Mass spectrometry is an analytical method used to identify
chemical substances by ionizing the material, focusing
the resulting ions into a beam, then separating them according
to the ratios of their mass to their net electric charge.
The instruments have six basic components: 1) a high vacuum
system into which the substances are initially introduced,
which creates low pressure essential for the production
of free electrons and ions in the gas phase; 2) an ion
source which converts the sample into a beam of charged
particles; 3) a mechanism for focusing it into a narrower
beam; 4) acceleration of the beam through a voltage drop;
5) a mass analyzer that separates the beam into its components;
and 6) a detector that can observe or collect the separated
beams.
Traditional mass spectrometers,
such as thermal ionization mass spectrometers and gas
source mass spectrometers, vary mainly in type of ion
source employed. Accelerator mass spectrometers add
an additional step: injection of negatively charged
C ions from the material being analyzed into a nuclear
particle accelerator.
Mass spectrometers are used
to separate isotopes and measure the abundance of concentrated
isotopes when used as tracers in fields such as chemistry,
biology, and medicine. They are efficient at measuring
the ratio of a rare isotope to a common isotope much
more accurately than by using absolute ratios. The following
types of mass spectrometers are used commonly in hydrologic
studies:
|
