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Torgny Fornstedt

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Papers by Torgny Fornstedt

Research paper thumbnail of Peak deformations in preparative supercritical fluid chromatography due to co-solvent adsorption

Journal of Chromatography A, Oct 1, 2016

In supercritical fluid chromatography (SFC) the mobile phase comprises of carbon dioxide (CO2) as... more In supercritical fluid chromatography (SFC) the mobile phase comprises of carbon dioxide (CO2) as main solvent and smaller amounts of an organic polar solvent (often an alcohol) as co-solvent. The co-solvent is considered to function by changing the overall polarity of the eluent, i.e. by acting as a "modifier". However, recent studies indicate that the co-solvent methanol can also adsorb to some common SFC stationary phases. Hence, the co-solvent should also be able to function as an "adsorbing additive", i.e. an eluent component that competes with the injected solutes about the stationary phase surface. In this study it was found by fitting different mechanistic models to systematic experimental data, that the co-solvent methanol can have both functions: at low co-solvent fractions, methanol acts as an additive whereas at larger fractions it acts as a modifier. Moreover, it was found that when the co-solvent adsorbs more strongly to the stationary phase than the solute, "bizarre" deformations of the preparative band shapes can occur. This is illustrated by a solute that converts from a normal "Langmuirian" band shape to an "anti-Langmuirian" shape when changing from neat carbon dioxide (CO2) to an eluent containing co-solvent. This peak shape transition is dependent on both (i) the relative retention of the solute and co-solvent to the stationary phase in eluent containing neat CO2 and on (ii) the relative retention of the additive perturbation peak and the solute peak in eluent containing also co-solvent.

Research paper thumbnail of Thermodynamic characterization of the adsorption of selected chiral compounds on immobilized amyloglucosidase in liquid chromatography

Journal of Chromatography A, Jul 1, 2007

Research paper thumbnail of Studies on System Peaks in Ion-Pair Adsorption Chromatography: I. Evaluation of Ion-Pair Adsorption Constants and Effects by the Injection of Finite Analyte Amounts

Journal of liquid chromatography, Jun 1, 1987

Adsorption of a secondary amine, protriptyline, as phosphate ion-pair, to Nucleosil C18, was stud... more Adsorption of a secondary amine, protriptyline, as phosphate ion-pair, to Nucleosil C18, was studied. Two different techniques were compared; the traditional break-through and the system peak technique. Both techniques indicated that the adsorption of the ion-pair was best fitted to a 2-site adsorption model of the Langmuir type, indicating a heterogenous solid phase surface.The reliability of the system peak technique

Research paper thumbnail of Comparison between Experimental and Theoretical Profiles of High Concentration Elution Bands and Large System Peaks in Nonlinear Chromatography

Analytical Chemistry, Sep 1, 1994

Research paper thumbnail of Basic HPLC Theory and Definitions: Retention, Thermodynamics, Selectivity, Zone Spreading, Kinetics, and Resolution

Research paper thumbnail of Impact of stationary-phase pore size on chromatographic performance using oligonucleotide separation as a model

Journal of Chromatography A, Dec 1, 2020

Research paper thumbnail of A regularizing Kohn–Vogelius formulation for the model-free adsorption isotherm estimation problem in chromatography

Applicable Analysis, Feb 1, 2017

Research paper thumbnail of An adjoint method in inverse problems of chromatography

Inverse Problems in Science and Engineering, Aug 24, 2016

Research paper thumbnail of Separation of therapeutic oligonucleotides using ion-pair reversed-phase chromatography based on fundamental separation science

Journal of chromatography open, Nov 1, 2023

Research paper thumbnail of Protocol for the visualisation of axial temperature gradients in ultra high performance liquid chromatography using infrared cameras

Microchemical Journal, Sep 1, 2018

Research paper thumbnail of A fundamental study of the impact of pressure on the adsorption mechanism in reversed-phase liquid chromatography

Journal of Chromatography A, Jul 1, 2016

Research paper thumbnail of Studies on system peaks in ion-pair adsorption chromatography

Journal of Chromatography A, Dec 1, 1990

Adsorption of a secondary amine, protriptyline, as phosphate ion-pair, to Nucleosil C18, was stud... more Adsorption of a secondary amine, protriptyline, as phosphate ion-pair, to Nucleosil C18, was studied. Two different techniques were compared; the traditional break-through and the system peak technique. Both techniques indicated that the adsorption of the ion-pair was best fitted to a 2-site adsorption model of the Langmuir type, indicating a heterogenous solid phase surface.The reliability of the system peak technique

Research paper thumbnail of A closer study of methanol adsorption and its impact on solute retentions in supercritical fluid chromatography

Journal of Chromatography A, Apr 1, 2016

Research paper thumbnail of Validation of the Accuracy of the Perturbation Peak Method for Determination of Single and Binary Adsorption Isotherm Parameters in LC

Analytical Chemistry, Jul 3, 2004

Research paper thumbnail of Experimental and Theoretical Study of the Adsorption Behavior and Mass Transfer Kinetics of Propranolol Enantiomers on Cellulase Protein as the Selector

Analytical Chemistry, 1996

Research paper thumbnail of Utilisation of peak shape tunign to optimize preparative batch chromatography

Research paper thumbnail of An Experimental and Theoretical investigation on Mobile PhaseEffects on Competitive Adsorption Isotherms in Preparative LC

Research paper thumbnail of Assessment of physicochemical properties of sorbent materials in passive and active sampling systems towards gaseous nitrogen-containing compounds

Journal of Chromatography A, Aug 1, 2023

Research paper thumbnail of Modeling of preparative liquid chromatography

Research paper thumbnail of Impact of Methanol Adsorption on Robustness in Supercritical Fluid Chromatography

