Gas Chromatography

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Purpose: The purpose of the gas chromatography lab is to find out how different substances interact with the surface of a solid. Chromatography is a separation technique that depends on the relative distribution of the components of a mixture between a mobile phase and a solid stationary phase. Chromatography measures the tendency of a substance to interact with the surface of a solid or to remain in a mobile phase. When doing a chromatography lab the mobile phase has to be a substance that is either in a liquid or a gas state. In this lab the mobile phase was a gas, which is why this is called a gas chromatography lab. The different gases tested in this lab were CHCl3 and CH2Cl2. It is determined to what extent a gas interacts with the solid by injecting a known amount of the mobile gas into the carrier gas and then measuring the concentration that comes out at the end of the column. From this there was a detector that transferred the information to a computer were it was graphed. The tendency of the gas to interact with the solid is determined by the number of theoretical plates. A substance that interacts more strongly with the surface of the solid will take more time to be carried across the stationary phase.

Procedure: The pieces of a Gas Chromatograph are the gas supply, injector, column and the detector. The gas supply, or carrier gas, is the gas from the valves at the lab tables. First a coil had to be made out of copper, which would serve as the burner for the detection system. A pipet was used as the column to put the solid stationary substance into. The solid phase in this experiment was Tide. The pipet was filled with Tide detergent and cotton was inserted in both end of the pipet. The column was then secured horizontally to a ring stand using clamps. The tip of the column should be in a vertical position. The copper coil is then placed in the vertical part of the column with the coil about 1/8” above the end of the column. It is important that the copper coil be placed at the right height because if it is too low the flame will not get enough air and if the copper is to high the flame will burn below the coil.
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