Varian 4000 Gas Chromatograph-Mass Spectrometer (GC-MS)
This gas chromatograph-mass spectrometer (pictured at right)GC-MS Picture is 2007 addition to the department's instrument holdings. Gas chromatography-mass spectrometry is a widely utilized technique for the analysis and characterization of complex mixtures. The department has had this capability since the late 1980s when Prof. 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 which 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 purchase of this new instrument represents not only an update in the department's instrumentation, but also brings some new capabilities. The Varian 4000 GC-MS has an ion trap mass spectrometer while the previous instruments were quadrupole mass spectrometers. The two mass analyzers are equivalent in many ways, but the ion trap mass spectrometer's design makes chemical ionization and tandem mass spectrometry (MS-MS) affordable options. For the same price as a quadrupole capable of electron impact ionization we were able to obtain an ion trap instrument with electron impact and chemical ionization along with the ability to perform tandem mass spectrometry experiments.
Over the years GC-MS has been a technique used by several students in their senior research projects. This continues as a current senior chemistry major, Danielle Slomberg, is using the new GC-MS in a project involving the analysis of rural drinking water for pesticides such as atrazine. This instrument will also be used in the teaching of courses such as organic, quantitative analysis and instrumental analysis.