Mass Spectroscopy Theory Flashcards
(14 cards)
For the first stage, what are the 2 parts that can be done in order to form 1+ ions?
Electron impact
Electro spray ionisation
Describe the steps of electron impact.
- An electron is knocked off each particle by the high energy electrons to form 1+ ions.
- Positive ions are celerated by a negative electric plate.
Describe the steps of electro spray ionisation.
- Put sample in volatile solvent.
- Hypodermic needle attached to positive terminal of high voltage power supply.
- Particles gain a proton as they leave the needle.
- Positive ions are accelerated by a negative electric plate.
What is electron impact used for?
Used for elements and Low Mr compounds!
What is electro spray ionisation used for?
Used for High Mr compounds
How are ions formed in a time of flight (TOF) mass spectrome?
-
electron impact: High energy electrons are fired/bombarded - lose an electron.
OR - electro spray ionisation: a sample is dissolved in a volatile solvent, through a high voltage hypodermic needle - sample gains a H+ ion.
How is acceleration used in TOF m/z spectrome?
The ions are accelerated using an electric field so that all the ions have the same kinetic energy.
What is the equation for Ke (kinetic energy)?
Ke= 1/2 x m x v^2
What is the equation for the Velocity of a particle?
v= square root( 2Ke/m)
What particle will have a higher velocity? A particle with lower m/s, or the particle with the higher m/z?
The particle with the lower mass (m/z) because it takes less energy to move and it’s lighter lol
Talking about the Flight tube, what is an ion drift?
And ion drift is when the ions enter the flight tube, the ions with different masses have a different time of flight!
Talking about detection, what is a detector?
A detector is a *negatively charged plate- a Current is generated when ions hit the plate.
How to make the current bigger?
When more ions hit the detector, a bigger current is generated!
How can the mass of the ions hitting the detector be calculated?
They can be calculated from the time of flight, also, the mass spectrum shows the number of particles (abundances) of each mass that hits the detector!!
