Matrix-free high-resolution imaging mass spectrometry with high-energy ion projectiles

The importance of imaging mass spectrometry (MS) for visualizing the spatial distribution of molecular species in biological tissues and cells is growing. We have developed a new system for imaging MS using MeV ion beams, termed MeV-secondary ion mass spectrometry (MeV-SIMS) here, and demonstrated more than 1000-fold increase in molecular ion yield from a peptide sample (1154 Da), compared to keV ion irradiation. This significant enhancement of the molecular ion yield is attributed to electronic excitation induced in the near-surface region by the impact of high energy ions. In addition, the secondary ion efficiency for biologically important compounds (>1 kDa) increased to more than 10(10) cm(-2), demonstrating that the current technique could, in principle, achieve micrometer lateral resolution. In addition to MeV-SIMS, peptide compounds were also analyzed with cluster-SIMS and the results indicated that in the former method the molecular ion yields increased substantially compared to the latter. To assess the capability of MeV-SIMS to acquire heavy-ion images, we have prepared a micropatterned peptide surface and successfully obtained mass spectrometric imaging of the deprotonated peptides (m/z 1153) without any matrix enhancement. The results obtained in this study indicate that the MeV-SIMS technique can be a powerful tool for high-resolution imaging in the mass range from 100 to over 1000 Da.     

Pyrolysis—high-resolution mass spectrometry of biological materials

In a diseased state in man or animals a change at eh molecular level might occur. A pyrolysis-high-resolution mass spectrometric method has been developed to measure these changes. The mass spectra are used as fingerprints. A similar approach is reported using low-resolution mass spectrometry. The difference between low resolution and high resolution is that the number of mass spectral lines is strongly increased and therefore also the information content. As a result, a change at the molecular level will be more pronounced in high-resolution mass spectra. As an application, the results of toxicity studies on Daphnia magna are given. The experiments were performed with paraoxon, parathion and malathion. The changes at the molecular level in Daphnia magna appear to be substance-dependent.     

Precision of fragmentation patterns in high-resolution mass spectrometry

The effect of controlling the temperature of the ion source of a high-resolution mass spectrometer is to increase the confidence in mass spectral pattern coefficients of saturated molecules. Results are presented for both controlled and uncontrolled ion-source temperatures. Standard deviations have been calculated for selected summations of ion intensities and criteria have been suggested for maintaining meaningful analytical results in the study of petroleum distillates.     

Open-access high-resolution mass spectrometry in early drug discovery

Techniques such as mass spectrometry and NMR spectroscopy form an essential part of the medicinal chemist's toolbox for characterizing and assessing the purity of new molecules. Empowering medicinal chemists to gain early insight into their reaction products has a direct impact on productivity. Devolution of cutting-edge techniques from the specialist to the bench chemist also frees the specialist to concentrate on solving the more demanding of analytical problems. For open-access techniques to be taken up, they must be robust and be able to handle differing sample concentrations and varying sample complexities. This paper details the implementation of high-resolution liquid chromatography/mass spectrometry in open access to aid the medicinal chemist in characterizing desired products and identifying unexpected rearrangements, by-products and complete unknowns.     

基于高分辨质谱的石油组学分析技术的研究进展

随着原油重质化、劣质化程度的加深以及环境保护对燃油清洁性要求的日趋严格,对石油组成进行分子水平详细表征具有重大的现实意义和经济价值。依赖于高分辨质谱技术平台的石油组学分析技术成为实现这一目标的有力工具。本文以高分辨质谱技术平台为切入点,对石油组学定性定量分析技术的最新进展进行回顾和总结,并对其发展前景进行展望。     

Perceiving the chemical language of Gram-negative bacteria: listening by high-resolution mass spectrometry

