This lessons deals with the "source" of an isotope ratio mass spectrometer, that is, the portion of the instrument where ions are generated and accelerated into a mass or energy analyzer. The presentation introduces various methods of sample volatilization and ionization, including thermal ionization, electron impact, and sputtering. The process of thermal ionization is described in some detail and includes a discussion of filament assemblies, the Langmuir-Saha equation, and metal surface work functions. Various lens configurations used to accelerate and focus ions down the flight tube are also described.
A separate presentation on inductively coupled plasma (ICP) ion sources is also included here courtesy of Gary Hieftje (Indiana University). The lecture provides an in-depth introduction to the advantages and disadvantages of the ICP as an ion source for high precision isotope ratio measurements.