Part III of this four-part series continues the discussion of mass calibration. Part II of this four-part series described the use of perfluorinated compounds as calibrants for electron ionization (EI) and chemical ionization (CI) mass spectrometry (MS), and described links between time/intensity files recorded by a data system, the calibration file, and the properly calibrated mass spectrum (1). Here, Part III describes calibrants that are used in higher masses accessed with other ionization methods. Many of the basic details of calibration remain the same, including the linkage between time/intensity files and the calibration file, and the fact that an external calibration (using a calibrant separately introduced into the ionization source of the mass spectrometer) is intrinsic to proper operation of the mass spectrometer.
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