Gas Chromatography - Tandem Techniques - The Basic Principles of Mass Spectroscopy > The Sector Mass Spectrometer > Page 35

The sector mass spectrometer functions using the combined mass selection of both an electrostatic field and a magnetic field. For this reason it is often called a double focusing mass spectrometer. A diagram of a basic double focusing mass analyzer is shown in figure 23. Consider an ion, mass (mi) and charge (z) (in electron charge units) entering the electric field (E) at velocity (v). The ion will describe an arc of radius (r1) and then enter the magnetic sector.

The Sector Mass Spectrometer

 

The sector mass spectrometer functions using the combined mass selection of both an electrostatic field and a magnetic field. For this reason it is often called a double focusing mass spectrometer. A diagram of a basic double focusing mass analyzer is shown in figure 23. Consider an ion, mass (mi) and charge (z) (in electron charge units) entering the electric field (E) at velocity (v). The ion will describe an arc of radius (r1) and then enter the magnetic sector.

 

Now the electrostatic deflecting force must equal the centrifugal force for any ion to enter the magnetic sector entry slit at (r1). The centrifugal force and the electrostatic force can be equated algebraically, to give the conditions under which a given ion will enter the magnetic sector slit.

 

 

 

Figure 23. The Double Focusing Sector Mass Spectrometer