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Gas Chromatography - Gas Chromatography Analysis of a...

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Gas Chromatography: Analysis of a Hydrocarbon Mixture Jake Rietschy, Mike Olah and Aaron Schmick Chemistry 330
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Introduction: The composition and identity of an unknown hydrocarbon mixture were determined using gas chromatography. The retention times of the standard solution were compared to those of the unknown. Unknown solution A contained 51.6% dodecane and 48.4% octane, and unknown solution D contained 92.5% nonane and 7.33% undecane. Reactions, Mechanisms, and Theories: Chromatography is a way of separating components of a mixture based on their individual affinities for both the stationary phase and mobile phase. There are three main types of chromatography; column chromatography, thin layer chromatography (TLC), and gas chromatography (GC). Gas chromatography can be used as stated earlier for separations, to determine percent composition, or to identify a compound by comparison to a standard. Gas chromatography contains many different parts; the gas cylinder, flow regulator, injection port, oven, detector and recorder, however, the main chemistry occurs in the injection port and oven. In the injection port, the sample was instantly vaporized, so it could travel through the column in separate components. The injection port therefore must be hotter than the highest boiling point in the sample, in this case, 70 ºC. The sample needed to be injected quickly as not to produce misleading results, in which the components are mixed. The oven is a heated region which contains a coiled column in which the mobile and stationary phases reside. The particles of the sample travel through this area, spending time in both the mobile and stationary phases. The sample then passes into the detector where it passes over a wire conducting electricity. The sample absorbs a different amount of heat as compared to the gas from the mobile phase. This changes the way the wire conducts electricity and can then be interpreted by the recorder, as peaks on a chart.
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In gas chromatography the mobile phase is gaseous, usually an inert gas as to prevent reactivity with the samples, or the stationary phase. Helium, Argon, and Xenon are all good choices for a mobile phase. The gas should also have no affinity for the stationary phase.
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