mass spectrometry - Unit 4 AOS 2

Question 1

mass spectrometry

Answer 1

• Mass spectrometry is an analytical technique used to determine the relative masses of molecules.
• It uses investigation and measurement of the masses of isotopes, molecules and molecular fragments by ionising samples and separating the fragments produced, using a combination of electric and magnetic fields

Question 2

mass spectrometer

Answer 2

• A sample of molecules is bombarded by high-energy electrons, forming a number of mainly singly charged positive ions. The molecules undergo fragmentation, forming smaller positively charged ion fragments.

Question 3

ionisation

Answer 3

• Ionisation generates the parent or molecular ion (M+ ), according to the following reaction equation, by bombarding the sample with high energy electrons. Only positively charged ions are detected by the mass spectrometer.

molecule + e- → [molecule]+ + 2e-

Question 4

fragmentation

Answer 4

• Fragmentation of the unstable molecular ion produces a variety of smaller ions as different bonds are broken. The specific fragmentation pattern can help determine the structure of the original molecule.

Question 5

base peak

Answer 5

the most intense peak in a mass spectrum, which is assigned a relative abundance of 100%

Question 6

molecular ion peak

Answer 6

• the molecular ion is the ion formed when a neutral molecule is bombarded with high-energy electrons
• the peak in the mass spectrum that corresponds to the molecular ion, which has the highest m/z ratio

Question 7

mass spectrum axes

Answer 7

vertical: relative abundance (%)
horizontal: mass to charge ration (m/z)

Question 8

steps

Answer 8

1. if given the molecule, circle the fragments it could form and determine their masses.
2. subtract these masses from the molecular ion and it there is a peak at that point, it corresponds to that fragment.
3. ensure brackets and plus sign.