In general, chromatography is a term that describes techniques used to separate components of mixtures. In gas chromatography, a gas is used to carry a mixture across a bed of material. Because the gas moves it is called the mobile phase. The bed of material, on the other hand, is called the stationary phase because (you guessed it) it doesn't move. As the mobile phase carries the mixture across the stationary phase, some of the components of the mixture "stick" to the stationary phase more than others. Therefore, the components travel at different rates across the stationary phase, and exit the stationary phase at different times. The components of the mixture have been separated!
In gas chromatography (GC) the gaseous mobile phase is forced through the staionary phase using pressure. A simple GC would include a tank of gas, pressure and flow regulators to control the gas flow, an oven, an injector to allow injection of a small volume of the sample mixture under pressure, a column containing the bed of stationary phase, a detector to detect the presence of components as they exit the column, and some means to record the detector signal.
More sophistocated GCs may involve, electronic pressure and flow control of the mobile phase, robotic arms capable of injecting perhaps 100 samples unattended (autosamplers), mass spectral detectors capable of identifying components as they exit the column, and complete computer contral for automation.
Gas chromatography is a widely used technique that has been applied to a plethora of complex mixtures across a diverse sampling of disciplines
Our Agilent 6890 GC is the most sophistocated GC that we have. It is completely automated using Chemstation software, and is fitted with a 100 sample autosampler. The capillary column in this GC is capable of separating components from very complex mixtures. The mass spectral (MS) detector is one of the most powerful detectors for gas chromatography. Not only is it capable of detecting miniscule amounts of analytes in samples, it can provide information regarding the identity of each compound in the mixture.
To demonstrate the power
of GC-MS we have students shake a $1, $5, $10 or $20 bill with small volume
of methanol in a vial. The methanol extract, containing various compounds
from the currency, is injected into the Agilent GC-MS. Each peak on the chromatogram
represents one component of the mixture.
We have two HP 5890 GCs that are both equiped with autosamplers, and automated using Chemstation software. One of these GCs has dual flame ionization detectors (FID). The other has an FID and a hot wire detector. These have proven to be very reliable instruments. Having several GCs ensures that all students are provided with hands-on opportunities in the lab.
Our SRI 8610 is a rudamentary gas chromatography that uses a packed column and a hot wire detector. The simplicity of this instrument allows students to grasp the operating principles of gas chromatography without a lot of automation. However, the data collection software associated with this GC is powerful, and provides all the necessary tools to transfer knowledge of chromatogrpahy data analysis to more sophistocated systems.
Gas chromatography is a technique that has an enourmous application base. Below is a tiny sample of some examples of GC separations.
Hydrocarbon gas analysis
Fuel and fuel oil analysis
Oxygenated additives in gasoline
Determination of pesticides
Detection of disinfection by-products in drinking water
Detection of PCBs (polychlorinated biphenyls)
Underground storage tank leakage
Air pollution consituent analysis
Fast Analysis of Dioxin and Related Compounds
Residual solvents in pharmaceutical formulations
Determination of drugs in race horse urine
Blood alcohol analysis
Determination of illicit drugs
Monitoring drug purity
Determiniation of drug impurities to track sources
Clandestine lab analysis
Analysis of commonly abused inhalants
Food and Flavor
Quality control of alcoholic beverages
Fatty acid analysis
Detection of 145 components in rose oil (identified 127)
Volatile compounds in food packaging
GC Resource Sites
Several Vendors of GC Equipment
Several Vendors of GC Columns and Accessories