Solid Stationary Phase Research Articles

Enantioseparation of Malathion, Cruformate, and Fensulfothion Organophosphorus Pesticides by Mixed-Mode Electrokinetic Capillary Chromatography

Mixed-mode electrokinetic capillary chromatography (mixed-mode ECC) has been used for the enantioseparation of organophosphorus pesticides. In mixed-ECC, a combination of three pseudostationary phases including surfactants, neutral, and charged cyclodextrins, are used to resolve very challenging enantioseparation problems. The conditions mimic a mixture of micellar electrokinetic capillary chromatography (MECC) and dual-cyclodextrin electrokinetic capillary chromatography (dual-CECC) conditions. In this work SDS, carboxymethyl- g -CD, hydroxypropyl-BCD, and organic modifiers were mixed at various concentrations in order to achieve enantioseparation of three organophosphorus pesticides - cruformate (ruelene), malathion, and fensulfothion. The best condition for separation of ruelene enantiomers was by using a mixture of 70 mM SDS/15 mM carboxymethyl-BCD/45 mM hydroxypropyl-BCD/20% (v/v) acetonitrile in 20 mM borate buffer at pH 8.6, with applied voltage of 25 kV at 25°C. Malathion enantiomers were successfully resolved using either 10 mM SDS/50 mM CM-BCD/40 mM hydroxypropyl-BCD or 50 mM CM-BCD/50 mM hydroxypropyl-BCD/20% (v/v) methanol in 20 mM borate buffer. Fensulfothion enantiomers were successfully resolved using a mixture of 75 mM SDS/12.5 mM carboxymethyl-BCD/45 mM hydroxypropyl-BCD in the same 20 mM borate buffer. The results demonstrate the versatility of the mixed-mode ECC technique in handling very difficult separations such as the organophosphoramidate enantiomers. It offers options for selectivity control by combining three or more pseudostationary phases in the background electrolyte (BGE). The approach to optimization in mixed-mode ECC is generally more straightforward than the use of a solid stationary phase(s) in HPLC. In theory, the separation selectivity of such mixed-mode ECC system can be modified to the extremes of MECC and the dual-CECC of the chiral selectors.

Effect of emulsifiers on surface properties of sucrose by inverse gas chromatography

Inverse gas chromatography (IGC) was employed to characterize the changes in surface properties of sucrose particles coated with either lecithin or polyglycerol polyricinoleate. IGC was performed using polar and non-polar adsorbates at infinite dilution with the sucrose particles as the solid stationary phase. Coating the sugar surface with emulsifiers induced an increase in the lipophilicity of the sugar particles, i.e. a sharp decrease in the acidity of the surface. Yet the two emulsifiers induced a slightly different increase in the surface basicity. It was hypothesized that this observation was due to a difference in the molecular structure of the emulsifiers.

Oxidation of Low-Density Lipoproteins in the Presence of a Fullerene-Containing Silica Gel

The results of a study on the oxidation of low-density lipoproteins (LDLs) in the presence of a fullerene-containing silica gel in the sorbent phase (a solid stationary phase) and in the phase of an LDL solution (a liquid mobile phase) are presented. It was found that the main distinctive feature of the process of LDL oxidation in the presence of a fullerene-containing silica gel consists in its heterogeneity; that is, the oxidation simultaneously occurs in both of the phases. In this case, the effect of the oxidation process in a solid phase on the kinetics in a liquid phase can be described in terms of the nonuniform distribution of reactant concentrations in the phases of the system and the formation of a donor–acceptor complex. It was found that the concentration of oxidation products is an exponential function of LDL concentration; this fact is indicative of a free-radical chain mechanism of the LDL oxidation reaction in the presence of the sorbent. This relationship was described by an empirical equation, which is the same for either of the phases, and the parameters of this equation have precise physical meanings. It was found from calculations that both the formation of donor–acceptor complexes and the nonuniform distribution of LDL in the two-phase system are responsible for a considerable difference between the kinetics of sorbent-initiated LDL oxidation in the sorbent phase and the solution phase.

