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Addressing the Challenges to Identification in Gas Chromatography by Increased Resolution and Enhanced Detection Modalities. Chem Asian J 2018; 13:1849-1856. [PMID: 29975453 DOI: 10.1002/asia.201800556] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2018] [Indexed: 02/28/2024]
Abstract
In the past 15+ years, gas chromatography (GC) has undergone a renaissance in its implementation on the basis of the "disruptive" technology of comprehensive two-dimensional gas chromatography (GC×GC). With a foundation based upon a two-column GC separation approach, GC×GC significantly alters the classical multidimensional gas chromatography (MDGC) method by employing very fast separation on a second dimension (2 D) after a conventional one-dimensional (i.e., single column; 1D) column separation. This allows the experimentalist to apply the advantages of multidimensionality to the total sample rather than to just discrete zones of the 1D separation that characterizes MDGC. This requires a new "language" to describe GC×GC separations, applied to the first dimension (1 D) and 2 D, and consideration of the modulation processes that define the transfer of analyte from the 1 D to the 2 D. The present review is based on the FACS Foundation lectureship of the author given at the 17th Asian Chemical Congress of the Federation of Asian Chemical Societies (FACS). The award lecture and this manuscript is based on material deriving largely from research in the area of MDGC and GC×GC separations of the author.
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Improved Flow Modulator Construction for GC × GC with Quadrupole Mass Spectrometry. J Chromatogr Sci 2017; 54:1481-1488. [PMID: 27539394 DOI: 10.1093/chromsci/bmw121] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2015] [Revised: 05/25/2016] [Indexed: 11/13/2022]
Abstract
Improvement and testing of a flow modulator for the application in comprehensive two-dimensional gas chromatography separations is the subject of the presented paper. This improved setup constructed from two independent capillary branches each consisting of a pressure regulator, a pressure sensor, a two-way solenoid valve and a microfluidic T-connector, allows an independent and easy settings of the pressures and flow velocities in the modulator and provides system flexibility in an operation without need of any component exchange. The estimated flow rates were 0.4 mL/min in the first column and 3.2 mL/min in the second column. This setup was compared with the commercial Zoex cryogenic modulator for the separation of 17 selected solvents at isothermal conditions. Modulator working conditions were optimized and its separation power was demonstrated on the analysis of a lavender extract under an application of two orthogonal capillary column sets (nonpolar-polar vs. polar-nonpolar) and temperature program. The results were evaluated by two commercial software packages and discussed with respect to the identification compliance.
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Flow-modulated targeted signal enhancement for volatile organic compounds. J Sep Sci 2016; 39:2284-91. [DOI: 10.1002/jssc.201600054] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2016] [Revised: 03/10/2016] [Accepted: 04/10/2016] [Indexed: 11/09/2022]
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Considerations on the determination of the limit of detection and the limit of quantification in one-dimensional and comprehensive two-dimensional gas chromatography. J Chromatogr A 2015; 1396:117-30. [DOI: 10.1016/j.chroma.2015.03.084] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2015] [Revised: 03/31/2015] [Accepted: 03/31/2015] [Indexed: 12/01/2022]
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Optimization aspects of comprehensive two-dimensional gas chromatography. J Chromatogr A 2012; 1255:38-55. [DOI: 10.1016/j.chroma.2012.02.064] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2011] [Revised: 02/21/2012] [Accepted: 02/24/2012] [Indexed: 11/16/2022]
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Exploring the Possibilities of Cryogenic Cooling in Liquid Chromatography for Biological Applications: A Proof of Principle. Anal Chem 2012; 84:2031-7. [DOI: 10.1021/ac203252u] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Rethinking cycad metabolite research. Commun Integr Biol 2011; 4:86-8. [PMID: 21509189 DOI: 10.4161/cib.4.1.14084] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2010] [Accepted: 11/02/2010] [Indexed: 11/19/2022] Open
Abstract
Cycads are among the most ancient of extant Spermatophytes, and are known for their numerous pharmacologically active compounds. One compound in particular, β-methylamino-L-alanine (BMAA), has been implicated as the cause of amyotrophic lateral sclerosis/Parkinson dementia complex (ALS/PDC) on Guam. Previous studies allege that BMAA is produced exclusively by cyanobacteria, and is transferred to cycads through the symbiotic relationship between these cyanobacteria and the roots of cycads. We recently published data showing that Cycas micronesica seedlings grown without endophytic cyanobacteria do in fact increase in BMAA, invalidating the foundation of the BMAA hypothesis. We use this example to suggest that the frenzy centered on BMAA and other single putative toxins has hindered progress. The long list of cycad-specific compounds may have important roles in signaling or communication, but these possibilities have been neglected during decades of attempts to force single metabolites into a supposed anti-herbivory function. We propose that an unbiased, comprehensive approach may be a more appropriate means of proceeding with cycad biochemistry research.
