Chemistry
Gas Chromatography
Gas chromatography is a technique used to separate and analyze volatile compounds in a mixture. It involves the passage of a gaseous sample through a column with a stationary phase, where different compounds interact at different rates and are separated based on their unique properties. The separated compounds are then detected and quantified, making gas chromatography a valuable tool in analytical chemistry.
Written by Perlego with AI-assistance
Related key terms
1 of 5
11 Key excerpts on "Gas Chromatography"
eBook - PDF- Stephane Bouchonnet(Author)
- 2013(Publication Date)
- CRC Press(Publisher)
1 1 Concepts of Gas Chromatography 1.1 GENERAL POINTS 1.1.1 G ENERAL P RINCIPLE The role of a chromatograph is to separate the compounds of a mixture. When speaking of chromatography in the gas phase (or GC for Gas Chromatography), molecules that are to be separated volatilize and mix with a gas. This gas, called carrier gas , constitutes the mobile phase; it transports the analytes into an analytical column whose inner surface is covered with a chemical film (or stationary phase). The molecules are separated in time because they migrate in the column at various speeds; the length of each analyte course depends on its volatility and the interactions between the molecule and the chemical film. The analytes are detected at their exit from the column. Each molecule is charac-terized by a retention time that corresponds to the time that passed between the injec-tion of the analyte and its arrival at the detector. Concerning volatility, the separation principle is simple: the speed at which a compound migrates in the column relates to its boiling point. The boiling point is a thermodynamic measure that depends mainly on two factors: the molecular weight and polarity. A compound is as volatile as its molecular weight and polarity are low. The interaction between analytes and the stationary phase are more complex; one must chose the type of chemical film to use according to the nature of the molecules that need to be separated. The principle of Gas Chromatography can be approached in the following manner. Let’s imagine that various pieces of wood (symbolizing the analytes) are dropped from a bridge into a river (the analytical column). Water symbolizes the carrier gas. According to their weight, the pieces of wood will float more or less. Depending on their size, shape, and roughness, they will hit the river bank (the chemical film that constitutes the stationary phase) at various times and some will attach to it.
- Theodore Kuwana(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
PHYSICAL METHODS IN MODERN CHEMICAL ANALYSIS, VOL. 1 Gas Chromatography Judy P. Okamura Department of Chemistry San Bernardino Valley College San Bernardino, California Donald T. Sawyer Department of Chemistry University of California Riverside, California I. Introduction to Gas Chromatography 2 A. Description 2 B. Theory 5 II. Instrumentation 6 A. Detectors 6 B. Other Important Features 14 III. Choosing a Column 18 A. Introduction 18 B. Adsorption Columns 19 C. Columns for Gas-Liquid Chromatography . . . 23 D. Specific Stationary Phases 29 E. Column Preparation 30 F. Capillary Columns 32 IV. Operating Conditions 33 A. Temperature 33 B. Gas Flow Rate and the van Deemter Equation . . 34 C. Other Factors Which Affect Efficiency . . . . 38 V. Qualitative and Quantitative Analysis 39 A. Determination of the Retention of a Compound . 39 B. Qualitative Analysis 42 C. Quantitative Analysis 45 D. Electronic Integrators and Computers . . . . 49 VI. Applications of Gas Chromatography 49 A. General Analytical Methods 49 B. Preparative Gas Chromatography 50 C. Elemental Analysis 51 D. Surface Area Measurements 51 E. Physicochemical Constants 51 References 53 1 Copyright © 1978 by Academic Press, Inc. All rights of reproduction in any form reserved. ISBN 0-12-430801-5 2 Judy P. Okamura and Donald T. Sawyer I. Introduction to Gas Chromatography A. Descriptions 1. Gas Chromatography Gas Chromatography is a technique that provides the means to accomplish the efficient separation and sensitive analytical determination of the com-ponents in complex mixtures. The relative residence time of a given com-ponent in a column system is an identification characteristic, while the magnitude (area) of the detector response for the component as it emerges from the column is proportional to its concentration. Even when gas chro-matography is done under much less than optimum conditions, results are achieved that would require a great amount of work and finesse by other methods.
