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.
Rf values for TLC
Distance travelled by component/ distance travelled by solvent.
- always less than 1
Retention times for GC
The time taken for a component to pass from the injector to the detector.
- Different retention times - number of components
- Relative peak areas- the proportions of components in a mixture
retenttion time relies on
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.
Limitations of GC
- Similar retention times
- No retention time reference for unknown compounds
- Only substances that can be made volatile.
- 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.
- environmental analysis
- airport security
- space probes
- interaction of materials
- with the low-energy radiowave region
- of the electromagnetic spectrum.
CNMR and HNMR
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
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.
- 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!
- The heaviest ion, the original molecule.
- SOMETIMES: there is no m/z peak as it is so energetically unstable it breaks down.
- The most abundant fragment
Comparing two molecules
- key peaks (dont forget C-O)
- differences may be found in fingerprint region
- M/Z peak- same or different?
- key fragments