TOF MASS SPECTROMETRY Flashcards
What can TOF mass spectrometer be used for ?
to find :
relative atomic mass
relative molecular mass
relative isotopic mass
Definition of relative atomic mass (Ar)
the average mass of an atom of an element when measured on scale on which the mass of an atom 12C
is exactly 12
Definition of relative isotopic mass
the mass of an atom of an isotope of an element measured on scale on which the mass of an atom of 12C is exactly 12
Definition of relative molecular mass (Mr)
The average mass of a molecule when measured on scale on which the mass of an atom of 12C is exactly 12
what are the Five stages in TOF mass spectrometer in order
- vaporisation
- ionisation
- acceleration
- ion drift
- detection
what is vaporisation
The sample is vaporised so it can travel through the TOF mass spectrometer
what is ionisation
The sample is pushed through a nozzle making a high pressure jet. A high voltage is passed through causing
the loss of an electron . a gaseous + charged sample is produced we call this electrospray ionisation
what is acceleration
The + ions are passed through an electrical field. Particles with lower m/z charge ratio will accelerate quicker
what is ion drift
Particles travel through with a constant speed and kinetic energy . They drift through and particles with lower m/z charge ratio travel faster
what is detection
Ions are detected as electrical current is made when particle hits the plate . particles with lower m/z charge reach the detector first as they travel faster
how to calculate relative atomic mass
multiply the isotope abundance and percentage and divide by 100
how to calculate relative atomic mass when its not a percentages
instead of dividing by 100 add up the relative abundance and then divide
Why do samples need to be positively charged in the mass spectrometer
so that they can be accelerated by the field
