Mass Spectrometry

• The stages of TOF mass spec are

  • ionisation
  • acceleration
  • ion drift
  • detection
• in electron impact ionisation, an electron is fired at the vaporised sample using an electron gun, knocking an electron from each particle and giving it a +1 charge
• in electrospray ionisation the sample is dissolved in a solvent and pushed through a hypodermic needle at high pressure where a high voltage is applied. this causes each particle to gain a H+ ion.
• During acceleration in mass spec, the positively charged particles are accelerated using an electric field. All the particles are given the same kinetic energy.
• During ion drift the accelerated ions enter a vacuum. Since they have the same kinetic energy, their velocity is dependant on their mass. Smaller ions will move faster and larger ions slower.
• during detection, the detector detects the current created when the ions hit it and record how long it took. this is then used to calculate the mass/charge values