#PaperChromatography

#Chemistry

#SeparationTechniques

Introduction

• Paper chromatography (PC) is a type of planar chromatography whereby chromatography procedures are run on a specialized paper.

• PC is considered to be the simplest and most widely used of the chromatographic techniques because of its applicability to isolation, identification, and quantitative determination of organic and inorganic compounds.

• It was first introduced by German scientist Christian Friedrich Schonbein (1865).

• Paper chromatography is a separation technique in which paper or paper covered with a thin film of solvent is used as a stationary phase.

• The resolution of mixtures of solutes on filter paper may depend upon: surface adsorption and partition.

• The predominant factor of separation, however, is partition.

• In Adsorption, Paper impregnated with silica or alumina acts as adsorbent (stationary phase) and solvent as mobile phase.

• Moisture / Water present in the pores of cellulose fibers present in filter paper acts as stationary phase & another mobile phase is used as solvent In general paper chromatography mostly refers to paper partition chromatography.

• The adsorption chromatography is used for solid-gas chromatography and solid-liquid chromatography. Whereas, partition chromatography is the liquid–gas, and liquid-liquid.

Method

• Chromatography is used to separate substances and provide information to help identify them

• The components have different solubilities in a given solvent

  • E.g. Different coloured inks that have been mixed to make black ink

• A pencil line is drawn on chromatography paper and spots of the sample are placed on it

  • A pencil is used for this as ink would run into the chromatogram along with the samples

• The paper is then lowered into the solvent container, making sure that the pencil line sits above the level of the solvent so the samples don’t wash into the solvent container

  • The solvent used is usually water but it can be other substances such as ethanol

• The solvent travels up the paper by capillary action, taking some of the coloured substances with it

• Different substances have different solubilities so they will travel at different rates, causing the substances to spread apart

  • Those substances with higher solubility will travel further than the others

Interpretation

• We can use a chromatogram to compare the substances present in a mixture to known substances and make assumptions

  • Pure substances will produce only one spot on the chromatogram

  • Impure substances will produce more than one spot on the chromatogram

  • If two or more substances are the same, they will produce identical chromatograms

  • If the substance is a mixture, it will separate on the paper to show all the different components as separate spots

• It is common practice to include a known compound as a reference spot

  • This can help match up to an unknown spot or set of spots in order to identify it