ToF Mass Spectrometry

Question 1

1. What occurs in electron impact and why is it used?

Answer 1

Used for elements and low Mr compounds
High energy electrons are fired at the sample from an electron gun, knocking off an electron from each atom/molecule (+1 ion formed)

Question 2

1. What occurs in Electrospray ionisation and why is it used?

Answer 2

Used for high Mr compounds
Sample dissolved in volatile solvent
Injected through fine hypodermic needle as a fine spray into vacuum in ionisation chamber
High voltage applied to end of needle, needle positively charged
Particles gain a proton and become ions
Solvent evaporates leaving +1 ions

Question 3

2. What is the second step of ToF?

Answer 3

ions are accelerated using an electric field so all ions have same kinetic energy

Question 4

3. What is the third step of ToF?

Answer 4

Ions enter and travel along flight tube, which has negatively charged detector plate at the end (ions attracted to plate)
lighter ions travel faster and reach plate first

Question 5

4. What is the fourth step of ToF?

Answer 5

Detection
Current produced when ion hits plate
More ions that hit, higher the current