Objective: Gas chromatography is one of the valuable techniques in organic chemistry. It is use for the separation, identification, and analysis of all gas and volatile liquid mixtures, air, drugs, gasoline, moon dust and natural products. The objective of this experiment is to separate, by gas chromatographic techniques, a mixture of the three homologous series of alcohols and to determine the percentage of each an unknown mixture.
General Reactions: The gas-liquid chromatography involves a sample of a mixture of 1-propanol, 1-butanol, and 1-pentanol being vaporized and injected onto the head of the chromatographic column. The sample is transported through the column by the flow of inert, gaseous mobile phase. The column itself contains a liquid stationary phase which is adsorbed onto the surface of an inert gas. The temperature is critical during this process.
Specific Reactions: In the gas phase, the system must be confined to a pressure-tight volume in which the apparatus consist of a metal column in which the stationary phase is placed, the ends of which are closed with porous plugs. The temperature of the injection port should be higher than the boiling of the highest boiling component so that the mixture does not vaporize when is first introduce. The sample (mixture of 1-propanol, 1-butanol, and 1-pentanol) is then introduced at the head of the column in a small area and is then carried away by the carrier gas. The temperature of the column is lower than that of the injection port but high enough to prevent condensation of the components. Since the carrier gas flows continuously through the column due to the considerable amount of space in which the mobile phase flows. The molecules that make up the components of the sample are carried when they are not attracted to and immobilized by the stationary phase. The longer it is immobilized, the longer it will take to come out of to be extracted from the column.
Mechanism: the temperature of the detector should higher than the boiling point range of the mixture that way the sample clears it before a new sample is injected into the chromatograph. The mixture of 1-propanol, 1-butanol, and 1-pentanol will provide evidence of the separation during the column exit at the detector site. As each component is being extracted from the detector, a recorder which is attached to the detector is graphically documenting retention time. The chromatogram allows one to measure retention of times as well as relative concentration. Gas Chromatograph
Equipment and Chemicals
Equipment
1. Gas chromatograph
Chemicals known
1. 1-propanol
2. 1-butanol
3. 1-pentanol
4. Inert gas (helium, nitrogen, argon)
Unknown Chemical
1. Three-to-five carbon alcohol mixture
Experimental Procedure:
1. Introduce the sample at the head of the column.
2. Measure the retention times and relative time from the chromatogram.
3. Set the temperature of the range by the boiling range of the sample.
4. The temperature of the injection port should be higher than the boiling point of the highest component.
5. The temperature of the detector should be much higher than the boiling point range of the mixture.
6. Make sure the current of the inert gas is sufficient in order for the passing of the component.
7. Measure the peak area.
8. Multiply the height by half the base length or width at half height.
9. Set the gas chromatograph conditions as directed by professor.
10. Each column has different set of condition.
Clean up
1. Glass equipment should be wash individually with warm water.
2. Left over organic material should be dispose in proper containers. Do not dump in sink.
3. Turn off the air if used,
4. Put away your equipment in the drawer
5. Clean up your work areas
6. Close the fume hood sash completely
7. Wash hands thoroughly with soap and water before leaving the lab.
Data and Calculations
