Mass Spectrometry

Question 1

Mass spectrometry

Answer 1

An instrument used to determine the relative atomic masses

Works by forming ions and separating them according to the ratio of their charge:mass

Question 2

Stages of Mass Spectrometry

Answer 2

Ionisation
       Electro spray
       Electron Impact
Acceleration 
Deflection
Detection & Measurement

Question 3

Ionisation:

Electron Impact

Answer 3

Electron Gun fires high energy electrons at the sample

• > collisions occur
• > electron knocked off sample atom
• > produces a positive ion of the atom

Question 4

Ionisation:

Electro spray

Answer 4

Sample is dissolved in volatile solvent and ejected through a fine needle to produce aerosol
Tip of the needle is attached to the positive terminal of a high voltage power supply
Causes the particles to become ionised by gaining a proton to form XH+ ions

Question 5

Acceleration

Answer 5

In this stage, the positive ions are attracted to the negatively charged plate and accelerate towards it.
Lighter and more charged ions achieve a higher speed

Question 6

Deflection

Answer 6

High speed beam of positive ions are deflected by a strong, variable magnetic field
Field strength is steadily increased causing ions of Increasing m/z value to be deflected

Question 7

Which ions are great for Deflection?

Answer 7

Lighter ions

More charged ions

Question 8

Detection

Answer 8

When ions with same charge arrive at the detector, the lighter ions come first as they have higher velocities
The flight times are recorded
Positive ions pick up an electron causing a current to flow

Question 9

Measurement

Answer 9

Output from detector generates a mass spectrum showing abundance vs m/z ratio for each isotope

Question 10

What is a mass spectrometer kept under?

Answer 10

It is kept under a high vacuum -> prevents the ions from colliding with particles from the air