Mass Spectrometer

Question 1

What are the 4 stages of Mass spec?

Answer 1

Ionisation, Acceleration, Ion Drift, Detection

Question 2

What are the 2 common types of ionisation?

Answer 2

Electron Impact and Electrospray Ionisation

Question 3

What is electron impact ionisation and what is the general equation?

Answer 3

Sample is vaporised and high energy electrons are fired at it usually knocking off one electron from each ion.
X(g) –> X+(g) + e-
(high energy ionisation that causes fragmentation)

Question 4

What is electrospray ionisation and what is the general equation?

Answer 4

Solution pumped through a capillary needle and voltage is applied causing a aerosol to be formed. Solution evaporates leaving MH+(g) ions.
M + H+ –> MH+
(soft technique, doesn’t cause fragmentation)

Question 5

How is acceleration achieved in mass spec?

Answer 5

Electrical field applied to a series of plates giving the same kinetic energy to all ions. Ions with lower mass(m) to charge(z) ratio will be accelerated more.

Question 6

What happens during ion drift (mass spec)?

Answer 6

All ions leave the field with constant speed and kinetic energy. When they enter the drift region (no electric field), the lighter ions move towards the detector quicker.

Question 7

What happens during detection (mass spec)?

Answer 7

Detector detects the current created when the ions hit it and gain electrons and the detector records how long the ions took to pass through the instrument as well as the abundance of each.

Question 8

TOF Mass Spec Uses?

Answer 8

-Calculate the relative atomic mass
- Machines are small and light so can be used in space exploration (eg.Philae lander)
- Pharmaceutical industry to analyse drugs to check they’re the correct compound.