Direct Analysis of Thin-Layer Chromatography Separations of Petroleum Samples by Laser Desorption Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry Imaging
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We present an analytical method for direct analysis of thin-layer chromatography (TLC) separations of petroleum samples by laser desorption ionization (LDI) coupled to Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) imaging. LDI of TLC plates selectively ionizes condensed aromatic hydrocarbons and facilitates two-dimensional imaging of TLC-separated petroleum compounds. Molecular-level characterization available only with ultrahigh-resolution FT-ICR MS provides elemental composition assignment and surpasses conventional TLC readout-based flame ionization detection. Resolution and assignment of migrated molecules targeted by LDI combined with FT-ICR MS provides elemental composition assignment and, therefore, chemical information, i.e., heteroatom class, aromaticity (double bond equivalents), and carbon number. Here, three petroleum samples (a field deposit, a crude oil, and a tar ball) were TLC-separated by their solubility in n-heptane and imaged by LDI FT-ICR MS.Sample Preparation
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Electrospray ionization (ESI) can transfer large biopolymers and many noncovalently bound complexes into the gas phase and to preserve specific noncovalent biomolecular associations for subsequent mass spectrometric analysis. Although a number of details of the ESI process remain a subject of debate, it is now incontestable that many weak associations can survive transfer to the gas phase and are stable for periods of at least seconds. In this presentation, the application of ESI-Fourier transform ion cyclotron resonance (FTICR) mass spectrometry methods for the study of large biopolymers and their noncovalent complexes will be described. It will also be shown that competitive binding studies can be used to quickly establish relative binding affinities in solution, allowing combinatorial libraries to be rapidly screened. After measurements of the intact complex, dissociation studies can be conducted to probe the structure of the individual constituents of complexes. Studies comparing the relative stabilities of protein-ligand complexes in solution and desolvated in the gas phase will also be presented, and discussed from both fundamental and analytical perspectives.
Electron-capture dissociation
Biopolymer
Infrared multiphoton dissociation
Ion cyclotron resonance
Non-covalent interactions
Electron-transfer dissociation
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Fourier transform ion cyclotron resonance mass spectrometry enables the attribution of sum for-mulae on the basis of the measured m/z ratio to single compounds in a complex mixture due to its high mass accuracy and mass resolution. The aim of this PhD thesis was the characterisation of high complex, petroleum-derived materials by combining high-resolution mass spectrometry and ther-mal analysis.
Selected ion monitoring
Ion cyclotron resonance
Fourier transform spectroscopy
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Atmospheric pressure photoionization (APPI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) has significantly contributed to the molecular speciation of petroleum. However, a typical APPI source operates at 50 μL/min flow rate and thus causes a considerable mass load to the mass spectrometer. The recently introduced microchip APPI (μAPPI) operates at much lower flow rates (0.05−10 μL/min) providing decreased mass load and therefore decreased contamination in analysis of petroleum by FT-ICR MS. In spite of the 25 times lower flow rate, the signal response with μAPPI was only 40% lower than with a conventional APPI source. It was also shown that μAPPI provides very efficient vaporization of higher molecular weight components in petroleum analysis.
Ion cyclotron resonance
Selected ion monitoring
Vaporization
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Nano-electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (nano-ESI-FTICRMS) was employed for the analysis of the phytosiderophore 2'-deoxymugineic acid (DMA) and the candidate ligand for the intracellular iron transport in plants nicotianamine (NA). Due to the zwitterionic nature of NA and DMA, complementary mass spectra were obtained in positive and negative ionization modes. The technique was also used for speciation of their complexes with Fe(II) and Fe(III), respectively. The species observed at pH 7.3 are the 1:1 Fe-ligand complexes and no evidence for the existence of dimeric complexes was observed. NA and DMA differ only by one mass unit. Consequently, in the system NA + DMA + Fe(II)/Fe(III), there are pairs of iron species (i.e. NA-Fe(II) and DMA-Fe(III)) with the same nominal mass, which differ only by approximately 0.02 mass units. It is shown that high-resolution MS accompanied by accurate mass data analysis allows the unequivocal identification of all four iron species (NA-Fe(II), NA-Fe(III), DMA-Fe(II), DMA-Fe(III)) in one solution without separation. We also addressed the possible alteration of the oxidation state of chelated iron under nano-ESI conditions, but no redox reactions were observed under optimized conditions.
