Gas chromatography (GC) is a technique used to separate and identify volatile organic compounds in a mixture. It works by carrying the analyte compounds through a stationary phase (usually a liquid coated on a solid surface) using an inert gas as the mobile phase. Compounds are separated based on their differing solubilities and boiling points. The GC outputs a chromatogram showing the retention times and relative amounts of each compound in the mixture, allowing for qualitative and quantitative analysis. In this experiment, students will analyze an unknown alkane sample by GC and compare its chromatogram to a reference to identify the compounds present.

1. Gas Chromatography Experiment

2. Gas 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.

3. GC Instrument
Schematic diagram for gas chromatograph

4. Injection 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.

5. GC Chromatogram
The chromatogram 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.

6. 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.