Time of Flight Mass Spectrometry

Question 1

What is Stage 1 and what does it achieve?

Answer 1

1) Ionisation- Particles in sample are electrosprayed (dissolved in volatile solvent) to give them a +1 charge

Question 2

What is Stage 2 and what does it achieve?

Answer 2

2) Acceleration- Negatively charge plates attract ions so they all go into the ion drift with the same kinetic energy

Question 3

What is Stage 3 and what does it achieve?

Answer 3

3) Ion Drift- Ions travel through with a constant KE due to the lack of magnetic field, which means the ions are separated according to mass - light vs heavy, heavier=slower.

Question 4

What is Stage 4 and what does it achieve?

Answer 4

4) Ion Detection- Detector at the end is a negatively charged plate, where the ions pick up an electron and drop off as atoms. This causes a small flow each time an electron is picked up, and the time taken to cross the ion drift is registered. More ions=faster the current.

Question 5

What is Stage 5 and what does it achieve?

Answer 5

5) Data Analysis- Calculates the mass of ions and relative abundance of ions on a mass spectrum. They all have the same KE however heavier ions take more time as they have a heavier mass=less velocity.

Question 6

How is this equation used to find out the mass:

KE= 1/2 x Mass x Velocity2

Answer 6

Computer start timing ions through the ion drift until they hit the detector. The KE is already known (from how long negatively charged plate was in and how much) and so is the velocity.

Question 7

What tells us the relative abundance of an ion?

Answer 7

The current; higher current at ion detector means higher relative abundance.

Question 8

Why is this done in a vacuum?

Answer 8

It allows ions to travel through the ion drift with the same KE as they were through acceleration as the vacuum means no obstacles/forces to stop it or change its KE

Question 9

What is this method used for?

Answer 9

Finds the mass of separate ions