The Experts below are selected from a list of 1992 Experts worldwide ranked by ideXlab platform
Yongli Chen - One of the best experts on this subject based on the ideXlab platform.
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determination and evaluation of gas Holdup Time with the quadratic equation model and comparison with nonlinear models for isothermal gas chromatography
Journal of Chromatography A, 2013Co-Authors: Maoxue Chen, Yongli ChenAbstract:Gas Holdup Time (tM) is a basic parameter in isothermal gas chromatography (GC). Determination and evaluation of tM and retention behaviors of n-alkanes under isothermal GC conditions have been extensively studied since the 1950s, but still remains unresolved. The difference equation (DE) model [J. Chromatogr. A 1260: 215–223] reveals retention behaviors of n-alkanes excluding tM, while the quadratic equation (QE) model [J. Chromatogr. A 1260: 224–231] including tM is suitable for applications. In the present study, tM values were calculated with the QE model, which is referred to as tMT, evaluated and compared with other three typical nonlinear models. The QE model gives an accurate estimation of tM in isothermal GC. The tMT values are highly accurate, stable, and easy to calculate and use. There is only one tMT value at each GC condition. The proper classification of tM values can clarify their disagreement and facilitate GC retention data standardization for which tMT values are promising reference tM values.
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difference equation model for isothermal gas chromatography expresses retention behavior of homologues of n alkanes excluding the influence of Holdup Time
Journal of Chromatography A, 2012Co-Authors: Yongli Chen, Sarah A L CaccamiseAbstract:A difference equation (DE) model is developed using the methylene retention increment (Δtz) of n-alkanes to avoid the influence of gas Holdup Time (tM). The effects of the equation orders (1st–5th) on the accuracy of a curve fitting show that a linear equation (LE) is less satisfactory and it is not necessary to use a complicated cubic or higher order equation. The relationship between the logarithm of Δtz and the carbon number (z) of the n-alkanes under isothermal conditions closely follows the quadratic equation for C3–C30 n-alkanes at column temperatures of 24–260 °C. The first and second order forward differences of the expression (Δlog Δtz and Δ2log Δtz, respectively) are linear and constant, respectively, which validates the DE model. This DE model lays a necessary foundation for further developing a retention model to accurately describe the relationship between the adjusted retention Time and z of n-alkanes.
Richard Sacks - One of the best experts on this subject based on the ideXlab platform.
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vector model for window diagram optimization of tunable column ensembles for high speed gc
Journal of Separation Science, 2002Co-Authors: Heather Smith, Richard SacksAbstract:A previously described vector model of multiphase separations is dramatically simplified and applied to the problem of optimization of tandem column ensembles using pressure-tunable column selectivity. In the model, retention values for a set of target compounds on the two different stationary phases used in the column ensemble are plotted on a two-dimensional retention plane. Retention values for each mixture component are expressed in units of hold-up Time for the two different columns. Every mixture component occupies a single point on the retention plane. The orthogonal coordinates of a point represent retention for that component on the individual phases. A phase fraction axis is defined from the origin of the retention plane. The angle that this axis makes with the orthogonal retention axes is uniquely defined by the fractional contributions to the total hold-up Time from the individual columns. Coordinates along this axis define the ensemble retention using the column combination. Points on the retention plane corresponding to the mixture components are connected pairwise by separation vectors. The geometric center of each separation vector is connected to the retention origin by a locator vector. This pair of vectors provides all necessary information regarding the separation of the corresponding pair of mixture components using the chosen pair of stationary phases in the column ensemble. The separation of a peak pair using a particular column combination (Holdup Time fraction) is found by projection of the separation vector onto the phase fraction axis corresponding to the Holdup Time fraction. The relative resolution of the peak pair is found as the ratio of the separation vector projection length to the locator vector projection length. Minimum values of relative resolution considering all non-redundant peak pairs then are plotted versus the rotation angle of the phase fraction axis. The resulting window diagram identifies the Holdup Time fraction giving the best relative resolution of the most difficult to separate component pair.
