Mass Spec

Question 1

What are the three ways ions can be formed?

Answer 1

Electron ionisation
Chemical ionisation
Electrospray ionisation

Question 2

What is electron ionisation?

Answer 2

High energy electrons are collided with molecules and strip out an electron

Question 3

What conditions does electron ionisation occur in?

Answer 3

70eV

Question 4

How is fragmentation caused?

Answer 4

The excess energy imparted to species causes fragmentation

Question 5

What is fragmentation?

Answer 5

The ion falls apart but it is reproducible

Question 6

Why is fragmentation important?

Answer 6

As long as you have the right conditions, it will be reproducible

Question 7

What is chemical ionisation?

Answer 7

Sample molecules collide with preionised gas and are ionised by mechanisms such as proton transfer

Question 8

What is the role of CH5 + in chemical ionisation?

Answer 8

Proton transfer agent

Question 9

What is easiest to remove when you are ionising?

Answer 9

A lone pair

Question 10

What accelerates the ions?

Answer 10

An electric field

Question 11

What is the purpose of the mass analyser?

Answer 11

Ions are separated according to their mass-to-charge ratio

Question 12

Molecules with what lifetime value reach detector without breaking?

Answer 12

10 -5 seconds

Question 13

What is the nitrogen rule?

Answer 13

If a compound has an even number of nitrogen atoms, the molecular ion will appear at an even mass value

Question 14

What is Stevenson’s Rule?

Answer 14

The most probably fragmentation is the one that leaves the positive charge on the fragment with the lowest ionisation energy

Question 15

What type of ions are favoured?

Answer 15

Most stable

Question 16

Where is ionisation most likely to take place?

Answer 16

An electron is more likely to be lost from the highest potential energy molecular orbital as it is a loosely bound electron

Question 17

Which orbitals are the easiest to remove electrons from?

Answer 17

Non-bonding orbital is easier than pi orbital which is easier than sigma orbital

Question 18

What is the molecular ion of a primary or secondary alcohol like?

Answer 18

Usually very low

Question 19

What is the molecular ion like in a tertiary alcohol?

Answer 19

Often absent

Question 20

Do alcohols fragment?

Answer 20

Yes very easily