Chromatography

Sr. Stephanie Blaszczynski        Resurrection High School
Barbara Daiker                    Brookwood Junior High
Nancy Zipprich                    D. D. Eisenhower High School

Objectives:

1. Acquaint students with chromatography as a technique useful in separating
   mixtures.
2. Perform a paper chromatography separation of pigment mixture and analyze
   its separate parts by determining the Rf (retention factor).
3. Using leaf chromatography, show that the Rf is a constant.
4. Explain the application of chromatography in industry and medicine today.

Materials needed:

Kool-Aid: 7 g pkg. unsweetened grape Kool-Aid in 5 mL H2O, small jar with lid, 
filter paper, pencil 

Crayola markers: water-soluble markers, test tube and flask to hold it, pencil, 
ruler, cork 

Leaves: leaf extract: fresh leaves, sand, 5 mL ethyl alcohol or acetone, 
ground in mortar with pestle, filtered; solvent: 92% petroleum ether and 8%
acetone in a test tube with rubber stopper in 250 mL flask, filter paper 

Strategy:

 1. Elicit interest in chromatography by role playing to determine if grape
Kool-Aid contains blue dye to which person is allergic.

 2. Do a chromatogram of grape Kool-Aid.

 3. Define chromatography as: the process of separating small quantities of a
substance in a mixture (often a solution) through selective absorption.

 4. Have the class perform a chromatography lab using black and several other
colored water-soluble pen markers.

 5. While waiting for the completion of the chromatograms, use "Raft Analogy" as 
a model to conceptualize the process of chromatography, and introduce the 
terminology.  (Rafts=MIXTURES; current=SOLVENT/MOBILE PHASE; 
riverbed & stumps=STATIONARY PHASE; snagging on stumps=SELECTIVE ABSORPTION.) 
(1987 Dreyfus.) 

 6. Upon completion of chromatograms, have students measure Df (distance
solvent travels from original color dot), Ds (distance each color travels
from origin) and then calculate Rf (retention factor) for each color:
          Ds
    Rf = ----
          Df


 7. Use the process of chromatography to answer the questions: 1) why do some 
leaves look green and others look purple; 2) why do leaves turn color in the 
fall. 

 8. Run a leaf chromatogram to show that an Rf value is a constant under 
controlled conditions.  Expand to include different types of leaves.  (See any 
high school Biology text.) 

 9. Distinguish between the types of chromatography used in modern day analysis: 
thin layer, column and gas. 

10. Role play medical applications for chromatography by analyzing a 
chromatogram of ingredients of different headache remedies.  Compare this to a 
patient's blood sample to determine possible headache remedies an unconscious 
patient may have used.  (Chemicals in Action) 

11. Reaffirm that chromatography's use in industry and medicine make it "the
most versatile and powerful separation technique used by chemists today."

12. Motivate students to research current applications of chromatography, such 
as: fuel standards, air analysis, early disease detection from exhalents and the 
synthesis of new products from chromatogram analysis.   

References:

1. Brogie, E., Burns, M., and B. Maloney. NSTA 1988 Microscale Chromatography.
         1987 Dreyfus/Woodrow Wilson Institute.

2. Donovan, T., Poole, M., and D. Yack.  Chemicals in Action. Canada: Holt
         Rinehart and Winston, 1987.

3. Towle, A. Modern Biology and Modern Biology Laboratories. Holt, Rinehart
         and Winston, 1989.