Why pigments move farther than others

Some pigments dissolve in water easier and are pulled with the water farther up the paper. Others are more attracted to the paper and move more slowly. Usually smaller molecules will move farther than larger ones.

Beta carotene A small sample of plant pigment placed on chromatography paper travels up the paper due to capillary action. Beta carotene is carried the furthest because it is highly soluble in the solvent and because tit forms no hydrogen bonds with the chromatography paper fibers.

The least soluble pigment traveled the shortest distance, and that was the chlorophyll b. The chlorophyll a molecule was in the middle of the other two and showed an intermediate solubility. The pigments are carried along at different rates because they are not equally soluble. In the experiment pictured at left, the solvent used was comprised of nine parts petroleum ether and one part acetone.

A small amount of this solvent is added to a large test tube and capped with a rubber stopper. Note that chromatography solvent is highly volatile and flammable. The V-shaped tip of the paper is placed in the chromatography solvent and acts as a wick to draw the solvent up the paper, separating pigments according to their relative solubility and molecular weights.

The paper is allowed to remain in the solvent until the uppermost pigment band nears the top of the paper. This photograph shows the four main pigments separated from green plants using paper chromatography.

The primary pigments in green plants are chlorophylls, represented by chlorophyll a and b, which appear green. Visible light, or white light, is made up of the colors of the rainbow. Some of these colors are absorbed "used" by pigments and others are reflected. Pigments appear the color of the reflected light, so the chlorophyll pigments do not use the green portion of the spectrum.

This means that it must be less than 1. This is evident from its distance from the solvent front; only 0. The pigment that moved the slowest, and therefore the smallest distance was chlorophyll b.

Carotene pronounced CARE-a-teen — gold, orange. Anthocyanin pronounced an-tho-SIGH-a-nin — red, violet, can also be bluish. The orange colored band, made of the pigment called carotenoids. The yellow xanthophylls are the next most soluble, followed by the blue-green chlorophyll A. The least soluble pigment is the yellow green chlorophyll B. This makes chlorophyll b slightly more polar than chlorophyll a.

The purple and orange colors are more soluble in water, because of the rate in which they traveled as the filter soaked up the water. In general, the adsorptivity of compounds increases with increased polarity i. Larger molecules take longer to move up the chromatography paper or TLC plate, whereas smaller molecules are more mobile. Skip to content. Search for:. Home » QA.