Threshold photoionization in time-of-flight mass spectrometry

Multi-photon excitation in a time-of-flight mass spectrometer (TOF-MS) is shown to lead to threshold ions with defined internal energy. A powerful technique for the production of threshold ions is based on the excitation of high long-lived Rydberg states embedded in the ionization continuum. The Rydberg molecules are separated with suitable separation techniques from ions produced by a direct multi-photon ionization process. Finally, the ionization of the Rydberg molecules in a delayed pulsed electric field leads to threshold ions. This work reviews several separation techniques, and reports on applications of threshold ionization for investigation of the structure, energetics, and dynamics of neutral molecules, molecular cations, and cluster cations.     

基质辅助激光解吸电离飞行时间质谱法分析核糖核酸酶

应用基质辅助激光解吸电离飞行时间质谱法(MALD I-TOF-MS)成功地对核糖核酸酶相对分子量进行测定。探讨三种不同基质对其分析结果的影响,实验中发现α-氰基-4-羟基肉桂酸是适宜的基质,该方法是传统生物方法无法比拟的。     

高分辨率电喷雾电离飞行时间质谱仪测定大豆磷脂中的磷脂酰胆碱

首次实现了国内用自制高分辨率电喷雾电离飞行时间质谱仪(ESI-TOF-MS)检测大豆磷脂中的磷脂酰胆碱(PC),共检测出了52种磷脂酰胆碱.实验证明,高分辨率ESI-TOF-MS具有定性速度快、灵敏度高、精确度好的优点,是目前磷脂检测的最为有效的工具.     

Quantitative analysis of transient surface reactions on planar catalyst with time-resolved time-of-flight mass spectrometry

A procedure for the quantitative analysis of transient surface catalytic reactions in millisecond time resolution has been studied constructing a specially designed apparatus employing (1) pulsed-gas valves for the injection of reactant molecules onto catalysts and (2) a time-of-flight mass spectrometer (TOF-MS) to detect every reaction product simultaneously. For a better understanding of the catalytic activity and selectivity for products quantitatively, a procedure for measuring an amount of reactant molecules injected onto catalyst surface and calibrating the intensity of mass signal were proposed and implemented. We tested the applicability of this procedure for the quantitative analysis of products of NO+H(2) reaction on Pt-Al(2)O(3) catalysts (a planar catalyst: Pt-Al(2)O(3)Si substrates inserted into a micro-tube-reactor with SiC balls). Although the surface area of the planar catalyst was very small, the mass signal intensities of the reaction products were found to be sufficient for the above procedure. We measured the fragmentation patterns and the inherent sensitivity factors in the TOF-MS using the mixture of the internal standard gas Ar and the N-containing gases. The relative sensitivity factors for NH(3), N(2), NO, and N(2)O and the relative intensities of fragment peaks to the molecular ion peak of H(2)O and N(2)O were estimated. The procedure constructed here has enabled us to analyze the transient consecutive secondary catalytic reactions as well as primary reactions based on the formation rate of product molecules per millisecond instead of the mass signal intensities of the reaction products.     

Correlation time-of-flight spectrometry of ultracold neutrons

The features of the correlation method used in time-of-flight spectrometry of ultracold neutrons are analyzed. The time-of-flight spectrometer for the energy range of ultracold neutrons is described, and results of its testing by measuring spectra of neutrons passing through interference filters are presented.     

