1.1 Atomic Structure (Time Of Flight) Flashcards
What is an isotope?
Atoms with the same number of protons but a different number of neutrons
How is Ar calculated from percentage abundance of isotopes?
(Atomic mass x percentage) + (atomic mass x percentage) / 100 (or the total abundance)
What is the definition of relative atomic mass?
The average mass of an atom of that element compared to 1/12 of the mass of carbon 12
What is a mass spectrometer used for?
The mass and abundance of isotopes
What is the ionisation with electon bombardment step in TOF?
Step 1
An electron is knocked off of each particle by the high energy electrons being fired to form +1 ions.
For lower mass compounds
What is the equation for Electron Bombardment?
X (g) —> X+ + e-
What is electrospray ionisation?
Step 1 of TOF
Sample enters a volatile solvent which is then squirted by a nedle attached to a positive terminal
Removes a proton
For high Mr compounds
What is the formula for electrospray ionisation?
X (g) + H+ —-> XH+
What is the acceleration phase of TOF?
The now positive ions are attracted to a negatively charged plate giving them the same kinetic energy
What causes the speed to vary during Acceleration?
Mass of ion
What happens during ion drift?
Ions drift down the drift chamber
This is where time of flight is calculated
What is the equation for time of flight?
TOF= distance / velocity
TOF= distance / root 2KE/M
What happens during detection in TOF?
- Ions hit a negatively charged plate
- Electrons are gained by ions
- The more molecules hitting the plate at the same time the greater the abundance
How is mass charge ratio calculated?
- A spectrum is produced during TOF
X axis= m/z ratio
Y axis= percentage abundance
The molecular peak is the M/Z value for the molecule
What causes the smaller peaks around the main peak on a TOF spectrum?
- Isotopes
- Fragmentation
