This document summarizes an experiment using paper chromatography to analyze ink samples from four pens (A, B, C, D) and compare them to a sample from a ransom note to determine which pen was used. Paper chromatography works by separating the components in a mixture based on how strongly they interact with the stationary phase (paper) versus the mobile phase (water). Components that interact more strongly with water will travel farther up the paper. By comparing the ink patterns from the pens to the sample from the note, the pen used can be identified.

1. Lab #4: Chromatography

2. Paper Chromatography
Separation of a mixture by taking advantage of the
differing attractive forces of the substances
within a mixture with those of a transport
medium and a solvent.
Stationary Phase – (the paper) does not move.
Holds the sample.
Mobile Phase – (the water) a solvent that rises
up the paper (stationary phase) and reacts with
the sample.
Components of the mixture react with both phases.
The higher a components polarity the faster it
will react with and move with the water(mobile
phase). Less polar components will react better
with the stationary phase (the paper) and travel
slower.

3. How does this work?
• Because molecules in ink and other
mixtures have different characteristics
(such as size and solubility), they travel at
different speeds when pulled along a piece
of paper by a solvent (in this case, water).
For example, black ink contains several
colors. When the water flows through the
black ink, the molecules of each one of the
colors behave differently, resulting in a sort
of “rainbow” effect.
Many common inks are water soluble
and spread apart into the component dyes
using water as a solvent. If the ink you are
testing does not spread out using water, it
may be “permanent” ink. In such
cases, you will have to use a different
solvent such as rubbing alcohol.

4. Whodunnit?
A picture of this cuddly teddy bear was sent to
his family along with a ransom not that read;
“I hav the bare.
If you’s ever wants to
see him again you’s
better gives me what I
asks for. If you’s what
call the cops thing will
go very bad.”

5. The culprits
Kermit the Frog Big Bird Cookie Monster Bert (NLN)
Caught with Caught with Caught with Caught with
Pen A Pen B Pen C Pen D

6. Standard Chromatograph
Chromatograph of ink sample
taken from ransom note.

7. Standard Chromatograph

8. Materials
• Assorted black Pens
• 1000 mL Beaker
• Chromatography Paper
• Pencil
• Ruler
• Water

9. Procedure
1. Acquire a strip of chromatography paper.
2. Fold the top of the strip and staple it to create a loop.
3. Draw a line in pencil across the bottom of the strip about 3 cm from the edge and attach a
paper clip to the bottom of the paper.
4. Place a dot of ink from each of the four sample pens (A, B, C, D) across the line. Label the
dots in pencil to identify the pen they came from.
5. Poke a pencil through the loop you just made. Use the pencil to suspend the strip in a small
glass or container.
6. Carefully add water to the glass until it reaches the bottom of the paper strip just below
the ink dot. Be sure the ink stays above the water and the paper stays in the water.
7. Allow the water to soak up the strip (20 mins) and watch what happens to the ink drop.
Record these changes as observations in your lab report
8. After about 20 minutes remove the strip from the water and mark in pencil where the
water line has stopped. This indicates the distance traveled by the solvent.
9. Compare the results of your chromatography paper to the standard chromatograph of the
sample of ink taken from the ransom note to determine which pen was used to write the
note.

10. Conclusion
• From the results of your chromatography
experiment determine which pen’s ink
matches the ink sample from the note
• Read pages 662-664 in the text book.
• Answer questions 1, 2, 3, 4, 5

11. http://mrmartinschemistryblog.blogspot.com/