3.1.1.2 Mass Number And Isotopes

Question 1

What is isotopic abundance?

Answer 1

It determines how much of each isotope there is

Question 2

What are the stages of a time of flight mass spectrometer?

Answer 2

Vacuum: apparatus kept in a vacuum, prevents ions colliding with air
Ionisation: sample dissolved in volatile substance, droplets lose electrons to become ions
Acceleration: ions are drawn to negative plate, lighter ions move faster
Ion drift: ions pass along flight tube
Detection: lighter ions reach detector first, positive ions pick up an electron which causes a current to flow
Data analysis: signal creates a mass spectrum

Question 3

How do you work out molecular peaks?

Answer 3

Write down every possible combination of atoms

Question 4

What is the difference between high and low mass spectrometry?

Answer 4

High: 5 decimal places
Low: 1 decimal place

Question 5

How can mass spectrometry be used to find the relative molecular mass of a molecule?

Answer 5

The peak with the largest m/z value is the molecular ion peak
It’s m/z value is equal to the relative molecular mass of the molecule

Question 6

How is abundance measured in a TOF mass spectrometer?

Answer 6

Ions are detected by gaining electrons

The abundance is determined by the size of the current