该离子源是在真空MALDI的基础上研究发展起来的,广泛应用于生物大分子及其相关领域的研究。该离子源较真空MALDI电离更加柔和,产生的碎片离子更少,又由于其工作在大气压下,可作为外接离子源方便地与各类质谱分析器联用,大大扩展了基体辅助激光解析离子源的应用范围。文章详细介绍了AP-MALDI的基本原理、结构及技术进展。此外,还对该离子源在生物高聚物分析方面的最新应用进行了介绍。     

稳定团族离子B6N5^2的产生和结构

用脉冲激光气化氮化硼固体样品，并由飞行时间质谱测量，首次发一同Ｂ６Ｎ５＾＋的质谱峰强度明显高于其它团簇离子，是一种稳定的团簇离子。本文也报导了用ａｂｉｎｉｔｉｏ方法计算Ｂ６Ｎ５＾＋的几种稳定结构。     

调控声子提高Tm3+掺杂体系的频率上转换荧光

应用激光光谱学技术,探讨了Tm³⁺离子掺杂透明氟氧化物玻璃陶瓷体系中声子调控对红色激光抽运荧光辐射性质的影响. 研究了基质结构和样品环境温度与电声子相互作用的联系以及声子变化对于荧光辐射产生的影响. 发现改变基质材料的SiO₂含量能影响蓝色上转换荧光效率. 另外,依据温度与声子能量之间的联系,通过改变样品环境温度可明显调节低声子基质材料中掺杂离子激发态能级的布居速率,改变上转换效率. 关键词： 荧光辐射 声子 无辐射弛豫 荧光寿命     

基质与分析物的摩尔比和激光能量对分析物离子信号的影

介绍了一种基质辅助激光解吸电离的进样方法-气溶胶进样方法．包含基质和分析物的气溶胶粒子在大气压力下直接进入气溶胶飞行时间质谱仪,粒子产生的散射光信号由光电倍增管收集,通过外部的时序电路,给出气溶胶粒子粒径的信息并触发266 nm Nd:YAG激光器,可以同时获得气溶胶粒子的粒径和基质辅助激光解吸电离质谱与其他的液体进样方式相比,它可以实现单粒子进样,因而样品消耗较少．主要研究了基质与分析物的摩尔比和激光能量对分析物离子信号的影响,合适的摩尔比和激光能量分别为50-110:1和200-400μJ．     

光谱学方法研究Tm3+离子的上转换发光影响因素

应用激光光谱学的研究手段和方法,探讨了红色激光抽运Tm3+离子掺杂纳米体系中上转换荧光辐射性质的影响因素.通过变化基质和改变样品的环境温度,研究了声子能量大小对Tm3+离子掺杂纳米体系中上转换效率的影响.结果显示:合适声子能量可以有效提高Tm3+离子蓝色上转换效率.此外,依据声子能量与温度之间的联系,改变样品环境温度可调节低声子基质材料中Tm3+离子激发态能级的布居速率,改变上转换效率.     

光谱学方法研究Tm~(3+)离子的上转换发光影响因素

应用激光光谱学的研究手段和方法,探讨了红色激光抽运Tm3+离子掺杂纳米体系中上转换荧光辐射性质的影响因素.通过变化基质和改变样品的环境温度,研究了声子能量大小对Tm3+离子掺杂纳米体系中上转换效率的影响.结果显示:合适声子能量可以有效提高Tm3+离子蓝色上转换效率.此外,依据声子能量与温度之间的联系,改变样品环境温度可调节低声子基质材料中Tm3+离子激发态能级的布居速率,改变上转换效率.     

Matrix assisted laser desorption/ionization of potassium adapted angiotensine II using femtosecond laser pulses

Matrix assisted laser desorption/ionization (MALDI) measurements with femtosecond laser pulses at a central wavelength of 400 are presented. The examined analyte is potassium adapted angiotensine II whereby the matrix is a combination of sinapic acid and α-cyano-4-hydroxycinamic acid. Pulse energy dependent measurements are performed in order to investigate the MALDI processes for the obtained potassium adapted angiotensine II complexes. The results show the higher stabilization tendency of the potassium adapted angiotensine II which could be used to bring very fragile non-stable macromolecules into the gas phase. The outlined approach is an attempt to explain the underlying MALDI process by focusing on the mass spectra of potassium adapted angiotensine II.     

Ultrahigh resolution mass spectrometry and accurate mass measurements for high-throughput food lipids profiling

In the present study, accurate mass measurements by ultrahigh resolution mass spectrometry with Orbitrap-Exactive working at resolving power R: 100,000 (m/z 200, full width at half maximum) with an accuracy better than 2?ppm in all the mass range (m/z 200 to 2000) were used to show a detailed molecular composition of diverse edible oils and fats. Flow injection was used to introduce samples into the mass spectrometer, obtaining a complete analysis of each sample in less than 10 min, including blanks. Meticulous choice of organic solvents and optimization of the ion source and Orbitrap mass analyzer parameters were carried out, in order to achieve reproducible mass spectra giving reliable elemental compositions of the lipid samples and to prevent carry over. More than 200 elemental compositions attributable to diacylglycerols, triacylglycerols (TAGs), and their oxidation products have been found in the spectra of food lipids from different origin. Several compounds with very close molecular mass could only be resolved through ultrahigh resolution, allowing detailed and robust TAG profiling with a high characterization potential. Copyright ? 2012 John Wiley & Sons, Ltd.     

