This is a two week lab in which you are faced with a problem that is regularly encountered in any scientific laboratory: the extraction and separation of a mixture into its various components and, the confirmation of the identity of the components that made up the original mixture. 

    In the experiment in question we are curious as to the mixture of food dyes that is used to make up the brown coating on an M&M.  However before we can attempt to tackle that problem we need a method to extract the various food dyes that make up the colors in M&M's without extracting other components, such as sugars etc., that would later interfere with our analysis.  Thus this first week will be devoted to the extraction process. 

Food Colorings

    The color of food is an integral part of our culture and enjoyment of life. Who would deny the mouth-watering appeal of a deep-pink strawberry ice cream on a hot summer's day or a golden Thanksgiving turkey garnished with fresh green parsley? 

    Even early civilizations such as the Romans recognized that people "eat with their eyes" as well as their palates. Saffron and other spices were often used to provide a rich yellow color to various foods. Butter has been colored yellow as far back as the 1300s. 
    Food color additives are dyes, pigments or substances that impart color when applied to a food, drug, cosmetic, or the human body. The Food and Drug Administration (FDA) is responsible for regulating all color additives used in the United States. All color additives permitted for use in foods are classified as "exempt from certification" or "certifiable". 

    Color additives that are exempt from certification include pigments that are derived from natural sources such as vegetables minerals or animals, and man-made counterparts of natural derivatives. 

    Certifiable color additives are man-made, with each batch being tested by the manufacturer and the FDA. This "approval" process, known as color additive certification, assures the safety, quality, consistency and strength of the color additive. 

    Color additives are available for use in food as either "dyes" or "lakes". Dyes dissolve in water, lakes are the water insoluble form of the dye, are more stable than dyes, and are ideal for coloring products containing fats and oils. 

    There are nine certified colors approved for use in food in the United States. Five can be found in M & M ® candies, these are listed in Table 1. 

References:

Food and Drug Administration (FDA) HFI 140 
5600 Fishers Lane, Rockville, MD 20857 

"Food Additive Toxicology", J.A. Maga, A.T. Tu, Editors, Marcel Dekker Inc. Press, New York, 1995. 

Structures of Some Common Food Dyes:

Color  Bright Blue Common Food Uses Beverages, dairy products, powders, jellies, confections, condiments, icing.	Color Royal Blue Common Food Uses Baked goods, cereals, snack foods, ice-cream, confections, cherries.
Color Orange-red Common Food Uses Gelatins, puddings, dairy products, confections, beverages, condiments.	Color Lemon-yellow Common Food Uses Custards, beverages, ice-cream, confections, preserves, cereals.
Color Orange Common Food Uses Cereals, baked goods, snack foods, ice-cream, beverages, dessert powders, confections

Experimental Procedure:

Extracting the Dyes:

1. You will need six ~15cm strips of white woolen yarn (one for each of the colors in a bag of M&M's ). To remove the fluorescent dyes from the yarn, place each strip into a different large test tube with enough household vinegar (5% acetic acid) to just cover it, approx. 10mL (1mL=~1cm on the side of the test tube). Place the tubes into the beaker of boiling water for 5 mins.
    
2. Remove the test tubes from the water bath. Using a stirring rod, fish out the strips of yarn and place on a paper towel. After the test tubes are cool enough to touch, discard the vinegar, and rinse the test tubes with tap water and then with distilled water.  Place 5 candy pieces of the same color into each tube.  Pour enough vinegar into each tube to just cover all of the candy pieces.
    
3. One at a time, hold a tube with a test tube holder and dip it into boiling water to heat the vinegar and dissolve the color coating, so that the candies turn white. The color comes off very fast, usually within a few seconds, so it is usually not necessary to keep it in there for longer than 10 seconds. Be careful to dissolve as little as possible of  the white layer (sugar) under the colored layer and do not dissolve any of the chocolate. Immediately decant the colored solution into a clean test tube, trying not to transfer any of the sediment. Repeat with the remaining five tubes.
    
4. Now you need to extract the dye from the solution onto the strips of yarn. To do this, place one piece of yarn into each test tube of colored solution and top off the level of vinegar so that there is at least 4mL (4cm). Heat the tubes in the boiling water bath for 5 mins. You can remove the tubes from the water when the solution is milky-white and the yarn is the color of the dye, in other words, when all of the dye has been extracted from the solution.
    
5. Remove the dyed yarn from the solution and rinse it with distilled water.  If you wish you may cut ~2cms off each piece of yarn.  Let these dry on a piece of paper, and you may take them away with you.  A memento if you wish!
    
6. Now it is necessary to extract the dye from the yarn and get it back into solution. 

   Into 6 large clean test tubes place a piece of yarn and  3mL of 1M ammonia. Make sure that the yarn is immersed and mix with a stirring rod, rinsing the stirring rod before placing it in each tube so as not to mix any of the colors. 
    

7. Heat the tubes containing the yarn and ammonia in the water bath for 5 mins. or until the color of the yarn has faded.   Remove the yarn.
    
8. You now may need to concentrate each color.  To get some feel for just how concentrated each color should be, take a small test tube and using a dropper add 5 drops of water to the test tube.  This is the amount of each color that you require.
    
9. To concentrate your dyes, place the dye in a washed Erlenmeyer flask and very carefully heat it on a Bunsen Burner.  Take care here, if the dye goes dry then the heat from the burner will decompose the dye.
    
10. When concentrated, return the dye to a clean small test tube and stopper it.  Wash the Erlenmeyer thoroughly and repeat with the remaining colors.
     
11. Store all the dyes in your locker for the next experiment.