Gas Chromatography/Mass Spectrometry
Gas Chromatography and Mass Spectrometry combines the identification power of gas chromatography with the quantitative analysis of mass spectrometry. Gas chromatography is a widely used laboratory technique that allows you identify specific parts of a mixture of substances. Mass spectrometry helps determine the molecular weight and components of the individual compounds. Where instruments of analysis are concerned, it is considered to be the “benchmark” of all systems. GC/MS has been used for a variety of different reasons from drug analysis to fire and explosions and airport security. Although this machine is highly recognized by technicians in the field of forensic science, it has also been used to aid in environmental and medical studies. By combining these two instruments laboratory technicians and investigators can get a quick and accurate analysis of mixtures in a rather short amount of time. This paper will focus on the development of these two systems, the advantages of GC/MS, the drawbacks that can happen, and what changes have been made to overcome them. History and Development
Chromatography or “color write” first dates to 1903 with the work of the Russian scientist, Mikhail S, Tswett. Archer Martin and James developed liquid–liquid chromatography in 1940s and published a paper that laid the foundation for the development of GC for which Martin earned a Nobel Prize. During the 1950’s two gentlemen, Fred McLafferty and Roland Gohlke, introduced the use of a mass spectrometer as a detector in gas chromatography (Harrison, 2006). When GS/MS instruments were first created they were very large and bulky in size. Some have been compared to being bigger than a dining room table. The development of miniaturized affordable computers have served a great role in the simplification in using this instrument, similarly it has allowed great improvements in how much time it takes an analysis of a sample. In his article, Stephen Harrison states that, “today you can put a GC/MS into a small suitcase and carry it to any location on a plant or factory or even a crime scene” (Harrison, 2006). Like most instruments used in chemical analysis, it is very important to calibrate each instrument and make sure all functional parts are working properly.
A gas chromatograph generally consists of six parts: Gas carrier, Interface, Pneumatic controls, Oven, Column, and the Injector. The sample is injected into the injector port with a needle or syringe. The gas carrier pushes the substance and aids travel through the column. An alternate term for carrier gas is also known as mobile phase. Several gases are used for this such as nitrogen, hydrogen, and helium which is the most common because it does to react or convert the sample. The sample moves through the metal tube or column that is packed with a substrate material (silica particles) or hollow capillary columns containing the stationary phase. The mixture breaks apart and travels through the column and into the detector at different times. The amount of time it takes an individual component of a mixture to travel through the column is known as the retention time. This retention time is what identifies the compound. The ovens in GC machines can have temperatures ranging from 5 to 400 degrees Celsius. The pneumatic controls regulate the pressure and flow of the gases that are fed through the column (Crawford Scientific, 2014) Once the sample has completed its separation phase in the GS system, it then travels through the transfer line (interface) and into the mass spectrometer. The MS system is designed to separate gas phase ions according to their mass-to-charge ratio (m/z) value by accelerating and subjecting them to an electric current or magnetic field (Crawford Scientific, 2014). Using electrical or magnetic fields the...
References: Crawford Scientific. (2014). Mass Spectrometry Fundamental GC-MS Inroduction. Retrieved from Chromacademy: http://forensicscienceeducation.org/wp-content/uploads/2013/04/Fundamental_GC-MS_Introduction.pdf
Crawford Scientific. (n.d.). Theory and Instrumentation of GC Ibtroduction to Gas Chromatography. Retrieved from Chromacadmey: http://forensicscienceeducation.org/wp-content/uploads/2013/02/Theory_and_Instrumentation_Of_GC_Introduction.pdf
Douglas, F. (n.d.). GC/MS Analysis. Retrieved from Scientific Testimony: http://www.scientific.org/tutorials/articles/gcms.html
GC/MS & GC/MS/MS Methods. (2010). Retrieved from Actlabs: http://www.actlabs.com/page.aspx?menu=65&app=221&cat1=534&tp=2&lk=no
Harrison, S. (2006). GC–MS: The Superior Forensic Tool. Retrieved from linde-gas.com: http://hiq.linde-gas.com/internet.lg.hiq.global/en/images/GC-MS-The%20Superio%20Forensic%20Tool_The%20Column%20March%202011899_89897.pdf
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