Paper Chromatography

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Analysis of Food Colorings by Paper Chromatography

Introduction
Paper Chromatography one method for testing the purity of compounds and identifying substances. This is a useful technique because it is relatively quick and requires small quantities of material. Separations in paper chromatography involve the same principles as those in thin layer chromatography. The substances are distributed between a stationary phase and a mobile phase. The stationary phase is usually a piece of high quality filter paper. The mobile phase is a developing solution that travels up the stationary phase, carrying the samples with it. Components of the sample will separate on the stationary phase according to how strongly they absorb to the stationary phase versus how much they dissolve in the mobile phase.

Method

In order to carry out this experiment we had to obtain 45 ml of the chromatography solvent and 21.5 x 11.5 cm rectangle of chromatography paper. The solvent was poured into a clean 600-mL beaker. Using a pencil and ruler, a 1.5cm line was drawn across the long edge of the paper in the short edge. Starting from the left end of the line, we marked off 10 points 2cm apart from one another. Each point was labeled with the letters beneath the points. Two unknown color samples were also obtained for analyzing. The food colors were spotted on the chromatographic paper at the points prescribed, using a separate capillary tube for each spot. Once all the points have been spotted, the paper was set aside for a few minutes to allow the spots to dry. After all the spots were dried, the paper was rolled into a cylinder and carefully stapled together without the edges of the paper touching. The paper cylinder was placed into a jar into the solvent ensuring that the paper doesn’t touch the walls. The development chamber (jar) was tightly sealed and left undisturbed while the paper ascends. When the...
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