Mass Spectrometry

Question 1

How are compounds accelerated towards the detector?

Answer 1

the compound enters the mass spectrometer in solution

it is ionised and the positive ions are accelerated as a beam of ionised molecules

these then fly through the detector

Question 2

How is the molecular mass identified?

Answer 2

times of flight are measured

these depend on the mass to charge ration m/z of the ion

Question 3

How is the output presented?

Question 4

How does fragmentation occur?

Answer 4

many of the ions will then break up because some of their bonds break as they are ionised, so there are other ions of smaller molecular masses

each of these fragment ion produces a line in the mass spectrum

Question 5

How are fragments useful?

Answer 5

can provide information that will help to deduce the structure of the compound

they also act as a ‘fingerprint’ to help identify it

Question 6

How does Gas Chromatography Mass Spectrometry done?

Answer 6

seperates mixtures which uses a stream of gas to carry a mixture of vapours through a tube packed with a powdered solid

the different components of the mixture emerge from the column at different times

their amounts are measured and they are fed straight into a mass spectrometer which produced a mass spectrum of each and allows them to be identified

Question 7

What is high resolution mass spectrometry?

Answer 7

measure masses to 3 or 4 decimal places

allows us to work out the molecular formula of the parent ion

it makes use of the fact that isotopes of atoms don’t have exactly whole number atomic masses, except carbon-12

allows molecules that have the same atomic mass to 1.dp to be identified