Determination of the heat of formation of ortho-benzyne by ion cyclotron resonance spectroscopy.

Ion Cyclotron Resonance Spectroscopy has been employed to obtain a value for the heat of formation of ortho-benzyne of 118 ± 5 kcal mol^?1.     

Analysis of anions in hydrofluoro ethers by ion chromatography

Hydrofluoro ethers (HFES) are considered to be an ideal cleaning solvent in applications like vapor degreasing and wet cleaning. It is also a good solvent replacement for CFCs (chlorofluorocarbons), HCFCs (hydrochlorofluorocarbons), HFCs (hydrofluorocarbons) and chlorinated solvents because they have a short atmospheric lifetime and low global warming potential. Based upon their properties, hydrofluoro ethers are ideally suited for the demands of the electronics industry. However, the electronics industry requires these solvents to have high purity, especially in the area of residual anions. This paper will present information on an extraction methodology for the transfer of anions from the hydrofluoro ether to water. Then, an analytical method utilizing ion chromatography that is capable of detection of 10 anions (fluoride, acetate, formate, chloride, nitrite, bromide, nitrate, sulfate, oxalate, and phosphate) in the part per billion level will be demonstrated.     

The resolution obtained from low energy ion scattering using an ion cyclotron resonance spectrometer

The resolving power of the low energy ion scattering technique with FT-ICR spectrometry is discussed. Resolution improvement due to simultaneous registration of scattered ions with different masses is shown.     

High-resolution ion isolation with the ion cyclotron resonance capacitively coupled open cell

For ion cyclotron resonance, a capacitively coupled open cell variant with fourfold radial symmetry was constructed and tested for axial excitation-ejection of large ions at high resolution. With a reverse of frequency sweep direction, this cell gave substantial improvements in signal-to-noise ratio due to linearization of the excitation electric field. Single isotopic peaks of ubiquitin (8.6-kDa) and carbonic anhydrase (29-kDa) molecular ions could be isolated by selective stored waveform inverse Fourier transform excitation, which yielded an order of magnitude higher isolation resolving power than previously achieved at high mass-to-charge ratio values.     

Fourier transform ion cyclotron resonance: state of the art

This short review summarizes recent and projected advances in Fourier transform ion cyclotron resonance mass spectrometry instrumentation and applications, ranging from petroleomics to proteomics. More details are available from the cited primary literature and topical reviews.     

Theory of space-charge shift of ion cyclotron resonance frequencies

A theory of ion space-charge influence on the observed ion cyclotron resonance frequency in static field ion traps is presented. The dependence of this influence on ion density, ion cloud shape, and trapping geometry is investigated. Four trapping geometries are specifically analyzed: the Penning trap, the cubical ICR cell, the common rectangular ICR cell, and an elongated ICR cell. This treatment is readily extended to other geometries. The theory applies to common situations where the exciting or detecting antennae fields are not homogeneous, and individual particle motions are excited/detected as opposed to center-of-mass motions.     

The long-lived molecular ion of propionitrile: An ion cyclotron resonance study

Evidence has been reported that primary loss of H and of HCN from the molecular ions of propionitrile, isobutyronitrile and butyronitrile in the mass spectrometer is preferentially preceded by hydrogen migration from C-2 to C-1. Ion cyclotron double resonance spectra of proton (or deuteron-) transfer products derived from propionitrile-2-d2 and -3-d3 and a series of bases provide evidence that such migration occurs also in long-lived propionitrile molecular ions.     

Quantitation of ion abundances in fourier transform ion cyclotron resonance mass spectrometry

To improve the analytical usefulness of Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS), an extensive survey of various methods for quantitation of peak magnitudes has been undertaken using a series of simulated transient response signals with varying signal-to-noise ratio. Both peak height (five methods) and peak area (four methods) were explored for a range of conditions to determine the optimum methodology for quantitation. Variables included dataset size, apodization function, damping constant, and zero filling. Based on the results obtained, recommended procedures for optimal quantitation include: apodization using a function appropriate for the peak height ratios observed in the spectrum (i.e., Hanning for ratios of about 1:10, three-term Blackman-Harris for ratios of ～1:100, or Kaiser-Bessel for ratios of ～1:1000); zero filling until the peaks of interest are represented by 10–15 points (generally obtained with one order of zero filling); and use of the polynomial y=(ax ²+bx+c) ⁿ and the three data points of highest intensity of the peak to locate the peak maximum, Y _max=(?b ²/4a+c) ⁿ . In this peak fitting procedure, which we have termed the “Comisarow method,” n is 5.5, 9.5, and 12.5 for the Hanning, three-term Blackman-Harris, and Kaiser-Bessel apodization functions, respectively. Accuracy of quantitation using an optimal peak height determination is about equal to that for peak area measurements. These recommendations were found to be valid when tested with real FTICR-MS spectra of xenon isotopes.     

