Mass spectrometry

• What is the main purpose of a mass spectrometer?

  To determine the relative atomic mass of an element
• How does a mass spectrometer ionize atoms?

  By bombarding them with a beam of electrons
• What happens to positive ions in a mass spectrometer?

  They are accelerated and passed through a magnetic field
• What does the extent of deflection of ions depend on?

  The mass-to-charge ratio (m/z) of the ions
• What does a mass spectrum show?

  The relative abundance of each ion plotted against m/z ratio
• What does the mass spectrum of an element indicate?

  A peak for each isotope present
• How is the relative atomic mass calculated?

  Relative atomic mass = Σ(isotope mass × % abundance)/100
• What is the relative atomic mass of chlorine with isotopes ³⁵Cl and ³⁷Cl?

  35.5
• What are the steps in a time of flight mass spectrometer?

  1. Ionisation: Sample ionised by high-energy electrons
  2. Acceleration: Positive ions accelerated by electric field
  3. Time of flight: Ions travel to detector; time depends on m/z
  4. Detection: Arrival times recorded; data processed to produce mass spectrum
• How does the time of flight relate to the m/z ratio?

  Time of flight is proportional to the square root of m/z
• What can mass spectra determine about isotopes?

  The relative abundance of different isotopes
• What does a taller peak in a mass spectrum indicate?

  Higher relative abundance of that isotope
• What are the steps in ionisation mass spectrometry?

  1. Ionisation: Sample ionised using various methods
  2. Mass separation: Ions separated by m/z ratio using mass analyser
  3. Detection: Separated ions detected and measured; results displayed as mass spectrum
• What methods can be used for ionisation in mass spectrometry?

  Electron ionisation, chemical ionisation, electrospray ionisation
• What is the role of a mass analyser?

  To separate ions according to their m/z ratio
• What does the signal intensity in a mass spectrum indicate?

  The abundance of ions in the original sample
• What applications does ionisation mass spectrometry have?

  Drug discovery, environmental monitoring, and more
• What is the mass spectrum for a pure sample containing one isotope like?

  It shows a single peak
• What does the mass spectrum for element X indicate?

  Two isotopes with mass numbers 20 and 22
• How can the exact percentage abundances of isotopes be calculated?

  From the areas under the peaks in the spectrum
• How do different mass analyzers separate ions?

  Using oscillating electric fields, time of flight, or magnetic fields
• What is the significance of mass spectrometry in analytical chemistry?

  It identifies and quantifies substances in samples
• What is the mass spectrum for a sample containing different isotopes like?

  It shows multiple peaks for each isotope
• What does the mass spectrum provide information about?

  The composition and structure of the sample
• What is the role of the computer in mass spectrometry?

  To process data and produce a mass spectrum
• What is the relationship between the mass spectrum and molecular weight?

  The molecular weight can be determined from the mass spectrum
• How does ionisation mass spectrometry differ from other analytical techniques?

  It separates ions based on mass-to-charge ratio
• What is the importance of the relative abundance of isotopes?

  It helps in identifying elements and their isotopic composition
• What is the significance of the peaks in a mass spectrum?

  They represent different isotopes of an element
• Ionization

  Sample is bombarded with high-energy electrons to create ions.
• Acceleration

  Positive ions are accelerated by an electric field to give them an initial velocity.
• Time of Flight

  Ions travel through a field-free region (drift tube) towards the detector, with arrival times dependent on m/z ratio.
• Detection

  Arrival times are recorded by the detector, typically using a digital technique.
• Data Processing

  Recorded data is processed to produce a mass spectrum, converting arrival times to m/z ratios and graphing the result.