The Experts below are selected from a list of 60 Experts worldwide ranked by ideXlab platform
Fabrice Gritti - One of the best experts on this subject based on the ideXlab platform.
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slow injector to column sample transport to maximize resolution in liquid Chromatography Theory versus practice
Journal of Chromatography A, 2019Co-Authors: Fabrice Gritti, Nobuo TanakaAbstract:Abstract A simple chromatographic model including extra-column sample bandspreading is built and validated experimentally. It is used to quantify the advantage of slowly transporting under isocratic elution of the injected sample band along the pre-column volume of the chromatographic system compared to the conventional injection method at constant flow rate. For fast analyses ( 30 s), the model allows for the determination of the optimum and slow injection speed that maximizes the trade-off between the analysis time and the isocratic peak capacity. For 2.1 mm × 20 mm columns packed with 2 μm particles and a highest retention factor of 10, the optimum injection speed is about 10–15% of the operating column flow rate for a maximum relative gain of 5% in overall isocratic peak capacity at constant elution time. Overall, the proposed injection method is directly applicable for enhanced resolution of weakly retained polar compounds in RPLC without the need of changing separation conditions, which may strongly increase the retention times of the late apolar eluters.
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achieving quasi adiabatic thermal environment to maximize resolution power in very high pressure liquid Chromatography Theory models and experiments
Journal of Chromatography A, 2016Co-Authors: Fabrice Gritti, Martin Gilar, Joseph A JarrellAbstract:A cylindrical vacuum chamber (inner diameter 5 cm) housing a narrow-bore 2.1 mm×100 mm column packed with 1.8 μm HSS-T3 fully porous particles was built in order to isolate thermally the chromatographic column from the external air environment. Consistent with statistical physics and the mean free path of air molecules, the experimental results show that natural air convection and conduction are fully eliminated for housing air pressures smaller than 10(-4) Torr. Heat radiation is minimized by wrapping up the column with low-emissivity aluminum-tape (emissivity coefficient ϵ=0.03 vs. 0.28 for polished stainless steel 316). Overall, the heat flux at the column wall is reduced by 96% with respect to standard still-air ovens. From a practical viewpoint, the efficiency of the column run at a flow rate of 0.6 mL/min at a constant 13,000 psi pressure drop (the viscous heat power is around 9 W/m) is improved by up to 35% irrespective of the analyte retention. Models of heat and mass transfer reveal that (1) the amplitude of the radial temperature gradient is significantly reduced from 0.30 to 0.01 K and (2) the observed improvement in resolution power stems from a more uniform distribution of the flow velocity across the column diameter. The eddy dispersion term in the van Deemter equation is reduced by 0.8±0.1 reduced plate height unit, a significant gain in column performance.
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on the relationship between band broadening and the particle size distribution of the packing material in liquid Chromatography Theory and practice
Journal of Chromatography A, 2011Co-Authors: Fabrice Gritti, Tivadar Farkas, Josuah Heng, Georges GuiochonAbstract:Abstract The influence of the particle size distribution (PSD) on the band broadening and the efficiency of packed columns is investigated on both theoretical and practical viewpoints. Each of the classical contributions to mass transfer kinetics, those due to longitudinal diffusion, eddy dispersion, and solid–liquid mass transfer resistance are measured and analyzed in terms of their expected and observed intensity as a function of the PSD of mixtures of the commercially available packing materials, 5 and 3 μm Luna-C 18 (2) particles (Phenomenex, Torrance, CA, USA). Six 4.6 mm × 150 mm columns were packed with different mixtures of these two materials. The efficiencies of these columns were measured for a non-retained and a retained analytes in a mixture of acetonitrile and water. The longitudinal diffusion coefficient was directly measured by the peak parking method. The solid–liquid mass transfer coefficient was measured from the combination of the peak parking method, the best model of effective diffusion coefficient and the actual PSDs of the different particle mixtures measured by Coulter counter experiments. The eddy diffusion term was measured according to a recently developed protocol, by numerical integration of the peak profiles. Our results clearly show that the PSD has no measurable impact on any of the coefficients of the van Deemter equation. On the contrary and surprisingly, adding a small fraction of large particles to a batch of small particles can improve the quality of the packing of the fine particles. Our results indirectly confirm that the success of sub-3 μm shell particles is due to the roughness of their external surface, which contributes to eliminate most of the nefarious wall effects.
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relationship between trans column eddy diffusion and retention in liquid Chromatography Theory and experimental evidence
Journal of Chromatography A, 2010Co-Authors: Fabrice Gritti, Georges GuiochonAbstract:Abstract Experimental results demonstrate that trans-column eddy diffusion depends on the retention of compounds. The combination of elution profiles recorded in different points of the exit column cross-section and of the height equivalent to a theoretical plate (HETP) of small molecules clearly show a strong link between retention and column performance in liquid Chromatography. These results validate a new model of trans-column eddy diffusion in packed columns. The contribution to the column HETP of the trans-column eddy diffusion term decreases with increasing retention factor from k′ = 0 to k′ = 3 above which it becomes negligible. The best column performance in RPLC is observed for the most retained compounds. This is due to the combination of the lack of a residual trans-column eddy diffusion contribution and the vanishing contribution of the instrument to band broadening.
