International Journal of Mass Spectrometry and Ion Physics最新文献

Particle bombardment of liquid glycerol deuterated on carbon has provided evidence for (MD)⁺ ion formation via a radical cation intermediate. This discovery has important mechanistic implications for the ionization of compounds dissolved in glycerol.

A unified theory of ion optics is developed, which can be applied to all ion-optical devices used currently in particle spectrometers. The second-order trajectory calculation has been performed in unified fields consisting of crossed electric and magnetic fields with arbitrary distributions. Nine parameters (in the second-order approximation) are necessary to designate respective ion-optical devices as well as their arbitrary superpositions. Correction for the relativistic effect on particle mass is included, which is necessary for relativistically fast particles.

Evidence for the intervention of excited states of Au⁺, Ag⁺ and Cu⁺ in chemical reactions is gathered from differences in the chemistry of the interaction of these ions with hexane, cyclohexene, benzene and propene, and of Au⁺ only with butadiene and cyclohexane. Most ions are explained by insertions into CC bonds; only in the case of Au⁺ is there unequivocal evidence for insertion into CH bonds. The products of decyclotrimerization reactions dominate the Au⁺ and Cu⁺ spectra of cyclohexene and benzene, and the Au⁺ spectrum of cyclohexane.

Proton-bound dimers of amines fragment to give the individual protonated bases in proportions which depend upon the proton affinities of the amines, the collision energy, and the target gas thickness in a triple quadrupole mass spectrometer. The behavior of these dimers observed with the triple quadrupole is similar to that observed with a reversed geometry mass spectrometer suggesting that the kinetic method of assigning amine proton affinities is applicable to the triple quadrupole. This is shown explicitly. Furthermore, the effect of precursor-ion internal energy on this measurement is delineated through MS/MS experiments covering excitation through collisions at various energies and target pressures. The effect of varying target thickness and collision energy are shown to be small when structurally similar amines comprise the dimer, but in the cases of dimers of phenylethylamine and pyridine with primary alkylamine partners, differences between literature values of proton affinities and the measured gas-phase basicities are observed. These entropic effects are interpreted on the basis of the relative steric hindrance to protonation of phenylethylamine (PEA), pyridine (PYR) and the primary alkylamines (ALK), that is, the order of steric hindrance appears to be PEA > ALK > PYR. For the primary alkylamine dimers, entropic effects appear to cancel within experimental error. Using data taken under various collision conditions, the proton affinity of 3-aminopentane is assigned as 221.7±0.3 kcal mol⁻¹.

Fundamental principles for obtaining mass spectral isotopic distributions are applied to a general computer program which can be used to calculate and present in tabular and graphic form the isotopic contributions for any molecular formula. A unique feature is the retention of the isotopic distribution, exact mass, and absolute abundance for all individual peaks at each mass. Special considerations have been made for the large number of isotopic combinations which occur for many higher mass compounds. The computer program accepts the input of a molecular formula followed by interactive input of a number of parameters which affect the final presentation of the theoretical distribution profile.

A simplified scheme is presented to distinguish between surface and gas-phase fragmentation of molecular ions in SIMS or FABMS experiments. The scheme is based on the measurement of the polar angle distribution of ejected parent and daughter cluster-ions and is derived from straightforward considerations of classical mechanics. Examples are given for chlorobenzene, benzene and pyridine adsorbed onto Ag(111) at 153 K.

This time-of-flight mass spectrometer utilizes the ²⁵²Cf fission fragment-induced ionization of organic solids and electrostatic desorption. It is designed for the high sensitivity needed in the quantitative analysis of pharmaceuticals and can be combined with a high-performance liquid chromatograph. The solute emerges into a rough vacuum stage sampling up to twelve fractions in a vacuum-drying process. Samples with low vapor pressure are introduced periodically into the ion source by means of an interfacing disk and analysed successively. The sensitivity of ion detection employing conversion electrons and microchannel plates is investigated. The performance of the mass spectrometer is discussed in terms of mass resolution, efficiency and reproducibility.

Electrostatic collimation or focussing of the electron beam has been used in the ion source of an isotope-ratio mass spectrometer and its performance evaluated. The design details of the ion source and the mass spectrometer are given. The sensitivity is comparable to that in the magnetic collimation mode. The reproducibility of the sensitivity with electrostatic collimation for various filament assemblies is good. The output vs. pressure curves determined for electrostatic collimation, magnetic collimation and a combined electrostatic and magnetic collimation show good linearity. This combined field collimation is also found to give good sensitivity, comparable to the conventional source, but at a much lower electron emission.

The electrostatically-collimated ion source was used for precision isotope ratio determinations of nitrogen gas samples collected from a cylinder. The relative internal standard deviation on a single sample ratio was better than 0.025%. The relative external standard deviation for repeated analysis of 19 samples drawn from the same cylinder over an 8-hour period was 0.08%. The advantages of using such an ion source are listed.

The mixing of glycerol-d₅ in glycerol-d₈ has been found to be slow on the time scale of a typical secondary ion mass specrometry (SIMS) experiment. Surface renewal by processes such as diffusion is therefore an insufficient explanation of the exceptional sample longevity observed for SIMS spectra of molecules in glycerol solution. Other explanations for this longevity are suggested.

A new experimental arrangement for angle-resolved mass spectrometry is described featuring a needle which delivers collision gas to the source slit of a reversed geometry mass spectrometer. In this experiment the scattering angle is defined by pre-collision electrical deflection of the parent ion beam, as contrasted with post-collision selection of the direction of the daughter ion beam. Advantages are rapid access to any desired angle, coupled with an improvement in ion intensity and in angular resolution evident from measured breakdown curves. Collision-induced dissociation spectra of the methanol molecular ion, recorded over a range of scattering angles, agree well with previous results. Experiments which record ions that survive collisions, i.e., scatter without fragmentation, indicate that scattering of polyatomic ions through substantial angles (0–6°) makes a significant contribution to the phenomena underlying angle-resolved mass spectrometry.