Atomic structure

• mass spectrometry

  Analytical technique used to identify different isotopes and find the overall relative atomic mass of an element
• Time of flight

  Records the time it takes for each isotope to reach a detector. Using this, Spectra can be produced showing each isotope
• ionisation

  A sample of an element is vapourised and injected into the mass spectrometer where a high voltage is passed over the chamber. This causes electrons to be removed from the atoms (ionised) leaving 1+ charged ions in the chamber.
• Acceleration

  These positively charged ions are then accelerated towards a negatively charged detection plate
• ion drift 


  The ions are the deflected by a magnetic field into a curved path. the radius of their path is dependant on the charge and mass of the ion
• Isotopes

  isotopes are atoms of the same element with the same atomic number but with a different number of neutrons resulting in a different mass number
• Detection

  When the positive ions hit the negatively charge detection plate, they gain an electron producing a flow of charge. The greater the abundance the greater the current produced.
• Analysis 


  These current values are then using combination with the flight times to produce a spectra print out with the relative abundance of each isotope displayed
• letter used to represent the atomic number of an atom

  Z
• Atomic number 


  Number of protons in an atom
• letter which represents mass number

  A
• Relative atomic mass

  Average mass of all isotopes of an element compared to the 1/12 the mass of an carbon-12
• Electron impact

  • Use for organic or inorganic molecules with a low formula mass
  • hi energy electrons are fired at the sample from an electron gun
  • this knock off one electron from each atom to form a plus one ion
• Electrospray ionisation

  Use for substances with high molecular mass, including biological molecules e.g. protein