Ion Reflector Research Articles

傾斜電界型イオンリフレクタによるＴＯＦ質量分析計の分解能の改善

A new gradient electric field type ion reflector for a time-of-flight mass spectrometer has been developed in order to improve mass spectral resolution by time focusing. A retarding field in the reflector has two terms; One term proportional to penetrating depth of ions into the reflector and a constant term. In the TOF mass spectrometer consisting of a free ion drift region and the ion reflector, the motion of the same m/z ions is quasi-single oscillation of the same period. Therefore the flight times of the same m/z ions are focused to a constant, even if the initial kinetic energy of the emitted ions are distributed. In this paper, the theory of time focusing effect, the results of the computer simulation and the experimental results with laser desorption are reported.

レーザー脱離ＴＯＦ質量分析法による高質量分子イオンの検出

A laser desorption time-of-flight (TOF) mass spectrometer has been developed in order to analyze non-volatile, thermally labile and high mass organic compounds, in which the “gradient electric field type ion reflector” was used for time focusing. Higher detection sensitivity for high mass ions was achieved by adding a blind type ion-electron converter to the micro-channel plate (MCP) ion detector. Two TOF spectrum measurement systems were constructed, with which two measurement methods called as “AD method” and “TDC method” were able to be selected to obtain the spectrum sensitively and accurately in a short time.For sample preparation, “metal fine powder and glycerol matrix” method was confirmed to be very effective to increase the yield of high mass molecular ions.This mass spectrometer was successfully applied to the detection of quasi-molecular ions from many high mass organic compounds, such as Cytochrome-C (mol. wt. 12,384), Bovine Trypsin (mol. wt. ~24,000) and Carboxypeptidase-A (mol. wt. 34,472).

Resonance-enhanced 2PI detection of ammonia clusters via a linear reflectron TOF mass spetrometer

Ammonia clusters are resonantly two-photon ionized using a tunable pulsed UV laser (208–215 nm) and are subjected to time-of-flight (TOF) mass analysis with a linear ion reflector. The small ammonia clusters (from dimer to heptamer) exhibit broad vibronic structures, almost the same over the wavelength region studied.

Peak shape determination in laser microprobe mass analysis

Potential distribution and ion trajectory calculations involving time development of the ion motion in laser microprobe mass spectrometers have been performed. Potential distribution calculations were based on the Fourier transformation technique since this offers improved effectiveness. The time-dependent ion trajectories that were calculated showed different flight times for ions with different initial conditions. Transmission properties of the angle focusing “einzel” lens are discussed with special emphasis on lens potential and ion formation position dependence. Qualitative agreement with experimental findings is demonstrated. It was shown that, if the geometrical parameters of the instrument are optimized, an arrangement promising similar performance to that of LAMMA 500 can be obtained but with more compact design. Peak shape calculations were carried out for different initial kinetic energy and departing angle distributions. Peak broadening, shift, and asymmetry could be explained in terms of the width of ion energy distribution. However, no dramatic broadening was observed according to the second-order energy focusing property of the ion reflector.

A simple thermal ion source for examination of a laser ionization mass spectrometer

A simple and inexpensive thermal ion source has been used to examine some ion optical properties of a laser ionization mass spectrometer. Calibration of the kinetic energy cut-off of the ion reflector revealed an offset between the applied potential and the cut-off energy in accordance with the angle of incidence. Shifting of the image by the reflector influences signal intensity, and the ion lens contributes to kinetic energy discrimination.

Ion kinetic energy measurements on laser-induced plasmas in laser microprobe mass analysis (LAMMA). Part 2. Titanium dioxide

Kinetic energy distributions of various ionic species from a TiO 2 film have been obtained using the energy cut-off property of an ion reflector in a laser microprobe mass spectrometer. The energy distributions of elemental ions are more positive and broader than those of polyatomic ions. They all have a substantial contribution in the “negative” energy range. At higher laser energy densities, the ion kinetic energy distributions become broader and shift towards “lower” energy values. Chemically different ion species have different energy distributions. The energy distributions are attributed predominantly to the locus of ion formation in the accelerating electrostatic field.

Recent developments in techniques utilising time-of-flight mass spectrometry

A review is given of a number of techniques which utilise the ability of the time-of-flight mass spectrometer to provide a complete mass spectrum for each ionisation event. These include pulsed laser ionisation, fission fragment mass spectrometry, SIMS and pulsed field desorption. Mention is also made of the improvement in performance of the conventional TOFMS by use of electrostatic ion reflector and time-focussing methods.

Ion kinetic energy measurements on laser-induced plasmas in laser microprobe mass analysis (LAMMA). Part I. Methodology

A method for the measurement of kinetic energy distributions of ions produced in a laser microprobe mass spectrometer employing the energy cut-off property of an ion reflector has been developed. The method is insensitive to time of ion formation and to miscalibration of the flight-time equation, but requires accumulation of many spectra from uniform samples. When applied to elemental carbon foil, measurement of ion kinetic energy reveals that ionic species occur with different kinetic energy distributions. A substantial fraction of the ions having less kinetic energy than the full acceleration energy was observed.

Self-triggered channel ion source

An ion source made from a continuous dynode electron multiplier of the straight channel type and an ion reflector device is described. Its principle of operation is based on a continuous self-sustained ion and electron cascade in the multiplier channel. Operating characteristics and the analysis of the ions produced are presented. The intensity of the total ion current delivered (10(-9) to 10(-8) A) is enhanced by at least six orders of magnitude relatively to previously described similar devices. This source, as illustrated, may be used in gaseous mass spectrometry.

Spectromètres de masse à temps de vol avec guides de particule

Two time-of-flight mass spectrometers have been designed. The first consists of an arrangement of a pulsed ion source, an electrostatic particle guide and a detector; an ion reflector was added in the second apparatus. The use of a particle guide appears to be particularly efficient in the second case for the analysis of low-energy beams. The higher the initial kinetic energy of the ions, the more important is the corresponding increase in sensitivity.

熱陰極電離真空計のＸ線限界改善法

A new method is proposed for improvement on soft x-ray limit of a Bayard-Alpert type hot cathode ionization gauge. In a gauge with an open end grid and an x-ray shielding plate having a hole for ion extraction, it is found that the ion collector electrode placed at a suitable distance beneath the hole can be effectively protected from the illumination of x-ray flux directly from the grid surface. A hemispherical ion reflector and a pair of flat plates placed each other with a slight gradient are also examined about their behavior as an x-ray reflector. The gauges of different types are proposed. A modified extractor gauge with the open end grid and hemispherical x-ray reflector, which consists of a part of glass envelope of the test tube, was examined experimentally and the sensitivity of 7-8 Torr -1 was obtained.