The mass resolution of a time-of-flight (TOF) mass spectrometer is directly proportional to its total flight pathlength. Multi-turn or multi-passage ion optical geometries are necessary to obtain fight distances of sufficient length within reasonable size limitations. We have investigated ion optics for a multi-turn TOF mass spectrometer with electrostatic sectors. The concept of 'perfect' focusing conditions is introduced. Furthermore, a new type of multi-turn TOF mass spectrometer, the MULTUM Linear plus, was developed. It consists of four cylindrical electric sectors and 28 electric quadrupole lenses. It has a vacuum chamber 60 × 70 × 20 cm in size. Mass resolution is demonstrated to increase according to the number of ion cycles. A mass resolution of 350 000 (m/z = 28, FWHM) was achieved after 501.5 cycles. The MULTUM Linear plus analyzer is not simple, however; 28 electric quadrupole lenses are used. In order to reduce the number of ion optical parts, an improved multi-turn TOF mass spectrometer, the MULTUM II, consisting of only four toroidal electric sectors, was also developed. The possibility of tandem mass spectrometric applications using multi-turn TOF mass spectrometers is also discussed.
We have developed a new nano-beam time-of-flight secondary neutral mass spectrometry system: laser ionization mass nanoscope or LIMAS. The primary ion beam column was equipped with a Ga liquid metal ion source and aberration correction optics. The primary ion beam was down to 40 nm in diameter under a current of 100 pA with an energy of 20 keV. The sputtered particles were post-ionized under non-resonance mode by a femtosecond laser. The post-ionized ions were introduced into a multi-turn mass spectrometer. A mass resolution of up to 40 000 was achieved. The vacuum of the sample chamber was maintained under an ultrahigh vacuum of 2 Â 10 À8 Pa. This instrument would be effective for ultrahigh sensitive analysis of nanosized particles such as return samples from asteroids, comets, and planets.
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