Analysis of poly(bisphenol A carbonate) by size exclusion chromatography/matrix-assisted laser desorption/ionization. 2. self-association due to phenol end groups

We report here a case of apparent failure of the size exclusion chromatography/matrix-assisted laser desorption/ionization (SEC/MALDI) method to provide polymer fractions with narrow molar mass distribution, showing that intermolecular chain association is responsible for this phenomenon. Poly(bisphenol A carbonate) (PC) chains terminated with hydroxyl groups undergo self-association by hydrogen bonding, providing macromolecular aggregates with higher hydrodynamic volume. These aggregates are eluted through SEC columns at the same volume as higher molar mass chains, which remain non-associated. Thus, self-association affects negatively the SEC fractionation experiments, and even the sharpest SEC fractions contain a heterogeneous mixture of PC chains of different size. When the off-line SEC/MALDI procedure is applied, the SEC fraction is diluted in the matrix which, being a dissociating medium (carboxylic acid) for hydrogen-bonded aggregates, suppresses the chains' self-association. Therefore, the MALDI spectra of these PC fractions indicate a polydisperse character, with irregular bimodal distributions of peaks. As a consequence, in the presence of chain association, the SEC/MALDI method for the calculation of molar masses of polymers cannot be directly applied. In the present case we have found that, under opportune experimental conditions, self-association in polycarbonates can be avoided, so that nearly monodisperse SEC fractions can be obtained and the SEC/MALDI method can be applied. Our results also show that MALDI is a very sensitive technique for the detection of association of polymers in dilute solutions. Copyright 1999 John Wiley & Sons, Ltd.     

Analysis of dammar resin with MALDI-FT-ICR-MS and APCI-FT-ICR-MS

Comprehensive analysis of high-resolution mass spectra of aged natural dammar resin obtained with Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR-MS) using matrix-assisted laser desorption/ionization (MALDI) and atmospheric pressure chemical ionization (APCI) is presented. Dammar resin is one of the most important components of painting varnishes. Dammar resin is a terpenoid resin (dominated by triterpenoids) with intrinsically very complex composition. This complexity further increases with aging. Ten different solvents and two-component solvent mixtures were tested for sample preparation. The most suitable solvent mixtures for the MALDI-FT-ICR-MS analysis were dichloromethane-acetone and dichloromethane-ethanol. The obtained MALDI-FTMS mass spectrum contains nine clusters of peaks in the m/z range of 420-2200, and the obtained APCI-FTMS mass spectrum contains three clusters of peaks in the m/z range of 380-910. The peaks in the clusters correspond to the oxygenated derivatives of terpenoids differing by the number of C(15)H(24) units. The clusters, in turn, are composed of subclusters differing by the number of oxygen atoms in the molecules. Thorough analysis and identification of the components (or groups of components) by their accurate m/z ratios was carried out, and molecular formulas (elemental compositions) of all major peaks in the MALDI-FTMS and APCI-FTMS spectra were identified (and groups of possible isomeric compounds were proposed). In the MALDI-FTMS and APCI-FTMS mass spectrum, besides the oxidized C(30), triterpenoids also peaks corresponding to C(29) and C(31) derivatives of triterpenoids (demethylated and methylated, correspondingly) were detected. MALDI and APCI are complementary ionization sources for the analysis of natural dammar resin. In the MALDI source, preferably polar (extensively oxidized) components of the resin are ionized (mostly as Na(+) adducts), whereas in the APCI source, preferably nonpolar (hydrocarbon and slightly oxidized) compounds are ionized (by protonation). Either of the two ionization methods, when used alone, gives an incomplete picture of the dammar resin composition.     

On-line matrix addition for detecting aerosol particles

Single aerosol particles were measured by matrix-assisted laser desorption/ionization (MALDI) with an aerosol time-of-flight mass spectrometer (ATOFMS). The inlet to the ATOFMS was coupled with an evaporation/condensation flow cell that allowed matrix addition by condensation onto the particles. The coated particles entered the ion source through three-stage differentially pumped capillary inlet and were then ionized by a focused 266 nm Nd:YAG laser. The mass spectra and aerodynamic size of the single particles can be obtained simultaneously. The on-line matrix addition technique makes it possible to identify biological aerosols in real-time.     

