Analysing Substances LO: Describe how you would detect artificial food colourings (D) Explain how colourings can be identified using chromatography. (C) Compare and Contrast modern techniques with those found in the school (B) Starter What types of food additives are there ?

Preservative – Make food last longer Flavouring – Include extra flavour, or bring out the taste already there Colouring – To make it look nice, or replace the colour that has been lost Antioxidant – Make food last longer Sweetener – Substitute for sugar, usually much sweeter Thickener – To give body to food

Scientists have a lot of ways to detect food additives. What methods can you think of ?

Chromatography This works because some chemicals dissolve better than others. xxx Most soluble Least soluble Paper = Stationary phase Solvent = Mobile phase

Note that….. The Stationary phase does not have to be paper. The mobile phase does not have to be water. Sometimes you need special light or a chemical spray to see you results

Practical You are going to analyse food colourings using chromatography.

Method for chromatography -On a piece of chromatography paper draw a straight line across on end of the paper about 1cm in from the short edge of the paper. Fold the paper in half lengthways and then open out. -Still using the pencil place a small cross on the line that you have drawn for each ink that you are testing. It is important that the crosses are at least ½ cm apart and that they are not at the edge of the paper or the crease in the middle of the paper. -Use the pencil to write which colouring you are using under the cross. -Use a clean capillary tube to put a small dot of the colouring that you are going to test onto the cross. Do this for each colouring. -Place about ½ cm of water into the bottom of a beaker. -Stand the paper up in the water making sure that it does not touch the sides of the beaker. -Let the colouring travel up the paper with the water until it is at least half way up. -Remove the paper from the water and draw on where the water came up to using a ruler.

Looking at the results xxxx E104E375E118Sample

Instrumental Analysis -Highly accurate and sensitive. -Quicker. -Very small samples can be analysed. -Very expensive. -Takes special training. -Often gives results that can only be looked at by comparing with known substances.