Topic 1 - Atomic Structure

Question 1

What does a mass spectrometer do?

Answer 1

Gives accurate information about relative atomic mass and can be used to identify elements

Question 2

What conditions does TOF have to be done under?

Answer 2

A high vacuum so new ions don’t collide with molecules in the air.

Question 3

What is electrospray ionisation?

Answer 3

The sample is dissolved in a volatile and polar solvent.

Then injected through a fine hollow needle connected to a terminal of a high voltage supply which leads the sample (X) to gain a proton and form a positive ion (XH+)

The solvent evaporates into the vacuum and the ions do not.

Question 4

When do you use electrospray ionisation?

Answer 4

Used for large organic molecules so fragmentation doesn’t occur.

Question 5

What is electron impact?

Answer 5

Sample is vapourised and injected at low pressure

The electron gun fires high energy electrons at the sample and knocks off an outer electron from the sample causing an ion to be formed.

Question 6

When is electron impact used for?

Answer 6

Used for elements and substances with low MR.

Not used for larger molecules due to fragmentation.

Question 7

What happens in acceleration?

Answer 7

The positive ions formed from ionisation are accelerated to a constant KE by a negatively charged plate.

Question 8

What happens in the flight tube?

Answer 8

The ions spread out and hit the detector at different times as lighter ions reach the detector first as they travel fastest since their velocity is dependent on their mass.

Question 9

What happens in the detection stage of TOF?

Answer 9

There is a negatively charged detection plate which the positive ions reach and gain an electron which causes a movement of electron which produces a current.

The amount of current produced is proportional to the abundance of the species

Question 10

What are on the axis of the TOF Mass Spectrometer?

Answer 10

Relative abundance on y

Mass/Charge ration on x