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Chemical signature of ecstasy volatiles by comprehensive two-dimensional gas chromatography. Forensic Sci Int 2011; 209:11-20. [DOI: 10.1016/j.forsciint.2010.11.008] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2010] [Revised: 11/13/2010] [Accepted: 11/18/2010] [Indexed: 10/18/2022]
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Modulation in comprehensive two-dimensional gas chromatography: 20 years of innovation. Anal Bioanal Chem 2011; 401:2335-49. [DOI: 10.1007/s00216-011-5100-6] [Citation(s) in RCA: 79] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2011] [Revised: 05/10/2011] [Accepted: 05/11/2011] [Indexed: 11/25/2022]
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12
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Rapid sequential separation of essential oil compounds using continuous heart-cut multi-dimensional gas chromatography–mass spectrometry. J Chromatogr A 2011; 1218:2626-34. [DOI: 10.1016/j.chroma.2011.02.060] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2010] [Revised: 01/28/2011] [Accepted: 02/23/2011] [Indexed: 11/26/2022]
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13
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Selectable one-dimensional or two-dimensional gas chromatography–mass spectrometry with simultaneous olfactometry or element-specific detection. J Chromatogr A 2010; 1217:2903-10. [DOI: 10.1016/j.chroma.2010.02.045] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2009] [Revised: 02/08/2010] [Accepted: 02/18/2010] [Indexed: 11/22/2022]
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14
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Comprehensive two-dimensional gas chromatography improves separation and identification of anabolic agents in doping control. J Chromatogr A 2010; 1217:127-35. [DOI: 10.1016/j.chroma.2009.10.075] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2009] [Revised: 10/12/2009] [Accepted: 10/26/2009] [Indexed: 11/21/2022]
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15
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Multidimensional chromatography in food analysis. J Chromatogr A 2009; 1216:7110-29. [DOI: 10.1016/j.chroma.2009.08.014] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2009] [Revised: 08/06/2009] [Accepted: 08/10/2009] [Indexed: 02/03/2023]
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16
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Chapter 2 Basic Instrumentation for GC×GC. ACTA ACUST UNITED AC 2009. [DOI: 10.1016/s0166-526x(09)05502-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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17
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Implementations of two-dimensional liquid chromatography. J Chromatogr A 2008; 1189:109-68. [DOI: 10.1016/j.chroma.2008.01.086] [Citation(s) in RCA: 233] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2007] [Revised: 01/14/2008] [Accepted: 01/16/2008] [Indexed: 11/29/2022]
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Abstract
While LC finds enormously widespread use in almost all areas of chemical science, the technique is limited as a means of identification because compounds do not elute with unique retention times. This limitation spurred the growth of hyphenated instrumental methods of analysis, such as LC-MS/MS, which because of the MS/ MS detection became a method of identification. However, techniques like LC-MS/ MS are specialised and require high initial purchase and running costs, inhibiting the more widespread growth of the technique. In an attempt to increase the separation power of LC, multi-dimensional LC was developed. This expanded the separation space and subsequently has allowed the development of methods with fingerprinting ability due to the lower probability of component overlap. The work in this study illustrates the application of 2-D LC as a means of chemical fingerprinting. We employed a sample base of various low molecular weight oligostyrenes and their diastereomers that represent a population of compounds whose selectivities in a one-dimensional separation are almost unity and hence essentially impossible to separate. Yet in a 2-D domain almost all individual components occupy unique 2-D retention times.
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Partial Modulation Method via Pulsed Flow Modulator for Comprehensive Two-Dimensional Gas Chromatography. Anal Chem 2004; 76:6064-76. [PMID: 15481955 DOI: 10.1021/ac0492463] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A partial modulation method by using a pulsed-flow modulator for comprehensive two-dimensional gas chromatography is proposed. The method is based on the fact that when a pulsed flow of inert gas is introduced into the conjunction between a primary and a secondary column, the concentration of analyte is disturbed, and a plug of higher or lower concentration is created. The plug, which forms a spike signal coupled to the primary GC signal, is then separated in a secondary column, creating a new dimension of GC information. The modulation is partial because only a fraction of the primary signal is modulated and converted into the secondary signal; the remaining primary signal stays unchanged. Therefore, this method yields a comprehensive two-dimensional chromatogram and a primary one-dimensional chromatogram in a single GC run. In this study, the modulation mode, modulation index, and modulation percentage are discussed and the reproducibility of peak areas and retention time are investigated. With a 5.8% modulation percentage and a primary peak half-width 1.7 times wider than the modulation time, the standard deviation for the peak areas are 0.15% for the primary and 0.78% for the secondary chromatograms. Chromatograms of laboratory-mixed hydrocarbons and of high-temperature fuel oil no. 6 standard are demonstrated.
