Mass spectrum

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Electron ionization mass spectrum of toluene [1]
Note parent peak corresponding to molecular mass M = 92 (C7H8+) and highest peak at M-1 = 91 (C7H7+, quasi-stable tropylium cation).

A mass spectrum is an intensity versus m/z (mass-to-charge ratio) plot that represents a chemical analysis.[2] The mass spectrum of a sample is a pattern representing the distribution of ions by mass (more correctly: mass-to-charge ratio) in a sample. It is a histogram usually made using an instrument called a mass spectrometer. Not all mass spectra of a given substance are the same. It can depend on the operating conditions of the instrument. For example, some mass spectrometers break the analyte molecules into many pieces; others observe the intact molecular masses with little fragmentation. A mass spectrum can represent many different types of information based on the type of mass spectrometer and the specific experiment; however, all plots of intensity vs. mass-to-charge are called "mass spectra".

Common fragmentation processes for organic molecules are the McLafferty rearrangement and alpha cleavage.

In the past, chemists with PhD degrees were needed to interpret mass spectra. Today, computer programs read the data and identify the compounds in a sample.

References[change | change source]

  1. NIST toluene spectrum.
  2. International Union of Pure and Applied Chemistry. "mass spectrum". Compendium of Chemical Terminology Internet edition.

Other websites[change | change source]