Separation of Substances in Rotating Coiled Columns: From Trace Elements to Microparticles

The potentialities of rotating coiled columns in countercurrent chromatography (CCC) and centrifugal field-flow fractionation (CFFF) are demonstrated. A rotating coiled column is a fluoroplastic or steel coil wound around a rigid cylindrical drum, which revolves about its axis and, at the same time, revolves around the central axis of the device called planet centrifuge. The stationary (liquid, solid, or heterogeneous) phase is retained in the column because of the centrifugal force field, and the mobile liquid phase is continuously pumped through the column. The methods for recovery, separation, and preconcentration of various trace elements in geological samples and high-purity substances with the use of two-phase liquid systems (CCC) are developed. Procedures are proposed for the continuous sequential extraction of various element species from soil and for the recovery of polycyclic aromatic hydrocarbons from sewage sludge with the use of natural suspensions or solid particulates as stationary phases. It is also shown that rotating coiled columns can be used in a new field, microparticle fractionation by CFFF.

Gradient formation in membrane unit for differential precipitation of proteins

AbstractA new protein fractionation technique presented transfers ammonium sulfate to create a gradient of ammonium sulfate inside a membrane unit for differential precipitation of proteins called “centrifugal precipitation chromatography.” Because it does not require any solid support, it should provide a better alternative to the conventional chromatography with solid stationary phase. To understand the phenomena and achieve a better separation, a mathematical model explaining the ammonium sulfate gradient formation inside the stationary membrane unit is investigated. The model is extended with empirical correlation to the centrifugal membrane unit—a new approach for protein purification. The model agreed well with the experiments for both stationary and centrifugal units. Upon using the model to calculate the ammonium sulfate gradient formation in a membrane unit, this new technique can be useful in separating a mixture of proteins whose solubility in ammonium sulfate solution differs. To demonstrate the technique experimentally, mixtures of proteins are loaded into the column; the partial resolution between proteins is achieved with the step concentration switch of the inlet ammonium sulfate solution.

Comparison of Various Process Engineering Concepts of Preparative Chromatography

Liquid chromatography utilizing porous solid phases (adsorption chromatography) is one of the most powerful and versatile methods of modern analytical chemistry. Its widespread application is due in part to the development of a broad range of combinations of solid stationary and liquid mobile phases. Normal phase and reverse phase chromatography with pure and chemically modified silica, respectively, affinity chromatography, can be cited as examples. In addition to its use as an analytical method, chromatography is becoming increasingly important in the preparative scale for the isolation of pure substances in the pharmaceutical industry, in biotechnology, and in the production of fine chemicals. In many cases, the required purity criteria can only be met with chromatographic techniques, as in the resolution of racemates. From a process engineering viewpoint, a better understanding of concentration profile deformations caused by intended overloading of separation columns has recently been acquired. In particular, this concerns the description of displacement and entrainment effects associated with the competitive adsorption. A series of alternative operating modes has been developed and used to enhance yields and productivities. In spite of a number of attempted comparative studies, quantitative information about optimizing these processes is lacking. This article will compare four different process engineering concepts of preparative chromatography on the basis of a uniform theoretical model.

Mechanisms of unsteady mixing of heat carrier with its flowrate variation and flow swirling—I. Calculation methods and experimental study of transient processes

The results of experimental and theoretical studies of the unsteady mixing process of heat carrier in a helical tube bundle when heat carrier flowrate is increased and decreased are presented. In experiments, the axisymmetric nonuniformity of a heat release field was modeled and temperature fields of heat carrier were measured at the tube bundle cross-section. Theoretically, the temperature fields were calculated using the two-temperature flow model of a two-phase homogenized medium with a stationary solid phase. Effective turbulent transfer coefficients were determined from comparison of the experimental and predicted temperature fields of heat carrier. New generalizing relations are derived to calculate effective turbulent transfer coefficients used to close a system of equations describing unsteady thermal and hydraulic processes in such tube bundles. The physical phenomena that characterize the specific features of heat transfer from flow swirling in complex-geometry channels for different types of hydrodynamic unsteadiness are considered. Examples of calculation of transient processes, as applied to a vehicular nuclear reactor, are presented.

