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.

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.

Laser-Ionization TOF Mass Spectrometer Characterization of Benzene Destruction in Atmospheric Pressure Pulsed Discharge

Benzene is a major industrial air pollutant and can cause serious human health disorders. In this paper an investigation on benzene destruction, in an atmospheric-pressure fast-flow pulsed DC-discharge by means of laser ionization combined with time-of-flight （TOF） mass spectrometry, is reported. Most by-products including transient reactive species from the benzene discharge were characterized by molecular beam sampling combined with TOF mass spectrometry. It is showed that, with a gas mixture of 0.5% C6H6 in Ar, benzene can be effectively destroyed by discharge plasma. The intermediate species consisted of small fragments of CnHm （n=3-5, m = 1-11）, cycle-chain species of CnHm （n =6-9, m = 7-10） and polycyclic species CnHm （n ≥9, m = 8-12）. The alternation of mass peaks （intensity） with even/odd electrons was observed in the measured mass spectra. The results indicated that the alternation is mainly due to the different ionization potentials of the open shell and close shell species. Based on the examination of the features of the species＇ composition, the primary reaction pathways are proposed and discussed.

MicrobMatcher: a microbial comparison software based on matrix-assisted laser desorption/ionization with time-of-flight mass spectrometry

Matrix-assisted Laser Desorption/Ionization with Time-of-flight Mass Spectrometry (MALDI-TOFMS) was investigated as a method for the rapid identifica-tion of species. Current demand in microbial identi-fication is how to compare unknown strains to the known one quickly, semi-automatically and accurately. In this paper, we present a software tool that allows flexibly microbial matching in a user-friendly way, by letting the users to customize comparison parameters including: in vitro transcription enzyme, mass tolerance,minimum fragment length, intensity threshold and corresponding weights. We provide three spectral scoring functions to compute the affin-ity between the species. Therefore, the precision of microbial comparison increases. To test and verify this tool, we employed experimental spectral data based on MALDI-TOFMS and the gene sequences of E.coli and Salmonella. This software is written in Java for cross-platform intention.

Temporal and spatial study of differently charged ions emitted by ns-laser-produced tungsten plasmas using time-of-flight mass spectroscopy

Tungsten(W)is an important material in tokamak walls and divertors.The W ion charge state distribution and the dynamic behavior of ions play important roles in the investigation of plasma–wall interactions using laser-ablation-based diagnostics such as laser-induced breakdown spectroscopy and laser-induced ablation spectroscopy.In this work,we investigate the temporal and spatial evolutions of differently charged ions in a nanosecond-laser-produced W plasma in vacuum using time-of-flight mass spectroscopy.Ions with different charge states from 1 to 7(W+to W7+)are all observed.The temporal evolutions of the differently charged ions show that ions with higher charge states have higher velocities,indicating that space separation occurs between the differently charged ion groups.Spatially-resolved mass spectroscopy measurements further demonstrate the separation phenomenon.The temporal profile can be accurately fitted by a shifted Maxwell–Boltzmann distribution,and the velocities of the differently charged ions are also obtained from the fittings.It is found that the ion velocities increase continuously from the measured position of 0.75 cm to 2.25 cm away from the target surface,which indicates that the acceleration process lasts through the period of plasma expansion.The acceleration and space separation of the differently charged ions confirm that there is a dynamic plasma sheath in the laser-produced plasma,which provides essential information for the theoretical laser-ablation model with plasma formation and expansion.

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.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry traces the geographical source of Biomphalaria pfeifferi and Bulinus forskali,involved in schistosomiasis transmission

