Paper Chromatography

Introduction Chromatography is a widely used method of separating mixtures into their component parts. Paper chromatography separates substances using two things (called phases) The first thing is chromatography paper; also called the stationary phase Next we have a solvent – called the mobile phase

Basic Principles When the paper comes in contact with the solvent, the solvent moves up the paper The solvent that is used depends upon the substances you are trying to separate. Commonly used solvents include water, alcohol (ethanol or isopropanol) and acetone.

Separation the different components of a mixture will travel different lengths along a piece of paper when a solvent is allowed to travel up it The length that a specific component will travel along the paper is dependent upon several forces.

Propelling Forces and Retarding Forces The main propelling force is the flow of the solvent the rate that a substance will flow in that solvent is dependent on its solubility More soluble Less soluble The main retarding force is the degree to which the substance adheres (sticks) to the paper A substance with a strong adherence will not travel as far as a substance with low adherence

Solubility If a component of a mixture is completely soluble in a solvent then it will travel farther along the paper than a component that is not soluble or only partially soluble. The degree to which a substance is soluble depends on the solvent Generally speaking, a polar substance will have a greater solubility in a polar solvent (like dissolves like) and non polar substances will be more soluble in a non-polar solvent

Rf Values To quantify the degree to which a substance is moved by a solvent, Rf values are used Rf stands for “Retardation Factor“(sometimes called “rate of flow”) Is a simple calculation: Rf = distance substance moved distance of lead front of solvent

Rf Value Calculation Here the Rf values of two substances in a mixture are calculated