Lecture Notes on Isotopes and Mass Spectrometry

Isotopes

• Definition: Different versions of a given element.
• Characteristics:
  • Same number of protons.
  • Different number of neutrons.
• Atomic Mass: Each isotope has a different atomic mass.

Determining Isotopes and Abundance

• Technique Used: Mass Spectrometry (also referred to as Mass Spectroscopy).
• Purpose: Identify various isotopes of an element and their relative abundance in nature.

Mass Spectrometry Process

1. Sample Preparation: A sample of the element (e.g., zirconium) is heated up.
2. Ionization:
   • Bombarded with electrons.
   • Electrons knocked off atoms, ionizing them.
   • Ionized atoms possess a charge.
3. Acceleration:
   • Charged ions are accelerated through electric plates.
4. Deflection:
   • Ions move into a magnetic field.
   • Magnetic field bends/deflects ion paths.
   • Deflection depends on mass:
     • Larger mass: Less deflection.
     • Lower mass: More deflection.
5. Detection:
   • Different isotopes are detected based on deflection.
   • Abundance is measured by the number of ions detected at certain points.

Results Representation

• Graphical Display:
  • Horizontal axis: Atomic mass (in unified atomic mass units) or mass to charge ratio.
  • Example with zirconium:
    • Mass number variations: 96, 94, 92, 91, 90.
    • Majority (over 50%) have mass number 90.
• Alternative Measurement: Mass to Charge Ratio
  • Mass: Mass of the ion.
  • Charge: Charge of the ion.
  • Adjustment: Necessary if charge is not +1 (e.g., for charge +2, adjust accordingly).

Key Concepts

• Higher mass to charge ratio ions are deflected less.
• Lower mass to charge ratio ions are deflected more.
• Graphs from mass spectrometry show isotope types and abundance based on deflection characteristics.