Discover what is in pigment using chromatography.
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.
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.
Numbered evidence pens are given to the
students. Be sure to remind the students to recap the pens after use.
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.)
When a team finishes the test strips,
they are to compare their runs with the instructor's.