PC1

Question 1

Describe ionisation

Answer 1

Electrospray ionisation:

The sample is dissolved in a solvent and pushed through a small nozzle at a high pressure. A high voltage is applied to it, causing each particle to gain a H+ ion. The solvent is then removed, leaving a gas made up of positive ions

Electron spray impact:

The sample is vaporised and an ‘electron gun’ is used to fire high energy electrons at it. This knocks off one electron from each particle, so they become 1+ ions

Question 2

Describe acceleration

Answer 2

The positive ions are accelerated by an electric field. The electric field gives the same kinetic energy to all ions. The lighter ions experience a greater acceleration

Question 3

Describe ion drift

Answer 3

The ions enter a region with no electric field. They drift through it at the same speed as they left the electric field. So the lighter ions will be drifting at higher speeds

Question 4

Describe detection

Answer 4

The detector detects the current created when the ions hit it and records how long they took to pass through the spectrometer. This data is then used to calculate the mass/charge values needed to produce a mass spectrum

Question 5

Define relative molecular mass (Mr)

Answer 5

The average mass of a molecule on a scale where an atom of carbon-12 is exactly 12

Question 6

Describe relative atomic mass (Ar)

Answer 6

The average mass of an atom of a scale where an atom of carbon-12 is exactly 12

Question 7

Define ionisation energy

Answer 7

The energy needed to remove 1 electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous +1 ions

Question 8

Why is the time of flight mass spectrometer kept under a vacuum?

Answer 8

To prevent molecules in the air from colliding with the electrons