Page 115 - Tandem Techniques

Page 96

The quadrupole mass spectrometer is compact, rugged and easy to operate and consequently is a
popular instrument to use in tandem combinations. It is easily interfaced with a wide range of
chromatographic systems. Unfortunately, the mass range of the quadrupole spectrometer does not
extend to very high values but, as will be seen when dealing with different interfaces, under certain
circumstances multiple charged ions can be generated and identified by the mass spectrometer. This, in
effect, significantly increases the mass range of the device.

The quadrupole mass spectrometer can also constructed in such a way as to be able to provide a MS/MS
performance. This is achieved by combining three quadrupole units in series. A diagram of a triple
quadrupole mass spectrometer is shown in Figure 2.33. The sample enters the ion source and is usually
fragmented by either an electron impact or chemical ionization process. In the first analyzer the various
charged fragments are separated in the usual way, which then pass into the second quadrupole section
sometimes called the collision cell. The first quadrupole behaves as a straightforward mass
spectrometer.

Figure 2.33
The Triple Quadrupole Mass Spectrometer.

Instead of the ions passing to a sensor, the ions pass into a second mass spectrometer. In this way a
specific ion can be selected for further study. In the center quadrupole section the selected ion is further
fragmented by collision ionization and the new fragments then pass into the third quadrupole which
functions as a second analyzer. The second analyzer