1.4- The Mass Spectrometer

?
  • Created by: Heather
  • Created on: 04-10-14 15:02
What does a mass spectrometer measure?
The Relative Atomic masses of an atom
1 of 18
What scale are the atomic masses measured?
The scale on which the mass of the atom of Carbon-12 is defined as exactly 12,
2 of 18
Why is carbon-12 used as the scale?
It is the only isotope that has an exact atomic mass that is a whole number
3 of 18
Give an example of a use of a mass spectrometer?
They are used by forensic scientists to help identify substances like illegal dugs
4 of 18
What conditions is the spectroemeter kept under and why?
In a high vacuum so the ions dont collide with air molecules which might stop them reaching the detector,
5 of 18
What state is the sample put into the mass spectrometer?
In a gaseous state and if a solid, it is vapourised first by heating,
6 of 18
What is an outline of what happens in a mass spectrometer?
Atoms are converted to ions, accelerated and deflected accordin to their masses adn their charges and arrive at a detector.
7 of 18
What is the first stage of the mass sepctrometer?
Ionisation- A beam of electrons from an 'electron gun' knocks out electrons from atoms or molecules of the sample so they form positive ions. Majority of atoms lose one electron but 5% lose two electrons
8 of 18
What is the second stage of the mass spectrometer?
Acceleration- These positive ions are attracted towards the negatively charged plates and are accelerated to a high speed. The speed they reach depends on their mass- the lighter the ions the faster they go
9 of 18
What is the third stage of the mass spectrometer?
Deflection- Beam of ions moves into a magnetic field at right angles to its direction of travel. The magnetic field deflects the beam of ion into an arc of a circle.
10 of 18
What does the deflection of the ion depend on?
It depends on the ratio of its mass to charge (m/z). Heavier atoms are delfected less than lighter ones and 2+ ions are deflected twice as much as 1+ ions. it also depend on the magnetic field strength- the strogner the field, the greater deflection
11 of 18
What is the fourth stage of the mass spectrometer?
Detection- The magnetic filed is graudually increased so that ions of increasing mass enter the detector one after the other. Ions stirke the detector, accept electrons, lose their charge and create a current,
12 of 18
What is the current produced proportional to?
Current is proportional to the abundance of each ion,
13 of 18
What do the cimputer do when the ion hits the detector? What is produced?
From the strength of the magentic fild at which a partiuclar ion hits the detector, a computer works out the value of the mass to charge ratio, m/z, of the original ion and a mass spectrum is produced,
14 of 18
What is a mass spectrum?
A graph of relative abundance of ions against the mass to charge ration (m/z)
15 of 18
So what are the four key stages in a mass spectrometer?
Ionisation, acceleration, deflection and detection
16 of 18
How resolute is a mass spectrometer?
It can measure to 5 decimal places which is called High Resolution mass spectrometry and low resolution mass spectrometry is to the nearest whole number,
17 of 18
How are mass spectrometers used in space?
In space probes like the Viking Martian Lander which are used to identify the elements in rock samples
18 of 18

Other cards in this set

Card 2

Front

What scale are the atomic masses measured?

Back

The scale on which the mass of the atom of Carbon-12 is defined as exactly 12,

Card 3

Front

Why is carbon-12 used as the scale?

Back

Preview of the front of card 3

Card 4

Front

Give an example of a use of a mass spectrometer?

Back

Preview of the front of card 4

Card 5

Front

What conditions is the spectroemeter kept under and why?

Back

Preview of the front of card 5
View more cards

Comments

No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all Spectroscopy resources »