What is the aim of a chromatography of photosynthetic pigments experiment?

Question

*what does RF mean ?

Answer 1

The aim of the experiment is to seperate the various photosynthetic pigments like chlorophyll A, chlorophyll B, xanthophylls,etc

By calculating the Rf values one can confirm the type of pigment.

Rf stands for resolution front. to understand Rf one needs to understand the set up of a chromatography apparatus. Let us take the example of chormatography technique used to separate photsynthetic pigments. the apparatus consists of a standing glass chamber about 15cm in height having a base of about 5X5 cm.

in this chamber a little amount of organic solvent is put,say upto a height of 0.5 cm. a strip of whattman filter paper is taken and the photosynthetic pigment is applied as a spot at one end of this stip (abt 0.5 cm from the end). this stripped is dipped in the organic solvent(the photosynthetic pigment towards the solvent) .the glass chamber is kept covered. now, the solvent of the chamber starts moving up on the whattman filter paper strip. as it moves up, it carries the photosynthetic pigments with it also.along the lenght of the whatman strip the various photosynthetic pigments separate owing to various factors such as molecular weight of the pigment. the solvent travells the maximum length as compared to different pigments.

the Rf can be defined as the ratio of the distance travelled by a pigment to the distance travelled by the solvent.

Rf=distance travelled by pigment / dist travelled by solvent

Eg.. if chlorophyll A travells 3 cm and the solvent travells 6 cm then Rf of chlorophyll A = 3/6 = 0.5

similarly if chlorophyll B travells 2 cm then Rf= 2/6=0.33

Answer 2

The pigments in leaves absorb light energy and convert it to chemical energy. This energy is transferred to and trapped inside chemicals such as glucose and starch.

2. Several different pigments are involved in the absorption of light. This experiment shows how these pigments can be extracted from plants and then separated.

3. Chromatography is a method used to separate chemically similar substances. Once the separation is complete, a chromatogram is formed.

4. The distance that a pigment travels over the thin layer plate depends on two factors:

a) the solubility of that pigment in each of the chemicals in the solvent. The more soluble a pigment the greater the distance it will travel.

b) the adsorption of the pigment to the thin layer plate. The more strongly a pigment is adsorbed to the silica of the plate the more slowly it will travel.