eBook - PDFSystematic Materials Analysis
Materials Science and Technology, Vol. 3
- J. H. Richardson, R. V. Peterson, J. H. Richardson, R. V. Peterson(Authors)
- 2013(Publication Date)
- Academic Press(Publisher)
The stationary phase may be a solid material and the mobile phase either a liquid (liquid-solid chromatography) or a gas (gas-solid chromatography). Alternatively, the stationary phase may be a liquid and the mobile phase either a liquid (liquid-liquid chromatography) or a gas (gas-liquid chromatography). Gas Chromatography includes both gas-liquid and gas-solid systems. Introduction Gas Chromatography is an analytical technique whereby the sample to be analyzed is volatilized, injected into a flowing carrier gas stream; and passed through a column, where the heterogeneous sample is separated into its individual constituents; the individual constituents are then detected and measured by a detector as they emerge from the column. The time required for the detection of each sample component, under a controlled set of con-ditions, provides the qualitative information. The magnitude of the detector response may be used to obtain a quantitative interpretation. The technique of Gas Chromatography is one of the most rapidly developed methods to become available to the analyst in modern times. Since its introduction by James and Martin (1952) it has been expanded to include the qualitative and quantitative analyses of both organic and inor-ganic samples, which may be either liquids, solids, or gases, in their initial states. References to the use of this method are found in practically all fields of endeavor throughout the spectrum of the physical and biological sciences. The instrumentation, applications, and user modifications have become so numerous and varied that separate volumes dealing only with a single topic or application have been published. It is not the purpose of this undertaking to cover in detail each topic, but rather to attempt to provide a general understanding of the gas-chromatographic technique and its potential uses. Included are references that will allow the reader to pursue, in detail, any area discussed.
eBook - PDFChemical Analysis
Modern Instrumentation Methods and Techniques
- Francis Rouessac, Annick Rouessac, John Towey(Authors)
- 2022(Publication Date)
- Wiley(Publisher)
Chemical Analysis: Modern Instrumentation Methods and Techniques , Third Edition. Francis Rouessac and Annick Rouessac, translated by John Towey. © 2022 John Wiley & Sons Ltd. Published 2022 by John Wiley & Sons Ltd. Companion Website: www.wiley.com/go/Rouessac/Analysis3e Gas Chromatography Chapter 2 G as chromatography (GC) separates compounds that may be vaporized without decomposition when heated. To do so, analytes, in contact with the gaseous mobile phase, are brought to high temperatures. The same goes for the stationary phase caught in the column. GC can be paired with many types of detection, especially mass spectrometry, which often helps in positive identification of analytes. This versatile and very sensitive technique is known for its quick optimization of 38 Chapter 2: Gas Chromatography analytical conditions, and thanks to current advances, such as high-speed or multidimensional Gas Chromatography, it is a very attractive and essential resource when studying volatile compounds. 2.1 COMPONENTS OF A GC INSTALLATION A gas chromatograph is composed of three components within a single surround. These components include the injector, the column, and the detector associated with a temperature-controlled oven that enables the column to attain high temperatures (Figure 2.1). The mobile phase that transports the analytes through the column is a gas referred to as the carrier gas . The carrier gas flow, which is precisely controlled, enables great reproducibility of the retention times. Analysis starts when a very small quantity of sample is introduced in either liquid or gas form into the injector, which has the dual function of vaporizing the sample and mixing it with the gas flow at the head of the column. The column is usually a narrow-bore tube that coils around itself with a length that can vary from 1 m to over 100 m, depending upon the type and the contents of the stationary phase.
