How to Use a Gas Chromatograph

2013-05-22 15:59:38 liting

Gas chromatography is a technique used in chemistry to analyze the components of a sample compound. It can typically determine the purity of a particular substance in a solution, and it can also separate specific components in the sample. A gas chromatograph (GC) uses a narrow tube known as a column that contains a column filling called the stationary phase. The sample is transported through the column with a carrier gas and each component in the sample requires a different amount of time to pass through the stationary phase.
1.Set the conditions for a particular test. Conditions such as temperature, carrier gas and gas flow rate must be carefully controlled for each GC test. Other important factors include the specific stationary phase and the exact dimensions of the column.
2.Inject a known volume of a gaseous or liquid sample into the entrance of the column. The specific method depends on the state that the sample is in. A gas requires a gas source switching system, a liquid will use a microsyringe and a solid sample will need microextraction fibers.
3. Allow the carrier gas to move each analyte through the column. Each analyte will require a different amount of time to pass through the column if the composition of the stationary phase has been carefully chosen. This time is known as the analyte's retention time.
4. Monitor the sample's outlet stream with a detector. A GC is connected to a detection device, such as a mass spectrometer, that will allow the sample to be properly analyzed. There are many different possible detectors, depending on the specific sample and application.
5. Analyze the results of the GC. The GC typically produces a two-dimensional graph that shows the detector's response versus the retention time. This requires considerable general expertise from the analyst in addition to specific knowledge about the test sample.