www . Science-Projects . com

SUMMER Fall COLORS FALL

 
| Site's Table of Contents | Site's Index |

| Previous and a few Future Projects in the South Hill Enterprise |

CHROMATOGRAPHY OF PLANT PlGMENTS

It was in the early 1940's that paper chromatography was invented by an observant person who saw application in how inks made rainbox hues when they "ran" on water-spattered paper. If you do not understand the principles behind "affinity" chromatography, you might find it helpful to look at an analogy.

Equipment

• Various leaves
• a coin (quarters and halves work well)
• chromatography paper
  | Sources | Remember to handle paper strips by the edges only.
• solvent: 9 parts petroleum ether/l part acetone (5 mls/group). (Ordinary lighter fluid is petroleum ether and is the cheapest way to get it; acetone (warning) can be bought in paint departments.)

DO THIS WORK OUTSIDE AS THE PETROLEUM ETHER AND ACETONE ARE HIGHLY FLAMMABLE!
Or in a fume hood.

1. Obtain a strip of chromatography paper, and very lightly pencil a line across the paper about 1.5 cm from the end.
   
2. Place a leaf over a piece of chromatography paper and roll, with great force, the rounded end of a spoon or the knurled edge of a coin over the leaf (perhaps using a ruler as a guide) A particularly good specimen is a leaf that is sharply divided in its colors. The "roll" should be made across that demarcation line as shown to the right. (The use of an inverted rounded soup spoon works especially well for students who are not bulging with muscles as the thumb can easily exert the pressure needed by pressing on the upside-down bowl of the spoon.)
   
3. The pigments of the leaf are driven into the paper on the lightly pencilled line.
   
4. This can be chromatographed in a physical setup such as:
   
5. The solvent of1 part acetone and 6 to 9 parts of petroleum ether (or cigarette lighter fluid or naphtha or mineral spirits) should be used in a fume hood or outside (unless you want to get a headache or have the excitement of an exploded lab). Pour the solvent into your apparatus, but only so high. The paper should not be more than about 1 cm deep into the solvent. Immediately cover the apparatus so that the fumes will saturate the atmosphere around the paper as the liquid slowly ascends or soaks its way up the paper.
   
6. It will take awhile for the liquid's front on the paper to move up to within a short distance of the top. That is the time to "stop" the chromatogram. Do not let it run to the top or else you should do the whole thing over with a new strip, and new printing of the pigments, etc.
   

Discuss the pigments: what colors (wavelengths) do they absorb? Why are there more than one pigment? (HINT)

You textbook probably says that during the summers, the red pigments are masked by the green. How can you check this out? If you have done so, what were your results?

Just to show you that this chromatography is not just merely playing with colors, consider a taxonomic survey and its implications.

For more on photosynthetic pigments, including looking a absorption spectra, isolating chloroplasts, and running in vitro photosynthesis reactions, click . Also see THIS about why you usually don't see any red pigments on your chromatograms of summer leaves, but do in fall leaves.

A sources for chromatography paper: The author of this website has tried many other types of commercially available paper but finds none are as good as the true "chromatography paper." If you happen to know of an easily procurable paper from a neighborhood source, please inform this author.

• Nasco Science: cat.no. SB16079M (roll: 1 inch x 100 yards); less than $20.
• Nebraska Scientific: no cat. no. are given (roll: 1.5 inches x 100 yards); less than $60.

Acetone is a strong organic solvent so make sure that you don't damage countertops and floor tiles with spills and dribbles. Almost all plastics are highly susceptible to acetone, but polyethylene and polypropylene are not damaged.

| Site's Table of Contents | Site's Index |