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adsorption mechanisms and effect of temperature in reversed phase liquid Chromatography meaning of the classical van t hoff plot in Chromatography
Analytical Chemistry, 2006Co-Authors: Fabrice Gritti, Georges GuiochonAbstract:The effect of temperature on the adsorption and retention behaviors of a low molecular weight compound (phenol) on a C18-bonded silica column (C18-Sunfire, Waters) from aqueous solutions of methanol (20%) or acetonitrile (15%) was investigated. The results of the measurements were interpreted successively on the basis of the linear (i.e., overall retention factors) and the nonlinear (i.e., adsorption isotherms, surface heterogeneity, saturation capacities, and equilibrium constants) chromatographic methods. The confrontation of these two approaches confirmed the impossibility of a sound physical interpretation of the conventional Van’t Hoff plot. The classical linear Chromatography Theory assumes that retention is determined by the equilibrium thermodynamics of analytes between a homogeneous stationary phase and a homogeneous mobile phase (although there may be two or several types of interactions). From values of the experimental retention factors in a temperature interval and estimates of the activity c...
Georges Guiochon - One of the best experts on this subject based on the ideXlab platform.
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on the relationship between band broadening and the particle size distribution of the packing material in liquid Chromatography Theory and practice
Journal of Chromatography A, 2011Co-Authors: Fabrice Gritti, Tivadar Farkas, Josuah Heng, Georges GuiochonAbstract:Abstract The influence of the particle size distribution (PSD) on the band broadening and the efficiency of packed columns is investigated on both theoretical and practical viewpoints. Each of the classical contributions to mass transfer kinetics, those due to longitudinal diffusion, eddy dispersion, and solid–liquid mass transfer resistance are measured and analyzed in terms of their expected and observed intensity as a function of the PSD of mixtures of the commercially available packing materials, 5 and 3 μm Luna-C 18 (2) particles (Phenomenex, Torrance, CA, USA). Six 4.6 mm × 150 mm columns were packed with different mixtures of these two materials. The efficiencies of these columns were measured for a non-retained and a retained analytes in a mixture of acetonitrile and water. The longitudinal diffusion coefficient was directly measured by the peak parking method. The solid–liquid mass transfer coefficient was measured from the combination of the peak parking method, the best model of effective diffusion coefficient and the actual PSDs of the different particle mixtures measured by Coulter counter experiments. The eddy diffusion term was measured according to a recently developed protocol, by numerical integration of the peak profiles. Our results clearly show that the PSD has no measurable impact on any of the coefficients of the van Deemter equation. On the contrary and surprisingly, adding a small fraction of large particles to a batch of small particles can improve the quality of the packing of the fine particles. Our results indirectly confirm that the success of sub-3 μm shell particles is due to the roughness of their external surface, which contributes to eliminate most of the nefarious wall effects.
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relationship between trans column eddy diffusion and retention in liquid Chromatography Theory and experimental evidence
Journal of Chromatography A, 2010Co-Authors: Fabrice Gritti, Georges GuiochonAbstract:Abstract Experimental results demonstrate that trans-column eddy diffusion depends on the retention of compounds. The combination of elution profiles recorded in different points of the exit column cross-section and of the height equivalent to a theoretical plate (HETP) of small molecules clearly show a strong link between retention and column performance in liquid Chromatography. These results validate a new model of trans-column eddy diffusion in packed columns. The contribution to the column HETP of the trans-column eddy diffusion term decreases with increasing retention factor from k′ = 0 to k′ = 3 above which it becomes negligible. The best column performance in RPLC is observed for the most retained compounds. This is due to the combination of the lack of a residual trans-column eddy diffusion contribution and the vanishing contribution of the instrument to band broadening.
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adsorption mechanisms and effect of temperature in reversed phase liquid Chromatography meaning of the classical van t hoff plot in Chromatography
Analytical Chemistry, 2006Co-Authors: Fabrice Gritti, Georges GuiochonAbstract:The effect of temperature on the adsorption and retention behaviors of a low molecular weight compound (phenol) on a C18-bonded silica column (C18-Sunfire, Waters) from aqueous solutions of methanol (20%) or acetonitrile (15%) was investigated. The results of the measurements were interpreted successively on the basis of the linear (i.e., overall retention factors) and the nonlinear (i.e., adsorption isotherms, surface heterogeneity, saturation capacities, and equilibrium constants) chromatographic methods. The confrontation of these two approaches confirmed the impossibility of a sound physical interpretation of the conventional Van’t Hoff plot. The classical linear Chromatography Theory assumes that retention is determined by the equilibrium thermodynamics of analytes between a homogeneous stationary phase and a homogeneous mobile phase (although there may be two or several types of interactions). From values of the experimental retention factors in a temperature interval and estimates of the activity c...
Michal J Markuszewski - One of the best experts on this subject based on the ideXlab platform.
