mass spectrometer

Examples of mass spectrometer in the following topics:

• Mass Spectrometer

  • Mass spectrometers use electric or magnetic fields to identify different materials.
  • Mass spectrometry (MS) is the art of displaying the spectra (singular spectrum) of the masses of a sample of material.
  • Mass spectrometers, as diagramed in , separate compounds based on a property known as the mass-to-charge ratio.
  • The elements or molecules are uniquely identified by correlating known masses by the identified masses.
  • Schematics of a simple mass spectrometer with sector type mass analyzer.

• The Mass Spectrometer

  • In order to measure the characteristics of individual molecules, a mass spectrometer converts 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:
  • A mass spectrometer operating in this fashion is outlined in the following diagram.
  • The heart of the spectrometer is the ion source.
  • A perpendicular magnetic field deflects the ion beam in an arc whose radius is inversely proportional to the mass of each ion.

• Mass Spectrometry to Measure Mass

  • Mass spectrometers separate compounds based on a property known as the mass-to-charge ratio: the mass of the atom divided by its charge.
  • The ion source is the part of the mass spectrometer that ionizes the compound.
  • Here is how a mass spectrometer would analyze a sample of sodium chloride (table salt).
  • The mass analyzer part of the spectrometer contains electric and magnetic fields, which exert forces on ions traveling through these fields.
  • A sample is loaded onto the mass spectrometer, where it undergoes vaporization and ionization.

• Examples and Applications

  • Cyclotrons, magnetrons, and mass spectrometers represent practical technological applications of electromagnetic fields.
  • We will explore some of these, including the cyclotron and synchrotron, cavity magnetron, and mass spectrometer.
  • The following figure illustrates one type of mass spectrometer.
  • The mass spectrometer will segregate the particles spatially allowing a detector to measure the mass-to-charge ratio of each particle.
  • Schematics of a simple mass spectrometer with sector type mass analyzer.

• High Resolution Spectra

  • In assigning mass values to atoms and molecules, we have assumed integral values for isotopic masses.
  • By designing mass spectrometers that can determine m/z values accurately to four decimal places, it is possible to distinguish different formulas having the same nominal mass.
  • The table below illustrates this important feature, and a double-focusing high-resolution mass spectrometer easily distinguishes ions having these compositions.
  • Mass spectrometry therefore not only provides a specific molecular mass value, but it may also establish the molecular formula of an unknown compound.
  • Tables of precise mass values for any molecule or ion are available in libraries; however, the mass calculator provided below serves the same purpose.

• Characteristics of Mass Spectra

  • A mass spectrum will usually be presented as a vertical bar graph, in which each bar represents an ion having a specific mass-to-charge ratio (m/z) and the length of the bar indicates the relative abundance of the ion.
  • Most of the ions formed in a mass spectrometer have a single charge, so the m/z value is equivalent to mass itself.
  • Modern mass spectrometers easily distinguish (resolve) ions differing by only a single atomic mass unit (amu), and thus provide completely accurate values for the molecular mass of a compound.
  • The highest-mass ion in a spectrum is normally considered to be the molecular ion, and lower-mass ions are fragments from the molecular ion, assuming the sample is a single pure compound.
  • The molecules of these compounds are similar in size, CO2 and C3H8 both have a nominal mass of 44 amu, and C3H6 has a mass of 42 amu.

• Basic Techniques in Protein Analysis

  • The basic technique for protein analysis, analogous to DNA sequencing, is mass spectrometry.
  • Mass spectrometry is used to identify and determine the characteristics of a molecule .
  • If the mass is measured with precision, then the composition of the molecule can be identified.
  • Matrix-Assisted Laser Desorbtion Ionisation - Time Of Flight (MALDI-TOF) Mass Spectrometer.
  • Mass spectrometry can be used in protein analysis.

• Isotopes

  • Since a mass spectrometer separates and detects ions of slightly different masses, it easily distinguishes different isotopes of a given element.
  • Thus, the bromine molecule may be composed of two 79Br atoms (mass 158 amu), two 81Br atoms (mass 162 amu) or the more probable combination of 79Br-81Br (mass 160 amu).
  • The center and right hand spectra show that chlorine is also composed of two isotopes, the more abundant having a mass of 35 amu, and the minor isotope a mass 37 amu.
  • Fluorine and iodine, by contrast, are monoisotopic, having masses of 19 amu and 127 amu respectively.
  • It should be noted that the presence of halogen atoms in a molecule or fragment ion does not change the odd-even mass rules given above.

• The Spectrometer

  • A spectrometer uses properties of light to identify atoms by measuring wavelength and frequency, which are functions of radiated energy.
  • A spectrometer is an instrument used to intensely measure light over a specific portion of the electromagnetic spectrum, to identify materials.
  • shows a diagram of how a spectrometer works.
  • When the spectrometer produces a reading, the observer can then use spectroscopy to identify the atoms and therefore molecules that make up that object.

• Vibrational Spectroscopy

  • The exact frequency at which a given vibration occurs is determined by the strengths of the bonds involved and the mass of the component atoms.
  • Furthermore, the number of observed absorptions may be decreased by molecular symmetry, spectrometer limitations, and spectroscopic selection rules.