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Gas Chromatography:
- GC is used widely in many analytical laboratories, including forensic police labs, synthetic chemical labs, and drug testing labs.
- GC uses a stationary phase to impede the movement of a mobile test substance.
- Different substances are attracted to the matrix by different amounts, and therefore journey along it at different speeds.
- In GC, the sample is injected into the machine, where it is vaporised. It is then washed over the matrix by an inert gas.
- Low molar mass gasses required:
- Hydrogen
- Helium
- Nitrogen
- Some substances will be more attracted to the matrix than others. These will take much longer to reach the detector.
- The detector measures the abundance of a substance at a given time, and this data is plotted on a graph.
- Most polar = one that travels slowest.
- MP under pressure passed through column containing SP
HPLC:
- High performance liquid chromatography is a development of column chromatography in which the eluent is pumped through the column at high pressure.
- This results in better and faster separation than can be achieved in standard column chromatography.
- MP- liquid (usually a mixture of Water/acetonitrile/methanol)
- MP under pressure passed through column containing SP (silica)
- Sample must be soluble in MP
- Suitable for high molecular weight samples.
- Samples must be soluble
Chromatograms:
- Retention time is a similar measure of the interaction between compounds and MP/SP.
Gas chromatography is not that useful for identifying substances (it is better as a separation technique). When used with Mass spectrometry, it becomes very effective.
Most important (chromatography method) is paper and TLC.
