Mass spectrometry is a method of separating and analyzing the atoms and molecules in a chemical sample. In mass spectrometry, scientists ionize the atoms and molecules in a sample—that is, convert them into electrically charged particles called ions. A device called a mass spectrometer then separates the various ions according to their mass and electric charge. People sometimes refer to mass spectrometry as mass spectroscopy << spehk TROS kuh pee, >> but many scientists reserve the term spectroscopy to describe methods of analysis that rely on light.
Mass spectrometry has many important uses in chemistry and biology. Chemists use it to determine the molecular weights of elements, isotopes (different forms of the same element), and compounds, and to analyze the composition and structure of complex molecules. Environmental scientists use mass spectrometry to detect and measure the amounts of pollutants in water and soil. Biologists and medical researchers use mass spectrometry to analyze proteins and other biological substances isolated from bacteria, viruses, and bodily fluids.
To carry out mass spectrometry, scientists use several techniques to ionize chemical samples. One method, electron bombardment, shoots a beam of electrons at the sample. Another method, electrospray ionization, ionizes a sample by forcing it through a charged needle. The sample is then fed into a mass spectrometer.
Mass spectrometers use electric fields and magnetic fields (areas of electric charge and magnetic force) to separate ions. A magnetic sector mass spectrometer, the most basic kind, uses an electric field to accelerate the ions and a magnetic field to deflect them onto a detector. The amount that an ion is deflected depends on how heavy it is—that is, on the ratio of its mass to its charge. By varying the intensity of the magnetic field, the device causes different ions to hit the detector at different times. This results in a graph called a mass spectrum that shows the relative numbers of ions with different ratios of mass to charge. Most mass spectrometers send this information to a computer that can store, manipulate, and interpret the data.
See also Spectroscopy .
