NCSU – Dept. of Chemistry – Lecture Demonstrations
Organic Chemistry
Food Chromatography
Description: Materials containing different dyes are separated on filter paper
using an aqueous mobile phase.
Materials:
Markers
Kool-Aid (grape,orange,etc.)
Hard candy (Skittles,M&M’s)
Food coloring
Cups
Filter paper
Procedure:
This demonstration is best suited for younger audiences.
1. Prepare the samples by dissolving each in a small amount of water. For
the hard candies, only the outer shell needs to be dissolved.
2. Cut a small hole in the center of the filter paper for the wick. Spot the filter
paper by dipping one end of a toothpick in the liquid sample and gently
spotting the filter paper as shown below.
3. Roll up a separate piece of filter paper and insert this into the hole. This
will serve as the wick which will deliver the mobile phase (water) to the
samples to be separated. Fill the cup ¼ with water and place filter paper
with inserted wick into cup. Allow chromatogram to develop, this should
take several minutes. For best results, remove the filter paper before the
water reaches the edges of the paper.
Top View
Side View
Filter paper (or coffee filter)
Hole for wick
1
4
3
wick
2
Pencilled circle
Locations for substances to be tested
spaced equally around circle
NCSU – Dept. of Chemistry – Lecture Demonstrations
Organic Chemistry
Discussion: In this demonstration, a physical change takes place in which the
individual dyes responsible for the observed color of the food are separated. In
this experiment our mobile phase is water and our solid phase is the filter paper.
The dyes move faster or slower on the solid phase depending on their solubility
in water. Therefore, those dyes which are more soluble in water are more likely
to travel with the mobile phase and are observed further away from the starting
spot. The distance between the starting and ending point can be measured and
compared to the distance that the mobile phase traveled. This ratio is known as
the Rf (ratio-to-front) and is specific for individual samples and mobile phases.
Safety: Participants should be encouraged not to ingest used materials.
Disposal: Materials can be flushed down the drain.
References:
In Countertop Chemistry; The Science House, NC State University: 2005 edition;
p 10-12.
Video:
http://www.youtube.com/watch?v=IRZ4lHEe1DI (markers)
http://www.youtube.com/watch?v=jzf0stGQhrk