Paper Chromatography

Title Paper Chromatography

Aim To conduct chromatographic investigation of extracts and make comparison of the chromatograms

Hypothesis

Principle
Plants contain photosynthetic pigments which are used to absorb energy, and converting it to chemical energy. The pigments can be found inside the thylakoids and intergranal lamella. There are two classes of pigments: chlorophyll and carotenoids.

Chlorophylls are green pigments which include chlorophyll a and b. Carotenoids are yellow, orange, red or brown pigments but usually masked by the green chlorophylls.

Spinach leaves and Zebrina leaves are used in this experiment. Spinach leaves contain chlorophyll a and b and carotenoids as major pigments as well as smaller amounts of other pigments such as xanthophylls and phaeophytins which look like chlorophyll except that the magnesium ion Mg2+ has been replaced by two hydrogen ions 2H+. The vacuoles of Zebrina contain red pigments anthocyanin that gives the plant a purple color.

Paper chromatography is a technique by which chemical substances can be separated and identified. We use this method in this experiment to separate the mixture of pigments in chloroplast, after the pigments are extracted form leaves with organic extracting solvent: acetone-diethyl ether mixture.

When a paper strip containing a small spot of concentrated pigment is dipped in a mixture of developing solvent, the pigment will be carried up the paper strip as the solvents move up. Pigments separate because they move at different speeds – their speed depends on their solubility and molecular mass.

The furthest point reached by the pigments on the paper is called the solvent front. This can be used as a reference point for describing the relative distance of travel of different pigments in a chromatogram. The symbol used to designate this relative distance of travel is RF, which is the distance moved by the pigment / distance moved by the solvent front.

The RF is constant when...