The mass spectrometer is an instrument that can measure the masses and relative concentrations of atoms and molecules and Mass Spectrometry is an analytical technique that identifies the chemical composition of a compound or sample based on the mass-to-charge ratio of charged particles. The design of a mass spectrometer has three essential modules, an ion source-which transforms the molecules in a sample into ionized fragments, a mass analyzer-which sorts the ions by their masses by applying electric, and magnetic fields and a detector-which measures the value of some indicator quantity and thus provides data for calculating the abundances each ion fragment present.

The mass spectrometer technique has both qualitative and quantitative uses, such as-

1. Identification of unknown compounds

2. Determining the isotopic composition of elements in a compound

3. Determining the structure of a compound by observing its fragmentation

4. Quantifying the amount of a compound in a sample using carefully designed methods

5. Studying the fundamentals of gas phase in ion chemistry

6. Determining other physical, chemical or biological properties or compounds.

Mass spectrometers are sensitive detectors of isotopes based on their masses. They are used in carbon dating and other radioactive dating processes. The combination of a mass spectrometer and a gas chromatograph makes a powerful tool for the detection of trace quantities of contaminants or toxins. A number of satellites and spacecraft have mass spectrometers for the identification of the small numbers of particles intercepted in space.

Mass spectrometers are also widely used in space missions to measure the composition of plasmas. Foe example, the cassini spacecraft carries the Cassini Plasma spectrometer (CAPS), which measures the mass of ions in Saturn's magnetosphere.

Mass spectrometry is an important method for the characterization of proteins. Pharmacokinetics is often studied using mass spectrometry because of the complex nature of the matrix (often blood or urine).

Mass spectrometers are used for the analysis of residual gases in high vacuum systems.

An atom probe is an instrument that combines time-of-flight mass spectrometry and field ion microscopy to map the location of individual atoms.

Mass spectrometers were used in hospitals mostly found in the operating room for respiratory gas analysis from 1975 till the end of the century.