massspectrometry

Mass spectrometry is an analytical technique that measures the mass-to-charge ratio of ions to identify and quantify molecules in a sample. In a typical instrument, neutral molecules are ionized to form charged species, which are then separated by a mass analyzer and detected. The resulting spectrum displays ion masses and intensities, enabling molecular identification, structural insights, and concentration measurements.

The method originated in the early 20th century with scientists such as J. J. Thomson and F. W. Aston, and has evolved with improvements in ionization sources, mass analyzers, and detectors. Modern mass spectrometers combine an ion source, a mass analyzer, and a detector with a data system for analysis and interpretation.

Ionization methods include electron ionization for volatile small molecules, electrospray ionization for large biomolecules, and matrix-assisted laser desorption/ionization for macromolecules and polymers. Other methods such as atmospheric pressure chemical ionization are common in mixtures and liquid samples.

Mass analyzers separate ions by their mass-to-charge ratio; common types include time-of-flight, quadrupole, ion trap, Orbitrap, and FT-ICR. High-resolution or accurate-mass MS improves molecular formula assignment. Tandem mass spectrometry (MS/MS) adds a second stage of isolation and fragmentation for structural elucidation.

Mass spectrometry is frequently coupled with separation techniques such as gas chromatography (GC-MS) or liquid chromatography (LC-MS). Its applications span proteomics, metabolomics, pharmaceutical analysis, environmental monitoring, and food safety. Limitations include instrument cost, operator expertise, and matrix effects requiring careful calibration and validation.