Introduction to Chromatography
Purpose:
To gain familiarity with the technique of paper chromatography. To separate the components of a
mixture using chromatography.
Chemical Principles:
Chromatography is a method for achieving the separations of substances in a mixture. The name for
the method derives from the fact that it was first applied to the separation of colored substances
(Greek: chromos, color). Although the effectiveness of the separation is most easily detected if the
components of the mixture are colored, the method is applied today to all kinds of mixtures.
Filter paper is a good material upon which to conduct a chromatographic experiment. We will be
using chromatography paper. Many substances that are soluble in water are more or less tightly
absorbed onto the surface of the fibers of the paper. A spot of solution containing several components
is placed into a thin layer of solvent within a chromatography tube or another container. As the
solvent climbs up the paper by capillary action, those substances that are not absorbed by the paper
will move at the same rate as the solvent. Substances that are bound very tightly to the paper will not
move at all. Those substances that weakly interact with the paper will move, but more slowly than the
solvent.
Equipment:
Chromatography tubes
Rulers
Forceps
Chromatography paper
Scissors
Overhead (vis a vis) Markers
Black
Brown
Blue
Green
SAX Brown
PMOP Black
Flair (Papermate) Pens
Black
Blue
Chemicals:
Distilled water
Expresso Black
Experimental Procedure:
1. Obtain a piece of chromatograph paper. Cut the paper into pieces that are approximately 9 cm in
length. You will also need to trim a little from the side of the paper so that they will fit into the test
tubes.
2. Choose a colored pen and make a small, but dark, dot using the marker on the center of the paper
about 1 cm from the bottom of the strip. Write the type of pen used to make the mark on the top of the
piece of paper.
3. Place distilled water in a chromatography tube to a depth of approximately ½ cm. (The solvent
level should not touch the mark on the chromatography paper when the paper is placed in the test
tube.) Carefully place the chromatography paper in the tube. The paper should stand vertically in the
tube; it may be necessary to place a crease along the piece of paper to allow it to stand in the tube
without touching the sides.
4. Place the chromatography tube in a test tube rack and leave it undisturbed. Allow the solvent to
travel up the paper until an adequate separation of colors has occurred. When the separation is
complete, or when the solvent has nearly reached the writing at the top of the paper, remove the paper
from the tube. Place the chromatography paper on a paper towel to dry.
5. Repeat steps 2 through 5 with each of the different types of markers. Tape your chromatography
papers onto your report sheet once they are dry.
6. Obtain an unknown sample. Identify the type of pen used by comparing the results for the
unknown with your other samples. Record your results on the report sheet.