Mass spectrometry

• What is a mass spectrometer used for?

  To analyse elements or compounds
• What type of mass spectrometer should you know how to operate?

  A time of flight (TOF) mass spectrometer
• What information can a mass spectrometer provide about an element?

  Relative atomic mass and relative abundance of its isotopes
• What happens when a sample is introduced into a TOF mass spectrometer?

  It undergoes ionisation, acceleration, ion drift, and detection
• What are the four main steps in the operation of a TOF mass spectrometer?

  1. Ionisation
  2. Acceleration
  3. Ion drift
  4. Detection
• What is the first step in the operation of a TOF mass spectrometer?

  Ionisation
• What is the purpose of ionisation in a mass spectrometer?

  To convert the sample into ions before analysis
• What are the two methods of ionisation in a mass spectrometer?

  1. Electrospray ionisation
  2. Electron impact ionisation
• How does electrospray ionisation work?

  The sample is dissolved in a solvent and pushed through a nozzle at high pressure with a high voltage applied
• What happens during electron impact ionisation?

  An electron gun fires high energy electrons at the vaporized sample, knocking off electrons and creating +1 ions
• What occurs during the acceleration step in a mass spectrometer?

  The positive ions are accelerated by an electric field, giving them constant kinetic energy
• Why do lighter ions accelerate more than heavier ions in a mass spectrometer?

  Because they are given the same energy but have less mass
• What happens to ions during the ion drift phase?

  They drift through a region with no electric field at the same speed they left the electric field
• How does the detection phase work in a mass spectrometer?

  The detector records the current created when ions hit it and measures the time taken for ions to pass through
• What is the significance of lighter ions reaching the detector first?

  It allows for the calculation of mass/charge values needed to produce a mass spectrum
• What are the learning objectives related to mass spectrometry?

  • Know that mass spectrometry provides accurate information about relative isotopic mass and abundance
  • Understand the principles of TOF mass spectrometry
  • Be able to interpret simple mass spectra of elements
  • Know that mass spectrometry can identify elements
• What is a key requirement for particles entering a mass spectrometer?

  They need to be ionised
• Why is ionisation necessary for particles in a mass spectrometer?

  Without ionisation, particles cannot be accelerated by the electric field or detected
• What does mass spectrometry help to identify?

  Elements
• What does a mass spectrum represent?

  A graphical representation of the mass/charge values of ions
• How does the process of ionisation affect the results of mass spectrometry?

  Ionisation converts neutral particles into charged ions, allowing them to be manipulated by electric fields
• What is the relationship between the mass of ions and their speed during the ion drift phase?

  Lighter ions travel faster than heavier ions during the drift phase
• What is the role of the electric field in the acceleration phase of a mass spectrometer?

  The electric field provides constant kinetic energy to all ions
• What is the purpose of the detector in a mass spectrometer?


  To detect the current created when ions hit it