Torgny Fornstedt - Profile on Academia.edu (original) (raw)

Papers by Torgny Fornstedt

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 &amp;quot;modifier&amp;quot;. 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 &amp;quot;adsorbing additive&amp;quot;, 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, &amp;quot;bizarre&amp;quot; deformations of the preparative band shapes can occur. This is illustrated by a solute that converts from a normal &amp;quot;Langmuirian&amp;quot; band shape to an &amp;quot;anti-Langmuirian&amp;quot; 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.

Journal of Chromatography A, Jul 1, 2007

Immobilized amyloglucosidase was used as a chiral stationary phase (CSP). First, the retention an... more Immobilized amyloglucosidase was used as a chiral stationary phase (CSP). First, the retention and enantioselectivity of several model chiral amines and acids were investigated. We found that this CSP was unable to separate the enantiomers of acids, though all selected amines could be resolved. The adsorption of (R)-and (S)-propranolol and its influence on column temperature and 2-propanol content in the eluent were then studied in detail, using a three-step methodology. The adsorption was first evaluated using Scatchard plots; thereafter, the adsorption was characterized in detail by calculating the adsorption energy distribution. With this model-independent information, a better judgment could be made of the possible adsorption models selected in the last step, the model fitting to the data. In the case examined, the bi-Langmuir model (containing nonselective and enantioselective sites) describes the system well. The retention of (R)-and (S)-propranolol at low temperatures increases with the content of 2-propanol in the eluent, due to the increased saturation capacity of the enantioselective sites. The retention is an enthalpy-driven process at both types of sites, whereas the enantioseparation is due to differences between the entropy changes of the two enantiomers at the enantioselective sites. The enthalpy of adsorption at the nonselective sites is almost identical at the two concentrations of 2-propanol in the eluent. Enantioselective adsorption, on the other hand, is more exothermic at higher modifier content (20%). Thus, at high temperatures the retention decreases with increasing modifier content, whereas the opposite (unusual) trend is the case at low temperatures.

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

Analytical Chemistry, Sep 1, 1994

This paper presents a detailed study on the local pressures acting on the surface of a quasi-rigi... more This paper presents a detailed study on the local pressures acting on the surface of a quasi-rigid cylinder during vertical water entry into a flat water surface. This water entry event is an approximation of bottom wave slamming of cylindrical structures, which is a typical problem for many naval constructions. Hence, the results from this research can be used during the design of cylindrical structures in a slamming sensitive environment. The paper shows the impact pressure results of a large set of slamming drop experiments with a cylindrical model, on a rigorously instrumented test set-up using state-of-the-art equipment. The obtained experimental data is compared in detail with the governing theoretical formulations concerning cylinder slamming. For deadrise angles larger than 4.25°, a good agreement is found with an averaged version of the Wagner theory. This indicates that the Wagner theory is a good estimate for impact pressures acting on a horizontal rigid cylinder during vertical water entry, for deadrise angles larger than 4.25°.

Liquid chromatography is a very important separation method used in practically all chemistry fie... more Liquid chromatography is a very important separation method used in practically all chemistry fields. For many decades, it has played a key role in academic and industrial laboratories where it is used to analyze or purify components from complex mixtures. For example, it is used to separate proteins/drugs from impurities and to analyze drugs and endogenous components in biological materials. Most breakthroughs in biochemical and pharmaceutical sciences would probably not have been possible without chromatography. Chromatography is generally considered to have been developed in the early twentieth century by the Russian botanist Tswett. He found that he could separate components from plant extracts by flushing a sample with organic solvents through a glass tube packed with an inorganic adsorbent. Distinct bands of various colors evolved and migrated at different rates down the column. The bands corresponding to the different plant pigments could be collected at the outlet at the bottom of the tube. Tswett chose to call his technique "chromatography," which means "color writing" in Greek. The name has been kept for historical reasons, although it is not very descriptive of the method in general. His publications had, however, little impact, and the technique fell into oblivion for several decades. Chromatography is based on the partitioning of solutes between two phases and is, therefore, related to simple liquid-liquid extraction. In chromatography, however, one phase (the mobile phase) is in constant movement relative to the other one (the stationary phase). The sample molecules are partitioned between the phases; those in the stationary phase are retained, whereas those in the mobile phase move. The interaction between the solutes and the stationary phase is most often based on adsorption. During a chromatographic separation, a solute normally partitions between the phases many thousand times. The basis of separation is that different kinds of molecules on average spend different amount of time in the stationary phase. Due to the large number of partitioning steps, chromatography has enormous resolving power and can separate mixtures of components with very similar physical properties. In the most common format, called column chromatography, the stationary phase is a highly porous solid material packed inside a cylindrical column (steel or glass), whereas the mobile phase is a liquid, a gas, or a supercritical fluid. If a successful separation has been 1