负热电离飞行时间质谱仪及其用于硼酸中硼同位素比值的测定

在自行研制的热电离飞行时间质谱仪(TI-TOF-MS)基础上,通过对仪器的重新设计和电源的改造,研制了负离子热电离飞行时间质谱仪(NTI-TOF-MS)。文中介绍NTI-TOF-MS仪器的结构及性能特点,通过对仪器性能进行测试,获得了仪器的分辨率,仪器在m/z为219amu处的分辨率为1369。文中应用NTI-TOF-MS法测量了核纯级硼酸样品中硼的同位素比值,测量的结果为¹⁰B/¹¹B=0.2403±0.0007。     

Laser ablation with resonance-enhanced multiphoton ionization time-of-flight mass spectrometry for determining aromatic lignin volatilization products from biomass

We have designed and developed a laser ablation∕pulsed sample introduction∕mass spectrometry platform that integrates pyrolysis (py) and∕or laser ablation (LA) with resonance-enhanced multiphoton ionization (REMPI) reflectron time-of-flight mass spectrometry (TOFMS). Using this apparatus, we measured lignin volatilization products of untreated biomass materials. Biomass vapors are produced by either a custom-built hot stage pyrolysis reactor or laser ablation using the third harmonic of an Nd:YAG laser (355 nm). The resulting vapors are entrained in a free jet expansion of He, then skimmed and introduced into an ionization region. One color resonance-enhanced multiphoton ionization (1+1 REMPI) is used, resulting in highly selective detection of lignin subunits from complex vapors of biomass materials. The spectra obtained by py-REMPI-TOFMS and LA-REMPI-TOFMS display high selectivity and decreased fragmentation compared to spectra recorded by an electron impact ionization molecular beam mass spectrometer (EI-MBMS). The laser ablation method demonstrates the ability to selectively isolate and volatilize specific tissues within the same plant material and then detect lignin-based products from the vapors with enhanced sensitivity. The identification of select products observed in the LA-REMPI-TOFMS experiment is confirmed by comparing their REMPI wavelength scans with that of known standards.     

A measuring complex for time-of-flight spectrometry of fast neutrons

A measuring complex for solving problems of fast neutron spectrometry using the time-of-flight method has been developed on the basis of an ЗГП-15 electrostatic tandem accelerator operating in a pulsed mode. The pulse repetition rate of the accelerator is 2.5 MHz, and the pulse duration is τ ≤ 1 ns. The accelerator components, some features of their performance, and their main parameters are described. The complex has been used to investigate the differential neutron emission cross sections for different constructional materials. A method providing the stable performance of its measuring channels has been proposed and tested.     

Structural investigation of bacterial lipopolysaccharides by mass spectrometry and tandem mass spectrometry

Mass spectrometric studies are now playing a leading role in the elucidation of lipopolysaccharide (LPS) structures through the characterization of antigenic polysaccharides, core oligosaccharides and lipid A components including LPS genetic modifications. The conventional MS and MS/MS analyses together with CID fragmentation provide additional structural information complementary to the previous analytical experiments, and thus contribute to an integrated strategy for the simultaneous characterization and correct sequencing of the carbohydrate moiety. © 2010 Wiley Periodicals, Inc., Mass Spec Rev 29:606–650, 2010     

飞行时间质谱仪国内研究状况及发展趋势

本文介绍飞行时间质谱仪的发展历史,对近二十年来国内飞行时间质谱仪的研制状况做较全面的概述。最后结合国内情况,介绍飞行时间质谱仪为适应不同应用领域研究对象的需要,目前主要的两个发展方向,一个是发展超高分辨、高灵敏度的高档仪器,另一个是发展小型台式仪器。     

MALDI-TOF mass spectrometry of bacteria

The development of MALDI-TOF mass spectrometry methods for the characterization of bacteria is reviewed and discussed. The general use of MALDI for the characterization of large biomolecules led directly to obvious applications involving the analysis of isolated bacterial proteins. More surprising was the observation that MALDI-TOF mass spectrometry could be applied directly to crude cellular fractions or cellular suspensions and that the resulting data from such complex mixtures could provide evidence for chemotaxonomic classification. Versatility and the rapidity of analysis led to the rapid development of a number of MALDI-TOF methods involving bacteria. Examples of some of the applications covered in this review are the analysis of bacterial RNA and DNA, the detection of recombinant proteins, the characterization of targeted or unknown proteins, bacterial proteomics, the detection of virulence markers, and the very rapid characterization of bacteria at the genus, species, and strain level. The demonstrated capability of taxonomic classification at the strain level, using unprocessed cells, opens the possibility that MALDI-TOF and similar mass spectrometry approaches may contribute significantly to fulfilling emerging needs for the development of near real-time methods for the characterization of bacteria.     

