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Mass Spectrometry
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Helps to identify compounds
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For most m/z will be the same as molecular mass
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founds Mr to decimal places – identifying compounds with
similar Mr
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Sample placed in strong magnetic field and exposed to a range of different frequencies
of radio waves
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Amount of energy absorbed depends on environment
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About positions of atoms and how many atoms of that
type molecule contains
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Most common solvent is CDCl3
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The differences in
absorption are measured relative to it
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Is standard because it has absorption peak
at lower frequency than most substances
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Chemical shift- the difference in the radio frequency absorbed by

the nuclei in the molecule being analysed and that absorbed by the
same nuclei in TMS
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Small
amount of TMS may be added to make reference peak on the
spectrum
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Peaks match up with chemical shift given in data booklet
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One peak represents one hydrogen environment
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The peak is split if there are hydrogen atoms on adjacent C
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Effect is
called spin-spin coupling
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They always split into one more than the no of H
on the neighbouring C atoms
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Integration traces - relative area under each peak
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This can be used to work out structures of compounds
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Chromatography:
Used to separate molecules/ substances in a mixture
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Rf = distance travelled by sample/distance travelled by solvent
Made of mobile phase – where molecules can move – gas or liquid
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Distance moved depends on: solubility in mobile phase,
retention/adsorption to the stationary phase
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Stationary phase- molecules can’t move
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Gas Chromatography:
Column contains stationary phase
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Carrier gas is an insert gas (Hydrogen) which
is the mobile phase (He, N) to push a sample through the column
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Components dissolve in the liquid or adsorb onto the solid, evaporate back into gas and then
redissolve as they travel further
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High-Performance Liquid Chromatography (HPLC)
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Done under high pressure
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Often silica bonded with
different hydrocarbons
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– methanol or water
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Separated due to different parts being attracted by different amounts to the solid – take
different times to travel through the column
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It’s absorbed and UV detector measures
how much was absorbed
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Shows the retention
times of components of the mixture
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Used to identify the compound
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Different types of techniques can be combined to identify compounds
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