The gas chromatograph-mass spectrometer (pictured at right) was added to our instrument holdings in 2007. Gas chromatography-mass spectrometry is a widely utilized technique for the analysis and characterization of complex mixtures. We’ve had this capability since the late 1980s, when professor Robert Lamb purchased the department’s first GC-MS with a grant from the National Science Foundation. This instrument is the one used routinely in the determination of organics in environmental samples, for the drug screening of athletes (e.g., at the Olympics), and for the monitoring of fuels at the Indy 500 race. The system, shown in the picture, consists of a gas chromatograph (GC) directly attached to a mass spectrometer (MS), with an automated sample changer on top.
The GC portion of this system provides high-resolution separation of volatile organic solutes in a mixture in the gas phase. As each solute exits the GC column, it is diverted into a mass spectrometer that is capable of both monitoring the amount of and identifying the chemical nature of the solute. In this way, both quantitative and qualitative information about the mixture can be obtained.
The MS portion of the system takes each gaseous solute exiting the GC and ionizes it in an electron beam. The ions formed by a specific solute will depend on the nature of the bonds in the molecule, and both ionized molecules and ion fragments of the molecule are possible. The ions are then directed down a separator, which isolates and counts the ions according to mass. The sequence and relative intensity of the mass peaks give information about the chemical identity of the solute. The absolute intensity of the peaks provides information about the amount of substance present.
The Varian 4000 GC-MS has an ion trap mass spectrometer, which makes chemical ionization and tandem mass spectrometry (MS-MS) affordable options. Over the years, GC-MS has been a technique used by several students in their senior research projects. This instrument is also used in courses such as organic, quantitative analysis and instrumental analysis.
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