Nanotechnology-Enabled Sensors

5.10 Mass Spectrometry 271
beam experiences a strong magnetic field perpendicular to its direction, the
ions are deflected in an arc whose radius is inversely proportional to the
mass of the ion. Lighter ions are deflected more than heavier ions. By
varying the strength of the magnetic field in time, ions of different masses
impinge on a detector that is placed at the end of a curved tube at different
times. 15
Fig. 5.47 The Mass Spectrometry setup.
Fig. 5.48 shows an example of a mass spectrum of a relatively simple
carbon dioxide molecule, CO2. Mass spectra are generally presented as a
graph having vertical bars, where each bar represents an ion having a specific
mass-to-charge ratio (m/z) and the length of the bar indicates its relative
abundance. The ion with the highest abundance is assigned to 100, and
it is referred to as the base peak. CO2 has a nominal mass of 44 amu. As
can be seen in Fig. 5.48, the molecular ion is the strongest ion in the CO2
mass spectrum. Carbon dioxide’s mass spectrum is very simple, as its
molecule is comprised of only three atoms. In this graph, the molecular ion
is the base peak, and the only fragment ions are CO (m/z=28) and O
(m/z=16).