Chromatography

Chromatography & The Plant and Photosynthesis Lab

 

Background: Chromatography is a process in which a chemical mixture is separated, and the substances will be shown in different colored bands on chromatography paper. There are few factors that allow chromatography to happen, such as  sizes of the molecules, solubility of the pigments, light intensity, and the attraction between chromatography paper with the molecules. Chromatography is important for scientists  to separate organic and inorganic compounds, so that scientists can analysis what make up the compounds.

Process and Method: In the experiment, the chromatography paper gives pigments a surface to separate, so it allows the molecules in the mixture to move. The solvent is to separate the pigments of the chloroplasts by moving the pigments up onto the paper, and it must be an organic solvent.

 

The distance travelled by compound is the D unknown, and the distance travelled by solvent is D solvent. The distance travelled relative to the solvent is called the R_f value.  The R_f  value is useful to scientists because it can be used to determine the compounds made up the studied subjects. 

The picture below shows the travel distance of  different pigments in black mark pen ink.

 

In the Plant and Photosynthesis Lab, we separated the individual pigments involved in photosynthesis.

First, we cut the end of the chromatography paper strip into a triangle, and then we used a coin to roll on the leaf to draw a line of green leaf pigment.

Afterwards, we poured approximately 2 ml of the “chromatography solvent” in the vial, carefully placing the paper strip into a vial with “chromatography solvent”, make sure that the paper strip just touches the bottom, and then place the cap on the vial immediately.

Wait for the solvent to migrate up the chromatography paper strip, then the color will be shown.

Data: There are two colors shown on the paper: green and yellow.

Rf of Green is : (5.8)/(6.0) =0.967

Rf of Yellow is: (4.7)/(6.0) = 0.783

Analysis and Conclusion: The Rf of the yellow band is smaller, which means the yellow pigment is more attracted to the solvent and thus has a more difficult time moving up the paper strip.

Interestingly, my lab partner Bharathi used a PURPLE leaf, but the result turns out to be very similar.

The final pigments occurred on the paper were always  green and light green, which means purple leaf contains the same pigment as green leaf does, and the leaves, regardless what color of pigments they contain, all undergo photosynthesis. 

 

My question is: Why there are only two colors rather than more? What does the green color imply about the leaf chloroplast?

Source(s):

N.p., n.d. Web. 6 Sept. 2013. <

<http://www.chemguide.co.uk/analysis/chromatography/paper.html>.

Phschool. N.p., n.d. Web. 9 Feb. 2013. <http://www.phschool.com/science/biology_place/labbench/lab4/design1.html>.