Column Chromatography Lab

Introduction

Chromatography is an extensive range of laboratory technique which aims to separate complex mixtures into their components which are distributed between a stationary phase bed and a mobile phase. There are various methods of chromatography. One method of mixture separation by chromatography is the column chromatography. Column chromatography gives a clear visual separation of components throughout the column. It is a cheap, simple method however it is time consuming. Another method of chromatography is thin layer chromatography which can be used to determine the number of components present within a mixture and to monitor column chromatography (Mohrig, et al., 2006). Thin Layer Chromatography is commonly used because it is a sensitive,

In this practical, about 2.0 grams of leaves were weighed out, torn into confetti sized pieces. These leaf pieces were placed into the mortar and added with 5.0mL of acetone. The components of the mixture were extracted using 5mL of hexane and acetone. The crude extracts were then filtered with a filter paper and a funnel into a test tube. A small amount of anhydrous sodium sulfate was added to remove the excess water. The crude extracts were added with silica gel to dry it up. The second part after extraction was the column chromatography method. The column was packed with about 70g of silica gel. Using a glass rod to control the flow, hexane was added into the column. The column was then pumped to avoid air bubbles. The crude extract of the leaves was pipetted onto the top of the silica gel gently to keep it at a straight layer. Hexane was poured and run to elute the non-polar compounds. This procedure was repeated a number of times to separate the components. The separated component was collected in a test tube at the bottom of the

Compounds can be identified by measuring the Rf values.
Column chromatography is a method of separating components within a mixture using a column that is commonly used in organic chemistry. This method of separation is similar as thin layer chromatography however column chromatography can separate mixture at a larger volume. In column chromatography, the stationary phase is packed into a glass column. Silica gel was used as the stationary phase in this practical. The more polar compound will remain on the stationary phase at a longer time than a less polar compound. A less polar compound will be eluted from the column first. The mixture is pipetted onto the stationary phase gently and a mobile phase which is known as the eluent is passed through the column by a pumping system. As the eluent, which in this practical is the hexane, flows through the column, the mixture separates and the different compounds can be collected when the compound reaches the end of the column (Wilson & Walker, 2010). Factors that influence the separation and rate of elution include polarity of the solvent. With increasing polarity of the mobile phase, the substrate travels at a faster rate. Another factor that influences the separation include the substrate interaction with stationary phase in which the stronger the interaction, the slower the movement of the substance (Totah, 2011). The major advantage of column chromatography