Background Freshwater snails of the genera Bulinus spp.,Biomphalaria spp.,and Oncomelania spp.are the main intermediate hosts of human and animal schistosomiasis.Identification of these snails has long been based on mor-phological and/or genomic criteria,which have their limitations.These limitations include a lack of precision for the morphological tool and cost and time for the DNA-based approach.Recently,Matrix-Assisted Laser Desorp-tion/lonization Time-Of-Flight(MALDI-TOF)mass spectrometry,a new tool used which is routinely in clinical microbi-ology,has emerged in the field of malacology for the identification of freshwater snails.This study aimed to evaluate the ability of MALDI-TOF MS to identify Biomphalaria pfeifferi and Bulinus forskali snail populations according to their geographicalorigin.Methods This study was conducted on 101 Bi.pfeifferi and 81 Bu.forskali snails collected in three distinct geo-graphical areas of Senegal(the North-East,South-East and central part of the country),and supplemented with wild and laboratory strains.Specimens which had previously been morphologically described were identified by MALDl-TOF MS[identification log score values(LSV)≥1.7],after an initial blind test using the pre-existing database.After DNA-based identification,new reference spectra of Bi.pfeiferi(n=10)and Bu.forskali(n=5)from the geographical areas were added to the MALDI-TOF spectral database.The final blind test against this updated database was per-formed to assess identification at the geographic source level.Results MALDI-TOF MS correctly identified 92.1%of 101 Bi.pfeifferi snails and 98.8%of 81 Bu.forskali snails.At the final blind test,88%of 166 specimens were correctly identified according to both their species and sampling site,with LSVs ranging from 1.74 to 2.70.The geographical source was adequately identified in 90.1%of 91 Bi.pfeifferi and 85.3%of 75 Bu.forskalii samples.Conclusions Our findings demonstrate that MALDI-TOF MS can identify and differentiate snail populations according to geographical origin.It outperforms the current DNA-based approaches in discriminating laboratory from wild strains.This inexpensive high-throughput approach is likely to further revolutionise epidemiological studies in areas which are endemic for schistosomiasis.

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.

The dissociation pathways of N_2^+ in intense femtosecond laser fields

Using a neutral N2 beam as target, this paper studies the dissociation of N2^＋ in intense femtosecond laser fields （45 fs, ～ 1 × 10^16 W/cm^2） at the laser wavelength of 800 nm based on the time-of-flight mass spectra of N＋ fragment ions. The angular distributions of N^＋ and the laser power dependence of N^＋ yielded from different dissociation pathways show that the dissociation mechanisms mainly proceed through the couplings between the metastable states （A, B and C） and the upper excited states of N^＋.A coupling model of light-dressed potential energy curves of N2^＋ is used to interpret the kinetic energy release of N^＋.

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.

A Time-of-flight Mass Spectrometric Study of the Laser Desorption Dissociation of C_(60) and C_(70)

1 Introduction C60 and other cage-like carbon molecules, or the fullerenes, have become one ofthe most interesting materials in physics, chemistry and materials science in recentyears. In 1985, C60+ ion was found to be prominent in the laser-ablation mass spec-trum of graphite and unusual stability was proposed for C60 later. The discovery byKratschmer and his co-workers of a method for producing macroscopic.quantities ofC60 and C70 in 1990 has stimulated great interest to investigate the properties of C60and other fullerenes. Many papers have been concerned with the dissociationand stability of C60 and its ions. Studies of C60+ dissociation by means

Studies on extracting solutions of endohedral rare-earth metallofullerenes by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Thirteen extracting solutions of rare-earth metallofullerenes containing La,Ce,Pr,Nd Sm,Eu,Gd,Tb,Dy,Ho,Er,Tm and Yb respectively have been investigated by means of matrix-assisted laser desorpuon/ ionization time-of-flight mass spectrometry.The influences of the positive-ion/negative-ion mode,laser intensity,ma trix and mass discrimination to the analytical results are studied,based on which the optimal analytical conditions have been determined.The results show that the extracting solutions contain large quantities of rare-earth metallofullerenes besides empty fullerenes.On the basis of comparing their relative intensities,the different structure stabilities and solubilities of metallofullerenes with different rare-earth metals encapsulated into the fullerene cages,as well as some possible reasons to those differences,are discussed.

Xe-Kr laser induced collisional ionization system and experimental preparation of its initial state: Four-photon resonant excitation

This paper proposes a novel one-colour Xe-Kr laser induced collisional ionization system. Considering the level scheme of the system, it finds that the initial state of the reaction--the four 4f levels with even J of Xe-can be prepared through method of four-photon resonant excitation by dye laser with wavelength of -440 nm. Absorption of an additional photon （the transfer laser） of the same wavelength will complete the laser induced collisional ionization process. The resonance enhanced ionization spectrum of Xe by four laser photons at -440nm is measured through time-of-flight mass spectrometry, this aims at the preparation of the initial state of the system proposed. The Stark broadening of the measured spectrum is observed and consistent with the previous study. Analysis of the measured resonance ionization spectrum implies the feasibility of -440 nm four-photon resonant excitation of the initial 4f state of the Xe Kr system proposed in this paper, which prepares for a further experiment of laser induced collisional ionization.