Journal of Chromatography A, Dec 1, 2020

We update an earlier review of smoking bans and heart disease, restricting attention to admission... more We update an earlier review of smoking bans and heart disease, restricting attention to admissions for acute myocardial infarction. Forty-five studies are considered. New features of our update include consideration of non-linear trends in the underlying rate, a modified trend adjustment method where there are multiple time periods post-ban, comparison of estimates based on changes in rates and numbers of cases, and comparison of effect estimates according to post-ban changes in smoking restrictiveness. Using a consistent approach to derive ban effect estimates, taking account of linear time trends and control data, the reduction in risk following a ban was estimated as 4.2% (95% confidence interval 1.8-6.5%). Excluding regional estimates where national estimates are available, and studies where trend adjustment was not possible, the estimate reduced to 2.6% (1.1-4.0%). Estimates were little affected by non-linear trend adjustment, where possible, or by basing estimates on changes in rates. Ban effect estimates tended to be greater in smaller studies, and studies with greater post-ban changes in smoking restrictiveness. Though the findings suggest a true effect of smoking bans, uncertainties remain, due to the weakness of much of the evidence, the small estimated effect, and various possibilities of bias.

Applicable Analysis, Feb 1, 2017

Competitive adsorption isotherms must be estimated in order to simulate and optimize modern conti... more Competitive adsorption isotherms must be estimated in order to simulate and optimize modern continuous modes of chromatography in situations where experimental trial-and-error approaches are too complex and expensive. The inverse method is a numeric approach for the fast estimation of adsorption isotherms directly from overloaded elution profiles. However, this identification process is usually ill-posed. Moreover, traditional modelbased inverse methods are restricted by the need to choose an appropriate adsorption isotherm model prior to estimate, which might be very hard for complicated adsorption behavior. In this study, we develop a Kohn-Vogelius formulation for the model-free adsorption isotherm estimation problem. The solvability and convergence for the proposed inverse method are studied. In particular, using a problem-adapted adjoint, we obtain a convergence rate under substantially weaker and more realistic conditions than are required by the general theory. Based on the adjoint technique, a numerical algorithm for solving the proposed optimization problem is developed. Numerical tests for both synthetic and real-world problems are given to show the efficiency of the proposed regularization method.

Inverse Problems in Science and Engineering, Aug 24, 2016

How to determine adsorption isotherms is an issue of significant importance in chromatography. A ... more How to determine adsorption isotherms is an issue of significant importance in chromatography. A modern technique of obtaining adsorption isotherms is to solve an inverse problem so that the simulated batch separation coincides with actual experimental results. In this work, as well as the natural least-square approach, we consider a Kohn-Vogelius type formulation for the reconstruction of adsorption isotherms in chromatography, which converts the original boundary fitting problem into a domain fitting problem. Moreover, using the first momentum regularizing strategy, a new regularization algorithm for both the Equilibrium-Dispersive model and the Transport-Dispersive model is developed. The mass transfer resistance coefficients in the Transport-Dispersive model are also estimated by the proposed inverse method. The computation of the gradients of objective functions for both of the two models is derived by the adjoint method. Finally, numerical simulations for both a synthetic problem and a realworld problem are given to show the robustness of the proposed algorithm.

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

Journal of chromatography open, Nov 1, 2023

Microchemical Journal, Sep 1, 2018

Protocol for the visualisation of axial temperature gradients in ultra high performance liquid ch... more Protocol for the visualisation of axial temperature gradients in ultra high performance liquid chromatography using infrared cameras. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Microc(2017),

Journal of Chromatography A, Jul 1, 2016

A fundamental investigation of the pressure effect on individual adsorption sites was undertaken ... more A fundamental investigation of the pressure effect on individual adsorption sites was undertaken based on adsorption energy distribution and adsorption isotherm measurements. For this purpose, we measured adsorption equilibrium data at pressures ranging from 100 to 1000 bar at constant flow and over a wide concentration range for three low-molecular-weight solutes, antipyrine, sodium 2naphthalenesulfonate, and benzyltriethylammonium chloride, on an Eternity C18 stationary phase. The adsorption energy distribution was bimodal for all solutes, remaining clearly so at all pressures. The bi-Langmuir model best described the adsorption in these systems and two types of adsorption sites were identified, one with a low and another with a high energy of interaction. Evidence exists that the low-energy interactions occur at the interface between the mobile and stationary phases and that the high-energy interactions occur nearer the silica surface, deeper in the C18 layer. The contribution of each type of adsorption site to the retention factor was calculated and the change in solute molar volume from the mobile to stationary phase during the adsorption process was estimated for each type of site. The change in solute molar volume was 2-4 times larger at the high-energy site, likely because of the greater loss of solute solvation layer when penetrating deeper into the C18 layer. The association equilibrium constant increased with increasing pressure while the saturation capacity of the low-energy site remained almost unchanged. The observed increase in saturation capacity for the high-energy site did not affect the column loading capacity, which was almost identical at 50-and 950-bar pressure drops over the column.

