Chromatography

Goal: Determine which pen was used to write the will.  The will seems to have criminal motif.

·        Explain how thin layer chromatography (TLC) is used to separate the ink.
·        To understand chemical and physical properties beyond the TLC.
·        To understand how ink is made up with several organic dyes.
·        To understand physical properties of light and color.

Equipment:

will
pens (Victim’s and suspects’)
scissors
TLC paper or silica gel plate (2”x4”)
TLC spotting capillary tubes
1000 ml beaker or jar as TLC developing chamber
EtOH
water
test tubes
large filter
paper
piece of aluminum foil (5”x5”)

Procedures

1.      The instructor wil divide the will in same portion into a number of groups.

2.      Trim the will down in size so that the only remaining piece is a piece that contains the ink. This is the unknown sample.

3.      Place the trimmed paper into a test tube and add few drops of denatured ethanol.

4.      Shake the test tubes vigorously to extract the ink from the paper.

5.      Obtain a silica gel plate (handle it by the edges to avoid chipping or contaminating)

6.      Draw a line across the plate about 1.5 cm from the bottom with a pencil.  Since this line is where the students will spot their known and unknown ink samples, they will place a dot with a pencil at equal intervals depending on number of samples.

7.      For the unknown sample, use a capillary tube to spot sample several times on the plate.  Wait until the spot completely dries between applications, and place your finger over the end of the capillary tube to avoid spotting too much ink at once.  Be careful not to make the spot too large but to get a sufficient amount of ink on the plate.

8.      For the known sample, spot each sample once with pens that the instructor has provided.  Students should not leave any unwanted impression into the plate by pressing down too hard. 

9.      Label each dot so that they will be able to identify each sample.

10.  Make the TLC developing chamber by using 1000 ml beaker or any jar similar in size that may be substituted for the beaker. 

11.  If the filter paper happens to be a circular shape, cut an edge so that it will rest along the bottom of the beaker evenly.  Place it in the beaker.

12.  Fill the beaker adequately with ethanol, but no higher than the line drawn on the plate.

13.  The filter paper will get wet and it will stick to the side of the beaker.

14.  Cover the beaker with the aluminum foil and let it sit for approximately 10 minutes.

15.  Remove the foil, then lean the TLC plate against the filter paper.  Makes sure that bottom covers the solvent, but not higher than the line.

16.  The beaker will be covered with the aluminum foil while the TLC plate is being developed.

17.  Take out the TLC plate when the solvent reaches 80% of the plate.

18.  Observe chromatogram according to description shown in the Background/Theory page.

19.  Draw TLC plate and write down every component of R_f values.

·        Why is an aluminum cover and filter paper used for the TLC development process? (chamber can evenly fill with fumes to achieve equilibrium)
·        How will the concentration of ethanol affect this development?
·        We retrieve ink of the last will by dissolving it under denatured ethanol.  Besides doing this, what other way can we set up this experiment to obtain similar results?

·        2 class period for theory and background
·        2 lab periods for experimentation and data collection
·        1 class period for analyzing and group discussion
·        Research assignment time – presentation and conclusion