mass spectrometry

Question 1

1st, 2nd ,3rd lines

Answer 1

• m+1
• molecular ion
• base peak (largest)

Question 2

what is m/z

Answer 2

• m/z means mass ÷ charge
  -The deflection by the magnetic field depends on both the mass and the charge of an ion
  -most ions have a +1 charge so assume that m/z is the same as mass

Question 3

what is the relative intensity

Answer 3

-The height of the peaks in the mass spectrum shows the abundance of the ions of each mass – this is called the relative intensity
- relative intensities depend mostly on the stability of ions

Question 4

base peak

Answer 4

• tallest peak and its relative intensity is set at 100%
• All other relative intensities are expressed relative to the base peak = 100%
• The base peak is usually the most stable ion formed

Question 5

molecular ion

Answer 5

• ion that consists of the whole molecule, minus one electron.
• Its mass is the same as the relative molecular mass of the molecule.
• has heaviest mass i.e. furthest to the right
• An electron collides with a molecule and knocks an electron out, resulting in a positively charged ion.
  M + e− → M+ + 2e−

Question 6

m+1 peak

Answer 6

• molecular ion with a mass 1 unit heavier than the normal molecular ion.
• In organic molecules this is usually caused by the presence of one atom of carbon-13 in the molecule, in place of the much more abundant carbon-12 isotope.
• Carbon-13 has an abundance of 1.1% of carbon atoms = M+1 peak is very small compared to the M peak (molecular ion).

Question 7

what is a fragment

Answer 7

• Excess energy from the ionisation process can cause bonds in the molecular ion to break= result in smaller fragments, one of which will also be positively charged.
  M+ → X+ + Y
  or
  M+ → X + Y+
• Only the positive fragment will be detected
  most common fragments are made by breaking only one bond in the molecular ion