Gram-negative bacteria use N-acylhomoserine lactones (AHLs) as their command language to coordinate population behavior during invasion and colonization of higher organisms. Although many different bacterial bioreporters are available for AHLs monitoring, in which a phenotypic response, e.g. bioluminescence, violacin production, and β-galactosidase activity, is exploited, mass spectrometry (MS) is the most versatile detector for rapid analysis of AHLs in complex microbial samples, with or without prior separation steps. In this paper we critically review recent advances in the application of high-resolution MS to analysis of the quorum sensing (QS) signaling molecules used by Gram-negative bacteria, with much emphasis on AHLs. A critical review of the use of bioreporters in the study of AHLs is followed by a short methodological survey of the capabilities of high-resolution mass spectrometry (HRMS), including Fourier-transform ion cyclotron resonance (FTICR) MS and quadrupole time-of-flight (qTOF) MS. Use of infusion electrospray ultrahigh-resolution FTICR MS (12 Tesla) enables accurate mass measurements for determination of the elemental formulas of AHLs in Acidovorax sp. N35 and Burkholderia ubonensis AB030584. Results obtained by coupling liquid chromatography with a hybrid quadrupole linear ion trap-FTICR mass spectrometer (LC–LTQ-FTICRMS, 7-T) for characterization of acylated homoserine lactones in the human pathogen Pseudomonas aeruginosa are presented. UPLC–ESI-qTOF MS has also proved to be suitable for identification of 3O-C₁₀HSL in Pseudomonas putida IsoF cell culture supernatant. Aspects of sample preparation and the avoidance of analytical pitfalls are also emphasized.

Two-dimensional separations with electrospray ionization ambient pressure high-resolution ion mobility spectrometry/quadrupole mass spectrometry

The coupling of ion mobility spectrometry (IMS) instruments with mass spectrometers has been described since early in IMS development, most commonly with quadrupole mass analyzers. The recent development of IMS with time-of-flight (TOF) instruments has demonstrated that the time compatibility (IMS milliseconds and TOFMS microseconds) of the two techniques enables rapid two-dimensional separations to be performed, theoretically in the order of seconds for a complete analysis. This study presents a unique way to operate a traditional IMS/QMS system to attain separations similar to those achieved with IMS/TOF. For this new approach, the quadrupole was slowly scanned in the single-ion monitoring mode while IMS spectra were continually embedded in each m/z step. In this way, two-dimensional separations (IMS drift times and m/z) were obtained using the traditional IMS/QMS arrangement. An example of a five amino acid separation (quadrupole scan of 40 m/z values at a rate of approximately 7 steps/min) led to a complete two-dimensional analysis within 6 min, comparable to rapid chromatographic separations with mass spectrometry. Proposed approaches to reduce the analysis time are discussed and a reduction in the analysis time to less than 1 min is feasible when the IMS/QMS separation conditions are optimized.     

Determination of exemestane and 17-hydroxyexemestane by high-performance liquid chromatography coupled with tandem mass spectrometry and high-resolution mass spectrometry

An approach was developed for determining and confirming the presence of exemestane and its metabolite 17-hydroxyexemestane in urine. It is based on the application of high-performance liquid chromatography coupled with electrospray ionization mass spectrometry (HPLC-MS/MS) and atmospheric pressure chemical ionization high-resolution mass spectrometry (HPLC-HRMS). To detect hydroxyexemestane, the analysis of the hydrolyzed fraction of urine is preferable. The recovery rates of exemestane and 17-hydroxyexemestane were 83 and 91%, respectively. The detection limits were 1 ng/mL for HPLC-MS/MS and 2.5 ng/mL for HPLC-HRMS. In spite of a considerable effect of ionization suppression, the sensitivity and selectivity of the determination are affected by the selection of the optimal detection conditions in HPLC-MS/MS and by the high accuracy of mass determination in mass spectrometry with orbitrap detection, enabling resolution at a level of 5 ppm. The procedures can be used for screening and confirmatory analysis.     

