Mass Spectrometry

Question 1

What is the symbol to represent mass number?

Answer 1

A

Question 2

What is the symbol to represent atomic (proton) number?

Answer 2

Z

Question 3

What is mass spectrometry used for?

Answer 3

• Finds the abundance and mass of each isotope in an element allowing us to determine it’s relative atomic mass.
• Find the relative molecular mass of substances made of molecules

Question 4

The order of (TOF) mass spectrometer?

Answer 4

Ionisation->Acceleration->Flight Tube->Detection

Question 5

What is the two different types of ionisation?

Answer 5

Electron impact and Electrospray ionisation

Question 6

Why is the whole apparatus kept under a Vacuum?

Answer 6

-Mass spectrometer kept under a vacuum to prevent the ions that are produced from colliding with molecules from the air.

Question 7

What is the process of Electron impact(ionisation)?

Answer 7

1) Sample being analysed is vaporised then goes into mass spec.
2) High energy electrons are fired at the sample.
3) Electrons from an electron gun=hot wire filament with a current running through it that emits high energy electrons.
4) Electrons knocks off 1 electron from each particle=form of 1+ ion.

Question 8

What is the process of electrospray ionisation?

Answer 8

1) sample dissolved in a volatile solvent(example water)
2) sample forced through a fine hypodermic needle to give a fine mist.
3) Tip of needle attached to the positive terminal of a high-voltage power supply.
4) Produces tiny positively charged droplets that have gained a proton from the solvent.
5) Solvent evaporates from the droplets into the vacuum =droplets get smaller until they contain a single positively charged ion.

Question 9

Describe the acceleration process?

Answer 9

• positive ions attracted to negatively charged plate.
• positive ions accelerated using an electric field so that they have the same kinetic energy
• lighter ions and more highly charged=higher speed(velocity)

Question 10

Describe the Detection process?

Answer 10

• positive ions hit a negatively charged plate. When they hit the detector plate, positive ions discharged~gains electrons from plate
• This generates a movement of electrons and hence an electric current that is measured
• The size of the current= A measure of the number of ions hitting the plate

Question 11

Describe the ion drift/ flight tube process

Answer 11

• positive ions pass through a hole in negatively charged plate, forming a beam and travel along a tube (flight tube), to a detector
• TOF of each particle depends on its velocity which depends on its mass

Question 12

Data analysis process:

Answer 12

The signal from the detector is passed to a computer which generates a mass spectrum