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Evaluation and Prediction of Stereoisomerizations in Comprehensive Two-Dimensional Chromatography. ACTA ACUST UNITED AC 2004; 44:1671-9. [PMID: 15446825 DOI: 10.1021/ci049899k] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Conformational and configurational changes such as isomerizations, epimerizations, diastereomerizations and, enantiomerizations are important for the investigation of a large variety of processes ranging from protein folding to the stereostability of drugs. Under optimized conditions, these processes lead to an elution profile characterized by a plateau formation between the two interconverting species in chromatographic separations in a certain temperature range. By temperature-dependent measurements and subsequent computer simulation of the experimental chromatograms, the forward and backward rate constants k1 and k(-1), the Gibb's energy DeltaG++, activation enthalpy DeltaH++, and entropy DeltaS++ can be obtained. Due to its high efficiency two-dimensional chromatography is able to resolve the time-dependent distribution of the two species in the second dimension, thereby yielding the precise ratio of stereoisomers. An algorithm for the simulation and evaluation of two-dimensional chromatographic experiments has been developed, based on the theoretical plate model, which allows the determination of rate constants and barriers of isomerization, epimerization, and enantiomerization processes from two-dimensional chromatographic experiments. In the present article a detailed description of the extended theoretical plate model required for the simulation, the methods available, and examples for the evaluation of complex experimental data and the prediction of the separation conditions to observe isomerization, epimerizations, and enantiomerizations in two-dimensional chromatography are given.
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Simulation of Elution Profiles for Two-Dimensional Dynamic Gas Chromatographic Experiments. Anal Chem 2003; 75:4452-61. [PMID: 14632049 DOI: 10.1021/ac0301144] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The interconversion of E and Z isomers of acetaldoxime 1 and butyraldoxime 2 have been investigated by comprehensive two-dimensional dynamic gas chromatography (DGCxDGC) and computer simulation. Time-resolved cryogenic modulation is capable of revealing the precise isomeric ratio as a fine structure under the dynamic elution profile, which is characterized in one-dimensional experiments by a plateau formation or peak coalescence caused by interconversion of the isomers during the separation process. The chromatographic theoretical plate model has been extended for the computer simulation of comprehensive two-dimensional dynamic chromatographic experiments. A novel program, ChromWin 2D, based on the new algorithm has been developed for computer simulation to evaluate and predict the elution profiles of DGCxDGC experiments. ChromWin 2D allows the determination of rate constants and barriers of isomerization, epimerization, and enantiomerization processes occurring during chromatographic separations. The Eyring activation parameters of the E/Z and Z/E isomerization barriers in the presence of the stationary phase BP21 (poly(ethylene glycol) terephthalate terminated) were determined by temperature-dependent experiments between 80 and 90 degrees C for 1 and 70 and 130 degrees C for 2. The thermodynamic Gibbs free energy of the E/Z equilibrium of the isomers has been determined from the time-resolved chromatograms by cryogenic modulation. The method described here constitutes a new and important tool for the determination of isomerization barriers, which are of great interest, for example, for the quantitative determination of derivatized aldehydes, such as dinitrophenylhydrazine derivatives, in trace analysis.
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Abstract
Comprehensive two-dimensional gas chromatography (GC x GC) is a novel technique which is rapidly gaining importance for the analysis of complex samples. In the present review, attention is devoted to the principle and advantages, and main characteristics such as modulation, column combinations, detector requirements and data processing, of the technique. Specifically, GC x GC of a variety of real-life samples is discussed to demonstrate the applicability of the technique, with emphasis on the usefulness of the ordered-structure principle and on the analyte-identification power provided by a combination with time-of-flight mass spectrometric detection.
