L2 - Mass Spectrometer

Question 1

What are the 4 steps?

Answer 1

ionisation

acceleration

flight tube / ion drift

detection

Question 2

What are the 2 types of ionisation?

Answer 2

electron impact (or electron ionisation)

electrospray isolation

Question 3

ionisation

Explain electron impact

Answer 3

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

This technique is used on samples with a low formula mass

It can potentially cause fragmentation

Question 4

ionisation

Explain electrospray isolation

Answer 4

The sample is dissolved in a volatile solvent + injected through a hypodermic needle to form a mist

The tip of the needle is attached to a positive terminal of a high voltage power supply, and particles in the sample become charged by gaining a proton from the solvent.

This technique is used on samples with high molecular mass

It rarely results in fragmentation

Question 5

2

explain acceleration

Answer 5

The positive ions are accelerated by a plate with a negative electric field so that they have the same kinetic energy

Question 6

3

explain the flight tube

Answer 6

As all Particles have the same kinetic energy, lighter particles move through the flight tube faster than the heavier ones

Question 7

4

explain detection

Answer 7

When ions hit a detector plate, they gain an electron producing an electric current.

The more of an ion there is in a sample, the larger the measured current will be.

Using a computer we can produce a ‘mass spectrum’ which tells us the relative abundance of each ion