time of flight mass spectrometer

• what conditions does the time of flight mass spectrometer be in?

  in a vacume otherwise air particles would ionise and register in the detector
• what are the 4 steps?

  1. ionisation
  2. acceleration
  3. ion drift
  4. detection
• what are the two types of ionisation?

  electron impact and electrospray ionisation
• what is electron impact?

  1. vapourised sample injected at low pressure
  2. electron guns fire high energy electrons at the sample
  3. outer electron knocked out
  4. positive ion is formed
• what is electrospray ionisation?

  1. sample dissolved in volatile, polar substance
  2. sample injected through a fine needle producing mist or aerosol
  3. the tip of the needle has a high voltage
  4. proton (H+) gained to the sample
  5. positive ion formed
• why do we use electron impact?

  when an element or substance has a low formula mass

  electron impact causes larger organic molecules to turn into fragments
• why do we use electrospray ionisation?

  the softer conditions means larger organic molecules wont be turned to fragments
• describe acceleration?

  positive ions ate accelerated by an electric field to a constant kinetic energy
• what does the velocity of an ion depend on although all have the same kinetic energy?

  the size of the particle, lighter particles have a faster velocity
• describe ion drift?

  positive ions drift through the tube
• describe detection?

  when positive ions hit the metal detector , electrons are transferred from the detector to the positive ions this generates a current , the current is directly proportional to the abundance of species
• how do i measure the Mr of a molecule using electron impact ionisation? what is the peak called?

  • fragments will occur resulting in alot of peaks
  • the peak with the highest m/z will be due to the complete molecule
  • this is equal to the mr
  • this is called the parent ion or molecular ion
• how do i find the mr from electrospray ionisation?

  • fragments do not occur
  • so one peak is equal to the mass of MH+ ion
  • to find Mr you subtract 1
• write how many electrons each sublvl holds:

  • s sublvl - 2
  • p sublvl - 6
  • d sublvl- 10
  • f sublvl - 14
• what is the shape of the s sub level?

  spherical
• what is the shape of the p sub level?

  dumbell
• what is the definition of 1st ionisation energy?

  enthalpy change when one mole of electrons are removed from one mole of gaseous atoms forming one mole of positive gaseous ions
• what is the definition of 2nd ionisation energy?

  when one mole of single positive gaseous ions turn into one mole of double positive gaseous ions
• why are the arrows in orbitals in opposite directions?

  represent the different spins of the electrons in orbital
• factors that effect ionisation energy?

  1. attraction of the nucleus
  2. distance from the electrons from the nucleus
  3. sheilding
• what do successive ionisation energies tell us ?

  information about the electronic structure of an element
• why are successive ionisation energies always larger?

  • after the first electron is removed, a positive ion is produced
  • this created a stronger attraction for the remaining electrons
  • so more energy is required to remove another electron
• how do successive ionisation energies tell us about electronic configuration?

  each large jump tells us its a new shell