Electrospray mass spectrometry of phospholipids

Phospholipids play a central role in the biochemistry of all living cells. These molecules constitute the lipid bilayer defining the outer confines of a cell, but also serve as the structural entities which confine subcellular components. Mass spectrometry has emerged as a powerful tool useful for the qualitative and quantitative analysis of complex phospholipids, including glycerophospholipids and the sphingolipid, sphingomyelin. Collision induced decomposition of both positive and negative molecular ion species yield rich information as to the polar head group of the phospholipid and the fatty-acyl substituents esterified to the glycerophospholipid backbone. This review presents the current level of understanding of the mechanisms involved in the formation of various product ions following collisional activation of molecular ion species generated by electrospray ionization of the common glycerophospholipids, including phosphatidic acid, phosphatidylethanolamine, phosphatidylcholine, phosphatidylinositol, phosphatidylglycerol, phosphatidylserine, cardiolipin, and sphingomyelin. Recent advances in the application of matrix assisted laser desorption ionization is also considered. Several applications of mass spectrometry applied to phospholipid analysis are presented as they apply to physiology as well as pathophysiology.     

Atmospheric pressure photoionization mass spectrometry

Atmospheric pressure photoionization (APPI) is the last arrival in the family of atmospheric pressure ionization (API) methods to couple mass spectrometry (MS) to liquid-phase separation techniques. The basic idea was to further extend the fields of application of liquid chromatography (LC)-MS to those molecules that are not, or are poorly amenable, to electrospray (ESI) or APCI. The present review explores the literature. After a short introduction with an historical background and the premises for its development, we describe the technique, its physical principles, and the factors that affect its efficiency. The review also presents a survey of applications in different fields.     

加速器质谱及应用

本文简要介绍现代核分析技术——加速器质谱的基本原理、技术发展以及在地球科学、考古学、环境科学和生命科学中的应用。     

Detection and registration of ion clots in laser time-of-flight mass spectrometers

A number of factors influencing the measurement errors of analytic signals detected with secondary electron multipliers (SEMs) and registered with fast ADCs are analyzed. Such signals are generated in laser time-of-flight mass spectrometry at the stage of ion detection and recording of mass spectra. In particular, the effect of statistical factors and sources of systematic errors during both measurements of isotope ratios and elemental analysis is considered. Such errors as the statistics of formation of ion clots, the limited range of ADC records, discrimination during detection of ions of different masses, and others are considered. It is shown that, without taking into account the features of operation of SEMs and ADCs, both the statistical and systematic errors of measuring isotope ratios may reach several percent. The proposed operating modes of the detector, with allowance for its features, the design of the recording system, and use of formulas for calculating and correcting errors, allow their reduction to ～0.10–0.01%     

A hardware and software system for the laser time-of-flight mass spectrometer

The hardware and software system for a laser time-of-flight mass spectrometer is based on the double-level principle. At the upper level, the personal computer automatically controls online recording and processing of mass spectra with the highest priority. The monitoring and stabilization functions are fulfilled by controllers of the second control level. The exchange between the controllers and personal computer takes place in the periods between mass-spectrum recording and processing. The use of the hardware and software system has made it possible (i) to form short mass peaks with a half-height duration of up to 10 ns, (ii) to decrease a scatter of relative sensitivity coefficients from two or three down to one order of magnitude, and (iii) to increase a dynamic range of the recorded mass spectra up to 1?1 × 10⁹.     

