6.1 Introduction, operating principle
Mass spectrometry is one of the most popular analysis methods. A
mass spectrometer analyzes the composition of chemical substances by
means of partial pressure measurement under vacuum.
Figure 6.1: Total and partial pressure
Analyses are typically performed in the field of research &
development and in the production of products that are used in daily
- Research & Development
- Catalysis research
- Drug development
- Development of new materials
- Monitoring production processes
- in metallurgy
- in chemical synthesis
- in semiconductor production
- in surface technology
- Trace and environmental analysis
- Aerosol and pollutant monitoring
- Doping tests
- Forensic analysis
- Isotope analysis to identify the origin
- Analysis of products in
- the chemical industry
- high purity gas production
- the automotive (supply) industry (leak detection)
- Quality assurance of food products
Mass spectrometers are used to analyze gases. Solid or liquid
substances can also be analyzed if they are vaporized in an upstream
inlet system. The gas is diluted by pumping it down to a low pressure
(molecular flow range) in a vacuum chamber and ionizing it through
electron bombardment. The ions thus generated are separated in a mass
filter according to their charge-to-mass ratio.
Figure 6.2: Components of a mass spectrometer
Figure 6.2 shows the typical components of a mass spectrometer
- The substances to be analyzed are admitted to a vacuum
chamber through the inlet system via a capillary or metering
valve, for example, and then are
- pumped down with the vacuum system to the
system’s working pressure.
The actual analyzer is located in the vacuum and consists of the
- The ion source ionizes neutral gas particles, which
- separated in the mass filter on the basis of their
mass-to-charge ratio m/e.
- The ion current is measured using a Faraday detector or
a secondary electron multiplier (SEM) after the ions have left the
separating system. The current is a measure of the partial pressure
of the respective gas molecules or a measure of fragments that may
have been generated in the ion source.
- A data analysis system processes the ion currents
measured with the aid of the detector and presents these currents in
various forms. Today, data analysis software programs are capable of
supporting the user in interpreting mass spectra.
Mass spectrometers differ as a result of the wide variety of
available versions. The main difference consists of the separating
systems. The following four types of mass filters are in widespread
- Sector field devices use the deflection effect of a
magnetic field on moving charge carriers.
- Time-of-flight mass (TOF) spectrometers utilize the
differing velocities of molecules of equal energy for the purpose of
- In ion traps, the trajectories of the ions are
influenced by a high-frequency field.
- Quadrupole mass spectrometers utilize the resonance of
moving ions in a high-frequency field (similar to ion traps).
Our discussion will be confined to sector field mass
spectrometers and quadrupole mass spectrometers, as these are the mass
spectrometers that are most widely used in the field of vacuum