Lab #12: Food Dye Chromatography Introduction: The purpose of this experiment is to use paper chromatography to separate the components of seven Food, Drug, and Cosmetic (FD&C) food dyes. The word chromatography is derived from two Greek words meaning color (chroma) and writing (graphein) – “color writing”. The Rf value of each substance will be calculated and compared to determine the composition of the food dyes in an unknown mixture. Pre-Lab Questions: 1. Investigate the technique of paper chromatography. How is it set up? How does it work? In the technique of paper chromatography, you apply a sample near one corner of a sheet of filter paper. An edge of the paper close to the test spot is then soaked in another solvent in which the components of the mixture are soluble in varying degrees. The solvent penetrates the paper by capillary action and, in passing over the sample spot, carries along with it the various components of the sample. Separation of the components is brought about if there are differences in their relative solubilities in the two solvents. The separated components appear as individual spots on the path of the solvent. 2. What is the primary factor influencing the distance the sample will move along the chromatography paper compared to the solvent? Different samples will spend varying amounts of time interacting with the paper and the solvent. The components move with the flowing solvent at velocities that are dependent on their solubilities in the stationary and flowing solvents. Through these different interactions, the samples will move different distances along the chromatography paper. 3. Check for food labels at home or in a grocery store and find items with food dyes in them. List the foods and the FD&C dyes included in the ingredient list. Gatorade: Yellow 5 Procedure/Materials: Develop your plan to determine the identity of the food dyes in your unknown mixture. Maintain a list of materials used. Pigment tray Beaker Water Colors (food coloring) Paper Paper towel Rulers pencil Data Table: Construct a table containing the data you collected that is needed to determine Rf. Make a color drawing of your chromatography paper. To compare and identify compounds separated by paper chromatography, you can calculate the Rf (rate of flow) value for each dye using the formula below. Rf = distance traveled by dye distance traveled by solvent front To maintain consistency, always measure from the pencil line marked at the bottom of the chromatography paper to the center of each spot. Record the distance traveled for each of the dyes. Post Lab Questions: 1. Calculate the Rf value for each dye in the pure solutions. Show all work. 2. Identify the dyes present in the unknown mixtures. Include supporting data, Rf calculations and reasoning for your conclusions. UA---- R. 40.45 3. Compare the Rf values of the pure dyes. Which pairs of dyes appeared to have very similar properties, based on their Rf values, despite their different colors? Red No. 40 and UA had similar Rf values as did Blue No. 1 and Green No. 3 4. Which food dye(s) had the greatest interaction with or affinity for the paper versus the solvent? Explain. A high interaction or affinity for the paper would takes a lot of time and the sample would not move very much resulting in a low distance traveled. Red No. 3 has a very low distance traveled, showing it has more affinity for the paper than the solvent. 5. You are asked to mix an additional experimental unknown and want to make sure the mixture is a challenging one. Using observations and data from the completed experiment, develop a new three-dye component mixture that may be difficult to analyze. Explain why you chose this mixture. A mixture containing Blue No. 1 and Green No. 3 might be hard to separate due to rate-of-flow values. A mixture containing Yellow No. 5 and Yellow No. 6 is visually hard to separate.
