How Mass Spectrometry Works

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. 

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.

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.

 

Trichloroethene Spectrum

Description

Molecular Model

Mass
Fully intact trichloroethene molecule

Trichloroethene molecular model

130
Missing one chlorine atom

Trichloroethene molecular model fragment 1

95
Missing two chlorine atoms

Trichloroethene molecular model fragment 2

60
hydrogen

Trichloroethene molecular model Hydrogen Atom

1
carbon

Trichloroethene molecular model Carbon Atom

12
chlorine

Trichloroethene molecular model Chlorine Atom

35