Modeling of solidification of metal-matrix particulate composites with convection

A multiphase model for the alloy solidification of metal-matrix particulate composites with convection is developed. Macroscopic transport equations are written for each phase, with unknown parameters modeled through supplementary relations pertinent to the solidification of a binary alloy matrix containing a stationary solid phase and generally nonstationary spherical particles. The model is applied to various one- and two-dimensional systems containing an Al-7 wt pct Si/SiC composite. One-dimensional sedimentation results in nonclustering and clustering particle systems show good agreement with experiments. One-dimensional composite solidification results illustrate the effect of particle clustering and cooling direction on the final macroscopic particle distribution. Two-dimensional results in various unreinforced and reinforced systems illustrate macroscopic particle segregation and its effect on buoyancy-driven melt convection and species macrosegregation. Results indicate a nearly uniform particle distribution for relatively small particles due to negligible particle settling prior to entrapment. For relatively large particles, significant particle settling prior to entrapment results in large denuded and packed zones in the casting. Fluid flow and macrosegregation during solidification are substantially reduced in the presence of particles, due to the relatively large interfacial drag exerted on the liquid by the stationary mush and particle phases.

Effect of colloids on volatile contaminant transport and air‐water partitioning in unsaturated porous media

The presence of mobile colloids in subsurface environments can enhance subsurface contaminant migration by reducing retardation effects. We developed a mathematical model based on mass balance equations to describe the transport and fate of colloidal particles and a volatile contaminant in an unsaturated porous medium. When colloids are present in an unsaturated medium, the system representation include four phases: an aqueous phase, a carrier phase, a stationary solid matrix phase, and the air phase. Colloidal mass transfer between the aqueous and solid matrix phases and between the aqueous phase and the air‐water interface, and the contaminant mass transfer between aqueous and colloidal phases and between the aqueous phase and the air‐water interface are represented by kinetic expressions. Nondimensionalized governing equations are solved to analyze colloid and contaminant transport in an unsaturated column. A sensitivity analysis of the transport model was utilized to assess the effects of several parameters on model behavior. Results show that the effect of colloids on a volatile contaminant transport is highly dependent on the properties of the contaminant and the colloidal surfaces. The presence of an air‐water interface retards the volatile contaminant migration because of mass transfer rate across the air‐water interface, offsetting the facilitating effect of colloids. We tested the effects of varying Henry's constant and the contaminant mass transfer across the air‐water interface. The equilibrium assumption for the contaminant mass transfer across the air‐water interface may be valid for volatile contaminants with dimensionless Henry's constants less than one. As Henry's constant increases, the contaminant mass transferred across the air‐water interface is approximately 20% larger at 46% air saturation than at 15% air saturation because of a larger volume of air. At 15% air saturation, air phase contaminant reaches the equilibrium concentration at about 18 pore volumes with a large dimensionless Henry's constant (H+=). However, at 46% air saturation, it takes over 20 pore volumes to reach the equilibrium concentration, even with a smaller Henry's constant (H+quals;1).

Vergleich verschiedener verfahrenstechnischer Konzepte der präparativen Flüssigchromatographie

AbstractLiquid chromatography utilising porous solid phases (adsorption chromatography) is one of the most powerful and versatile methods of modern analytical chemistry. Its widespread application is due in part to the development of a broad range of combinations of solid stationary and liquid mobile phase. Normal phase and reverse phase chromatography with pure and chemically modified silica gel, respectively, affinity chromatography, and ion chromatography can be cited as examples [1]. In addition to its use as an analytical method, chromatography is becoming increasingly important in the preparative‐scale isolation of pure substances in the pharmaceutical industry, in biotechnology, and in the production of fine chemicals. In many cases, the required purity criteria can only be met with chromatographic techniques, as in the resolution of racemates. From a process engineering viewpoint, a better understanding of concentration profile deformations caused by intended overloading of separation columns has recently been acquired [2]. In particular, this cncerns the description of displacement and entrainment effects associated with the competing adsorption. A series of alternative operating modes has been developed and used [3] for enhancing yields and productivities. In spite of a number of attempted comparative studies [4] there is a lack of quantitative information about optimized process. This article aims to compare four different process engineering concepts of preparative chromatography on the basis of a uniform theoretical model.

