Organic Chemistry Laboratory - CH 201 (2010-2011) Experiment 4B
Column and Thin-Layer Chromatography of Capsicum Frutescens L. Pigments
John Cyril Abanto*, Vernalyn Abarintos and Clarice Gail Abella Department of Chemistry, College of Science
University of Santo Tomas, Espana Street, Manila 1050
Abstract: The experiment was done to separate and analyze the components of chili pepper. Chromatography was used because of its powerful technique in separating mixtures. In this experiment the Chili pepper pigments was extracted using DCM, the extract was then introduced into the column and eluate was collected, a technique called column Chromatography. Using the Thin Layer Chromatography the purity of the components was tested. The UV lamp was used to spot the UV visible components and the Retention Factor was computed.
Keywords: Column Chromatography, Thin-Layer Chromatography, Retention Factor ____________________________________________________________
Chromatography (color writing) is a separation technique used to identify the components of a mixture and to purify a compound. The mixture dissolves in a solvent, the mobile phase, as it passes through an adsorbent material, the stationary phase. Mikhail Tswett developed this process to separate the pigments in green leaves. He dissolved the leaf extract in an organic solvent and let the solution run down through a vertical glass tube with chalk powder. A variety of pigments flowed through the column at different rates, while a series of bands appeared on the white chalk column
Several chromatographic techniques are being used today such as gas chromatography (GC), high-pressure liquid chromatography (HPLC), and thin layer chromatography (TLC). Liquid chromatography, or column chromatography, is patterned from Tswett’s experiment. Solvents are added to into a stationary phase, alumina or silica gel, packed into a glass column. There are two types of column chromatography depending on the flow of solvent: gravity column chromatography and flash chromatography. In flash chromatography, the solvent is forced down the column by positive air pressure; while in gravity column chromatography, the solvent is allowed to flow by gravity, or perlocation.
The objective of this experiment is to separate and analyze pigments of capsicum frutescens, specifically chlorophylls (chlorophylls a and b, pheophytin) and carotenoids (carotenoids α and β, xanthophylls) through the process of gravity column chromatography.
2. Experimental Section
Ten red peppers were deseeded and chopped. It was then pounded using a mortar and pestle with sand in it. The mixture was then titrated and filtered with 20 ml CH2Cl2. A small piece of cotton was placed inside a 10 ml plastic syringe with the needle tip removed and was replaced by a burette stopper. Slurry of silica in hexane was prepared. Slurry of silica was pipetted quickly using a clean dropper to avoid the silica of drying out. One drop of the chili pepper extract was placed on top of the silica. After allowing it to go down and absorbed another drop of the extract was placed on top of the silica. This process was done several times. No liquid extract was left on top of the silica. The first eluting solvent which was hexane was added to the silica allowing it to go down. The same procedure was done with the second solvent hexane-CH2Cl2, third solvent CH2Cl2 and fourth solvent CH2Cl2-MeOH. The pigments were collected in a clean dry test tube when the color is about to be eluted out of the column. The samples were then covered with aluminum foil and protected from direct sunlight....