Mass spectrometry

Created by

Hania Mojescik

Cards (17)

What are the four stages of mass spectrometry?
Ionisation, acceleration, ion drift and detection
What are the two types of ionisation?
Electrospray ionisation (ESI) and electron impact (EI)
Which type of ionisation is known as soft ionisation?
Electrospray ionisation (ESI)
Which type of ionisation is known as hard ionisation?
Electron impact (EI)
What is the equation for ESI?
M(g) + H^+ -> MH^+(g)
What is the equation for EI?
X(g) -> X^+(g) + e^-
What is the definition of electrospray ionisation?
The sample is dissolved in a polar solvent and pushed through a small nozzle at high pressure. A high voltage is applied, causing the molecule to gain a proton. The ionised particles are then separated from the solvent, leaving a gaseous sample of ions.
What is the definition of electron impact?
The sample is vapourised and then bombarded by high energy electrons fired from an electron gun. This causes the sample to lose its outermost electron.
What happens during the acceleration stage?
The positive ions are accelerated by an electric field to give a constant kinetic energy
What happens during the ion drift stage?
Ions leave the electric field at different speeds depending on their mass / charge ratio. The heavier the particle, the lower the speed and the greater time taken to reach the detector
What happens during the detection stage?
The detector is a negatively charged plate and when the positive ions hit it, they pick up an electron and create a current. The detector records the time taken to reach it and the current
What is current directly proportional to?
abundance
Why is the sample ionised?
So they are able to pick up electrons and create a current but also so they’re affected by the electric field
What is the kinetic energy equation?
KE = mass x 1/2 x velocity^2
How do you find the mass in time of flight?
Mass = mr / L (avogadros constant)
What is the velocity equation?
Velocity = distance / time
What does m/z ratio stand for?
Mass/charge ratio