TABLE OF CONTENTS Once ions have been formed and introduced into a mass spectrometer, a mass analyser is used to separate them based upon their mass-to-charge ratio through the application of electric and magnetic fields. There are a number of different mass analysers described in the following subsections. Many modern instruments feature several mass analysers coupled together for use in tandem mass spectrometry (see Chapter 4) and other applications. When a mass spectrometer is constructed of several mass analysers of a different type, it is referred to as a hybrid instrument. This section begins with the simplest mass analyser, the time-of-flight tube.
As the name implies, time-of-flight (TOF) mass spectrometers separate ions and measure their m/z based on the time they take to pass ("fly") from the ion source to the detector. The flight tube is usually 1 2 m in length and the basis of the separation makes no use of either electric or magnetic fields. Ions are separated in the field-free region of the flight tube before reaching the detector. A simple representation of a TOF mass spectrometer is shown in Figure 3.12.
Ions are first formed in the source and then "pushed" down the flight tube through the application of a high accelerating potential (V) of the same polarity of the ions applied to a lens or grid. The kinetic energy of ions of mass, m, and charge, z, is given by...
