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Mass Spectrometry

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:

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