Anatomy of a Mass Spectrum

A detector measures and amplifies the ion current of mass-resolved ions. A data system records, processes, stores, and displays data in a form that a human eye can easily recognize (computer screen or printer output). 

A vacuum system maintains a very low pressure in the mass spectrometer. The ion source region is usually maintained at a pressure of 10 to 10 torr somewhat lower pressure is required in the mass analyzer region (around 10 torr). Most instruments use a differential pumping system to maintain an optimal vacuum. 

The simplest and most common means of ion formation in mass spectrometry is to bombard the gas-phase sample molecules with a beam of electrons. During this process, an electron is removed from the highest-occupied molecular orbital (HOMO) of the sample molecule to form a positively charged molecular ion  

Fragment ions may also form. The data output is in the form of a mass spectrum. 

---