Chromatography is a laboratory procedure that effectively separates individual components found in a mixture. The process relies on the affinity each component has with respect to a solid material, called the stationary phase, and a solvent, called the mobile phase. You can design a basic chromatographic procedure, called paper chromatography, in order to separate different food colours using common household products. Individual food colours will move, or migrate, through a paper filter as the solvent is absorbed by capillary action. This article will provide you with a basic technique for separating food colours.
Dissolve the coloured surface from Skittles or M&M candy in 1ml of water. Different colours can be combined to create a mixture of different food dye components to be separated.
Cut coffee filter into strips measuring 1cm by 10cm. The filter strip will provide the stationary phase for conducting paper chromatography.
Place a 2mm spot of candy coloured water on the filter paper strip with the toothpick. The spot should be placed 1.5 to 2cm above the bottom of the filter paper and be easy to see. If the spot does not appear dark in colour, the paper can be spotted again after the initial spot dries to maintain the 2mm diameter.
Pour isopropyl alcohol in the glass with a depth of 1/2 cm. Alcohol is a solvent and provides the mobile phase. The sides of the glass should remain dry. Excess isopropyl alcohol on the sides of the glass could absorb into the filter paper during the test.
Place the bottom end of the filter paper into the alcohol. The area spotted with the coloured water does not contact the alcohol. The alcohol will slowly move up the filter paper as it is absorbed by capillary action. Placing a cover over the glass could help reduce evaporation of alcohol.
Observe the individual colours separate on the filter paper. Dyes with stronger affinity to alcohol will move more quickly than dyes with stronger affinity to the filter paper. Eventually individual colours will become apparent.
Remove filter paper when alcohol is 1cm from the top of the filter paper. The paper should be placed on a flat surface and allowed to dry. The separation of colours can still be observed after the paper is dry.
Test and compare candies with different colour coatings. Some candy surface colour result from more than one food colouring present. Comparing different colours provides an interesting experiment.
Coffee filters provide a reasonable stationary phase for separating different food colour dyes. However, laboratory grade cellulose filter paper provides better separation. Laboratory grade filter paper is available from educational and laboratory supply companies.
Isopropyl alcohol is not fit for consumption. Children should only conduct this experiment in the presence of an adult.