Time of flight mass spectrometry

Question 1

Outline the 4 stages of time of flight mass spectrometry in 4 bullet points.

Answer 1

1. Electron impact / Electrospray ionisation
2. Ion acceleration
3. Ion drift
4. Ion detection

Question 2

What is electron impact ionisation?

Answer 2

An electron is fired from an electron gun and knocks off an electron from the sample to form a positive ion.

Question 3

What is electrospray ionisation?

Answer 3

The sample is dissolved in a volatile solvent and forced through a fine hypodermic needle. The tip of the needle is attached to a high voltage current which causes each molecule to gain a proton, forming a positive ion. The solvent then evaporates away.

Question 4

What is ion acceleration?

Answer 4

The ions are passed through an electric field and all gain the same amount of kinetic energy. As Ke = 1/2mv^2 particles with greater mass have less velocity so a greater time of flight.

Question 5

What is ion drift?

Answer 5

The positive ions enter a region with no electric field and drift towards an ion detector at the same velocity they left the electric field with. The particles with lower m/z ratios drift at faster speeds.

Question 6

What is ion detection?

Answer 6

The positive ions hit the detector plate and each gain an electron, causing a current to flow. This current is proportional to the abundance of each isotope. A computer analyses the flight times and plots a graph of relative abundance over mass to charge ratio (m/z).

Question 7

science is cool

Answer 7

:)