Studies on system peaks in ion-pair adsorption chromatography

Journal of Chromatography A, Dec 1, 1990

Journal of Chromatography A, Apr 1, 2016

Surface excess adsorption isotherms of methanol on a diol silica adsorbent were measured in super... more Surface excess adsorption isotherms of methanol on a diol silica adsorbent were measured in supercritical fluid chromatography (SFC) using a mixture of methanol and carbon dioxide as mobile phase. The tracer pulse method was used with deuterium labeled methanol as solute and the tracer peaks were detected using APCI-MS over the whole composition range from neat carbon dioxide to neat methanol. The results indicate that a monolayer (4 Å) of methanol is formed on the stationary phase. Moreover, the importance of using the set or the actual methanol fractions and volumetric flows in SFC was investigated by measuring the mass flow respective pressure and by calculations of the actual volume fraction of methanol. The result revealed a significant difference between the value set and the actually delivered volumetric methanol flow rate, especially at low modifier fractions. If relying only on the set methanol fraction in the calculations, the methanol layer thickness should in this system be highly overestimated. Finally, retention times for a set of solutes were measured and related to the findings summarized above concerning methanol adsorption. A strongly non-linear relationship between the logarithms of the retention factors and the modifier fraction in the mobile phase was revealed, prior to the established monolayer. At modifier fractions above that required for establishment of the methanol monolayer, this relationship turns linear which explains why the solute retention factors are less sensitive to changes in modifier content in this region.

Analytical Chemistry, Jul 3, 2004

An analytical validation of the precision and accuracy of the perturbation peak (PP) method for d... more An analytical validation of the precision and accuracy of the perturbation peak (PP) method for determination of single and competitive thermodynamic isotherm parameters was performed using frontal analysis as a reference. The isotherm parameters of 11r-hydroxyprogesterone were determined in an achiral system and the isotherm parameters of (+)-methyl L-mandelate and (-)-methyl D-mandelate were determined in a chiral system, both for the single components and for the competitive binary mixture. The experimental errors in the PP method using different injection techniques were investigated, and we devised a new injection technique for the determination of competitive isotherm parameters that considerably reduced the experimental errors and also made both perturbation peaks detectable. We showed that the PP method with the new injection technique can be used to determine isotherm parameters directly from a racemic mixture. These parameters agreed well with those determined using several enantiomer ratios. Elution-band profiles simulated using the isotherm parameters showed excellent agreement with experimental profiles.

Analytical Chemistry, 1996

This chapter analyzes the experimental data using impedance spectroscopy to reduce water pollutio... more This chapter analyzes the experimental data using impedance spectroscopy to reduce water pollution by nitrate ions. The adsorption is through a synthesized layered double hydroxide (Zn 3 -Al-Cl-LDH). The kinetic study data analysis by pseudo-first-order and pseudo-second-order models is highly correlated they were found to fit very well the pseudo-second-order. This is confirmed by fast kinetic modeling of experimental data according to the pseudo-second-order. Furthermore, the Nyquist plots suggest that the grains and grain boundaries have contributed to the conduction mechanism of the material at different adsorption times and monitoring of the adsorption phenomenon. The investigation by impedance spectroscopy was used for modeling by an equivalent circuit. The real and imaginary functions of impedance complex are analyzed by modifying Cole-Cole relaxation. Revel most changes in the structure of the manifestation of the grains and the grains boundaries. The alternative current (AC) conductivity was investigated using the double power law of Jonscher. More importantly, the calculated value and the percentage of efficiency are evaluated in the adsorption. The water molecules and nitrate ions in the adsorbed were favored for the generation of the electrical response. The electrochemical impedance spectroscopy data are often interpreted by using electrical equivalent circuits.

Utilisation of peak shape tunign to optimize preparative batch chromatography

An Experimental and Theoretical investigation on Mobile PhaseEffects on Competitive Adsorption Isotherms in Preparative LC

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

Elsevier eBooks, 2023

In order to achieve an acceptable production rate at reasonable cost, preparative chromatography ... more In order to achieve an acceptable production rate at reasonable cost, preparative chromatography must be carried out with phase systems in which the kinetics of mass transfers and adsorption-desorption are fast. Accordingly, band protiles in overloaded chromatographic columns are best understood by considering the ideal model, while the process itself is most suitably modeled using the equilibriumdispersive model. The former model assumes an infinite column efficiency, while the latter lumps the contributions of axial dispersion and mass transfer resistances into a single apparent dispersion coefficient. The properties and solutions of these models are reviewed. 'Ihe conditions under which they give satisfactory results are summark&. The excellent agreement between the experimental band profiles of the components of binary mixtures and the individual band protiles calculated with the equilibrium-dispersive model is demonstrated. The degree of agreement is limited only by the accumcy with which the competitive equilibrium isotherms are accounted for.

Impact of Methanol Adsorption on Robustness in Supercritical Fluid Chromatography