Gas Chromatography and Mass Spectrometry
About Gas Chromatography
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 stationary 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 sophisticated 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 control 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.
KU Gas Chromatographs
Agilent 6890 GC With a 5973 Mass Spectral Detector
Our Agilent 6890 GC 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 a 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.
The peak at at 6.39 minutes was present for some samples, but not for others. The mass spectrometer detector on this instrument provides information that helps determine the identity of this compound. This mass spec works by bombarding the sample with a shower of electrons. These electrons cause the compound to fragment into smaller pieces. Then, the mass spec measures the masses of the fragments. The result is a mass spectrum which shows the abundance of each fragment. This fragmentation pattern is unique to a particular compound and can be used to conclusively identify the compound. Two mass spectra are shown below. The one on the left is the mass spectrum of the peak at 6.39 min. The one on the right is a mass spectrum of a cocaine standard. Pretty similar, eh?
Agilent 7890 GC with a G1888 Automated Headspace Sampler
Our new Agilent 7890 gas chromatograph is equipped with dual capillary columns and flame ionization detectors. Students get to use this gas chromatograph in Organic, Analytical, Environmental Analysis, Physical Chemistry, and Research. The automated headspace sampler is used to determine blood alcohol content, evaluate perfumes and fuels, and determine Henry's Law constants
Hewlett Packard 5890 GCs
We have two HP 5890 GCs that are both equipped with autosamplers, and are 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.
This GC has been used to determine the identity of accelerant used to start a fire. The blue chromatogram is a separation of the vapor above a sample of turpentine. The red chromatogram is from the vapor above a charred piece of wood that was doused with turpentine.
SRI 8610 Gas Chromatograph
Our SRI 8610 is a rudimentary 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 chromatography data analysis to more sophisticated systems.
Applications of Gas Chromatography
Gas chromatography is a technique that has an enormous 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
Determination 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