Comparison of one-dimensional and comprehensive two-dimensional separations by gas chromatography (original) (raw)
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Scientia Chromatographica, 2016
This paper presents a discussion on the implications of the modulation ratio (M R) in comprehensive two-dimensional gas chromatography (GC×GC) separations. Concepts are discussed in a tutorial manner, which is essentially in the form of a review. The M R is defined as the ratio of the width of a peak as it elutes from a first dimension (1 D) column, to the modulation period used in GC×GC operation; it is a dimensionless number. As demonstrated here, there are many parameters of GC×GC that depend on or can be interpreted by considerations of the M R value. These include, but are not limited to, the peak amplitude enhancement, the number of modulated peaks that are observed, detectivity of each of these peaks, the effect of chromatographic peak shape on the distribution of modulated peaks and how peak retention time on the first column can be derived from this distribution. Also considerations of the physical dimensions and phase coating of the second (2 D) column that is used in GC×GC (these control the total retention time of the peaks on the 2 D column) can be interpreted based on the M R , and how knowledge of this parameter can assist in interpretation of the separation of isomers.
Principles and applications of comprehensive two-dimensional gas chromatography
TrAC Trends in Analytical Chemistry, 2002
This issue of Trends in Analytical Chemistry celebrates 50 years of gas chromatography (GC)-the greatest enabling technology for chemical analysis of volatile compounds. However, what may be considered the most powerful separation tool in GCcomprehensive two-dimensional gas chromatography (GCÂGC)-is a development born of the 1990s. It was first described and almost fully established in the last decade of the twentieth century. The coming decades can be expected to see it flourish into a major operating mode of GC, when applications and fundamental principles will be further expanded, and, most importantly, its universal acceptance will be unquestioned. This article describes why the pioneers of GCÂGC have so much faith in the new opportunities afforded by this exciting technology.
A review of basic concepts in comprehensive two-dimensional gas chromatography
2002
The technique of comprehensive two-dimensional gas chromatography (GC×GC) is reviewed. A description of technical aspects of the method illustrates how the GC×GC result is achieved through the use of dual-coupled columns and the modulation of capillary chromatographic peaks. This review presents an expanded section dealing with the relationship between the modulation phase and frequency and the resulting peak pulse profiles. Experimental results that support the appreciation and understanding of the effects that pulsing has on a chromatographic peak are provided. The main goals of GC×GC analysis are discussed with respect to analytical sensitivity and peak capacity arising from zone compression effects and fast analysis on the second column. A typical application of GC×GC is presented, along with a consideration of implementation of the GC×GC method.
Analytica Chimica Acta, 2003
The two-dimensional (2D) data structure generated under a high resolution GC × GC system with a small number of samplings taken across the first dimension is evaluated for the purpose of the application of chemometric deconvolution methods. Chemometric techniques such as generalized rank annihilation method (GRAM) place high demands on the reproducibility of chromatographic experiments. For GRAM to be employed for GC × GC data interpretation, it is critical that the separation method provides data with a bilinear structure; the peak-shape and retention times on both columns must be reproducible. With a limited number of samplings across a 1 D (first dimension) peak (e.g. four to six samplings) repeatability of the pattern of the modulated peaks (controlled by the modulation phase) becomes important in producing a bilinear data structure. Reproducibility of modulation phase can be affected by both reliability of the modulation period and reproducibility of the retention time of the peak on the first column (which arises from oven temperature and carrier flow rate stability). Evaluation of within-run and run-to-run retention time reproducibility (retention time uncertainty) on both columns, and modulation phase reproducibility using a modulated cryogenic system for a pair of overlapping components (fatty acid methyl esters) was undertaken. An investigation of the quality of data to permit quantification of each component by using GRAM deconvolution, was also conducted. Less than 4% run-to-run retention time uncertainty was obtained on column 1 and less than 9% run-to-run and within-run retention time uncertainty was obtained on column 2, where these R.S.D. measures are reported normalised to peak widths on each respective dimension. The R.S.D. of duplicate quantification results by GRAM ranged from 2 to 26% although the average quantification error using GRAM was less than 5%.
New Perspectives on Comparative Analysis for Comprehensive Two-Dimensional Gas Chromatography
LCGC North America
Because of the growing number of analysis scenarios involving complex samples, comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC×GC–TOF-MS) is now a prominent technique for characterization. However, the limitations on time, expenses, and sample quantities, as well as the need for specialized expertise in comparative analysis, can prevent the discovery of analytes that distinguish multiple samples. This article provides an overview of the development and current status of comparative analysis for GC×GC–TOF-MS data and how key limitations can be overcome with a novel tile-based pairwise analysis method.
Modulation in comprehensive two-dimensional gas chromatography: 20 years of innovation
Analytical and Bioanalytical Chemistry, 2011
With almost 20 years having passed since John B. Phillips described the first comprehensive two-dimensional gas chromatography (GC×GC) separation, much has occurred in this ever-expanding field of separation science. GC×GC is currently one of the most effective techniques for the separation and analysis of complex mixtures, offering significantly greater peak capacities than conventional chromatographic methods. The technique is generally based upon separations performed on two chromatographic columns characterized by considerably different selectivities, joined together through a modulating interface. The modulator periodically traps or samples the primary column effluent, usually refocuses it into a narrow chromatographic band and injects the focused fraction into the secondary column. The modulator is often referred to as the 'heart' of the instrument, since a GC×GC separation is impossible without its use. This article reviews major innovations in GC×GC modulator development since its first use by Phillips in 1991. Emphasis has been placed on modulator design and function. Keywords Comprehensive two-dimensional gas chromatography. Instrumentation. Modulation. Review Abbreviations DVM diaphragm valve modulator GC gas chromatography GC × GC comprehensive two-dimensional gas chromatography LMCS longitudinally modulated cryogenic system PDMS polydimethylsiloxane RTM rotating thermal modulator TDM thermal desorption modulator VOC volatile organic compounds
Orthogonality considerations in comprehensive two-dimensional gas chromatography
2005
This study explores separation orthogonality with respect to comprehensive twodimensional gas chromatography (GC x GC) for a range of different column polarities in the first dimension (D-1), with two second dimension (D-2) column types. Systematic variation in the net polarity of the first dimension allows the effect of column phase relative polarity on analyte retention in both the first and second dimensions to be evaluated. First dimension polarity manipulation significantly affects elution temperature (T-e) of the analytes. This alters the magnitude of retention on the second dimension, and the extent of utility of separation space. By use of retention factor/temperature data in single column experiments, along with D-1 T-e data, retention on the D-2 column can be estimated. This allows the two-dimensional separation to be predicted, and compared with experimental data. Predicted GC x GC peak positions corresponded favourably with the experimentally derived chromatograms, yielding a simple approach for predicting two-dimensional separations, using unique column set combinations.