Mass spectrometry has been described as the smallest scale in the world, not because of its size but because of the size of the things it weighs. Mass spectrometry, also called mass spectroscopy, is an instrumental approach that allows for the mass measurement of molecules. The five basic parts of any mass spectrometer are a vacuum system, a sample introduction device, an ionization source, a mass analyzer and an ion detector. Combining these parts, a mass spectrometer determines the molecular weight of chemical compounds by ionizing, separating, and measuring molecular ions according to their mass-to-charge ratio. The ions are generated in the ionization source by inducing either the loss or the gain of a charge (e.g. electron ejection, protonation, or deprotonation). Once the ions are formed in the gas phase they can be electrostatically directed into a mass analyzer, separated according to mass and finally detected. The result of ionization, ion separation, and detection is a mass spectrum that can provide molecular weight or even structural information.
Mass spectrometers have become pivotal for a wide range of applications in the analysis of inorganic, organic, and bio-organic chemicals. Examples include dating of geologic samples, drug testing and drug discovery, process monitoring in the petroleum, chemical, and pharmaceutical industries, surface analysis and the structural identification of unknowns. Further, mass spectrometry is being continually improved and has recently had significant advances in its application to molecular biology, where it is now possible to analyze proteins, DNA, and even viruses.
Today's mass spectrometer is based on the seminal work performed by Sir J. J. Thomson of the Cavendish Laboratory of the University of Cambridge. Thomson's research, which led to the discovery of the electron in 1897, also led to the first mass spectrometer while he was measuring the effects of electric and magnetic fields on ions generated by ratios.