mass spectrometry Flashcards
What is relative atomic mass?
The average mass of an atom of an element on a scale where an atom of carbon 12 = 12.
What is relative isotopic mass?
The mass of an atom of an isotope of an element on a scale where an atom of carbon 12 = 12.
What is relative molecular mass?
The average mass of a molecule on a scale where an atom of carbon 12 = 12.
What are the two types of ionisation?
Electrospray and Electron Impact
How does electrospray ionisation work?
The sample is dissolved and pushed through a small nozzle at high pressure. A high voltage is applied to it, causing each particle to gain a H+ ion, so the sample is turned into a gas of positive ions.
How does electron impact ionisation work?
High energy electrons are fired at the vaporised sample, which knocks one electron off of each particle, turning them into 1+ ions.
What are the four stages of TOF mass spectrometry?
- Ionisation
- Acceleration
- Ion drift
- Detection
What happens in the ionisation stage?
The particles are ionised
What happens in the acceleration stage?
The positively charged ions are accelerated by an electric field so that they all have the same kinetic energy.
What happens in the ion drift stage?
The ions enter an area with no electric field, so they drift through it. Lighter ions drift heavier than fast ions.
What happens in the detection stage?
Because lighter ions travel at higher speeds than heavier ones, they reach the detector in less time. The detector detects charged particles and a mass spectrum is produced.
What is a mass spectrum?
mass/charge agaist abundance
