Statistical-Overlap Theory of Column Switching in Gas Chromatography:  Applications to Flavor and Fragrance Compounds

Samuel, Clint; Davis, Joe M.

doi:10.1021/ac011235b

Cited by 10 publications

(6 citation statements)

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“…13 However, MDGC techniques require prior knowledge of the sample mixture, and they result in decreased peak capacity in cases where more than 10 components are transferred from GC1 to GC2. 14 MDGC is appropriate for improving the resolution of a few closely eluting analytes, but is usually poorly suited for complex mixtures with multiple target analytes. Unlike heart-cut MDGC approaches, comprehensive twodimensional gas chromatography (GC × GC) separates the entire sample mixture in two dimensions with continuous detection and is thus more suited to nontargeted separation of all components in complex mixtures.…”

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confidence: 99%

Comprehensive Two-Dimensional Gas Chromatography Combustion Isotope Ratio Mass Spectrometry

et al. 2008

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We report the first coupling of comprehensive two-dimensional gas chromatography (GC x GC) to online combustion isotope ratio mass spectrometry (C-IRMS). A GC x GC system, equipped with a longitudinally modulated cryogenic system (LMCS), was interfaced to an optimized low dead volume combustion interface to preserve <300 ms full width at half-maximum (fwhm) fast GC peaks generated on the second GC column (GC2). The IRMS detector amplifiers were modified by configuration of resistors and capacitors to enable fast response, and a home-built system acquired data at 25 Hz. Software was home-written to handle isotopic time shifts of less than one bin (40 ms) and to integrate peak slices to recover isotope ratios from cryogenically sliced peaks. The performance of the GC x GCC-IRMS system was evaluated by isotopic analysis of urinary steroid standards. Steroids were separated by a nonpolar GC1 column (30 m x 0.25 mm, 5% phenyl), modulated into multiple 4- or 8-s cryogenic slices by the LMCS, and then separated on a polar GC2 column (1 or 2 m x 0.1 mm, 50% phenyl). GC2 peak widths from a 1-m column averaged 276 ms fwhm. Steroid standard sliced peaks were successfully reconstructed to yield delta(13)C VPDB values with average precisions of SD(delta(13)C) = 0.30 per thousand and average accuracies within 0.34 per thousand, at 8 ng on column. Two steroids, coeluting in GC1, were baseline separated in GC2 and resulted in delta(13)C VPDB values with average precisions of SD(delta(13)C) = 0.86 per thousand and average accuracies within 0.26 per thousand, at 3 ng on column. Results from this prototype system demonstrate that the enhanced peak capacity and signal available in GC x GC is compatible with high-precision carbon isotope analysis.

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confidence: 99%

Comprehensive Two-Dimensional Gas Chromatography Combustion Isotope Ratio Mass Spectrometry

et al. 2008

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“…However, v 2 17 s are insignificant for small mx 0 =X. Indeed, the numbers of peak maxima in traditional gas chromatograms of flavors and fragrances calculated with Pro ez GC have been predicted by SOT for nonpolar [12] and polar phases [13,26], and for columnswitching studies based on both phase types [15]. All these studies corresponded to small mx 0 =X.…”

Section: Comparison Of Theoretical and Pro Ez Gc P(n)smentioning

confidence: 90%

“…Simulation was used, because we do not know how to calculate the SD analytically. Monte Carlo simulations have been used before in point-process SOT [15,16]. As stated previously, an ensemble exists of possible ncolumn separations, all of which statistically resemble the actual one.…”

Section: Calculation Of Singlet Distribution By Montementioning

confidence: 99%

Validation of theory of n‐column separations with gas chromatograms predicted by commercial software

Williamson

Davis²

2007

J of Separation Science

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A probability theory for the average number of compounds resolved by the partial separation of complex mixtures on n columns was tested using commercial-software predictions of gas chromatograms. Such n-column separations are traditional means for addressing peak overlap, in which one chooses additional columns of different selectivity to separate compounds that cannot be separated by a single column. Gas chromatograms of five types of complex mixtures containing from 99 to 283 compounds were predicted for eight stationary phases using both optimized and other temperature programs. The number n of columns for different mixtures varied from 2 to 5. The numbers of compounds separated as singlet peaks at different resolution thresholds were compared to predictions, as evaluated with point-process statistical-overlap theory based on a Poisson distribution. A good agreement between theory and results was found in all cases corresponding to low saturation. Both good and poor agreements were found for cases corresponding to high saturation. A good agreement also was found for results based on resolving complex mixtures by a single column subject to two temperature programs. The moments and distribution of the number of resolved compounds were computed by Monte Carlo simulation, thus gauging the significance of departures between results and theory. The potential of such simulations to explore the limitations of theory was briefly investigated.

