Mass Spectroscopy

Question 1

What are the two possible first steps of ionisation

Answer 1

Electron impact or electro spray

Question 2

How is electron spray carried out?

Answer 2

Vaporise the sample
Fire electrons at it
Electrons knock an electron off

Question 3

How is electron spray carried out?

Answer 3

Sample dissolved in solvent
Injected through a hypodermic needle to give a mist
Picks up a H+ from solvent

Question 4

How is acceleration carried out?

Answer 4

Charged plates repel or attract the ions to accelerate them
Every ion is accelerated until they have equal kinetic energy Ek=1/2mv^2
Therefore lighter ions and more charged ions achieve a higher speed

Question 5

How is ion drift calculated?

Answer 5

Distance = speed x time

Question 6

How does detection happen?

Answer 6

Positive ion gains an electron when it hits negatively charged plate
Creates an electric current
Size of the current gives a measure of the number of ions (abundance)

Question 7

How is electron spray and electron impact analysed after detection

Answer 7

Electron impact - fragmentation common, penultimate peak is Mr, last peak could be carbon 13

Electron spray - penultimate peak is Mr because last peak has the H+ attached

Question 8

On the analysis graph what goes on either axis?

Answer 8

X axis - m/z (mass to charge ratio)

Y axis - Mr or abundance

Question 9

How can you compare two different isotopes from mass spectrometry?

Answer 9

As kinetic energy is the same then a simultaneous equation can be created with E=1/2mv^2
And v=d/t