10.2 Analysing chromatograms

• Use a ruler to draw a horizontal pencil line on the chromatography paper, 2 cm from the bottom. • Use a capillary tube to put a small spot of each of the known food colours and the unknown colour onto the pencil spots. • Pour water (solvent) into a beaker to a depth of 1 cm. • Attach the paper to a glass rod using tape and lower the paper into the beaker. The bottom of the paper should dip into the water. • Put a lid on the beaker to reduce evaporation of the solvent. Water will move up the paper and the colours will be carried up. • Remove the paper when the water has travelled three-quarters up. Use a pencil to mark the point where the water reached. Hang the paper up to dry.  Measure the distance from the pencil line to the centre of each spot. Then measure the distance moved by the water from the pencil line.  Rf value = Distance moved by chemical/ Distance moved by solvent.  Look up the Rf value in a database to identify the chemical, however, repeat with a different solvent to make sure it’s the right Rf value for the chemical.

Separate and identify mixture of amino acids, it can also tell you if it is a single compound or a mixture

Distance moved by substance/ distance moved by solvent

their distribution between the stationary and mobile phase

they have different rf values in different solvents