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Application of comprehensive two-dimensional gas chromatography to drugs analysis in doping control. J Chromatogr A 2003; 1000:109-24. [PMID: 12877168 DOI: 10.1016/s0021-9673(02)01998-2] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Comprehensive two-dimensional gas chromatography (GC x GC) now occupies a niche within the GC technology regime. The technique is undeniably unique in the manner in which the experiment is conducted, the way results are presented and the interpretive opportunities offered. For the 1000th volume of this journal it is appropriate to expand upon these features, and review the progress made in GC x GC to date. Firstly, brief general comment is made on multidimensional procedures, and to review key aspects of GC x GC. The use of the targeted multidimensional GC method allows absolute retentions in the second dimension of a GC x GC experiment to be estimated, and also offers a novel way to obtain enhanced response for resolved solutes. Then, to illustrate the utility of the technique, the application of GC x GC to the screening of drugs and their metabolites in biological fluids is described using prolintane metabolites in canine urine as an example, with samples taken at four time intervals after administration. This example illustrates the first application of GC x GC in the field of forensic toxicology, an area traditionally dominated by GC-MS. Most drug compounds were found to be retained on the 0.8-m second column for a greater time than the modulation period (3 s) used for initial analysis, under the conditions described. Hence a 0.4-m D2 BPX50 (50% phenyl methyl polysilphenylene) column was then used throughout, with most compounds retained less than 4 s. For the standard drug mixture, three overlapping drugs on the first dimension column (BPX5) were subsequently baseline resolved on the BPX50 column. For prolintane administration samples, the parent drug and metabolites could be effectively resolved from background matrix peaks. Likewise a 23-drug spike standard in horse urine blank gave acceptable resolution of the drugs from matrix peaks.
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Abstract
In the past 50 years. gas chromatography (GC) has played a most important role in the analysis of oil. In this review, the early history is briefly reviewed; next developments in this highly relevant application area since about 1985 are highlighted. The main topic of interest are the introduction and decisive role of capillary GC, the use of selective detection techniques, the versatility of coupled-column techniques and, specifically, the additional power of comprehensive two-dimensional GC.
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Comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometric detection applied to the determination of pesticides in food extracts. J Chromatogr A 2002; 965:207-17. [PMID: 12236526 DOI: 10.1016/s0021-9673(01)01324-3] [Citation(s) in RCA: 171] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The separation provided by conventional gas chromatography (1D-GC) can be significantly enhanced by using comprehensive two-dimensional GC (GC X GC) instead. Combination with mass spectrometric detection is desirable for unambiguous confirmation of target compounds and the provisional identification of unknowns. A GC X GC system using a cryogenic modulator was coupled to a time-of-flight mass spectrometric (TOF MS) detector. With the determination of pesticides in vegetable extracts as an example, it was demonstrated that GC X GC improves the separation dramatically. All 58 pesticides of interest could be identified using their full-scan mass spectra, which was not possible when using ID-GC-TOF MS. In addition, the high scan speed of the TOF MS allowed the deconvolution of compounds partly co-eluting in GC X GC.
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Optimization and characterization of comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometric detection (GC×GC-TOF MS). J Sep Sci 2002. [DOI: 10.1002/1615-9314(20020301)25:4<201::aid-jssc201>3.0.co;2-b] [Citation(s) in RCA: 132] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Chapter 7 Polychlorinated biphenyls. ACTA ACUST UNITED AC 2001. [DOI: 10.1016/s1567-7192(01)80010-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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Time-resolved cryogenic modulation for targeted multidimensional capillary gas chromatography analysis. J Chromatogr A 2000; 892:15-28. [PMID: 11045477 DOI: 10.1016/s0021-9673(00)00122-9] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Multidimensional gas chromatography (MDGC) is performed in a new manner, described in this paper. The method incorporates two directly coupled columns and employs a longitudinally modulated cryogenic trap located between the columns. No heartcutting process is used, but rather a method better termed selected zone compression pulsing is used. Compared with normal MDGC, where primary column effluent has to be temporarily diverted either to a monitor detector or to the second dimension column, the new procedure in its simplest mode passes all of the first column effluent to the second column. It is simply the times at which the modulation of the trap is performed that determines which target solutes will be selected for enhanced separation. This approach allows almost instantaneous separation of selected zones on the second column, and has the potential to significantly simplify the MDGC method. Since data are presented in a time-response format, and do not require transformation as previously described for comprehensive GC when using the longitudinal modulator, quantitation and report generation are essentially the same as in any GC method and data system. Advantages also include significant sensitivity improvement. By using cryofocussing, and benefiting from the zone compression effects along with fast GC conditions on the second dimension, new possibilities for MDGC can be realised. The method is demonstrated by using a mixture of semi-volatile aromatic hydrocarbons.
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