A Fourier-transform ion cyclotron resonance study of the 3,5-didehydrophenyl cation

The 3,5-didehydrophenyl cation has been generated in good purity via sustained off-resonance irradiation for collision-activated dissociation of 3,5-dinitrobenzoyl chloride in a Fourier-transform ion cyclotron resonance mass spectrometer. Differences in the ion-molecule reactivity of this species from that of its cyclic and acyclic isomers allowed isomeric distinction to be achieved. This study represents the first definitive identification of this fundamentally interesting, doubly aromatic ion. However, the formation of the 3,5-didehydrophenyl cation was found to be the exception rather than the rule, with most 1,3,5-substituted benzenes yielding mainly acyclic C6H3+ isomers under electron ionization conditions. This mixed ion population was attributed to isomerization of fragmentation intermediates rather than any intrinsic instability of the 3,5-didehydrophenyl cation.     

On the mechanism of secondary ion formation from poly(methylmethacrylate) under static secondary ion mass spectrometry conditions

The negative ion spectrum of a relatively thick layer (± 0. 5 μm) of poly(methylmethacrylate) (PMMA) with M?_w = 1890 and its positive ion spectrum of a very thin layer (± 1. 0 nm) on silver measured with a time of flight secondary ion mass spectrometer are presented. From the negative ion spectrum it is concluded that formation of enolate anions from PMMA under static secondary ion mass spectrometric conditions is an important ion formation process. From fragmentation products of the polymer, detected as silver cationized species in the positive ion spectrum, more evidence was found of a fragmentation mechanism for PMMA under static secondary ion mass spectrometric conditions recently proposed in the literature. From the relation between the information obtained from the two types of spectra an extension of this mechanism is obtained. This mechanism implies scission of the polymer chain by the primary ion bombardment with subsequent formation of enolate anions from the newly formed polymer chain-ends.     

Fullerenes from kerogen by laser ablation fourier transform ion cyclotron resonance mass spectrometry

Raw oil shale, kerogen (demineralized shale) and carbonaceous residues from kerogen pyrolysis in the range 350–700°C (at 50°C intervals) were studied by laser ablation Fourier transform ion cyclotron resonance mass spectrometry using the fundamental frequency of Nd: YAG laser (1064 nm). Normally, pyrolysis of the raw materials produces oil and the resulting residues have decreased hydrogen to carbon ratios and exhibit relative increases in aromatic carbons. Raw shale and kerogen give positive-ion spectra with mainly protonated species of m/z 100–400. Laser ablation positive-ion mass spectra of the pyrolysis products of the kerogen show the presence of C₆₀, C₇₀ and other fullerene ions with a distribution of higher mass fullerene ions up to m/z 4000. Using high laser powers (100–3000 MW cm^?2), the residue from pyrolysis at 350°C initially did not produce any fullerene ions (apart from traces of C₆₀ and C₇₀), but after continued ablation a cavity was formed in the target and a wide distribution of fullerene ions was obtained with subsequent laser pulses. Residues obtained from the pyrolysis of kerogen at 400–500°C produced fullerene ions at both low (4–200 kW cm^?2) and high laser powers. The 550°C pyrolysis residue gave only small amounts of C₆₀ and C₇₀ positive ions at low laser power whereas residues from the pyrolysis of kerogen above 550°C did not give fullerene ions over a wide range of laser powers. It is proposed from the above results that the changes in the aromatic nature of the kerogen residues with increasing pyrolysis temperature are directly related to the ease of fullerene formation. This is possibly due to the formation of large polycyclic aromatic systems at pyrolysis temperatures above 400°C, formed in the residues. It should be noted that the shale samples (raw or pyrolysed) did not generate fullerene ions under any of the conditions employed in these experiments.     

