To perform gas chromatography, often called GC, we use a gas chromatograph. A gas chromatograph is an instrument with a long column filled with small particles coated with a very thin layer of an absorbent. This layer is the stationary phase of the column. Helium runs through the column and is the mobile phase. A sample injected into the gas chromatograph is instantly vaporized in a heated injection chamber so that the components are in the gas phase and then it flows through the column. The helium is the carrier for your sample. This technique allows us to separate volatile organic compounds based on their physical properties and determine relative amounts of product yields. Coupled with a computer library, GC can also be used to identify organic compounds. To run a GC, you first need to prepare the sample for injection. Using a small syringe, collect between 1 and 5 microliters of the sample in the syringe, followed by a 3 to 4 microliters of air. Be sure that your sample is free of drying agent to avoid clogging the syringe. Once the sample is loaded into the syringe, insert the needle into the GC injection port. You will feel resistance as you insert the syringe. Continue to insert the needle through this resistant material called the septum until the glass is flush with the injection port. Be careful not to bend the syringe. You can now inject your sample into the gas chromatograph. When you inject your sample, make sure to promptly plunge the syringe without bending it. It is necessary to ensure that the entirety of the sample is injected at one time. At the same time you inject the sample, turn on the chart recorder. Make sure it is recording by checking the chart paper feed. If there is no paper or the paper jams, contact the TA for assistance. Wait until the entire sample has run through the column. While the sample runs through the column, clean the syringe that you used to inject your sample. Pull a solvent such as methanol into the syringe. Then empty it into a waste container to clean it of any remaining sample. When you are finished, turn off the chart recorder. Feed the chart paper to remove all chromatograms from the chart recorder. Cut with scissors.