X-ray tomography as risks to the health of the patient are virtually eliminated and additional
information on their medical condition can be obtained.
9.4—
Mass Spectrometry
Summary
Principles
Ionization and fragmentation of materials by a variety of means, principally by electron bombardment,
or the softer techniques of chemical ionization, field ionization or fast atom bombardment. Analysis of
the range of mass fragments produced. Elemental composition of non-volatile materials by application
of an RF spark.
Instrumentation
Source of high-energy electrons, ion accelerator, magnetic/electrostatic analyser, detector and recorder,
high vacuum pumping system.
Application
Identification and structural analysis of organic compounds. Determination of trace impurities in a wide
range of inorganic materials (spark source mass spectrometry).
Disadvantages
Complex and costly instrumentation, difficult to maintain.
Mass spectrometry is a technique for characterizing molecules according to the manner in which they
ionize and fragment when bombarded with high-energy electrons, or ionize with less fragmentation
using a range of 'softer' techniques (vide infra). It is not strictly a spectrometric method as
electromagnetic radiation is neither absorbed nor emitted. However, the data obtained are in a spectral
form in that the relative abundance of mass fragments from a sample is recorded as a series of lines or
peaks. The electron bombardment process produces many fragments carrying a charge, usually +1, and
this facilitates their separation and detection by electrical and magnetic means. Spectra must be
recorded under conditions of high vacuum (10–^4 – 10 –^6 N m–^2 ) to prevent loss of the charged fragments
by collision with molecules of atmospheric gases or swamping of the sample spectrum.
Instrumentation
The essential components of a mass spectrometer include a sample inlet system, an ionization source
and acceleration chamber where sample molecules are ionized, fragmented and accelerated into an
analyser or separator, and an ion detection and recording system (Figure 9.51(a)).