The purpose of this experiment
is to separate and identify the FD&C dyes from M&M's or
Skittles using paper chromatography.
This experiment is appropriate
for general, first-year college prep, or AP classes and could
be adapted for use with middle school physical science classes.
Wool yarn is used to separate the FD&C dyes present in the
coatings of M&M's and/or Skittles from other components of
the coatings. The resulting dyes are then separated using paper
chromatography. If commercial food colors are used as standards,
the separated dyes can be identified.
One and one-half to two lab
Care should be exercised when using
boiling water baths.
- M&M's and/or Skittles
- white household vinegar
- clear, colorless household ammonia solution
- food colors
- red litmus paper
- Bunsen burner
ring and wire gauze or hot plate
- 600-mL beakers 25-cm × 150-cm
- l0-mL graduated cylinder
- stirring rod
- evaporating dish
- test tube holder
- beaker tongs
- crucible tongs
- wool yarn
paper (Whatman #1)
- tooth picks
- aluminum foil
- Place a test tube containing a 10-15 cm length of white woolen
yarn and 10-15 mL of household vinegar in a boiling water bath
and heat for 4-5 minutes to remove any fluorescent dyes which
could interfere with the separation of the FD&C dyes. After
cooling, remove the yarn from the vinegar and let it drain.
- Place 5 or 6 M&M's or Skittles in a test tube with enough
household vinegar to cover the candies. Heat the tube in a boiling
water bath until the colored coating dissolves. Avoid dissolving
the interior of the candies.
- Carefully decant the solution which now contains the FD&C
dyes, some sugar, etc. into another test tube. Avoid transferring
- To extract the dyes, add the prepared length of woolen yarn
and 3 mL of vinegar to the test tube containing the dye solution.
Heat this tube in the boiling water bath for about 5 minutes with
occasional stirring. Remove the yarn and rinse it with a little
- To release the extracted dyes, place the yarn and about 5
mL of clear household ammonia solution in a clean test tube. Mix
with a stirring rod and then test the resulting solution with
red litmus paper to make sure that it is basic. If not, add a
bit more ammonia solution.
- Heat the tube containing the yarn and ammonia in a boiling
water bath for about 5 minutes with occasional stirring to release
the dyes. Remove the yarn and pour the solution containing the
dyes into an evaporating dish. Heat the evaporating dish gently
to concentrate the solution. Stop just short of dryness. If all
the liquid evaporates, add a drop or two of distilled water and
- Cut two l0-cm × 20-cm pieces of chromatography paper. Draw
a pencil line l cm from one long edge of each piece of paper.
Mark six or seven equally spaced positions along the pencil line.
Use toothpicks to place as small a drop of the concentrated dye
solution as possible on two of the positions on the pencil line
on each piece of paper. Allow the spots to dry and spot them again
in exactly the same positions to increase the amount of sample.
Spot a third time and a fourth time if the color 13 not very intense.
Use toothpicks to place one small drop of each food color sample
on the remaining positions on each piece of paper.
- Add 5 mL of vinegar to a 600-mL beaker. Carefully staple one
piece of chromatography paper into a cylinder and place the paper
in the beaker with the spots at the bottom of the cylinder. Be
careful that the paper does not touch the sides of the beaker.
Cover the beaker with aluminum foil and allow the chromatogram
to develop until the developing solution has climbed to about
l cm from the top of the paper. Remove the paper from the beaker,
open it out and allow the paper to dry on a piece of paper towel.
- Repeat step 8 using the second piece of chromatography paper,
but develop with 5 mL of clear ammonia solution.
- Use the following information to identify the specific dyes
present in the candy coatings.
|Crown Colony Kit||Blue #1|
|Crown Colony Singles||Red #40||Yellow #5|
|Yellow #5||Blue #1|
Remaining interiors of candies
may be disposed of with solid waste. Solutions that remain may
be flushed down the drain.
Paper chromatography is an important
separation technique that depends upon differences in how strongly
the dyes are adsorbed onto the paper (stationary phase) and how
soluble the dyes are in the developing solvent (mobile phase).
In paper chromatography, a small amount of the mixture to be separated
is placed close to the edge of a piece of paper. The edge of the
paper is then immersed in a developing solution. As the developing
solution ascends up the paper by capillary action, the. components
of the sample are carried along at different rates. To prevent
evaporation of the developing solution, this process is carried
out in a closed container.
Each component of the mixture will
move a definite distance on the paper in proportion to the distance
that the solvent moves. This ratio, Hf = distance component moves/distance
solution moves, can be calculated for each component to aid In
identification. Hf values are dependent upon the paper, the developing
solution, and the amount of sample used.
Candies, such as Mix's
or Skittles, contain FD&C dyes, sugar, and other organic and
Inorganic substances In their coatings. If the coating is dissolved
in an acidic solution, the FD&C dyes can be adsorbed from
the solution by wool. The dyes can be released from the wool in
an alkaline environment. Thus the dyes can be separated from other
substances in the coatings. This simplified equation represents
the equilibrium involved:
Wool + Dye + H+ <====> Dyed Wool+ A
solution of ammonia can be used to supply sufficient OH- to reduce
the concentration of the H+ and shift the equilibrium to the left
releasing the dyes.
Jenkins, C., Science and Children,
April 1986, p. 25. -- This article describes a chromatography experiment
for young children using Kool-Aid and lists the FD&C dyes
In various brands of food colorings.
- The yarn used In this experiment must be 10O% wool. To save
time, the teacher can pretreat the wool to remove fluorescent
- Two different developing solvents are used to illustrate the
significant dependence of this technique on the solvent used and
because the vinegar separates the yellow and blue dyes better
while the ammonia separates the reds and yellows better.
- Since it Is difficult to apply comparable quantities of the
extracted dyes and the food colors to the chromatogram, It is
likely that the Hf values will not be very reproducible. The separations
are sufficiently distinct that students can identify the components
McDuffie, T.E. Jr. and Anderson,
J., Chemistry Experiments from Daily Life, J. Weston Walch,
Publisher, 1980, p. 77. -- This work describes a similar experiment
which uses non-consumer solutions for the extraction and for developing
Submitted by John Hnatow
Woodrow Wilson Leadership Program in Chemistry
The Woodrow Wilson National Fellowship Foundation
CN 5281, Princeton NJ 08543-5281