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
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
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