CHROMATOGRAPHY - LAB

OBJECTIVE:
Discover what is in pigment using chromatography.

BACKGROUND:
Chromatography is a means of separating mixtures based on their solubility in a particular solvent.  It is widely used in the biological sciences to separate amino acids in a given sample of tissue or cells.  Paper chromatography is the technique that this lab will focus on.

During this lab, students will be using paper chromatography to separate different chemicals found in ink pens.  Prior to the lab, the instructor is to pick a particular marking pen to use in a chromatography experiment.  The students will then try to determine which pen was used by comparing their chromatography experiments with that of the instructor.

Chromatography works well using water as a solvent and a variety of different water based felt tip pens.  This lab is done as a "criminal investigation" using paper chromatography.  A note has been given to the principal excusing a student for being absent.  It has a number of clues suggesting it might not be real.  Poor spelling, penmanship looks like that of a student, signature is illegible, and written on school paper towels (or other suitable filter like paper).  The note only gives a first name of which there are many in school.  After eliminating some students because they were in school, the principal calls in the others, checks their backpacks for felt pens.  The principal finds four, numbers them as evidence (to protect the individual involved) and sends them to the school "crime lab" (your class) for testing.  You explain two additional pens have been added as controls to protect against possible false accusations.   

 PROCEDURE:

1. Teacher presents to class in a serious manner the "scenario" as described under background information.  Show students a copy of the note on the overhead, explaining the principal has kept the original except for the pieces cut from it for testing in the lab.  (Note should say something like... "Please excuse John from school on Sept 15-17 because of an illness... signed his parents (illegible scribble)."  Make sure there is a line under the signature, because this line will be used in the test.

2. Numbered evidence pens are given to the students.  Be sure to remind the students to recap the pens after use.

3. Teacher walks round room monitoring student progress.  Be sure students do not submerge the test line into the water.  If they do they must redo the test. (Lab set up will be given on the student's sheet.)

4. When a team finishes the test strips, they are to compare their runs with the instructor's.