Mass Spectrometer

Question 1

What happens in vacuum?

Answer 1

Whole appartus kept under high vacuum to prevent ions produced colliding with molecules in the air

Question 2

What happens in ionisation?

Answer 2

Sample investigated dissolved in solvent and forced through fine hollow needle connected to positive terminal of high voltage supply. Produces positively charged droplets which have lost electrons to positive charge of supply. Solvent evaporates from droplets into vacuum and droplets get smaller and smaller until they may contain no more than single positively charged ions

Question 3

Acceleration

Answer 3

Positive ions attracted towards negatively charged plate and accelerate towards it. Lighter ions and more highly charged ions achieve higher speed

Question 4

Ion drift

Answer 4

Ions pass through a hole to negatively charged plate forming a bean and travel along a tube (flight tube) to detector

Question 5

Detection

Answer 5

Ions with same charge arrive at detector lighter ones are first as they travel with higher velocities so arrive first. Flight times recorded. Positive ions pick up electron from detector causing current to flow

Question 6

Data analysis

Answer 6

Signal from detector passed to computer which generated mass spectrum.

Question 7

Stages of mass spectrometer?

Answer 7

Vacuum 
Ionisation 
Acceleration 
Ion drift 
Detection 
Data analysis