eBook - PDF- Gary D. Christian, Purnendu K. Dasgupta, Kevin A. Schug(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
Chapter 15 Gas Chromatography KEY THINGS TO LEARN FROM THIS CHAPTER Gas chromatograph GC columns—packed, capillary Stationary phases—polar to nonpolar GC detectors (see Table 15.2) Temperature programming Quantitative measurements—internal standards, spreadsheets for calculation Headspace analysis, thermal desorption, purging, and trapping Small columns for fast separations 2-D Gas Chromatography Gas Chromatography (GC) is one of the most versatile and ubiquitous analytical tech- niques in the laboratory. It is widely used for the determination of organic compounds. The separation of benzene and cyclohexane (bp 80.1 and 80.8°C) is extremely sim- ple by Gas Chromatography, but it is virtually impossible by conventional distillation. Although Martin and Synge invented liquid–liquid chromatography in 1941, the intro- duction of gas–liquid partition chromatography by James and Martin a decade later had a more immediate and larger impact for two reasons. First, as opposed to manu- ally operated liquid–liquid column chromatography, GC required instrumentation for application, which was developed by collaboration among chemists, engineers, and physicists; and analyses were much more rapid and done on a small scale. Second, at the time of its development, the petroleum industry badly needed improved analytical monitoring and immediately adopted GC. Within a few short years, GC was used for the analysis of almost every type of organic compound. The volume “75 Years of Chromatography, A Historical Dialogue” (L. S. Ettre and A. Zlatkis, Eds., Journal of Chromatography Library Volume 17, Elsevier Science, 1979) published on the occasion of the 75th anniversary of the discovery of chromatography by Tswett contains short individual accounts of all prominent scientists involved in the development of chromatography in the early years. As many accounts are very personal, this volume is a treasure that contains the excitement and energy of these years perhaps like no other.
eBook - PDF- Gary D. Christian, Purnendu K. Dasgupta, Kevin A. Schug(Authors)
- 2013(Publication Date)
- Wiley(Publisher)
Chapter Twenty Gas Chromatography Chapter 20 URLs Learning Objectives WHAT ARE SOME OF THE KEY THINGS WE WILL LEARN FROM THIS CHAPTER? ● Gas chromatograph, p. 620 ● GC columns—packed, capillary, pp. 623, 624 ● Stationary phases—polar to nonpolar, p. 626 ● GC detectors (see Table 20.2), p. 630 ● Temperature programming, p. 638 ● Quantitative measurements — internal standards, spreadsheets for calculation, p. 639 ● Headspace analysis, thermal desorption, purging, and trapping, pp. 641, 642 ● Small columns for fast separations, p. 643 ● 2-D Gas Chromatography, p. 645 Gas Chromatography (GC) is one of the most versatile and ubiquitous analytical tech- niques in the laboratory. It is widely used for the determination of organic compounds. The separation of benzene and cyclohexane (bp 80.1 and 80.8 ◦ C) is extremely simple by Gas Chromatography, but it is virtually impossible by conventional distillation. Although Martin and Synge invented liquid–liquid chromatography in 1941, the intro- duction of gas–liquid partition chromatography by James and Martin a decade later had a more immediate and larger impact for two reasons. First, as opposed to manu- ally operated liquid–liquid column chromatography, GC required instrumentation for application, which was developed by collaboration among chemists, engineers, and physicists; and analyses were much more rapid and done on a small scale. Second, at the time of its development, the petroleum industry badly needed improved analytical monitoring and immediately adopted GC. Within a few short years, GC was used for the analysis of almost every type of organic compound. Very complex mixtures can be separated by this technique.
eBook - PDF- Satinder Ahuja(Author)
- 2003(Publication Date)
- Academic Press(Publisher)
Modern chromatography embraces powerful resolution techniques that include Gas Chromatography, high-pressure liquid chromatography (see Chapter 10), supercritical fluid chromatography, and capillary electrokinetic chromatography (see Chapter 11). Gas Chromatography, where gas is used as a mobile phase, was first introduced in 1952 by James and Martin. 2 The technique was based on a suggestion made 11 years earlier by Martin in a study by Martin and Synge 3 on partition chromatography, for which they were presented the Nobel Prize in chemistry in 1952. As previously mentioned, the stationary phase can be a solid or a liquid immobilized on solid; the phase remains in the column. Both packed and open tubular columns can be used (see Section III). The observed separations in Gas Chromatography are based on the rela-tive vapor pressures of sample components and affinities for the stationary phase. The sensitivity, speed, accuracy, and simplicity of the gas chromato-graphic methods for the separation, identification, and quantification of volatile compounds or those that can be made volatile under gas chromatographic conditions has resulted in phenomenal growth of this technique. 4, 5 I. EQUIPMENT The basic components of a gas chromatograph are shown in Figure 1. It includes a cylinder of carrier gas equipped with a flow controller and pressure regulator. Helium is most frequently used as a carrier gas. Nitrogen or argon may also be used. The primary requirement is that the gas be inert and not interfere with the detection of the desired component(s). The carrier RECORDER DETECTOR FLOW CONTROL GAS INJECTOR ELUENTS COLUMN OVEN FIGURE 1 A block diagram of a gas chromatograph. 134 S. AHUJA gases commonly used for various frequently used detectors are given below. For electron-capture detection, the nitrogen used should be extremely dry. Carrier gases are available at various purity levels that range from 99.995% to 99.9999%.
