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Pfeiffer <strong>Vacuum</strong><br />
Page 86<br />
4<br />
<strong>Vacuum</strong> <strong>Technology</strong><br />
Mass Spectrometers and Residual Gas Analysis<br />
4.1 Introduction, operating principle<br />
Mass spectrometry is one of the most popular analysis methods today. A mass spectrometer<br />
analyzes the composition of chemical substances by means of partial pressure measurement.<br />
Mass and Charge<br />
Total pressure is the sum of all partial pressures in a given gas mixture<br />
In order to determine the partial pressure of a given component of a gas, it must be<br />
measured in isolation from the mixture<br />
This necessitates prior separation of the mixture<br />
This is accomplished on the basis of the ratio between mass and charge m / e<br />
No separation<br />
Total pressure<br />
Figure 4.1: Total and partial pressure measurement<br />
Analyses are typically performed in the field of research & development and in the production<br />
of products that are used in daily life:<br />
Analysis of products from the chemical industry<br />
Drug development<br />
Doping tests<br />
Quality assurance of food products<br />
Monitoring semiconductor production processes<br />
Isotope analysis<br />
Separation as a function of time or space<br />
Individual partial pressures<br />
Source: Pupp / Hartmann, Vakuumtechnik, Grundlagen und Anwendungen, Hanser Verlag<br />
Gaseous or liquid substances that vaporize under vacuum are admitted to a mass spectrometer.<br />
The gas is diluted by being partially pumped down to a low pressure (molecular flow<br />
range) in a vacuum chamber and ionized through electron bombardment. The ions thus generated<br />
are introduced to a mass filter and separated on the basis of their charge-to-mass ratio.<br />
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