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simultaneous temperature and Holdup Time ratio optimization for tandem column tunable selectivity with high speed gc
Analytical Chemistry, 1996Co-Authors: Michael Akard, Richard SacksAbstract:Analysis Time for high-speed, capillary column GC is reduced by the use of a pressure-tunable tandem combination of a nonpolar poly(methylsiloxane) (DB-5) column and a polar trifluoropropyl poly(methylsiloxane) (Rtx-200) column operated isothermally at an optimized oven temperature. By adjusting the pressure at the midpoint between the two columns, the residence Times of all sample components are adjusted to give the maximum resolution of the critical component pair. The result is a two-dimensional optimization where the column temperature and the midpoint pressure were adjusted to give the shortest possible analysis Time. A previously defined relative resolution function, which requires only empirical capacity factor data for the target compounds, is used as the dependent variable in the optimization algorithm. The resulting three-dimensional resolution map is projected parallel to the relative resolution axis in order to obtain a useful two-dimensional display from which the optimal operating conditions...
Maoxue Chen - One of the best experts on this subject based on the ideXlab platform.
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determination and evaluation of gas Holdup Time with the quadratic equation model and comparison with nonlinear models for isothermal gas chromatography
Journal of Chromatography A, 2013Co-Authors: Maoxue Chen, Yongli ChenAbstract:Gas Holdup Time (tM) is a basic parameter in isothermal gas chromatography (GC). Determination and evaluation of tM and retention behaviors of n-alkanes under isothermal GC conditions have been extensively studied since the 1950s, but still remains unresolved. The difference equation (DE) model [J. Chromatogr. A 1260: 215–223] reveals retention behaviors of n-alkanes excluding tM, while the quadratic equation (QE) model [J. Chromatogr. A 1260: 224–231] including tM is suitable for applications. In the present study, tM values were calculated with the QE model, which is referred to as tMT, evaluated and compared with other three typical nonlinear models. The QE model gives an accurate estimation of tM in isothermal GC. The tMT values are highly accurate, stable, and easy to calculate and use. There is only one tMT value at each GC condition. The proper classification of tM values can clarify their disagreement and facilitate GC retention data standardization for which tMT values are promising reference tM values.
Sarah A L Caccamise - One of the best experts on this subject based on the ideXlab platform.
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difference equation model for isothermal gas chromatography expresses retention behavior of homologues of n alkanes excluding the influence of Holdup Time
Journal of Chromatography A, 2012Co-Authors: Yongli Chen, Sarah A L CaccamiseAbstract:A difference equation (DE) model is developed using the methylene retention increment (Δtz) of n-alkanes to avoid the influence of gas Holdup Time (tM). The effects of the equation orders (1st–5th) on the accuracy of a curve fitting show that a linear equation (LE) is less satisfactory and it is not necessary to use a complicated cubic or higher order equation. The relationship between the logarithm of Δtz and the carbon number (z) of the n-alkanes under isothermal conditions closely follows the quadratic equation for C3–C30 n-alkanes at column temperatures of 24–260 °C. The first and second order forward differences of the expression (Δlog Δtz and Δ2log Δtz, respectively) are linear and constant, respectively, which validates the DE model. This DE model lays a necessary foundation for further developing a retention model to accurately describe the relationship between the adjusted retention Time and z of n-alkanes.
David R Wheeler - One of the best experts on this subject based on the ideXlab platform.
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a high speed high performance microfabricated comprehensive two dimensional gas chromatograph
Lab on a Chip, 2019Co-Authors: Joshua J Whiting, E B Myers, Ronald P Manginell, Mathew Moorman, John M Anderson, Cody M Washburn, Al Staton, Daniel Porter, Darin C Graf, David R WheelerAbstract:A small, consumable-free, low-power, ultra-high-speed comprehensive GC×GC system consisting of microfabricated columns, nanoelectromechanical system (NEMS) cantilever resonators for detection, and a valve-based stop-flow modulator is demonstrated. The separation of a highly polar 29-component mixture covering a boiling point range of 46 to 253 °C on a pair of microfabricated columns using a Staiger valve manifold in less than 7 seconds, and just over 4 seconds after the ensemble Holdup Time is demonstrated with a downstream FID. The analysis Time of the second dimension was 160 ms, and peak widths in the second dimension range from 10–60 ms. A peak capacity of just over 300 was calculated for a separation of just over 6 s. Data from a continuous operation testing over 40 days and 20 000 runs of the GC×GC columns with the NEMS resonators using a 4-component test set is presented. The GC×GC-NEMS resonator system generated second-dimension peak widths as narrow as 8 ms with no discernable peak distortion due to under-sampling from the detector.