eBook - PDFChromatography
Fundamentals and applications of chromatography and related differential migration methods - Part A: Fundamentals and techniques
- E. Heftmann(Author)
- 2004(Publication Date)
- Elsevier Science(Publisher)
. . . . . . . . . . . . . . . 351 8.5.3 Selected detectors . . . . . . . . . . . . . . . . . . . . . . . . 352 8.5.3.1 Ionization detectors . . . . . . . . . . . . . . . . . . . 352 8.5.3.2 Bulk physical property detectors . . . . . . . . . . . . . 358 8.5.3.3 Photometric detectors . . . . . . . . . . . . . . . . . . 358 8.5.3.4 Other detectors . . . . . . . . . . . . . . . . . . . . . 362 8.5.4 Dual detection . . . . . . . . . . . . . . . . . . . . . . . . . . 364 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364 Erich Heftmann (Editor) Chromatography, 6th edition Journal of Chromatography Library, Vol. 69A q 2004 Elsevier B.V. All rights reserved 319 8.1 INTRODUCTION Gas Chromatography (GC), which is now 50 years old [1], provides separation and quantitative analysis for volatile, thermally stable compounds in a broad variety of mixtures, from the simplest ( e.g. , purity tests of individual compounds) to the most complex ( e.g. , petrochemical assays of samples comprising hundreds of individual components). For the analysis of complex samples, no other physical method offers both the broad analysis of total sample and the specific information on individual components of the sample as is produced by GC. This is a direct consequence of the resolving power of long, narrow-bore (capillary) columns, coated with a thin film of stationary phase, which maximize the ability to separate closely related chemical components. There has been little advance in extending the upper limit of GC; 350–425 8 C is normally accepted as the upper boundary (determined by stationary-phase stability). The lower temperature limit is often not of too much concern, but sub-ambient operation allows the most volatile analytes to be chromatographed. The mass range of GC may therefore be defined as being from 2 to ca.
- R.L. Grob, M.A. Kaiser(Authors)
- 2000(Publication Date)
- Elsevier Science(Publisher)
5.6.2 Quantitative analysis by Gas Chromatography Quantitative GC i s concerned with how much of a component i s present i n a sample. For a more detailed coverage of the various techniques o f obta4ning quanti- t a t i v e data, the reader i s referred t o the excellent chapter by Debbrecht ( r e f . 82) and the book by Novak ( r e f . 83). All the commonly used detectors i n GC (TCD, FIO, ECD, FPD, etc.) produce a d i f f e r e n t i a l chromatogram, i.e., If conditions are ideal and t h e column e f f l u e n t flows through the c e l l uniformly, one obtains peaks which are gaussian i n shape. These may be mathematically described by eqn. 5.28: -1/2 - i2/4Dt n = 0.5m (dt) (5.28) where n = concentration of gas molecules; m = t o t a l quantity of d i f f u s i n g material; n = constant = 3.1416; D = d i f f u s i o n coefficient; t time; and i = distance molecules diffuse. The size of the peak i s proportional t o the amount of component I n t h e sample. i f t h i s i s true, the peak area and/or the peak height w i l l be proportional t o t h e amount of the component causing the peak. Peak height I s proportional t o the amount of a component contributing t o t h e peak if there !s no change i n t h e system which w i i i cause a change i n the peak width when comparing a sample t o a standard. Four parameters may Influence the peak width: ( 1 ) temperature, ( 2 ) flow r a t e of the mobile phase, ( 3 ) sample Injection, and (4) column overload. To maintain an accuracy of 1 % i n the analysis the temperature must be controlled t o w i t h i n +0.3OC, preferably - +0.loC and the flow r a t e controlled t o w i t h i n 20.1%. Poor sample i n j e c t i o n w i l l have an e f f e c t on peak width; peaks which emerge quickly (i.e., 1-2 times t h e hold-up volume) are affected the most. Peaks which are a t least t e n times t h e hold-up volume are affected the least.
