Field Fourier Transform Ion Cyclotron Research Articles

Analysis of VOCs in Liquids through Vaporization in a Tubular Oven Monitored by Chemical Ionization Mass Spectrometry.

The analysis of chemical compounds present at trace levels in liquids is important not only for environmental measurements but also, for example, in the health sector. The reference technique for the analysis of Volatile Organic Compounds (VOCs) in liquids is GC, which is difficult to use with an aqueous matrix. In this work, we present an alternative technique to GC to analyze VOCs in water. A tubular oven is used to completely vaporize the liquid sample deposited on a gauze. The oven is heated in the presence of a dinitrogen flow, and the gas is analyzed at the exit of the oven by a chemical ionization mass spectrometer developed in our laboratory. It is a low magnetic field Fourier Transform Ion Cyclotron Resonance (FT-ICR) optimized for real-time analysis. The Proton Transfer Reaction (PTR) used during the Chemical Ionization event results in the selective ionization of the VOCs present in the gas phase. The optimization of the desorption conditions is described for the main operating parameters: temperature ramp, liquid quantity, and nitrogen flow. Their influence is studied using a 100 ppmv aqueous toluene solution. The analytical method is then tested on a mixture of seven VOCs.

Online Coupling of Liquid Chromatography with Fourier Transform Ion Cyclotron Resonance Mass Spectrometry at 21 T Provides Fast and Unique Insight into Crude Oil Composition.

High magnetic field Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry provides the highest mass resolving power and mass measurement accuracy for detailed characterization of complex chemical mixtures. Here, we report the coupling of online liquid chromatography of complex mixtures with a 21 tesla FT-ICR mass spectrometer. The high magnetic field enables large ion populations to be analyzed for each spectrum for a high dynamic range, with 3.2 million mass resolving power at m/z 400 (6.2 s transient duration) or 1.6 million (3.1 s transient duration) while maintaining high mass accuracy for molecular formula assignment (root-mean-square assignment error < 0.150 ppm). Thousands of unique elemental compositions are assigned per mass spectrum, which can be grouped by the heteroatom class, double bond equivalents (the number of rings and double bonds to carbon), and carbon number. Figures of merit are discussed, as well as characterization of an Arabian heavy vacuum gas oil in terms of the ring number, compound class, double bond equivalents, and ion type. Consideration of elemental composition and retention order provides additional structural information.

Preparation, FPLC Purification and LC-FT-ICR-MS of Proteins.

High magnetic field Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometers provide extremely high mass resolution (resolving power of ~200,000 at 400 m/z) protein detection across a broad mass range, enabling analysis of fine structure of isotopic peak clusters that is missed in other types of mass spectrometers. The protocol detailed here describes preparation of cellular extracts for purification of DNA-binding proteins using multiple chromatographic chemistries via fast protein liquid chromatography (FPLC), and identification and quantitation of the protein isoforms and their post-translational modifications by liquid chromatography coupled to Fourier transform ion cyclotron resonance mass spectrometry (LC-FT-ICR-MS). This protocol benefits from selectively purifying proteins for identification and quantitation by high resolution FT-ICR, which has the resolution to definitively distinguish between acetylation and trimethylation post-translational modification (PTM) additions.

(Invited) Intramolecular Reactions for Gas-Phase Formation of Carbon-Entrapped Clusterfullerenes

Fullerenes that encapsulate clusters of atoms represent a fundamental interest in chemistry, materials, and carbon science due to their unique properties and nanoscale structures. Numerous cages that feature a combination of carbon, metal, and heteroatom-based clusters have been discovered since, for example, Sc3NC@C80 was first reported. Nanocarbon reactions that underlie formation of such compounds, however, are not well understood. Here, we experimentally investigate intramolecular reactions of metallofullerenes in the gas phase by means of laser-based techniques, analyzed by high magnetic field Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. A variety of structurally defined clusterfullerene cages (e.g., Sc3N@C68, Sc3N@C78, etc.) are probed under energetic conditions to decipher reactions that may lead to encapsulation of C atoms, as well as clusterfullerenes that include metal-loss products. An aim of the present work is to identify mechanistic processes and principles that guide formation of metallofullerenes that entrap carbon, metal, and heteroatom-based clusters.