Ion cyclotron resonance
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The combination of electrospray ionization (ESI) with Fourier transform mass spectrometry (FTMS) is a powerful tool in characterizing synthetic polymers. ESI permits the generation of intact, multiply charged high mass ions, whereas FTMS provides high mass resolution and correspondingly improved mass accuracy. However, under "nonideal" empirically determined operating conditions, a mass discrimination effect occurs as a function of accumulation time that can result in significant differences for calculated average mass values (Mn, Mw) and polydispersities. A multidimensional tuning process to eliminate the deleterious effects of mass bias is demonstrated for several sodiated poly(ethylene glycol) samples containing oligomers with masses covering a 600–3350 Da mass regime. In addition, experiments are performed in order to elucidate the possible mechanism(s) that cause the mass discrimination effect. It is proposed that extended collisions (reactive and nonreactive) occur in the hexapole to alter the energy (and velocity) distributions of the ions before injection into the trap. By choosing higher skimmer potentials, ions over a narrower energy "window" are preselected in the hexapole and exhibit lower overall mass bias effects.
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In this study, we used secondary electrospray ionization mass spectrometry assisted by an ion funnel (IF) operating at ambient pressure to find compounds in the mass range of 100–500 m/z in online breath fingerprinting experiments. In low‐resolution experiments conducted on an ion trap instrument, we found that pyridine is present in breath of individuals long after drinking coffee. In high‐resolution experiments conducted on a Fourier transform ion cyclotron resonance, we found more than 30 compounds in the mass range of 100–500 m/z in analogous online breath experiments. More than a third of these compounds have molecular weights above 200 Daltons and have not been mentioned in previous studies. In low‐resolution experiments as well as experiments without the IF, these compounds could not be detected. Copyright © 2012 John Wiley & Sons, Ltd.
Extractive electrospray ionization
Ambient ionization
Desorption electrospray ionization
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The relative abundances of M + 1 and M + 2 ions help to identify the elemental composition of the molecular ion (M). But scan speed, sensitivity, and resolution limitations of mass spectrometers have impeded determination of these abundances. Mass peak profiling from selected ion recording data (MPPSIRD) provided faster sampling and enhanced sensitivity, which permitted use of higher resolution. M + 2 profiles having only a few percent of the ion abundance of M were monitored at 20 000 resolution. The relative abundances, exact masses, and shapes of M, M + 1, and M + 2 mass peak profiles were determined. By applying five criteria based on these quantities, elemental compositions were determined even for ions too large (up to 766 Da) to be uniquely assigned from their exact mass and accuracy limits alone. A profile generation model (PGM) was written to predict these resolution-dependent quantities by considering all M + 1 and M + 2 ions for each candidate composition. The model also provided assurance that no other compositions were possible. Characterization of the M + 1 and M + 2 profiles by MPPSIRD and the PGM greatly expanded the practical ability of high-resolution mass spectrometry to determine elemental compositions.
Mass
Natural abundance
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The differences between harmonics and multi-charged peaks in mass spectrometry are often not obvious. This work conducts experiments using both electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) sources with Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) to investigate the difference between harmonics and multi-charged peaks for the first time. In particular, organometallic compounds, which were characterized by the isotope distribution in ESI, were investigated in detail. A comparison of the peaks of the three charges with the three frequency doubling results at high-resolution mass spectra demonstrated that these peaks may be clearly differentiated from one another. Fullerene (C60) was characterized using APCI in the negative mode by FTICR MS provided further evidence. In addition, harmonics are unavoidable, but can be relatively weakened. These results are helpful to obtain accurate and comprehensive spectral information from FTICR MS.
Ion cyclotron resonance
Selected ion monitoring
Atmospheric-pressure chemical ionization
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Ion cyclotron resonance
MALDI imaging
Selected ion monitoring
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