Gas Chromatography

Made using OCR chemistry textbook. Pages 80- 83. Gent and Richie.

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  • Created by: M
  • Created on: 19-12-12 18:34
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  • Gas Chromatography
    • Technique used to separate volatile components in a mixture.
      • Useful as many organic comp. have low boiling points
      • Phases
        • SP= thin layer of solid/liquid coated on inside of capillary tube (the inert support)
          • Tubing= chromatography column.
          • Liquid SP often long-chain alkene with high bp.
          • Solid SP include silicon polymers
        • MP= carrier gas which moves through column
          • Usually inert/ unreactive gas i.e. He/N
    • Producing the chromatogram
      • Mixture injected into GC and vapourised
        • Mobile carrier gas flushes mixture through column
          • Components slow down as they interact with SP. Greater solubility/ adsorption= slow more
            • Result= components leave column at different times and are detected. Computer displays gas chromatogram
      • Area under peaks proportional to amount of compound in sample
    • Retention time
      • Time for component to pass from column inlet to detector
      • Diff compound= diff RT. Compare with known RTs to identify
    • Limitations
      • 1000s of chemicals= same RT, peak shape and detector response
      • Some substances may 'hide' beneath one with a high conc. and same RT
      • Unknown compounds= no reference RT
    • GC-MS
      • Components separated by GC. Then analysed by MS= unique which allows +ve identification of each component in original mixture
      • Uses
        • Airport security  Forensics, Space probes, Environmental analysis


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