High field FT-ICR mass spectrometry data sets enlighten qualitative DOM alteration in lake sediment porewater profiles

This study investigates how changes in dissolved organic matter (DOM) quality can be evaluated considering all existing principal data pools from high field Fourier transform ion cyclotron mass spectrometry (FT-ICR-MS). We recommend five steps, including suggestions on underlying processes. Two different sediment profiles from a highly acidic mining lake in Germany with different mixis of the overlying lake water (dimictic vs. meromictic) were selected as a model for the analysis of sediment porewater sample to a depth of 30cm. FT-ICR-MS datasets of elemental composition were evaluated for the presence of specific CHO molecular series. In six (seven) porewater depth groups of 63 (127) different data pools were identified. In the first step, the data pools were evaluated with components present in all six (seven) samples (total common presence). This group of components was analysed via a statistical rank analysis of the mass peak intensities (inter sample rankings analysis). The second step comprised the allocation of components which were not present in all samples to specific data pools (partial common presence and different presence pools). Of these pools the largest (containing most components) were selected in the third step for visualization of DOM quality change using van Krevelen diagrams. Underlying DOM transformations were discussed in the fourth step. The fifth step comprised the parallel allocation of changes in DOM quality and in concentrations of inorganic compounds. We identified the principal changes in both depth profiles and thereby demonstrated the potential of DOM data pool evaluation for elucidating biogeochemical processes.

High field FT-ICR mass spectrometry for molecular characterization of snow board from Moscow regions

High field Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry analysis of eight snow samples from Moscow city allowed us to identify more than 2000 various elemental compositions corresponding to regional air pollutants. The hierarchical cluster analysis (HCA) of the data showed good concordance of three main groups of samples with the main wind directions. The North-West group (A1) is represented by several homologous CHOS series of aliphatic organic aerosols. They may form as a result of enhanced photochemical reactions including oxidation of hydrocarbons with sulfonations due to higher amount of SO2 emissions in the atmosphere in this region. Group A2, corresponding to the South-East part of Moscow, contains large amount of oxidized hydrocarbons of different sources that may form during oxidation in atmosphere. These hydrocarbons appear correlated to emissions from traffic, neighboring oil refinery, and power plants. Another family of compounds specific for this region involves CHNO substances formed during oxidation processes including NOx and NO3 radical since emissions of NOx are higher in this part of the city. Group A3 is rich in CHO type of compounds with high H/C and low O/C ratios, which is characteristic of oxidized hydrocarbon-like organic aerosol. CHNO types of compounds in A3 group are probably nitro derivatives of condensed hydrocarbons such as PAH. This non-targeted profiling revealed site specific distribution of pollutants and gives a chance to develop new strategies in air quality control and further studies of Moscow environment.

Efficient injection of low-mass ions into high magnetic field Fourier transform ion cyclotron resonance mass spectrometers

