Gas Chromatography ExperimentGas Chromatography Experiment

Gas ChromatographyGas Chromatography

- GC is a common technique used to separate and identify volatile organic

compounds (analytes). As the gas moves the analyte across the stationary phase,

the analyte will be in equilibrium with the gas and the liquid phase (usually suspended

on a solid surface).

- The mobile phase is an inert gas. Commonly used gases include N2, He, Ar, and

CO2, depended on the type of detector.

- The stationary phase is a high-boiling liquid film supported on an inert solid and

packed in either a fused silica (12 to 30 meter) capillary column or in a copper or

stainless steel (1.5 to 3.0 meter) metal column.

- This method depends upon the solubility and the boiling point of the volatile

organic liquid in order to separate them from a mixture.

- It’s both a qualitative (identity) and quantitative (how much) tool.

GC InstrumentGC Instrument

Schematic diagram for gas chromatographSchematic diagram for gas chromatograph

Injection PortInjection Port

Sample sizes for standard GC procedures typically involve 0.1 to 10.0

microliters of analyte solution injected into a heated sample port.

The needle must be inserted carefully to avoid bending or breaking.

GC ChromatogramGC Chromatogram

The chromatogramchromatogram shows:

1. the order of elution (order of components coming off

the column) related to boiling points and polarities of

the substances in the mixture,

2. the retention time (time of elution), and

3. the relative amount (peak area) of the components in the mixture.

Experimental Procedure

1. Instead of the acetates listed in the lab manual, we will work with a series of

alkanes. The gas chromatogram for these alkanes has already been done.

2. The TA provides only 1-2 drops of the GC unknown. Record the code in

your lab notebook.

3. Perform just one run of the unknown.

4. Compare your unknown chromatogram to the posted chromatogram of the

mixture containing all “knowns”.

In the same conditions used, same compound will come out

at the same retention time.