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Gas chromatography (GC), is commonly used in analytical chemistry for separating and analyzing compounds that can be vaporized without decomposition. Typical uses of GC include testing the purity of a particular substance, or separating the different components of a mixture (the relative amounts of such components can also be determined).
In gas chromatography, the mobile phase (or "moving phase") is a carrier gas, usually an inert gas like helium or an unreactive gas like nitrogen. The stationary phase is a microscopic layer of liquid or polymer on an inert solid support, inside a piece of glass or metal tubing called a column. The instrument used to perform gas chromatography is called a gas chromatograph (or "aerograph", "gas separator").
A gas chromatograph (GC) is an analytical instrument that measures the content of various components in a sample. The sample solution is injected into the chromatograph enters a gas stream, either helium or nitrogen, that transports the sample into the column. Inside the column, the various components are separated and the detector measures the quantity of the components that exit the column. To measure a sample with an unknown concentration, a standard sample with known concentration is injected into the instrument. The standard sample peak retention time (appearance time) and area are compared to the test sample to calculate the concentration.
In principle, gas chromatography is similar to column chromatography (as well as other forms of chromatography, such as HPLC, TLC), but has several notable differences. First, the process of separating the compounds in a mixture is carried out between a liquid stationary phase and a gas mobile phase, whereas in column chromatography the stationary phase is a solid and the mobile phase is a liquid. Hence, the full name of the procedure is "Gas–liquid chromatography," referring to the mobile and stationary phases, respectively. Next, the column through which the gas phase passes is located in an oven where the temperature of the gas can be controlled, whereas column chromatography generally has no such temperature control. Finally, the concentration of a compound in the gas phase is solely a function of the vapor pressure of the gas.
Fractional distillation is also similar to gas chromatography, since both processes separate the components of a mixture primarily based on boiling point (or vapor pressure) differences. However, fractional distillation is typically used to separate components of a mixture on a large scale, whereas GC can be used on a much smaller scale (i.e. microscale).
Vapor-phase chromatography (VPC), or gas–liquid partition chromatography (GLPC), are other terms for gas chromatography. These alternative names, as well as their respective abbreviations, are frequently used in scientific literature. Strictly speaking, GLPC is the most correct and preferred terminology.
After the components of oil is determined, chemical impurities can be removed. For example, hydrogen sulfide must be removed from produced gas via scavengers prior to sale. The current study seeks to offer a modified and improved method of laboratory evaluation. The critical aspect of this procedure is hydrogen sulfide detection. The classical method of using adsorbent solid indicator tubes has a number of drawbacks. They require some knowledge of the concentration prior to sampling, they detect mercaptans as well and hydrogen sulfide and the refills are quite costly. For this reason, it was decided to employ a different methodology. Hydrogen sulfide is detected in this procedure using gas sample injection on a gas chromatograph with a sulfur-specific flame photometric detector (SS-FPD), essentially a flame ionixation detector observed through a photomultiplier tube fitted with a 390 nm window. The retention time of the hydrogen sulfide component is approximately 2 minutes using an appropriate isothermal temperature profile and the method detects levels down to 500 ppb.
- Gas chromatography. Wikipedia. http://en.wikipedia.org/wiki/Gas_chromatography, 17 December 2014 revision. (Accessed 22 January 2015).
- Gas Chromatography. Shimadzu. http://shimadzu.com/an/gc/index.html. (Accessed 22 22 January 2015).
- Taylor, G.N., Matherly, R. The Laboratory Evaluation and Optimization of Hydrogen Sulphide Scavengers Using Sulphur Specific FPD Gas Chromatography. 2011. Presented at the SPE International Symposium on Oilfield Chemistry, The Woodlands, Texas, USA, 11-13 April. SPE-140401-MS. http://dx.doi.org/10.2118/140401-MS.
Noteworthy papers in OnePetro
Breviere, J., Herzaft, B., Mueller, N. 2002. Gas Chromatography - Mass Spectrometry (Gcms) - A New Wellsite Tool For Continuous C1-C8 Gas Measurement In Drilling Mud - Including Original Gas Extractor And Gas Line Concepts. First Results And Potential. Presented at the SPWLA 43rd Annual Logging Symposium, Oiso, Japan, 2-5 June. SPWLA-2002-J. https://www.onepetro.org/conference-paper/SPWLA-2002-J.
Caroli, E., Lafaurie, C., Barraud, B., et al. 2013. Quantitative Mud Gas Reconciliation with Downhole Fluid Analysis: Towards a Quantitative Fluid Log. Presented at the SPE Annual Technical Conference and Exhibition, New Orleans, Louisiana, 30 September-2 October. SPE-166246-MS. http://dx.doi.org/10.2118/166246-MS.
Freund, M. 1967. Developments in Gas Chromatography. Presented at the 7th World Petroleum Congress, Mexico City, 2-9 April. WPC-12806. https://www.onepetro.org/conference-paper/WPC-12806.
Hughes, F.G. 1963. High speed mass spectrometer as a gas chromatography detector in the determination of crude oil composition. Presented at the 6th World Petroleum Congress, Frankfurt am Main, Germany, 19-26 June. WPC-10415. https://www.onepetro.org/conference-paper/WPC-10415.
Nair, A.V., Kurawle, I.B., Kaul, M., et al. 2009. Mud Gas Isotope Logging Using Mass Spectrometry. Presented at the Asia Pacific Oil and Gas Conference & Exhibition, Jakarta, 4-6 August. SPE-121004-MS. http://dx.doi.org/10.2118/121004-MS. Williams, L.M. 1963. Composition of crude oils by gas chromatography : geological significance of hydrocarbon distribution. Presented at the 6th World Petroleum Congress, Frankfurt am Main, Germany, 19-26 June. WPC-10417. https://www.onepetro.org/conference-paper/WPC-10417.
Williams, L.M. 1963. Composition of crude oils by gas chromatography : geological significance of hydrocarbon distribution. Presented at the 6th World Petroleum Congress, Frankfurt am Main, Germany, 19-26 June. WPC-10417. https://www.onepetro.org/conference-paper/WPC-10417.
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