Low-mass cut-off restrictions for injecting ions from external ion sources into high magnetic fields impose limitations for wide mass range analyses with Fourier transform ion cyclotron resonance (FTICR) instruments. Radio-frequency (RF)-only quadrupole ion guides (QIGs) with higher frequencies can be used to overcome low-mass cut-off in FTICR instruments. RF signals (1.0 MHz to 10.0 MHz) were applied to QIGs to transfer externally generated ions from either electron ionization (EI) or electrospray ionization (ESI) sources into ICR cells of 9.4 T FTICR mass spectrometers. Efficiencies of QIGs were evaluated using externally generated ions from: EI of acetone, air, and perfluorotributylamine mixture, EI of gas chromatography (GC)-separated components of a standard sample mixture, and ESI of complex mixtures such as petroleum and fulvic acid samples. We were able to transfer ions with m/z as low as 26 from an external EI source into the ICR cell of a 9.4 T FTICR mass spectrometer and extend the operational low-mass range for ESI-FTICR analyses. High mass resolving power and mass measurement accuracy of GC/FTICR mass spectrometry were utilized to discriminate between oxygenated and non-oxygenated compounds in a 'Grob' sample. Ion losses based on SIMION ion trajectory predictions were consistent with experimental findings. We demonstrated that the use of high-frequency QIGs can extend the operational lower m/z range for both external EI- and ESI-FTICR mass spectrometers. By considering both ICR and Mathieu equations of motions to describe ion trajectories, theoretical ion ejection thresholds (consistent with our experimental findings) could be predicted.

On the Utility of Isotopic Fine Structure Mass Spectrometry in Protein Identification

Modern mass spectrometry (MS)-based protein identification and characterization relies upon accurate mass measurements of the (13)C isotopic distributions of the enzymatically produced peptides. Interestingly, obtaining peptide elemental composition information from its isotopic fine structure mass spectrum to increase the confidence in peptide and protein identification has not yet been developed into a bottom-up proteomics-grade analytical approach. Here, we discuss the possible utility and limitations of the isotopic fine structure MS for peptide and protein identification. First, we in silico identify the peptides from the E. coli tryptic digest and show the increased confidence in peptide identification by consideration of the isotopic fine structures of these peptides as a function of mass and abundance accuracies. In the following, we demonstrate that the state-of-the-art high magnetic field Fourier transform ion cyclotron resonance (FT-ICR) MS allows a routine acquisition of the isotopic fine structure information of a number of isobaric peptide pairs, including a pair of peptides originating from E. coli. Finally, we address the practical limitation of the isotopic fine structure MS implementation in the time-constraint experiments by applying an advanced signal processing technique, filter diagonalization method, to the experimental transients to overcome the resolution barrier set by the typically applied Fourier transformation. We thus demonstrate that the isotopic fine structures of peptides may indeed improve the peptide and possibly protein identification, can be produced in a routine experiment by the state-of-the-art high resolution mass spectrometers, and can be potentially obtained on a chromatographic time-scale of a typical bottom-up proteomics experiment. The latter one requires at least an order of magnitude increase in sensitivity of ion detection, which presumably can be realized using high-field Orbitrap FTMS and/or future generation of ultrahigh magnetic field FT-ICR MS equipped with harmonized ICR cells.

A Strategy for the Determination of the Elemental Composition by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry Based on Isotopic Peak Ratios

We propose a novel strategy for determining the elemental composition of organic compounds using the peak ratio of isotopic fine structure observed by high-magnetic field Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Using 3'-phosphoadenosine 5'-phosphosulfate and CTU guanamine as standard organic compounds, isotopic peaks derived from (15)N-, (34)S-, and (18)O-substituted forms were separated from (13)C-substituted species. Furthermore, these isotopic peaks were quantitatively detected and closely matched the natural abundance of each element. These data successfully led us to determine the one elemental composition in a standard independent manner. The approach should be particularly amenable to the metabolomics research field.

Acidic and neutral polar NSO compounds in Smackover oils of different thermal maturity revealed by electrospray high field Fourier transform ion cyclotron resonance mass spectrometry

Negative ion electrospray ionization (ESI) coupled with high field Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) allows for the direct detection of acidic NSO compounds in petroleum. The technique requires no chromatographic separation, is able to distinguish 18 different compound classes (e.g., neutral nitrogen, carboxylic acids and oxygenates), and can identify ∼14,000 distinct masses by ultra-high mass resolution and mass accuracy. We previously studied three crude oils from different geological origins [Organic Geochemistry 33 (2002b) 743–759]. Here, we expand our research by comparing two source-equivalent Smackover oils of different levels of thermal maturity. We observe clear differences in the distribution of NSO compound classes, types (number of rings plus double bonds within a class), and number of alkyl carbons. With increasing thermal stress, the relative amount of sulfur and oxygen containing compounds decreases, condensation and aromatization of the polar cores increase, and the number of alkyl carbons decreases, reflecting the distribution of saturated hydrocarbons.

