A food scientist uses paper chromatography to analyse the colouring agents present in two fruit drinks, A and B. After the experiment, the chromatogram shows several separated spots. Explain how the food scientist can use the chromatogram to determine whether the two drinks contain any of the same colouring agents.

The scientist measures the distance each spot travels from the baseline to its head and the distance the solvent front travels. The Rf value is calculated as

Rf = (distance spot moved)/(distance solvent front moved).

If two spots from drinks A and B have the same Rf value (i.e. they appear at the same height on the paper) they are considered to be the same colouring agent. By comparing all Rf values, the scientist can see which spots match and which do not, and thus determine whether the drinks contain any common colouring agents. The total number of spots in each chromatogram also tells how many different colouring agents are present in each drink.