• Created by: ava.scott
  • Created on: 21-09-14 22:46



An analytical technique that separates components in a mixture between a mobile phase and a stationary phase.

  • The mobile phase may be a liquid or a gas.
  • The stationary pahse may be a solid (TLC) or a liquid or solid on a solid support (GC).

A solid stationary phase separates by ADSORPTION.

A liquid stationary phase separates by RELATIVE SOLUBILITY.

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Rf values for TLC

Distance travelled by component/ distance travelled by solvent.

  • always less than 1
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Retention times for GC

The time taken for a component to pass from the injector to the detector.

Tells us:

  • Different retention times - number of components
  • Relative peak areas- the proportions of components in a mixture
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retenttion time relies on

boiling point

the higher the boiling point, the longer the retention time


high solubility means less time carried by the mobile phase, so a longer retention time.

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Limitations of GC

  • Similar retention times
  • No retention time reference for unknown compounds
  • Only substances that can be made volatile.
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  • provides a far more powerful analytical tool than chromatography alone
  • Gas chromatography separates the substances by relative solubility.
  • Mass spectra can be compared to a database for a positive identification of a component.


  • Forensics
  • environmental analysis
  • airport security
  • space probes


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NMR involves


  • interaction of materials
  • with the low-energy radiowave region
  • of the electromagnetic spectrum.
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CNMR analyse to:

  • different types of carbon present from shift values
  • possible structures

HNMR analyse to:

  • different types of proton environments present from shift value
  • relative numbers of each proton available from relative peak areas/integration trace
  • Number of non-equivalent hydrogens adjacent using spin-spin splitting patterns
  • Possible structures!!
  • D2O allows OH peaks to be identified
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TMS and Deuteration and MRI


  • A standard for chemical shift measurements


  • solvents (C D Cl3) as they do not create peaks in the spectrum.
  • Proton exchange using D2 O to replace O-H and N-H groups


  • Magnetic Resonance imaging (MRI)
  • to obtain diagnostic information about internal structures.
  • in body scanners.
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Combined techniques


  • to identify presence of functional groups


  • identify parts of structures
  • using molecular ion peaks and fragmentation
  • M/Z may not be there as is too unstable!
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Mass spectrometry

Molecular ion:

  • The heaviest ion, the original molecule.
  • SOMETIMES: there is no m/z peak as it is so energetically unstable it breaks down.

Base peak:

  • The most abundant fragment
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Comparing two molecules

Infra-red spectroscopy

  • key peaks (dont forget C-O)
  • differences may be found in fingerprint region

Mass spectrum

  • M/Z peak- same or different?
  • key fragments
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