eBook - PDF- Leslie S Ettre, John V Hinshaw(Authors)
- 2008(Publication Date)
- ICP(Publisher)
33. D. H. Desty, Chromatographia 8 , 452–455 (1975). 34. K. Grob and G. Grob, Wissenschaftl. Zeitschr. der Karl-Marx-Univ., Math.-Naturwiss. Reihe 26 (4), 379–384 (1977). 35. R. D. Dandeneau and E. H. Zerenner, J. High Resol. Chromatogr. 2 , 351–356 (1979). 36. R. D. Dandeneau and E. H. Zerenner, LCGC ( North America ) 8 , 908– 912 (1990). 37. R. D. Dandeneau, quoted by R. Stevenson, Amer. Lab. 30 (5), 30–34 (1998). 38. W. G. Jennings, Comparison of Fused-Silica and Other Glass Columns in Gas Chromatography (Huethig Verlag, Heidelberg, 1981). 39. S. R. Lipsky, W. J. McMurray, M. Hernandez, J. E. Purcell and K. A. Billeb, J. Chromatogr. Sci. 18 , 1–9 (1980). 40. S. R. Lipsky and W. J. McMurray, J. Chromatogr. 217 , 3–17 (1981). 41. S. R. Lipsky and M. L. Duffy, J. High Resolut. Chromatogr. 9 , 376–382, 725–730 (1986). 42. E. F. Barry, in Modern Practice of Gas Chromatography , ed. R. L. Grob, 3rd edn. (Wiley, New York, 1995), pp. 198–203. C h a p t e r 25 The Beginnings of Headspace Analysis ∗ Since the beginning of Gas Chromatography analysts have encoun-tered the need to analyze the volatile constituents of an essentially nonvolatile sample. If such a liquid sample is introduced into a gas chromatograph, the volatile components evaporate and their vapor is carried through the column by the mobile phase (the carrier gas). However, the nonvolatile matrix will remain in the injector and con-taminate it. The investigation of the volatile components present in a solid sample is even more complicated. Such a sample obviously can-not be introduced into the instrument: this requires an elaborate sam-ple preparation procedure consisting among others, extraction of the volatile components. Furthermore, some samples have a matrix that is somewhat volatile, but with a higher boiling point; thus, it eventually will evaporate in the injector but not together with the components of interest.
eBook - PDF- Semih Otles(Author)
- 2016(Publication Date)
- CRC Press(Publisher)
Enhanced sensitivity . Compared to 1D-GC separation, pronounced improvement of detection limits in GC GC system is obtained; thanks to compressing the peak in the modulation capillary and front part of the second column (following fast chromatography avoids band broadening of focused peaks). Furthermore, thanks to improved separation of analytes and matrix interferences (chemical noise) in the GC GC system, the signal to noise ratio is also improved. An example is given in Figure 7.11 that illustrates differences in 1D-GC versus GC GC analysis of limonene. Structured chromatograms . Thanks to complementary separation mechanisms occurring in both columns, the chromatograms resulting from particular GC GC setup are ordered, i.e., molecules have their de fi nite locations in the retention space based on their structure. In the reconstructed 2D contour plots, characteristic patterns are obtained, in which the members of homological series differing in their volatility are ordered along the fi rst-dimension axis (nonpolar capillary is typically employed in fi rst dimension), whereas the compounds differing by polarity are spread along the second-dimension axis. The formation of clusters of the various subgroups of compounds in a GC GC contour plot may be useful for the group type analysis. Improved identi fi cation of unknowns . Nontarget screening allows obtaining of overview of the sample constituents. This approach consists from: (1) peak fi nding and deconvolution (algorithm for Gas Chromatography in Food Analysis 133 recognizing of partly co-eluting peaks in the GC – MS chromatogram and obtaining their ‘‘ pure ’’ mass spectra), (2) library searching, and (3) further post-processing. Since a large amount of data have to be processed, automated data processing is employed. 7.4 SAMPLE DETECTION Depending upon the type of food compounds being measured several different detectors are available for this purpose (Table 7.5), each with its own advantages and drawbacks.
Index pages curate the most relevant extracts from our library of academic textbooks. They’ve been created using an in-house natural language model (NLM), each adding context and meaning to key research topics.
