Analysing Substances

  • Created by: Katie
  • Created on: 20-05-13 16:35
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  • Analysing Substances
    • Chromatography - Paper
      • E numbers - a number assigned to a food additive that has been approved for use in Europe. It is displayed on food packaging as it is used to preserve food.
      • It works due to some compounds in a mixtue dissolving easier than others in particular solvents.
        • Solubility determines how far they travel across the paper.
      • Additives may be added to foood in orfer to improve is appearance, taste or how long it lasts
    • Instrumental Methods
      • Machines are used to analyse products or special chemical products instead of humans.
      • Advantages
        • Accurate and sensitive
        • Quicker
        • It enables very small substances to be analysed
      • Disadvantages
        • Expensive
        • Takes special training in order to be able to use
        • Can only be interpreted in comparison with data from unknown substances
      • Uses
        • Analysing priducs
        • Health Care
        • Fighting pollution
    • Mass Spectrometry
      • Compounds can be identified using this method.
      • The first step is vapourisation - this is where a sampe is 'injected' into a high temperature chamber where it is vapourised. The particles in the vapour are sucked through the mass spectrometer by a pump.
        • Ionisation - electrons are fired at the sample to ionise it to form positive ions.
          • Acceleration - a strong electric field accelerates the ions forward.
            • The ions pass through a velocity sector, where electrical ad magnetic fields ensure that all the particles passing through have the same velocity.
              • Deflection - the charged particles pass through a uniform magnetic firls which deflects them sideways. The heavier the particle, the less it is deflected.
    • Gas Chromatography
      • Compounds in a mixture can be sperated using this mixture.
      • First the sample mixture is vaporised.
        • Second, the 'carrier' gas moves the vapour through the coiled column.
          • The compounds in the sample have differet attractions to the material in the column. The compounds with stronger attractions will take longer to get through the column.
            • We say they have a longer retention time. The compounds with weak attractions to the material in the column leaft first - shorter retention time.
              • Retention time - the time it takes a component in a mixture t pass through the column in gas chromatography.
                • Different compounds have different retention times due to how strong or weak the attractions are towards the material.


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