Mass spectrometry Flashcards
4 steps
Ionisation
Acceleration
Deflection
Detection
Molecular ion peak
When 1 electron is removed off the molecule in the mass spectra so has the highest M/Z charge ratio
What is the m/z of the molecular ion peak equal to?
The Mr of the compound
What causes an M+1 peak?
Traces of carbon 13 in the compound which increases the molar mass of the compound
When reading values of halogens, what’s important to remember?
There are isotopes such as Br-79 and Br-81 which can increase/decrease the m/z value by 1
What happens if 2 electrons are removed from the sample?
The mass/ charge ratio will half
Equation showing ionisation of molecule
Molecule +e- ——> [molecular ion]+ + 2e-
Fragmentation
Bombardment of electrons causes compound to fragment into an ion fragment and radical
What happens to radicals?
They are lost in the mass spectrum
How to identify a compound’s molecular structure from mass spectrum?
Identify all the peaks values based on Mr value = m/z ratio
Piece it together
Ionisation
When a sample is vaporised and a high voltage is spread over the sample
So electron is removed to produce a sample of gaseous 1+ ions
Acceleration
Positively charged ions are accelerated towards negatively charged plate
Ion drift
The ions are deflected in a magnetic field: into a curved path
The radius of curved path is dependent on the m/z ratio of the ion
Detection
They hit a negatively charged plate and gain an electron
Which products a charge
The flow of charge is dependent on abundance of each ion = produces a spectra
How does fragmentation occur?
Excess energy from ionisation causes bonds to vibrate more
Which causes bonds to weaken
And the molecular ion splits = fragmentation
