Inside of the vacuum chamber of a mass spectrometer.
Two halves of a vacuum chamber
used in mass spectrometry here at the
Environmental Services Program.

One of the detectors commonly used in the laboratory is the mass spectrometer.  Inside the mass spectrometer is a vacuum chamber where, as sample molecules are streaming in, they are bombarded with high energy. This energy causes the molecules to break apart into fragments. 

Trichloroethene Spectrum

The separation is based on mass and relative strengths of their molecular bonds.  Each chemical we analyze will have its own distinguishing pattern of masses and mass abundances called a mass spectrum.  Natural atomic isotopes cause clustered responses.  For example, about 1/4 of chlorine atoms found will have an atomic weight of 37, the remainder will be 35.

Molecular Models

Trichloroethene molecular model Fully intact trichloroethene molecule
Mass: 130

Trichloroethene molecular model fragment 1 Missing one chlorine atom
Mass: 95

Trichloroethene molecular model fragment 2 Missing two chlorine atoms
Mass: 60

Trichloroethene molecular model Hydrogen Atom hydrogen
Mass: 1

Trichloroethene molecular model Carbon Atom carbon
Mass: 12

Trichloroethene molecular model Chlorine Atom chlorine
Mass: 35