Basic Principles of TOF-MS

Initially, the repeller and extractor electrodes are kept at the same electrical potential in order to prevent deflection of the incoming ions. To obtain a mass spectrum, this voltage 

Field-free flight region (tube) (length f) 

Consequently, measurement of the time-of-flight allows determination of mfz. The arrival times of the ions provide a spectrum in the time domain, which through application of Equation 3.41 is readily converted into the more usual mass spectrum. 

From the kinetic theory of gases we know that tiie mean free path of a gas particle is given by ksTIQ pa), where ks is the Boltzmann constant, T is the absolute terrqierature, p is tiie pressure (in Pa) and cr is die collision cross section (in m ). A reasonable estimate of the collision cross section between a small molecular ion and N2 or O2 is 50 = 5 x 10 m, and thus 

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