基礎から学ぶマススペクトロメトリー/質量分析の源流 第10回 同位体の質量分析

The basic physical aspects of atoms and isotopes, as well as the physical and chemical processes responsible for variations in isotopic ratios are overviewed. The major techniques in current use for isotope ratio measurements are stable isotope mass spectrometry (MS), noble gas MS, thermal ionization MS, inductively coupled plasma MS, secondary ion MS, and accelerator MS. The types of ion sources suitable for use in isotope ratio MS are electron ionization for gases, thermal ionization for non-volatile elements, inductively coupled plasma ionization for the majority of elements, and sputtering ionization by means of a high energy positive or negative ion beam for solid target elements. A variety of ion detection methods using a Faraday cup, a Daly collector system, and an ion counting system with a secondary electron multiplier are capable of covering a wide dynamic range of ion beam intensity, from ∼10-8 to ‹10-19 A. Methods used for data processing and for evaluating the reliability of data for the isotope ratios that are obtained using MS are described.