A discharge-based proton transfer reaction (PTR) ion source was operated using a mixture of H₂O and rare gases such as He, Ne, Ar, and Kr in combination with a custom-built time-of-flight (TOF) mass spectrometer. In contrast to an “H₂O-only” discharge, which usually functions above a field strength (E/N) of 100 Td for a drift tube, an “H₂O-rare gas”-based discharge was operated successfully at E/N values between 30 and 50 Td. (E is the electric field strength (V cm^-1), N is the buffer gas number density (molecule cm^-3), and 1 Td=10^-17 cm² V molecule^-1.) The intensity of primary ions (H₃O⁺·(H₂O)_n) generated in the “H₂O-rare gas” discharge was comparable to that in the “H₂O-only” discharge. Although detection sensitivities decreased for nonpolar molecules such as isoprene, benzene, toluene, and p-xylene, they increased for polar molecules such as acetone and acetaldehyde. This suggests that the operation of the PTR-TOF mass spectrometer at low drift-tube field-strengths improves both the detection sensitivity and selectivity for the polar molecules. In addition, fragmentation in the drift tube was suppressed significantly for fragile species such as methyl nitrate, in the low E/N operation.

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Evolved gas analysis by mass spectrometry (EGA-MS) is well known as one of the thermal analysis methods for measuring the thermal behavior of evolved gases from a sample as a function of the temperature, which is controlled by a predetermined heating program. Presently, this method is recognized as a powerful tool for understanding the thermal pathways of materials. Since MS is a vacuum technique, in previous studies, many problems existed due to trade-offs between minimizing pyrolysate condensations and maximizing sample temperature/physicochemical measurement accuracy by efficient coupling of thermal systems with mass analyzers. In order to resolve these problems, several types of EGA-MS equipped with interface systems, which consist of capillary type and skimmer-type structures, have been developed successfully and investigated satisfactorily. This study can be summarized as follows:
1) A capillary interface structure that connects a sample chamber and a vacuum chamber for a simultaneous thermogravimetry mass spectrometry (TG-MS) system was modified to overcome condensation and memory effects and improve maintenance significantly. The effect of humidity on thermal decomposition of a sample was identified by TG-MS equipped with a specially designed furnace to prevent water condensation coupled with a humidity generator for adjusting the water vapor pressure in the atmosphere.
2) The applicability of EGA-MS using a skimmer interface system was expanded by adapting a pressure control function (PCF), which was devised for improving the serious structural disadvantage of the skimmer interface system.
3) Sample-controlled thermogravimetry (SCTG), by which the sample temperature is varied to maintain a constant rate of mass loss by controlling the furnace heating, has been successfully developed and applied to TG-MS. The demonstrated data proved that this novel feature improves the resolution and enhances the accuracy of identification and quantification, even for materials decomposing by consecutive reactions.
4) EGA-MS systems equipped with a photoionization (PI) attachment using a vacuum ultraviolet (VUV) deuterium discharge lamp as photon source have been developed successfully. It is proposed that the unique PI mass spectra obtained in real time by EGA-PIMS can satisfactorily characterize the decomposition products by only parent ions with no contribution as a result of fragmentation during ionization.
The design and construction of EGA-MS systems and their valuable applications are described briefly.

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In this paper, we describe mass spectrometric techniques using swift heavy ions, for biological application. Desorption of large biomolecular ions due to irradiation by swift heavy ions was first observed in 1974, and the time-of-flight mass spectrometry using fission fragments from a ²⁵²Cf source is called plasma desorption mass spectrometry (PDMS). PDMS has been successfully applied in the detection of large biomolecules up to 20 kDa. However, the number of PDMS studies decreased after the emergence of fast atom bombardment (FAB). In recent years, a new mass spectrometric technique, which is called imaging mass spectrometry, has attracted attention, and numerous studies have been conducted on matrix assisted laser desorption/ionization (MALDI) and secondary ion mass spectrometry (SIMS). We have developed a new system for imaging mass spectrometry using MeV-ion beams, which is termed MeV-SIMS. High-resolution MeV-SIMS imaging requires high secondary ion yields, beam focusing, and careful sample preparation. Here, we present our results on MeV-SIMS imaging and future prospects.

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Mass spectrometers separate ions according to each mass/charge value, which is not a dimensionless quantity. However, the m/z value indicated in the abscissa of mass spectra is defined as a dimensionless quantity and not a numerical value the same as the mass/charge value in kilograms/coulombs (kg/C) or in unified atomic mass units/coulombs (u/C). The numerical value of m/z converted from the mass/charge value depends on the unified atomic mass unit and the physical constant “elementary charge,” e that is also the atomic unit of charge. This conversion confuses many mass spectrometrists with regard to the abscissa labeling of mass spectra, e.g. the symbol “m/z” is considered as an abbreviation of the term “mass-to-charge ratio.”

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