Morio Ishihara

Ion optics for multi‐turn time‐of‐flight mass spectrometers with variable mass resolution

The ion optics of multi-turn time-of-flight (TOF) mass spectrometry was investigated. Two feasible systems using toroidal sector plus quadrupole lenses and cylindrical sectors plus quadrupole doublets were found. The combination of a linear TOF with a figure-of-eight type multi-turn system is proposed.

A new ray tracing code “ELECTRA”

Abstract A ray tracing code has been developed on the basis of the charge density method. This code can solve Laplaces equation and can integrate Lorentzs equation of motion in the two, axially symmetric three and three dimensional spaces. The calculation procedure used in the code is described. As an example of a three-dimensional field calculation, the distribution of the fringing field of an electrostatic quadrupole lens is derived, and the definite integrals which are necessary to calculate third-order aberrations are given. The features of the code are summarized.

Enhanced mass resolution without decrease of beam intensity in a four sector mass spectrometer

Abstract A novel use of a tandem mass spectrometer is proposed. Ion optical calculations indicated that operating a double-focusing tandem mass spectrometer as a single four sector mass spectrometer allows an increase in mass resolution without significantly decreasing the beam intensity. This feature was tested experimentally. An important aspect of the ion optics is the use of a set of three quadrupole lenses located between the two double-focusing mass spectrometers.

Interface for a four-sector mass spectrometer with a dual-purpose collision cell: High transmission at low to intermediate energies.

A new interface system that consists of an ion decelerator, a floating collision cell-chemical ionization ion source, and an ion extractor was designed and installed in the third field-free region of a four-sector tandem mass spectrometer. Important features include the use of cylindrical deceleration lenses and an extraction lens assembly. This new design was found to provide enhancement of ion transmission at low to intermediate ion kinetic energies (3 eV to 1 keV) compared with the standard collision cell design. Collision-induced dissociation experiments from 3 eV to 10 keV and ion-molecule reactions of mass-selected ions can be performed conveniently. A second, grounded, collision cell is located after the extraction lenses, which allows MS4 experiments to be carried out via the normal linked (B/E) scan function in MS2. Incorporation of chemical ionization capability into the electrically isolated collision cell makes it possible to carry out neutralization chemical-reionization mass spectrometry.

Recent development of ion-optical studies for mass spectrometer and mass spectrograph design

Abstract Ion-optical studies in the field of sector-type mass analyzers (mass spectrometer and mass spectrograph) investigated in our group are reviewed. First ion-optical predictions were made, and ion-optical calculations were checked by experiments. Good agreement between both results suggests that ion-optical calculation is reliable and indispensable for designing mass analyzers.

A high-performance mass spectrometer for very small size

Abstract A small bench-top mass spectrometer of the double-focusing type is designed and constructed. The sector magnet of the instrument is very compact due to the small deflection angle (27.8°) and its weight is only less than 30 kg though the magnet radius is 15 cm and the magnetic field is 1.52 T. The field arrangement of QQQHQCQ (Q: Quadrupole lens, H: Homogeneous magnetic sector, C: Cylindrical electric sector) is adopted to achieve high performance. A mass resolution of 5000 can be obtained with an entrance slit of 84 μm.

Peak broadening caused by a fifth-order aberration in the fringing field of an electrostatic analyzer

Abstract Ion optical effects of the fringing field of an electrostatic analyzer up to the seventh order were studied by a ray tracing method. It was observed that the fifth-order effect is most important in the effects higher than third order. This fifth-order effect is represented by a fringing field integral. The image aberration caused by this effect is discussed.

A new mass spectrograph.

The optical designs of two new types of mass spectrographs were studied. The first is a system that possesses a specially shaped magnet output boundary to satisfy the double-focusing condition for a wide mass range. The focal plane is usually curved. The second system is one in which a parallel ion beam is generated before the magnet, forming a straight double-focusing line. By introducing a quadrupole lens doublet such that the ion beam may be deflected in the same direction through the electric and magnetic fields, the overall image magnification can be arbitrarily controlled and stigmatic focusing achieved for the median ray.

Development on Multi-Turn TOF-SIMS with a Femto-Second Laser for Post-Ionization: First Application of OPTIMA (Osaka PosT-Ionization MAss spectrometer) for Presolar SiCs

In the Earth and Planetary science, high-sensitive, high-spacial resolution and high-mass resolution mass spectrometer is indispensable. So far, Secondary Ion Mass Spectrometers (SIMSs), of which spacial resolution is 1~10 μm, have been used for isotopic measurement of individual minerals in the terrestrial/extraterrestrial rocks. However, it is known that secondary ion yield of SIMS is very low (less than 1 %) and that most of sputtered “neutral” atoms/molecules are wasted. To overcome this weakness of SIMSs, we designed and has developed the post-ionization system using high-intensity laser, which enables to ionized the neutrals after the sputtering (we call it, “post-ionization”). Here we report on our recent progresses of a development of multi-turned TOF-SIMS with a femto-second laser for post-ionization (OPTIMA: Osaka PosT-Ionization Mass spectrometer) and also report the first application for presolar SiC grains from Murchison meteorite.