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ph gradient high performance liquid Chromatography Theory and applications
Journal of Chromatography A, 2004Co-Authors: Roman Kaliszan, Pawel Wiczling, Michal J MarkuszewskiAbstract:pH gradient high-performance liquid Chromatography (HPLC) is a method of reversed-phase high-performance liquid Chromatography suitable for ionogenic substances. It consists in programmed increase during the chromatographic process of the eluting strength of eluent with respect to the analytes separated. On the analogy of the conventional organic modifier gradient reversed-phase HPLC, in the pH gradient approach the eluting strength of the mobile phase increases due to its changing pH: increasing in case of acids or decreasing in case of bases. At the same time the content of organic modifier remains constant. A Theory of the pH gradient HPLC has been elaborated. The resulting mathematical model is easily manageable. Its ability to predict changes in retention and separation of analytes following the changes in chromatographic conditions is demonstrated. The pH gradient method is uniquely suitable to determine pKa values of analytes. An equation is presented allowing to calculate pKa values basing on appropriate retention data. The effects on pKa are discussed of the concentration of methanol in the mobile phase. The RP HPLC-derived pKa data correlate to the reference pKa values (w(w)pKa) but are not identical. That may be explained by the effects on the chromatographically determined pKa of the specific interactions of analytes with stationary phases. The proposed pH gradient RP HPLC procedure offers a fast and convenient means to get comparable acidity parameters for larger series of compounds, like drug candidates, also when the analytes are available only in minute amounts and/or as complex mixtures.
Pavel Dubský - One of the best experts on this subject based on the ideXlab platform.
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generalized model of the linear Theory of electromigration and its application to electrokinetic Chromatography Theory and software peakmaster 6 next generation
Electrophoresis, 2018Co-Authors: Michal Malý, Magda Dovhunova, Martin Dvořak, Gabriel S Gerlero, Pablo A Kler, Vlastimil Hruska, Pavel DubskýAbstract:The linear Theory of electromigration, including the first-order nonlinear approximation, is generalized to systems with any equilibria fast enough to be considered instantaneous in comparison with the timescale of peak movement. For example, this Theory is practically applied in the electrokinetic Chromatography (EKC) mode of the CZE. The model enables the calculation of positions and shapes of analyte and system peaks without restricting the number of selectors, the complexation stoichiometry, or simultaneous acid-base equilibria. The latest version of our PeakMaster software, PeakMaster 6-Next Generation, implements the Theory in a user-friendly way. It is a free and open-source software that performs all calculations and shows the properties of the background electrolyte and the expected electropherogram within a few seconds. In this paper, we mathematically derive the model, discuss its applicability to EKC systems, and introduce the PeakMaster 6 software.
Ken Broeckhoven - One of the best experts on this subject based on the ideXlab platform.
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kinetic plots for gas Chromatography Theory and experimental verification
Journal of Chromatography A, 2015Co-Authors: Sander Jespers, Kevin Roeleveld, Frederic Lynen, Ken Broeckhoven, Gert DesmetAbstract:Mathematical kinetic plot expressions have been established for the correct extrapolation of the kinetic performance measured in a thin-film capillary GC column with fixed length into the performance that can be expected in a longer column used at the same outlet velocity but at either the maximal inlet pressure or at the optimal inlet pressure, i.e., the one leading to an operation at the kinetic performance limit of the given capillary size. To determine this optimal pressure, analytical solutions have been established for the three roots of the corresponding cubic equation. Experimental confirmation of the kinetic plot extrapolations in GC has been obtained measuring the efficiency of a simple test mixture on 30, 60, 90 and 120m long (coupled) columns.
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using contemporary liquid Chromatography Theory and technology to improve capillary gradient ion exchange separations
Journal of Chromatography A, 2014Co-Authors: Bert Wouters, Ken Broeckhoven, Sam Wouters, Cees Bruggink, Yury Agroskin, Christopher A Pohl, Sebastiaan EeltinkAbstract:Abstract The gradient-performance limits of capillary ion Chromatography have been assessed at maximum system pressure (34.5 MPa) using capillary columns packed with 4.1 μm macroporous anion-exchange particles coated with 65 nm positively-charged nanobeads. In analogy to the van-Deemter curve, the gradient performance was assessed applying different flow rates, while decreasing the gradient time inversely proportional to the increase in flow rate in order to maintain the same retention properties. The gradient kinetic-performance limits were determined at maximum system pressure, applying t G / t 0 = 5, 10, and 20. In addition, the effect of retention on peak width was assessed in gradient mode for mono-, di-, and trivalent inorganic anions. The peak width of late-eluting ions can be significantly reduced by using concave gradient, resulting in better detection sensitivity. A signal enhancement factor of 8 was measured for a late-eluting ion when applying a concave instead of a linear gradient. For the analysis of a complex anion mixture, a coupled column with a total length of 1.05 m was operated at the kinetic-performance limit applying a linear 250 min gradient ( t G / t 0 = 10). The peak capacity varied between 200 and 380 depending on analyte retention, and hence on charge and size of the ion.