Determination of persistent organic pollutants by gas chromatography/laser multiphoton ionization/time-of-flight mass spectrometry

An authentic mixture of polychlorinated biphenyls was measured using a short wide-bore capillary column for the group separation of major components present in an actual sample of Kanechlor. The limits of detection were improved by ca. 2 fold in comparison with those obtained using a conventional capillary column, since the retention time was reduced and the amount of analytes introduced into the mass spectrometer per unit time could be increased. On the other hand, surface-water and sediment samples containing polycyclic aromatic hydrocarbons （PAHs） were collected from the river located in the vicinity of a waste water treatment plant. Even acenaphthylene, a minor component of the mixture could be measured for the sediment sample, and the concentra- tions were determined for several heavy PAHs. As demonstrated, a technique involving laser multiphoton ionization/time-of-flight mass spectrometry was useful as a sensitive and selective analytical tool for the trace analysis of persistent organic pollutants in an environmental sample.

Detection of Sialylated N-Linked Glycans by Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry

Native and methyl-esterified sialylated glycans were analyzed with 2,4,6-trihydroxyacetophenone（THAP）and 2,5-dihydroxybenzoic acid（DHB）as matrix by a matrix-assisted laser desorption/ionization time-of-flight mass spectrometer（MALDI-TOF MS）.High quality negative-ion spectra of commercial sialylated glycan were obtained with THAP as matrix.Detection limit of the glycan was less than 0.1 pmol.After methyl esterification of sialic acid（SA）residue,sialylated glycans were detected sensitively in the positive-ion mode using DHB as matrix.Neutral and sialylated glycans from the mixture of asialofetuin and fetuin were methylesterified and simultaneously recognized in one manipulation.Methyl esterification of SA residue offers a convenient and sensitive way to identify the structure of N-linked glycans for glycan profiling.

Automatic ^(40)Ar/^(39)Ar Dating Techniques Using Multicollector ARGUS VI Noble Gas Mass Spectrometer with Self-Made Peripheral Apparatus

A new fully automatic ^40Ar/^39Ar laboratory with a Thermo Scientific ARGUS VI mass spectrometer has been established in China University of Geosciences （Wuhan）. We designed and developed a mini efficient preparation system （80 mL）, a CO2 laser for heating samples, a crusher for extracting fluid inclusions within K-poor minerals and an air reservoir （31 L） and pipette （0.1 mL） system. The ARGUS VI mass spectrometer is operated by the Qtegra Noble Gas software, which can control the peripheral accessories, such as pneumatic valves, CO2 laser and crusher through a PeriCon （peripheral controller）. The experimental procedures of atmospheric argon ana- lyses, ^40Ar/^39Ar dating by laser stepwise heating and by progressive crushing in vacuo, can be fully automatically performed. The weighted mean of atmospheric ^40Ar/^36Ar ratios is 302.22＋0.03 （1σ, MSWD=0.74, n=200）, indicating that air reservoir and pipette system and the whole instrument sys- tem are very stable. This laboratory is a successful pioneer example in China to establish a new no- ble gas laboratory with self-made peripheral accessories expect for the mass spectrometer.

Mixed infection of Nocardia farcinica and Nocardia cyriacigeorgica in an immunocompromised patient:A case report

Rationale:Nocardia is a soil saprophyte,which can cause disseminated infection in immunocompromised patients.Early diagnosis and treatment can greatly improve prognosis.Patient concern:A 26-year-old male presented with repeated episodes of fever,cough and breathlessness for 3 months.Diagnosis:Mixed infection of Nocardia(N.)farcinica and N.cyriacigeorgica with diabetes and Cushing’s syndrome.Interventions:N.cyriacigeorgica was isolated from empyema fluid and N.farcinica from blood.Based on antimicrobial susceptibility,he was treated with imipenem,cotrimoxazole and amikacin.Outcome:Patient expired due to infection and delayed diagnosis.Lesson:Several cases of infection due to N.farcinica or N.cyriacigeorgica have been reported.But mixed infection caused by these two species is rare.Pulmonary and disseminated nocardiosis is associated with high mortality,especially in immunocompromised hosts.So early diagnosis and prompt treatment is needed.

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。

用于团簇研究的激光反射式飞行时间质谱仪

报道了新建造的用于团簇研究的反射式飞行时间质谱仪 ,包括反射式飞行时间质谱仪的结构、原理、真空系统、控制系统等 .初步性能测试表明 :激光溅射 /分子束载带型团簇离子源能够产生丰富的一元、二元团簇离子 ;质谱仪对离子的质量分辨接近 2 0 0 0 ,并且质量门也有较高的质量选择性 .系统用于团簇研究 ,得到了一些初步实验结果 .