The mass spectrometer

Question 1

What can you use your mass spectrometer to look for?

Answer 1

Can give information about:
Relative atomic mass
Relative molecular mass
Relative abundance of isotopes

Question 2

What are the four stages that occur in a mass spectrometer?

Answer 2

Electrospray ionisation
Acceleration
Ion drift
Detection

Question 3

Describe what happens in electrospray ionisation

Answer 3

• sample is dissolved in a polar solvent and pushed through a small nozzle at high pressure
• a high voltage is applied to it, causing the particles to lose an electron
• the ionised particles are separated from the solvent, leaving a gas made up of positive ions

Question 4

Describe what happens during acceleration

Answer 4

• positive ions are accelerated by an electric field
• particles need to be positively charged to be accelerated by the field
• the electric field gives the same kinetic energy to all the ions
• the ions with a lower mass/ charge ratio experience a greater acceleration - they’re given as much energy as heavier ions, but they’re lighter, so they accelerate more

Question 5

Describe what happens during ion drift

Answer 5

• ions leave the electric field with a constant speed and constant kinetic energy
• they enter a region with no electric field and drift through it at the same speed as the left of the electric field
• so ions with lower mass/ charge ratios will be drifting at higher speeds

Question 6

Describe what happens during detection

Answer 6

-Ions with a lower mass/ charge ratio travel through the drift region at higher speeds
- they reach the detector in less times than ions with a higher mass/ charge ratio
- 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