Chemical Analysis using paper chromatography
Artificial colouring may be separated by chromatography
- Food colouring may contain one dye or a mixture of dyes
- You place the food colouring (a few drops) in small cup with a few drops of solvent (water, ethanol etc.)
- Put spots of the coloured solution
- Get a piece of filter paper and draw a line on it – put spots of the coloured solution on the base line
- Roll up the filter paper and in a new beaker of solvent – make sure the solvent is below the base line
- The solvent will go up the filter paper and the colours will separate and stop at a different position on the filter paper
- g. if you have three spots then you would have at least three different colours in the dye
- This is used in industry all the time to analyse the content of substances – if you get the right mixture of solvent and dye then you very accurately separate different substances
- Machines now do this much more accurately – advantages are that they are fast, accurate, sensitive to the tiniest amounts of changes
Gas chromatography
- A gas is used to carry substances through a column packed with a solid material
- The substances travel through at different speeds – so they are separated
- The time taken to reach the other end is called a retention time
- It draws a graph called the gas chromatograph
- The number of peaks (called the molecular ion peak) shows the number of different compounds
- The time shown between the peaks shows the retention time
- The gas separates the substance and the gas spectrometer reads of their molecular mass – this means you can tell what the substance is
- The gas spectrometer shows you how much of the substance was in the original substance and tells you the molecular mass of each part of the substance – then you can work out the weighted mass