The Mass Spectrometer

Question 1

How many steps occur in a mass spectrometer?

Answer 1

Five

Question 2

List the five steps that occur in a mass spectrometer.

Answer 2

Vaporisation

Ionisation

Acceleration

Separation in a magnetic field

Detection

Question 3

Write a note on vaporisation.

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Answer 3

A small amount of the gas or liquid is injected into the instrument at the sample inlet

As there is a good vacuum inside the instrument, liquids quickly turn to gases

Therefore, this stage is called the vaporisation stage

If the material being studied is a solid, it may need to be heated in a special attachment in order to vaporise it

Question 4

What state must the sample be in before being studied?

Answer 4

Liquid or gas

Question 5

Why is it okay for a liquid sample to be used?

Answer 5

Because the liquid quickly turns to gas inside the instrument as it is a good vacuum

Question 6

How much of the sample is needed?

Answer 6

A small amount is needed

Question 7

How is the sample placed in the spectrometer?

Answer 7

It must be injected into the instrument at the sample inlet

Question 8

What must be done to any solid samples?

Answer 8

it may need to be heated in a special attachment in order to vaporise it

Question 9

Write a note on the ionisation stage.

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Answer 9

The purpose of this part of the apparatus is to turn the atoms or molecules into ions

This is done using an ‘electron gun’ in an ionisation chamber

This is simply a heated filament that gives off electrons

The electrons gun fires high-energy electrons at the atoms or molecules of the sample gas

Electrons are knocked off these particles of the sample gas and positive ions are produced

Question 10

What is the purpose of the ionisation stage?

Answer 10

The purpose of this part of the apparatus is to turn the atoms or molecules into ions

Question 11

What instrument is used to turn the atoms/molecules into ions?

Answer 11

An ‘electron gun’

Question 12

What is an electron gun?

Answer 12

A heated filament that gives off electrons

Question 13

What is the role of the electron gun?

Answer 13

It fires high-energy electrons at the atoms or molecules of the sample gas

Question 14

What happens when electrons are fired at the atoms/molecules?

Answer 14

Electrons are knocked off these particles of the sample gas and positive ions are produced

Question 15

Write a note on the acceleration stage.

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Answer 15

The positive ions produced in the previous stage pass between a series of negatively charged plates in the accelerator

These plates attract the positive ions from the mixture in the ionisation chamber and accelerate these positive ions to high speeds

A fine beam of ions then passes into the analyser unit

Question 16

What do the positive ions pass between?

Answer 16

A series of negatively charged plates in the accelerator

Question 17

What is the role of the negatively charged plates in the accelerator?

Answer 17

These plates attract the positive ions from the mixture in the ionisation chamber and accelerate these positive ions to high speeds

Question 18

What is formed from the acceleration stage?

Answer 18

A fine beam of ions

Question 19

Why is a vacuum necessary inside the instrument?

Answer 19

A good vacuum is needed so that the positive ions can travel through it without colliding with any air molecules

Question 20

Where does the fine beam of ions pass into?

Answer 20

The analyser unit

Question 21

Write a note on the Separation stage.

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Answer 21

In the analyser the positive ions are made to move in curved paths using a magnetic field produced by a powerful electromagnet

The lighter particles are easier to deflect

The heavier particles are more difficult to deflect

Thus, the lighter ions are pushed further off course than the heavier ions

Therefore, the single beam of positive ions is split into a number of beams

Therefore, the ions are separated according to their masses

Question 22

What are the positive ions made do in the analyser unit?

Answer 22

The positive ions are made to move in curved paths using a magnetic field produced by a powerful electromagnet

Question 23

What makes the positive ions move in curved paths in the analyser unit?

Answer 23

A magnetic field produced by a powerful electromagnet

Question 24

What produces the magnetic field?

Answer 24

A powerful electromagnet

Question 25

Which are easier to deflect the lighter or heavier particles?

Answer 25

The lighter particles are easier to deflect

Question 26

What happens to the lighter particles?

Answer 26

They are pushed further off course than the heavier ions

Question 27

The lighter particles are pushed further off course than the heavier ions, what does this result in?

Answer 27

This results in the single beam of positive ions being split into a number of beams

Question 28

The single beam of positive ions is split into a number of beams, what does this mean for the ions?

Answer 28

This means the ions have been separated according to their masses

Question 29

Define the principle of mass spectrometry.

Answer 29

The principle of mass spectrometry is that charged particles moving in a magnetic field are deflected to different extents according to their masses and are thus separated according to these masses