First signal on the cryogenic fourier-transform ion cyclotron resonance mass spectrometer

The construction and achievement of the first signal on a cryogenic Fourier-transform ion cyclotron resonance mass spectrometer (FTICR-MS) are reported here, demonstrating proof-of-concept of this new instrument design. Building the FTICR cell into the cold bore of a superconducting magnet provided advantages over conventional warm bore design. At 4.2 K, the vacuum system cryopumps itself, thus removing the requirement for a large bore to achieve the desired pumping speed for maintaining base pressure. Furthermore, because the bore diameter has been reduced, the amount of magnet wire needed to achieve high field and homogeneity was also reduced, greatly decreasing the cost/Tesla of the magnet. The current instrument implements an actively shielded 14-Tesla magnet of vertical design with an external matrix-assisted laser desorption/ionization (MALDI) source. The first signal was obtained by detecting the laser desorbed/ionized (LDI) C(60)(+*) ions, with the magnet at 7 Tesla, unshimmed, and the preamplifier mounted outside of the vacuum chamber at room temperature. A subsequent experiment done with the magnet at 14 Tesla and properly shimmed produced a C(60) spectrum showing approximately 350,000 resolving power at m/z approximately 720. Increased magnetic field strength improves many FTMS performance parameters simultaneously, particularly mass resolving power and accuracy.     

Fourier transform ion cyclotron resonance detection of multiphoton ionization spectroscopy

Fourier transform ion cyclotron resonance (FT-ICR) detection was tested for resonanceenhanced multiphoton ionization (REMPI) spectroscopy. The (2+1) REMPI spectra of acetaldehyde were obtained in the wavelength range 364–354 nm via a two-photon resonant 3s ← n Rydberg transition. The space-charge effects on the REMPI spectra were examined in the vicinity of the 0 ₀ ⁰ transition. The trapping efficiency measurement shows that all the ions produced from REMPI dissociation processes are arrested in the ion cyclotron resonance cell even in the presence of space-charge interactions. Axial kinetic energy release distributions of ions were extracted from the trapping efficiency data obtained under a new space-charge-free condition. FT-ICR peak heights were measured as a function of pressure at different laser powers, magnetic field strengths, and ion excitation methods to test for the detection linearity. The FT-ICR detection responds linearly to the number of ions in a low pressure limit. The product branching ratio was measured by using various ion excitation methods and was compared with the previous quadrupole mass spectrometric study. FT-ICR detection yields the mass-selected REMPI spectra and the product branching ratio in the absence of kinetic shifts.     

Dye laser-induced photodetachment of electrons from SH− studied by ion cyclotron resonance spectroscopy

The photodetachment of electrons from gaseous SH^? ions has been studied in an ion cyclotron resonance mass spectrometer using a flashlamp-pumped organic dye laser as a light source. The onset of the photodetachment process at 538.7 ± 0.3 nm (2.301₆ ± 0.001₃ eV, 18563 ± 10 cm^?1) agrees well with that obtained in an earlier study. Coarse structure in the photodetachment curve with a spacing of 11.8 nm (0.052 eV, 422 cm^?1) has been identified with spin-orbit coupling in the SH^. radical. Finer structure, with a spacing of ca. 2.5 nm (0.011 eV, 89 cm^?1), has also been observed in the curve, but remains unexplained.     

Gas phase studies of N-nitrosamines by ion cyclotron resonance spectroscopy

The gas phase basicities of a series of cyclic and acyclic N-nitrosamines were determined by ion cyclotron resonance techniques. The fragmentation pattern and ion-molecule reactions of these compounds are discussed in terms of high resolution mass spectrometry and deuterium labeling. The presence of a unique rearrangement of the molecular ion is discussed in terms of specific ion-molecule proton transfer reactions and fragment ion products.     

Determination of ion—molecule collision frequencies by Fourier transform ion cyclotron resonance spectroscopy

It is shown that nonreactive ion—molecule collision frequencies may be determined either by analysis of the transient signal resulting from excited ion cyclotron motion or by linewidth measurement of the Fourier transform of the transient signal.     

A fourier transform ion cyclotron resonance study of the gas phase negative ion chemistry of benzaldehyde

Fourier transform ion cyclotron resonance mass spectrometry has been used to investigate some aspects of the gas phase negative ion chemistry of benzaldehyde. It is shown that all protons are nearly equally acidic. Exothermic proton abstraction from the aldehydic position by NH₂^- leads to the formation of C₆H₅^-, ions. Reactions of several nucleophiles and benzaldehyde are discussed. Some of them proceed via a tetrahedral intermediate. Arguments are put forward to show that one of the reactions of the conjugate base of benzaldehyde involves benzaldehyde-hydrate molecules formed in the inlet lines towards the cell.