The Mass Spectrometer Flashcards
How many steps occur in a mass spectrometer?
Five
List the five steps that occur in a mass spectrometer.
Vaporisation
Ionisation
Acceleration
Separation in a magnetic field
Detection
Write a note on vaporisation.
4
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
What state must the sample be in before being studied?
Liquid or gas
Why is it okay for a liquid sample to be used?
Because the liquid quickly turns to gas inside the instrument as it is a good vacuum
How much of the sample is needed?
A small amount is needed
How is the sample placed in the spectrometer?
It must be injected into the instrument at the sample inlet
What must be done to any solid samples?
it may need to be heated in a special attachment in order to vaporise it
Write a note on the ionisation stage.
5
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
What is the purpose of the ionisation stage?
The purpose of this part of the apparatus is to turn the atoms or molecules into ions
What instrument is used to turn the atoms/molecules into ions?
An ‘electron gun’
What is an electron gun?
A heated filament that gives off electrons
What is the role of the electron gun?
It fires high-energy electrons at the atoms or molecules of the sample gas
What happens when electrons are fired at the atoms/molecules?
Electrons are knocked off these particles of the sample gas and positive ions are produced
Write a note on the acceleration stage.
3
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
What do the positive ions pass between?
A series of negatively charged plates in the accelerator
What is the role of the 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
What is formed from the acceleration stage?
A fine beam of ions
Why is a vacuum necessary inside the instrument?
A good vacuum is needed so that the positive ions can travel through it without colliding with any air molecules
Where does the fine beam of ions pass into?
The analyser unit
Write a note on the Separation stage.
6
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
What are the positive ions made do in the analyser unit?
The positive ions are made to move in curved paths using a magnetic field produced by a powerful electromagnet
What makes the positive ions move in curved paths in the analyser unit?
A magnetic field produced by a powerful electromagnet
What produces the magnetic field?
A powerful electromagnet
Which are easier to deflect the lighter or heavier particles?
The lighter particles are easier to deflect
What happens to the lighter particles?
They are pushed further off course than the heavier ions
The lighter particles are pushed further off course than the heavier ions, what does this result in?
This results in the single beam of positive ions being split into a number of beams
The single beam of positive ions is split into a number of beams, what does this mean for the ions?
This means the ions have been separated according to their masses
Define the principle of mass spectrometry.
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
