Mass spectrometry

Question 1

What is a mass spectrometer?

Answer 1

A machine that can be used to analyse elements or compounds

Question 2

What information does a mass spectrometer give you?

Answer 2

Relative atomic mass, relative molecular mass and the relative abundance of isotopes?

Question 3

What are the 4 steps involved in the time of flight mass spectrometry?

Answer 3

ionisation
acceleration
ion drift
detection

Question 4

What are the two types of ionisation?

Answer 4

Electrospray ionisation

Electron impact

Question 5

What are the stages in electrospray ionisation?

Answer 5

A sample is dissolved in a solvent and injected as a mist

The particles are ionised by gaining a proton from the solvent as they leave the needle, producing XH+ ions

Question 6

What is the formula for electrospray ionisation?

Answer 6

X(g) + H+ -> XH+(g)

Question 7

What are the stages in electron impact?

Answer 7

The sample is vapourised and high energy electrons are fired at it
The electrons come from a filament gun
This causes each particle in the sample to lose an electron

Question 8

What are the formulas for electron impact ionisation?

Answer 8

X(g) + e- -> X+(g) + 2e-

X(g) -> X+(g) + e-

Question 9

Why do samples have to be ionised?

Answer 9

so the ions are attracted to the negative plate and they can be accelerated as they are positive

Question 10

What is the second stage in time of flight?

Answer 10

Acceleration

Question 11

What is acceleration?

Answer 11

The positive ions in the sample are accelerated by an electric field

Question 12

What does the electric field give to all of the ions during acceleration?

Answer 12

the same amount of kinetic energy

Question 13

What type of ions have the greater acceleration?

Answer 13

The ions with the lower mass to charge ratio (lighter)

Question 14

What is the third stage in time of flight mass spectrometry?

Answer 14

Ion drift

Question 15

What do the ions leave the electric field with?

Answer 15

A constant speed and constant kinetic energy

Question 16

Which ions will drift at higher speeds through the region with no electric field (ion drift)? Why?

Answer 16

Ions with the lower mass to charge ratio

They drift at the same speed they left the electric field

Question 17

What is the last stage in time of flight?

Answer 17

Detection

Question 18

Which ions reach the detection plate first?

Answer 18

The ions with the lower mass to charge ratio (lighter)

Question 19

What happens at the detector?

Answer 19

The current that is created when ions hit it is detected

It is recorded how long they took to pass through the spectrometer

Question 20

What is the recording at the detector plate used to calculate?

Answer 20

relative abundance

Question 21

What is the definition of relative atomic mass?

Answer 21

The average mass of an atom of an element on a scale where an atom of carbon-12 is exactly 12

Question 22

How do you calculate relative atomic mass with percentages?

Answer 22

1) multiply the percentage relative isotopic abundance and the relative isotopic mass together
2) add up all of the totals
3) divide by 100

Question 23

How do you calculate the relative atomic mass when it is not given as a percentage?

Answer 23

1) multiply the relative isotopic abundance and the relative isotopic mass together for each isotope
2) add up all of the totals
3) divide by the total relative abundance