Chemical Analysis and Instrumental Methods

Chemical Analysis and Instrumental Methods

1. Artificial Colours can be seperated using paper chromatography

   • A food colouring might contain one dye or it might be a mixture of dyes
   • 1. Extract the colour from a food sample by placing it in a small cup with a few drops of slovent (water, ethonal etc)
     • 2. Put spots of the coloured solution on a pencil baseline on filter paper
       • 3. Roll up the sheet and put it in a beaker with some solvent - but keep the baseline above the level of solvent
         • 4. The solvent seeps up the paper taking the dyes with it. Different dyes form spots in different places
           • 5. Watch out though a chromatogram with four spots means at least four dyes not exactly four dyes. There could be five dyes with two of them making a spot in the same place

2. Machines can also analyse unknown substances

   • You can identify elements and compounds using instrumental methods
     • Advantages
       • Very sensitive can detect even the tiniest amount of substance
       • Very fast and tests can be automated
       • Very accurate

3. Gas chromatography

   • Seperate out a mixture of compounds to help identify the substances
   • 1 .A gas is used to carry substances through a column packed with a solid material
     • 2. The substances travel through the tube at different speeds so they are seperated.
       • 3. The time they take to reach the detector is called retention time. It helps identify substances
         • 4. The recorder draws a gas chromatograph. The number of peaks shows the number of different compounds in the sample
           • 5. The position of the peaks shows the retention time of each substance
             • 6. The gas chromatography column can also be linked to a mass spectrometer. This process is known as GC-MS and can identify the substances leaving the column very accurately
               • 7. You can work out the relative molecular mass of each substance from the graph it draws. You just read off from the molecular ion peak

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