PAPER CHROMATOGRAPHY

PAPER CHROMATOGRAPHY – Rf VALUES

Paper Chromatography is mainly useful for isolating very small quantities (milligram to gram) of a mixture. This is a handy procedure. Paper Chromatography is based on the variation in the partition coefficients of the components of a mixture between a stationary phase and a mobile phase. Stationary phase is usually water supported on a filter paper. Mobile phase is a flowing solvent unmixable or partly mixable with water.

Water is take up by filter paper and it will be always exist in the paper itself. In addition to the resultant of partition coefficient values, adsorption effects also take place to certain level.

PAPER-CHROMATOGRAPHY

The mixture solution is employed on to the filter paper likes a spot. After drying the spot, the filter paper is planted in an organic solvent in an air proof instrumentation. By keeping the mobile phase (organic solvent) in an air tight container, an condition of equally concentrated with solvent vapor is created. After the process, the paper is dried and the separated spots and solvent front are marked with a pencil and the distance from the point of origin spots are noted.

The ratio of the distance of spot of a particular component to the distance travelled by the solvent front is known as Rf value (retention factor) for that component.

Rf- value based on the factors like, paper type, direction of flow of solvent and temperature. It is a physical constant for a given compound at a given set of conditions of Chromatography. The values of Rf -are compared with the standardized values.

 

choice of paper in paper chromatography

In Paper Chromatography water is the stationary phase adsorbed on a filter paper. A piece of filter paper strip of about 25 x 5 cm is commonly used. In the place of strip of paper, a full page may also be used. When a whole page is used several separations may be carried along side by side under the same condition of solvent and temperature.

A typical multi page of four rolls capable of handling several paper squares may also be used. In order to present flow of the components in multiple separations, a slotted paper (Whatmann CRL/1 paper) is used. The paper is rolled into a cylindrical form and tied with white cotton. The paper roll is then kept in a petridish containing solvent properly covered with a tall beaker of 600 ml capacity.