MALDI-MS detection of noncovalent interactions of single stranded DNA with Escherichia coli single-stranded DNA-binding protein

The Escherichia coli single-stranded DNA binding protein (SSB) selectively binds single-stranded (ss) DNA and participates in the process of DNA replication, recombination and repair. Different binding modes have previously been observed in SSB?ssDNA complexes, due to the four potential binding sites of SSB. Here, chemical cross-linking, combined with high-mass matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS), is used to determine the stoichiometry of the SSB?ssDNA complex. SSB forms a stable homotetramer in solution, but only the monomeric species (m/z 19,100) can be detected with standard MALDI-MS. With chemical cross-linking, the quaternary structure of SSB is conserved, and the tetramer (m/z 79,500) was observed. We found that ssDNA also functions as a stabilizer to conserve the quaternary structure of SSB, as evidenced by the detection of a SSB?ssDNA complex at m/z 94,200 even in the absence of chemical cross-linking. The stability of the SSB?ssDNA complex with MALDI strongly depends on the length and strand of oligonucleotides and the stoichiometry of the SSB?ssDNA complex, which could be attributed to electrostatic interactions that are enhanced in the gas phase. The key factor affecting the stoichiometry of the SSB?ssDNA complex is how ssDNA binds to SSB, rather than the protein-to-DNA ratio. This further suggests that detection of the complex by MALDI is a result of specific binding, and not due to non-specific aggregation in the MALDI plume.     

Analysis of cancer cell lipids using matrix-assisted laser desorption/ionization 15-T Fourier transform ion cyclotron resonance mass spectrometry

A combination of methodologies using the extremely high mass accuracy and resolution of 15-T Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry (MS) was introduced for the identification of intact cancer cell phospholipids. Lipids from a malignant glioma cell line were initially analyzed at a resolution of >200,000 and identified by setting the mass tolerance to ±1 mDa using matrix-assisted laser desorption/ionization (MALDI) 15-T FT-ICR MS in positive ion mode. In most cases, a database search of potential lipid candidates using the exact masses of the lipids yielded only one possible chemical composition. Extremely high mass accuracy (<0.1?ppm) was then attained by using previously identified lipids as internal standards. This, combined with an extremely high resolution (>800,000), yielded well-resolved isotopic fine structures allowing for the identification of lipids by MALDI 15-T FT-ICR MS without using tandem mass spectrometric (MS/MS) analysis. Using this method, a total of 38 unique lipids were successfully identified.     

Developments in MALDI Mass Spectrometry: The Quest for the Perfect Matrix

Abstract

The topic of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry has received much attention over the past several years and with the award of the Nobel Prize to Tanaka based on his landmark paper in 1988, has received even more recent attention. This review focuses on the search for an ideal matrix and generally covers the period from the mid 1990's to the present. There have been a number of excellent and comprehensive reviews on MALDI ion formation and a brief summary of some of the most important conclusions is given here. With respect to the applications of MALDI, the present review focuses primarily on polymer analysis, although in this area too, excellent reviews have been published that include consideration of the MALDI method. Although we make some mention of other uses of MALDI (e.g., to proteins and peptides) and other biological applications, we emphasize the polymer uses in the present review.     

High-accuracy mass measurements in ion traps and storage rings

High-accuracy mass measurements have recently been performed on radioactive isotopes produced by proton-induced spallation at the on-line isotope separator ISOLDE at CERN and by heavy-ion projectile fragmentation at the fragment separator FRS at GSI. At ISOLDE, singly charged ions were injected into the Penning trap mass spectrometer ISOLTRAP and their masses determined by observing their cyclotron frequencies in the homogeneous magnetic field of the ion trap. At GSI, bare, hydrogen, or helium-like ions were injected into the experimental storage ring ESR, electron-cooled to the same velocity, and their masses determined by observing their revolution frequencies in the ESR. With ISOLTRAP and ESR, resolving power in the range of 4 × 10⁵< = m/Δ m(FWHM)< = 10⁷ and an accuracy up to \delta m/m~ 10^-7 were achieved for radioactive isotopes. Mass measurements of highly charged ions of stable isotopes were performed at Stockholm by use of SMILETRAP. In this case, a resolving power of about 10⁸ and an accuracy close to 10^-9 were obtained. This revised version was published online in August 2006 with corrections to the Cover Date.     

Chemical reactivity in matrix-assisted laser desorption/ionization mass spectrometry

During the control of a multistep organic synthesis on a soluble polymer (PEG) by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry, a chemical reactivity was encountered when the matrix was acidic, for the samples where the amino moiety of the anchored compounds was protected as a Schiff base. Such imine hydrolysis was proven to be solely mediated by the acidic matrix during analyses since the expected protected structures were detected when the experiments were duplicated with a non-acidic matrix. Even if MALDI mass spectrometry was found to be more convenient than electrospray ionization mass spectrometry for the monitoring of liquid phase organic syntheses, the chemical reactivity imparted by the use of a matrix must be taken into account to avoid erroneous spectra interpretations. Copyright 1999 John Wiley & Sons, Ltd.