What does chromatography allow a biologist to do

Chroma means color and graph means to write or draw. Paper chromatography is an analytical technique used to separate mixtures of chemicals sometimes colored pigments using a partitioning method. The paper in this method is called the stationary phase because it does not move and serves as a substrate or surface for the separation.

Analytes substances being analyzed are separated from each other based on a differential affinity to a solvent. The solvent dissolves and carries the analytes along the matrix of the stationary phase. Since the solvent moves through a wicking action, it is called the mobile phase.

The distance that the analyte migrates along the paper related to the total distance that the solvent or mobile phase moves is called the Retention Factor or R F. Place approximately 1 cm of mobile phase solution a very polar saltwater solution into the beaker. Separation by chromatography produces a chromatogram.

A paper chromatogram can be used to distinguish between pure and impure substances:. A paper chromatogram can also be used to identify substances by comparing them with known substances. Two substances are likely to be the same if:. In this chromatogram, the brown ink is made of a mixture of the red, blue and yellow inks. A drop of mixture solution is spotted near one end of the paper and then dried.

The end of the paper, nearest the spot, is then dipped into the solvent without submerging the spot itself. In ascending chromatography, the solvent is in a pool at the bottom and moves up by capillarity. In descending chromatography it is in a trough at the top and flows down by capillarity and gravity. The solvent flows along the paper through the spots and on, carrying the substances from the spot.

Each of these will, if the solvent mixture has been well chosen, move at a different rate from the others. After a time the paper is taken out and dried: the substances can be seen at once if coloured, or located by treating with a suitable locating agent. The distance a substance travels depends upon the resultant between propelling and retarding forces. Propellors a Solvent flow Usually the more soluble a substance is in the solvent, the more rapidly it will move along the paper. For example:.

Calculate the R f value of each spot:. Compare the R f values and colours of each spot in the inks. Describe their similarities and differences. Explain why the distances travelled by each spot were measured in mm, rather than in cm.

Measurements in millimetres are more precise than those in centimetres. They will give more precise R f values. It is important in this practical activity to use appropriate apparatus and methods. This includes the safe use and careful handling of substances.