The Mass Spectrometer

Question 1

What is a mass spectrometer?

Answer 1

A machine used to analyse elements or compounds.

Question 2

What mass spectrometer do we need to know?

Answer 2

A time of flight (TOF) mass spectrometer.

Question 3

What can a mass spectrometer do?

Answer 3

It can give you information about
•The relative atomic mass of an element.
•The relative abundance of an element’s isotopes.
•Or the relative molecular mass of a molecule (if used to analyse a compound).

Question 4

What happens when a sample is squirted into a TOF mass spectrometer?

Answer 4

•Ionisation
Electrospray ionisation
Electron impact ionisation
•Acceleration
•Ion drift
•Detection

Question 5

What needs to happen to the sample before it enters the TOF mass spectrometer?

Answer 5

It needs to be ionised.

Question 6

What happens during electrospray ionisation in TOF mass spectrometry?

Answer 6

• The sample is dissolved in a volatile solvent.
• Then it is injected through a hypodermic needle at high pressure to give a fine mist.
• The tip of the needle is attached to the positive terminal of a high voltage power supply.
• The particles are ionised by gaining a proton from the solvent as they leave the needle producing XH+ ions.
• The solvent evaporates away while the XH+ ions are attracted towards a negative plate where they are accelerated.

Question 7

What sort of molecules use electrospray ionisation?

Answer 7

Ones with a high molecular mass such as proteins.

Question 8

What happens during electron impact ionisation in TOF mass spectrometry?

Answer 8

• The sample is vapourised.
• Then high energy electrons are fired at it through an electron gun, which is a hot wire filament with a current running through it which emits the electrons.
• This usually knocks off one electron from each particle, forming a 1+ molecular ion.
• The ions are then attracted towards a negative plate where they are accelerated.

Question 9

What sort of molecules use electron impact ionisation?

Answer 9

Elements and substances with a low formula mass.

Question 10

What happens during acceleration in TOF mass spectrometry?

Answer 10

• Positive ions are accelerated by an electric field.
• The electric field gives the same amount of kinetic energy to all ions.
• This causes the ions with a lower mass to charge ratio to experience a greater acceleration because they are lighter.

Question 11

What happens during ion drift in TOF mass spectrometry?

Answer 11

• The ions leave the electric field with a constant speed and constant kinetic energy.
• They enter a region with no electric field.
• This means the ions drift through the region at the same speed as they came into it.
• The ions with the lower mass to charge ratio drift at a higher speed.

Question 12

What happens during detection in TOF mass spectrometry?

Answer 12

• Because the ions with a lower mass to charge ratio travel at higher speeds through the drift region, they reach the detector in less time than the ions with a higher mass to charge ratio.
• The detector detects the current created when the ions hit it and it records how long they took to pass through the spectrometer.
• The detector is a charged plate, gain an electron to make it an atom.

Question 13

What is the data collected during mass spectrometry used to do?

Answer 13

To calculate the mass to charge values needed to produce a mass spectrum.

Question 14

how does a TOF mass spectrometer work?

Answer 14

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