Research paper thumbnail of Peak deformations in preparative supercritical fluid chromatography due to co-solvent adsorption

Journal of Chromatography A, Oct 1, 2016

In supercritical fluid chromatography (SFC) the mobile phase comprises of carbon dioxide (CO2) as... more In supercritical fluid chromatography (SFC) the mobile phase comprises of carbon dioxide (CO2) as main solvent and smaller amounts of an organic polar solvent (often an alcohol) as co-solvent. The co-solvent is considered to function by changing the overall polarity of the eluent, i.e. by acting as a "modifier". However, recent studies indicate that the co-solvent methanol can also adsorb to some common SFC stationary phases. Hence, the co-solvent should also be able to function as an "adsorbing additive", i.e. an eluent component that competes with the injected solutes about the stationary phase surface. In this study it was found by fitting different mechanistic models to systematic experimental data, that the co-solvent methanol can have both functions: at low co-solvent fractions, methanol acts as an additive whereas at larger fractions it acts as a modifier. Moreover, it was found that when the co-solvent adsorbs more strongly to the stationary phase than the solute, "bizarre" deformations of the preparative band shapes can occur. This is illustrated by a solute that converts from a normal "Langmuirian" band shape to an "anti-Langmuirian" shape when changing from neat carbon dioxide (CO2) to an eluent containing co-solvent. This peak shape transition is dependent on both (i) the relative retention of the solute and co-solvent to the stationary phase in eluent containing neat CO2 and on (ii) the relative retention of the additive perturbation peak and the solute peak in eluent containing also co-solvent.

Research paper thumbnail of Thermodynamic characterization of the adsorption of selected chiral compounds on immobilized amyloglucosidase in liquid chromatography

Journal of Chromatography A, Jul 1, 2007

Research paper thumbnail of Studies on System Peaks in Ion-Pair Adsorption Chromatography: I. Evaluation of Ion-Pair Adsorption Constants and Effects by the Injection of Finite Analyte Amounts

Journal of liquid chromatography, Jun 1, 1987

Adsorption of a secondary amine, protriptyline, as phosphate ion-pair, to Nucleosil C18, was stud... more Adsorption of a secondary amine, protriptyline, as phosphate ion-pair, to Nucleosil C18, was studied. Two different techniques were compared; the traditional break-through and the system peak technique. Both techniques indicated that the adsorption of the ion-pair was best fitted to a 2-site adsorption model of the Langmuir type, indicating a heterogenous solid phase surface.The reliability of the system peak technique

Research paper thumbnail of Comparison between Experimental and Theoretical Profiles of High Concentration Elution Bands and Large System Peaks in Nonlinear Chromatography

Analytical Chemistry, Sep 1, 1994

Research paper thumbnail of Basic HPLC Theory and Definitions: Retention, Thermodynamics, Selectivity, Zone Spreading, Kinetics, and Resolution

Research paper thumbnail of Impact of stationary-phase pore size on chromatographic performance using oligonucleotide separation as a model

Journal of Chromatography A, Dec 1, 2020

Research paper thumbnail of A regularizing Kohn–Vogelius formulation for the model-free adsorption isotherm estimation problem in chromatography

Applicable Analysis, Feb 1, 2017

Research paper thumbnail of An adjoint method in inverse problems of chromatography

Inverse Problems in Science and Engineering, Aug 24, 2016

Research paper thumbnail of Separation of therapeutic oligonucleotides using ion-pair reversed-phase chromatography based on fundamental separation science

Journal of chromatography open, Nov 1, 2023

Research paper thumbnail of Protocol for the visualisation of axial temperature gradients in ultra high performance liquid chromatography using infrared cameras

Microchemical Journal, Sep 1, 2018

Research paper thumbnail of A fundamental study of the impact of pressure on the adsorption mechanism in reversed-phase liquid chromatography

Journal of Chromatography A, Jul 1, 2016

Research paper thumbnail of Studies on system peaks in ion-pair adsorption chromatography

Journal of Chromatography A, Dec 1, 1990

Adsorption of a secondary amine, protriptyline, as phosphate ion-pair, to Nucleosil C18, was stud... more Adsorption of a secondary amine, protriptyline, as phosphate ion-pair, to Nucleosil C18, was studied. Two different techniques were compared; the traditional break-through and the system peak technique. Both techniques indicated that the adsorption of the ion-pair was best fitted to a 2-site adsorption model of the Langmuir type, indicating a heterogenous solid phase surface.The reliability of the system peak technique

Research paper thumbnail of A closer study of methanol adsorption and its impact on solute retentions in supercritical fluid chromatography

Journal of Chromatography A, Apr 1, 2016

Research paper thumbnail of Validation of the Accuracy of the Perturbation Peak Method for Determination of Single and Binary Adsorption Isotherm Parameters in LC

Analytical Chemistry, Jul 3, 2004

Research paper thumbnail of Experimental and Theoretical Study of the Adsorption Behavior and Mass Transfer Kinetics of Propranolol Enantiomers on Cellulase Protein as the Selector

Analytical Chemistry, 1996

Research paper thumbnail of Utilisation of peak shape tunign to optimize preparative batch chromatography

Research paper thumbnail of An Experimental and Theoretical investigation on Mobile PhaseEffects on Competitive Adsorption Isotherms in Preparative LC

Research paper thumbnail of Assessment of physicochemical properties of sorbent materials in passive and active sampling systems towards gaseous nitrogen-containing compounds

Journal of Chromatography A, Aug 1, 2023

Research paper thumbnail of Modeling of preparative liquid chromatography

Research paper thumbnail of Impact of Methanol Adsorption on Robustness in Supercritical Fluid Chromatography

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