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“…Statistical-overlap theory, applied specifically to the MDGC analysis of flavour and fragrance compounds, has recently shown that separation is rarely complete in the second-dimension column in cases where 10 or more peaks are transferred from the first-dimension column as a single refocused heart-cut. 15 The requirements for GC × GC were met by the development of a modulation interface, which was capable of rapidly generating a continuous series of narrow injection bands (or pulses) in the secondary column, and by making the second-column separation fast enough to generate at least one complete chromatogram in the time taken for each single peak to elute from the first column. 16 The retention time window of the fast seconddimension chromatograms in GC × GC is typically less than 5 or 6 s. During the process (elution time) of each second-dimension chromatogram, the modulator accumulates sample for the subsequent delivery of the next injection pulse to the second column.…”

Section: Background To Comprehensive Gcmentioning

confidence: 99%

Opportunities for ultra‐high resolution analysis of essential oils using comprehensive two‐dimensional gas chromatography: a review

Shellie

Marriott

2003

Flavour & Fragrance J

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In comprehensive 2D gas chromatography, the entire sample is simultaneously subjected to analysis on two capillary columns. By using a suitable modulation interface between the primary and secondary columns, hundreds of fast, second-dimension chromatograms are produced. The data from these chromatograms are treated such that a 3D surface plot or a 2D contour plot of the components' individual retention times, on each column, as well as peak responses, are represented. In a properly tuned comprehensive 2D chromatogram, the individual sample components are spread throughout a 2D separation space, providing a significant increase in the probability of resolving a greater number of sample components without increasing the analysis time. Comprehensive 2D-GC has proved useful for high-resolution conventional essential oil analysis as well as high-resolution enantioselective essential oil analysis. Combining comprehensive 2D-GC with either a quadrupole or time-of-flight mass spectrometer gives a powerful 3D analysis technique, which is extremely effective for complex sample analysis. The present status and opportunities arising from these ultra-high resolution approaches are discussed herein. Copyright © 2003 John Wiley & Sons, Ltd.KEY WORDS: comprehensive two-dimensional gas chromatography; GC × GC; high resolution; essential oils; enantioselective analysis; mass spectrometry Trends in the Gas Chromatographic Analysis of Essential OilsThe complex nature of essential oils dictates that historically, very long capillary columns have been used in order to achieve adequate component resolution.1 Thus, the use of 25-50 m capillary columns of internal diameters of 0.25-0.32 mm is common. With the importance of retention indices in aiding the characterization of individual components, standardized operating conditions are often used which allow direct comparison with inhouse reference data or commercially available data sources (e.g. Ref.2). It must be acknowledged, however, that in many instances there is no absolute certainty of identity of peaks in the GC result. Currently there is a demand for faster GC separations, and despite the theory behind fast-GC having been formulated more than 40 years ago, 3-5 its widespread acceptance and routine use has only happened over the past decade or so. Cramers et al. 6 and references cited therein provide an overview and comparison of contemporary approaches to minimizing analysis time in GC. For fast-routine analysis of food, flavours and fragrances, the use of narrow-bore capillary columns will be the most commonly used approach for reducing analysis times.Using fundamental considerations, the required number of theoretical plates (N req ) to provide a given resolution (R s ) is:(1) where k is the retention factor, and α is the selectivity factor.The equation for retention time t R of the analysis (using reduced parameters) can be given by: Where h is the reduced plate height, d c is the inside column diameter, υ is the reduced carrier gas velocity, f 2 is the gas compress...

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Statistical-Overlap Theory of Column Switching in Gas Chromatography: Applications to Flavor and Fragrance Compounds

Cited by 10 publications

References 48 publications

Comprehensive Two-Dimensional Gas Chromatography Combustion Isotope Ratio Mass Spectrometry

Comprehensive Two-Dimensional Gas Chromatography Combustion Isotope Ratio Mass Spectrometry

Validation of theory of n‐column separations with gas chromatograms predicted by commercial software

Opportunities for ultra‐high resolution analysis of essential oils using comprehensive two‐dimensional gas chromatography: a review

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