AZ-1518 Photoresist analysis with synchrotron radiation using high-resolution time-of-flight mass spectrometry

With the aim of identifying molecular modifications among photoresists unexposed and previously exposed to the ultraviolet light the photon stimulated ion desorption (PSID) technique was employed in the study of the AZ-1518 photoresist. Data acquisition was performed at the Brazilian Synchrotron Light Source (LNLS), during a single-bunch operation mode of the storage ring and using high-resolution time-of-flight mass spectrometry (TOF-MS) for ion analysis. PSID mass spectra on both photoresists (unexposed and exposed) were obtained following the S K-shell photoexcitation and desorption ion yield curves have been determined for the main fragments as a function of the photon energy. The AZ-1518 photoresists presented different PSID spectra, showing characteristic fragments. Most of the analyzed ions showed larger relative yields for the exposed photoresist. Fragments related to the photochemical decomposition of the photoresist could be clearly identified. These results showed that the PSID technique is adequate to investigate structural changes in molecular level in unexposed and exposed photoresists.     

Analysis of high-boiling petroleum streams by high-resolution mass spectrometry

The major group types in petroleum streams may be analysed by high-resolution mass spectrometry. The method described here relies on a calibration matrix derived from the high-resolution spectra both of pure compounds and of cuts separated from petroleum. The analytical results have been assessed statistically for precision.     

Calculation of ion composition in organic high-resolution mass spectrometry

The theory of a method for the calculation of organic ion compositions is described. It is based on concepts of homologous groups and homologous increments of ‘mass defect.’ Unlike the common algorithms usually used for this purpose, the proposed method excludes the analysis and outcome of chemically unreal combinations of atoms. Reduction of the number of alternative compositions is discussed. The possibility of a single (non-alternative) solution is considered in the case of additional information on the presence of functional groups containing nitrogen and/or oxygen and also aromatic fragments easily identified by their infrared spectra. The efficiency of the method is demonstrated with the help of new software for DEC- and IBM-compatible computers.     

Identification of Barrenwort flavonoids by high-resolution tandem mass spectrometry

Fragmentation of the main Barrenwort flavonoids—icariin, icaritin, icarisides I and II, and epimedins A and B—is studied by tandem mass spectrometry. High-resolution mass spectra of positively charged ions of these compounds are obtained under the conditions of collision-induced dissociation. Characteristic fragment ions are determined, which ensured the classification of unknown compounds as Barrenwort flavonoids. Epimedin C was isolated from raw plant material by preparative liquid chromatography; its structure was confirmed by ¹H and ¹³C NMR spectra.     

Accurate mass measurement of DNA oligonucleotide ions using high-resolution time-of-flight mass spectrometry

Matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI) time-of-flight mass spectrometry (TOFMS) play an essential role in the analysis of biological molecules, not only peptides and proteins, but also DNA and RNA. Tandem mass spectrometry used for sequence analysis has been a major focus of technological developments in mass spectrometry, but accurate mass measurements by high-resolution TOFMS are equally important. This paper describes the role that high mass measurement accuracy can play in DNA composition assignment and discusses the influence of several parameters on mass measurement accuracy in both MALDI and ESI mass spectra. Five oligonucleotides (5-13mers) were used to test the resolving power and mass measurement accuracy obtained with MALDI and ESI instruments with reflectron TOF mass analyzers. The results from the experimental studies and additional theoretical calculations provide a basis to predict the practical utility of high-resolution TOFMS for the analysis of larger oligonucleotides.     

Thermal effects on the mass spectra of benzophenone oximes obtained by gas chromatography/electron ionization mass spectrometry

Benzophenone oxime and substituted benzophenone oximes can be pyroiyzed to the imines to a small extent in the heated transfer line from the gas chromatograph to the mass spectrometer source and to a large extent in the hot injection port of a gas chromatograph at high temperatures using the splitless mode of sample injection. The pyrolysis of the oximes to the imines appears to be largely a surface reaction and does not form the benzophenones as pyrolysis products. Decomposition of benzophenone oxime to benzophenone was produced by another reaction at the front of the chromatographic column. Thermal isomerizaton of benzophenone oxime to benzanilide was not observed under these conditions.     

