It measures the mass to charge ratio (m/z) of a sample and usually displays a resulting mass spectrum as a plot of component intensity as a function of m/z.
Mass spectrometers are used in a wide variety of applications from ensuring that our environment is clean and our food safe to eat, all the way through to neo-natal testing, assisting in the diagnosis of diseases or pioneering drug development.
These analytical instruments cover a broad spectrum of complexity from simple Residual Gas Analysers (RGAs) to highly complex Q-ToFs (Quadrupole Time of Flight) and Ion Trap mass analyser instruments.
One thing that unites all of these instruments is that they require to be operated under vacuum.
Just as there is a wide variety of instrument types, the range of vacuum equipment necessary for them to operate is also very diverse. An ion source might be running at atmospheric pressure with the inlet to the mass spectrometer at a pressure of tens of millibars, whereas a ToF or Orbitrap operating at 10-8 to sub 10-10 mbar.
More complex mass spectrometers often have multiple chambers housing complex ion optics operating at different levels of vacuum, often with additional gas flows being added mid instrument.