Shock tube/time-of-flight mass spectrometer for high temperature kinetic studies

A shock tube (ST) with online, time-of-flight mass spectrometric (TOF-MS) detection has been constructed for the study of elementary reactions at high temperature. The ST and TOF-MS are coupled by a differentially pumped molecular beam sampling interface, which ensures that the samples entering the TOF-MS are not contaminated by gases drawn from the cold end wall thermal boundary layer in the ST. Additionally, the interface allows a large range of postshock pressures to be used in the shock tube while maintaining high vacuum in the TOF-MS. The apparatus and the details of the sampling system are described along with an analysis in which cooling of the sampled gases and minimization of thermal boundary layer effects are discussed. The accuracy of kinetic measurements made with the apparatus has been tested by investigating the thermal unimolecular dissociation of cyclohexene to ethylene and 1,3-butadiene, a well characterized reaction for which considerable literature data that are in good agreement exist. The experiments were performed at nominal reflected shock wave pressures of 600 and 1300 Torr, and temperatures ranging from 1260 to 1430 K. The rate coefficients obtained are compared with the earlier shock tube studies and are found to be in very good agreement. As expected no significant difference is observed in the rate constant between pressures of 600 and 1300 Torr.     

Metabolomics applications of FT-ICR mass spectrometry

Metabolomics, also known as Metabolic Profiling, is an emerging discipline under the umbrella concept of systems biology. The goal of metabolomics is to know and understand the concentrations and fluxes of endogenous metabolites within a living biological system under study. General tools are being developed for the rapid measurement of many metabolites in a single experiment, most of which are mass spectrometric methods. FT-ICR has unique advantages, as a mass spectrometric method, in this regard. Applications of FT-ICR to metabolomics analyses will be discussed and reviewed in the context of the single publication currently available.     

Time-of-flight mass spectrometry for time-resolved measurements

A time-resolved time-of-flight mass spectrometer (TOF-MS) that can simultaneously monitor multiple species on the millisecond time scale has been constructed. A pulsed photolysis laser is used to initiate reaction, and then via a pinhole the reaction mixture is sampled by the TOF-MS. The ions are created by photoionization via either a discharge lamp or a pulsed laser. Comparison between the two ionization sources showed that the laser is at least an order of magnitude more efficient, based on the time to accumulate the data. Also, unlike the continuous lamp the pulsed laser is not mass limited. Frequency tripling the 355 nm output of a Nd:YAG laser provided a convenient laser ionization source. However, using a dye laser provided an equally intense laser ionization source with the ability to tune the vacuum ultraviolet (vuv) light. To show the versatility of the system the kinetics of the reaction of SO and ClSO radicals with NO(2) were simultaneously measured, and using the dye laser the vuv light was tuned to 114 nm in order to observe H(2)CO being formed from the reaction between CH(3)CO and O(2).     

Low-vacuum cylindrical ion trap mass spectrometry

Low-vacuum mass spectrometry is desirable because it reduces the size, weight, cost, and power of the instrument by reducing the workload of the pumping system. To investigate low-vacuum mass spectrometry methods, a cylindrical ion trap (CIT) instrument was built. The platform used an electron impact source as the ionization source, a custom CIT as the mass analyzer, and an electron multiplier as the ion detector. The dimensions of the CIT were r₀?=?10?mm and z₀?=?8.98?mm. Aiming at low-vacuum conditions, its working parameters were optimized. By increasing the frequency of the radio frequency (RF) voltage, optimizing the electron impact source, using a higher voltage on the electron multiplier, and improving the current preamplifier, the mass spectrometry of methyl salicylate was successively performed at helium buffer gas pressures up to 2?Pa, which was dozens of times higher than the upper pressure limit of ion trap mass spectrometers. More importantly, this pressure can be obtained using a single pump, avoiding the use of a bulky turbo pump. In addition, we measured and analyzed the mass deviation of methyl salicylate with the changes in the background gas pressure and RF voltage frequency. The results experimentally verified the theory that the stability regions expand with increasing pressure for the first time. The methods we explored could be used to develop next generation hand-portable instruments and bring new applications to mass spectrometry.