Saturday, July 2, 2011

Mass Spectrometry

Mass spectrometry (MS) is an analytical technique which is used to determine the mass of ions (or charged particles). The technique has both qualitative and quantitative uses, which include identifying unknown compounds, determining the isotopic composition of elements in a molecule, and determining the structure of a compound by observing its fragmentation. Other uses include quantifying the amount of a compound in a sample or studying the fundamentals of gas phase ion chemistry. Since ions are very reactive and short-lived, their formation and manipulation must be conducted in a vacuum.

To measure the characteristics of individual molecules, a mass spectrometer is used to convert them to ions so that they can be moved about and manipulated by external electric and magnetic fields. The three essential functions of a mass spectrometer, and the associated components, are: 1) a small sample is ionized, usually to cations by loss of an electron (the Ion Source); 2) the ions are sorted and separated according to their mass and charge (the Mass Analyzer); 3) the separated ions are then measured, and the results displayed on a chart (the Detector).

A mass spectrometer determines the mass of a molecule by measuring the mass-to-charge ratio (m/z) of its ion. Ions are generated by inducing either the loss or gain of a charge from a neutral species. Once formed, ions are electrostatically directed into a mass analyzer where they are separated according to m/z and finally detected. The result of molecular ionization, ion separation, and ion detection is a spectrum that can provide molecular mass and even structural information.