Quantitative and confirmative performance of liquid chromatography coupled to high-resolution mass spectrometry compared to tandem mass spectrometry

The quantitative and confirmative performance of two different mass spectrometry (MS) techniques (high-resolution MS and tandem MS) was critically compared. Evaluated was a new extraction and clean-up protocol which was developed to cover more than 100 different veterinary drugs at trace levels in a number of animal tissues and honey matrices. Both detection techniques, high-resolution mass spectrometry (HRMS) (single-stage Orbitrap instrument operated at 50 000 full width at half maximum) and tandem mass spectrometry (MS/MS) (quadrupole technology) were used to validate the method according to the EU Commission Decision 2002/657/EEC. Equal or even a slightly better quantitative performance was observed for the HRMS-based approach. Sensitivity is higher for unit mass resolution MS/MS if only a subset of the 100 compounds has to be monitored. Confirmation of suspected positive findings can be done by evaluating the intensity ratio between different MS/MS transitions, or by accurate mass based product ion traces (no precursor selection applied). MS/MS relies on compound-specific optimized transitions; hence the second, confirmatory transition generally shows relatively high ion abundance (fragmentation efficacy). This is often not the case in single-stage HRMS, since a generic (not compound-optimized) collision energy is applied. Hence, confirmation of analytes present at low levels is superior when performed by MS/MS. Slightly better precision, but poorer accuracy (fortified matrix extracts versus pure standard solution) of ion ratios were observed when comparing data obtained by HRMS versus MS/MS.     

基于高分辨质谱技术的婴幼儿食品中过敏原蛋白质的高灵敏检测

基于高效液相色谱-串联质谱(LC-MS/MS)技术,选择稳定性好、灵敏度高的特征肽段,利用平行反应监测(PRM)技术,实现了多类过敏原蛋白质的高灵敏度同时检测,并成功应用于婴幼儿食品中过敏原成分的分析。对于婴幼儿食品中蛋白质的提取,与传统的丙酮沉淀法比,采用膜上原位样品预处理方法(i-FASP)可实现更高的蛋白质提取效率和抗干扰能力。所检测的过敏原蛋白质的定量限(LOQ)最小可达到0.028 mg/L,其线性范围最宽可跨越4个数量级,且线性关系良好(相关系数R~2≥0.99)。该方法为食品中过敏原蛋白质组学快速分析提供了一种可靠的分析方法。     

The current role of high-resolution mass spectrometry in food analysis

High-resolution mass spectrometry (HRMS), which is used for residue analysis in food, has gained wider acceptance in the last few years. This development is due to the availability of more rugged, sensitive, and selective instrumentation. The benefits provided by HRMS over classical unit-mass-resolution tandem mass spectrometry are considerable. These benefits include the collection of full-scan spectra, which provides greater insight into the composition of a sample. Consequently, the analyst has the freedom to measure compounds without previous compound-specific tuning, the possibility of retrospective data analysis, and the capability of performing structural elucidations of unknown or suspected compounds. HRMS strongly competes with classical tandem mass spectrometry in the field of quantitative multiresidue methods (e.g., pesticides and veterinary drugs). It is one of the most promising tools when moving towards nontargeted approaches. Certain hardware and software issues still have to be addressed by the instrument manufacturers for it to dislodge tandem mass spectrometry from its position as the standard trace analysis tool.     

Current applications of high-resolution mass spectrometry in drug metabolism studies

This paper reviews high-resolution mass spectrometry (HRMS) approaches published in 2007–2011 for the elucidation of drug metabolism with a focus on new therapeutics, new drugs of abuse, and doping agents using time-of-flight, single-stage Orbitrap, ion trap Orbitrap, and other Fourier transform MS-based techniques. The present review provides an overview of metabolite-generating systems and assays used, sample preparation techniques, ionization and fragmentation techniques, as well as data mining strategies and software tools which were used in the reviewed papers. Furthermore, HRMS-specific topics such as demand for a certain resolution or a specific mass accuracy are discussed in detail and corresponding recommendations are given. Finally, the advantages and limitations of these methods are discussed.