17.1 Mass Spectrometry

Question 1

What happens to an organic compound when it is placed in a mass spectrometer?

Answer 1

It loses an electron and forms a positive ion. Called a molecular ion.

Question 2

What does a mass spectrometer detect?

Answer 2

The mass-to-charge ratio (M/Z) ratio of the molecular ion, which gives the molecular mass of the compound.

Question 3

How do you find the molecular mass from a mass spectrum?

Answer 3

Find the M+ peak on the right hand side of the graph. It is the CLEAR peak.

Question 4

What is the small peak 1 after the M+ mass?

Answer 4

The small proportion of the molecules that will have a Carbon-13 atom instead of a carbon-12 atom.

Question 5

What is fragmentation?

Answer 5

When some molecular ions break down into smaller fragments during mass spectrometry

Question 6

What are other peaks in a
mass spectrum caused by?

Answer 6

Fragment ions, formed from the breakdown of the molecular ion.

Question 7

What should a simple fragmentation do? (what should it form?)

Answer 7

Break down a molecular ion into a radical and a positively charged fragment ion.

Question 8

Why is the mass spectrum of each compound unique? (including isomers)

Answer 8

Because molecules will all fragment in slightly different ways depending on their structures

Question 9

How does a mass spectrometer work?

Answer 9

1- Sample is placed in mass spectrometer
2- Sample is vaporised, then ionised to form positive ions
3- Ions are accelerated, heavier ions move more slowly, but all molecules have the same kinetic energy
4- Ions are detected on a mass spectrum as a mass-to-charge ratio (M/Z)