Selective fragmentation of single isotopic ions of proteins up to 17 kDa using 9.4 Tesla Fourier transform ion cyclotron resonance

Correlated sweep excitation in a 9.4 Tesla magnetic field Fourier transform ion cyclotron resonance instrument has been used to select individual isotope peaks of oxidised insulin chain-B (RMM = 3.5 kDa) and apomyoglobin (RMM = 17 kDa). In the case of apomyoglobin the experimentally achieved “front-end” mass resolution for ion selection was very close to the theoretically predicted attainable resolution. Subsequently, collisionally-activated decomposition of these mass-selected single-isotope precursor ions was accomplished using sustained off-resonance irradiation (SORI). Single isotopic peak selection prior to collisional activation brought a significant decrease in complexity of the fragment ion spectra. Single isotope selection made it possible to assign complementary fragment ions unambiguously, which in turn simplified the assignment of the isotope content of the precursor molecule. In SORI, different isotopic ions of an isotopic cluster are expected to be affected differently by a fixed frequency excitation field. Selecting a single isotopic ion out of the isotopic cluster prior to collisional activation avoided this problem. The methods introduced are general and can be used to measure collisionally-activated decomposition spectra of single isotopic ions of macromolecules up to approximately 20 kDa.

Professor K.R. Jennings—Aston Medallist 1998

The British Mass Spectrometry Society (BMSS) have awarded the Aston Medal for 1998 to Keith to mark his many contributions to mass spectrometry. Keith worked with Professor J.W. Linnett in his post graduate days in Oxford on the reactions of atoms and small molecules using spectroscopic methods. Having completed his D.Phil. he was awarded a National Research Council Fellowship to work with Dr R.J. Cvetanovic on the mercury sensitisation of butane and on the addition of hydrogen atoms to olefins. He returned to England in 1960 to a lectureship at the University of Sheffield and became interested in mass spectrometry. His background in the kinetics of the reactions of small molecules was to form an admirable basis for the mass spectroscopic studies he was to undertake. He was appointed Reader in 1969. Keith’s first mass spectrometer was a modest one—an AEI MS10. However, it sufficed to interest him in metastable ions—a study which was to occupy him for many years. His first achievement in this area was to show that the [CH3] + ions produced from doubly charged benzene ions involved a release of 2.7 eV. Beynon, Saunders and Williams had shown how by measuring the peak width with an MS9, the energy release could be estimated. In 1964 Keith acquired an MS9 and using a modification of their method was able to show that his interpretation of the decomposition of doubly charged benzene ions was correct. His interest in ion–molecule reactions led to a thorough investigation of collision induced decomposition (CID). Keith came to the important conclusion that “structural inferences normally drawn from electron ionisation spectra could also be drawn from CID spectra”. Keith was appointed to the Chair of Physical Chemistry in the University of Warwick in 1972. In the early seventies he became the first person to operate an ion cyclotron spectrometer (ICR), which he used to very good effect in his investigations of ion–molecule reactions. In 1995 he was one of the recipients of a grant to acquire a high field Fourier Transform Ion Cyclotron Resonance mass spectrometer. Other interests included negative ion mass spectrometry and the location of double bonds in unsaturated compounds. In the early 1980s, Keith became interested in large biological molecules. In 1987 a grant was awarded to a number of investigators for the purchase of the first four sector instrument which was installed in 1989 and enabled the study of peptides of RMM 2500 and above. It was used among other things to study the effect of collision gas upon the CID of ions. In 1994 a grant for the purchase of a triple quadrupole mass spectrometer was obtained, and used with good effect in the study of polymers and biomolecules.