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Chemistry LibreTexts

15: Molecular Mass Spectrometry

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  • Mass spectrometry is an analytical technique that ionizes chemical species and sorts the ions based on their mass-to-charge ratio. In simpler terms, a mass spectrum measures the masses within a sample. Mass spectrometry is used in many different fields and is applied to pure samples as well as complex mixtures. A mass spectrum is a plot of the ion signal as a function of the mass-to-charge ratio. These spectra are used to determine the elemental or isotopic signature of a sample, the masses of particles and of molecules, and to elucidate the chemical structures of molecules, such as peptides and other chemical compounds.

    • 15.1: Mass Spectrometry - The Basic Concepts
      heavily edited by J. Breen
    • 15.2: Ionizers
      The following ionizers for mass spectrometry will be presented in this subsection: electron impact, chemical ionization, fast atom bonbardment, matrix assisted laser desorption (MALDI), thermospray, and atomospheric pressure ionization.  Electrospray ionization will be presened in it's own sun section of this chapter.
    • 15.3: Mass Analyzers (Mass Spectrometry)
      Mass spectrometry is an analytic method that employs ionization and mass analysis of compounds to determine the mass, formula and structure of the compound being analyzed. A mass analyzer is the component of the mass spectrometer that takes ionized masses and separates them based on charge to mass ratios and outputs them to the detector where they are detected and later converted to a digital output.
    • 15.4: Ion Detectors
    • 15.5: High Resolution vs Low Resolution
      heavily edited by J. Breen
    • 15.6: The Molecular Ion (M⁺) Peak
      This page explains how to find the relative formula mass (relative molecular mass) of an organic compound from its mass spectrum. It also shows how high resolution mass spectra can be used to find the molecular formula for a compound.
    • 15.7: Molecular Ion and Nitrogen
      just changed weights to masses and added the missing value for iodine- J Breen
    • 15.8: The M+1 Peak
      This page explains how the M+1 peak in a mass spectrum can be used to estimate the number of carbon atoms in an organic compound.
    • 15.9: Organic Compounds Containing Halogen Atoms
      This page explains how the M+2 peak in a mass spectrum arises from the presence of chlorine or bromine atoms in an organic compound. It also deals briefly with the origin of the M+4 peak in compounds containing two chlorine atoms.
    • 15.10: Fragmentation Patterns in Mass Spectra
      This page looks at how fragmentation patterns are formed when organic molecules are fed into a mass spectrometer, and how you can get information from the mass spectrum.
    • 15.11: Electrospray Ionization Mass Spectrometry
      Electrospray ionization is a soft ionization technique that is typically used to determine the molecular weights of proteins, peptides, and other biological macromolecules. Soft ionization is a useful technique when considering biological molecules of large molecular mass, such as the aformetioned, because this process does not fragment the macromolecules into smaller charged particles, rather it turns the macromolecule being ionized into small droplets.

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