Mass Spectroscopy

Question 1

What is mass spectroscopy doing?

Answer 1

• Provides Molecular Weight
• Provides valuable information about the molecular formula
• Does not use light (different from spectroscopy)
• Sample is destroyed
• High-energy electrons fragment the molecules
• Mass of the fragments is measured
• Information used to “reconstruct” the molecule

Question 2

Describe what the process of mass spectroscopy is

Answer 2

1. Negatively charged accelerator plate with narrow slit
   to allow ions to pass through
2. Charged particle passes through magnetic field
   (bends path) – Curvature of the bend depends on the
   m/z ratio (mass / charge)
3. Slit followed by detector – at any given magnetic field,
   only ions of one particular mass are bent exactly the
   right amount to pass through the detector. The
   detector signal is proportional to the number of ions
   striking it

Question 3

What is the mass spec rule of 13 calculation?

Answer 3

• Calculation used to determine the molecular
  formula based on mass
• Starts with the assumption of only having carbon
  and hydrogen atoms (C=12, H=1)
• Then heteroatoms are explored until an exact
  combination or all possible combinations are
  identified