Surface-modified silica gels as solid stationary phases in gas chromatography

Modifications of the precipitated silica gel were done by different treatments including calcination, hydrothermal treatment, silylation and treatment with alkali salt (NaCl). In addition, the hydrothermally treated silica gel was subjected to further treatments, namely silylation or modification by alkali metal. Density of surface hydroxyls ( N OH/100 Å 2) was determined thermogravimetrically and confirmed by infrared spectroscopy. Surface textural characteristics were investigated from nitrogen adsorption-desorption isotherms at −196 °C. It was found that the hydrothermal treatment has a pronounced influence in removing hydroxyls from the silica surface. Different pore systems were found to exist depending on the adopted treatments. The surface-modified silica gels were tested as GC solid stationary phases in terms of the separation efficiency for various groups of non-polar and polar solutes. Also, thermodynamic parameters (Δ H, Δ G and Δ S) were determined using n-hexane as a probe in order to show the sdsorbate-adsorbent interaction. It was observed that the non-polar solutes could be separated independent of the reactivity and porosity of the silica surfaces. The efficiency of the surface-modified silica gels to separate the aromatic hydrocarbons seemed to be strongly influenced by the density of the surface hydroxyls. It was suggested that the separation of the polar solutes ( n-alcohols) is enhanced by the inertness of the silica surface and a fraction of wider pores located mostly at 80 Å.

Transport of a non-volatile contaminant in unsaturated porous media in the presence of colloids

Stable colloidal particles can travel long distances in subsurface environments and carry particle-reactive contaminants with them to locations further than predicted by the conventional advective-dispersive transport equation. When such carriers exist in a saturated porous medium, the system can be idealized as consisting of three phases: an aqueous phase, a carrier phase, and a stationary solid matrix phase. However, when colloids are present in an unsaturated porous medium, the system representation should include one more phase, i.e. the air phase. In the work reported, a mathematical model was developed to describe the transport and fate of the colloidal particles and a non-volatile contaminant in unsaturated porous media. The model is based on mass balance equations in a four-phase porous medium. Colloid mass transfer mechanisms among aqueous, solid matrix, and air phases, and contaminant mass transfer between aqueous and colloid phases are represented by kinetic expressions. Governing equations are non-dimensionalized and solved to investigate colloid and contaminant transport in an unsaturated porous medium. A sensitivity analysis of the transport model was utilized to assess the effects of several parameters on model behavior. The colloid transport model matches successfully with experimental data of Wan and Wilson. The presence of air-water interface retards the colloid transport significantly counterbalancing the facilitating effect of colloids. However, the retardation of contaminant transport by colloids is highly dependent on the properties of the contaminant and the colloidal surface.

Colloid‐enhanced transport of chemicals in subsurface environments: A review

Abstract Ample published evidence demonstrates that colloidal particles can act as carriers to enhance the transport of contaminants in subsurface environments. Conventionally, soil and aquifer porous media are considered to have two phases: an immobile solid matrix and a mobile liquid. Published reports indicate that biocolloids, aluminosilicate clay minerals, and organic colloids can migrate to considerable distances during water flow in soils and aquifers. In the presence of such carriers, the system should be perceived as consisting of three phases: a stationary solid matrix phase, a carrier phase, and an aqueous phase. Particle transport through porous media has been clearly demonstrated in filtration studies, but a need exists to investigate the role of colloidal carriers upon contaminant transport in porous media and to model carrier‐enhanced migration of contaminants accurately. In order to assess the potential role of colloidal carriers in facilitating chemical transport in porous media, this rev...

A Kinetic Approach to Modeling Mobile Bacteria‐Facilitated Groundwater Contaminant Transport

Mobile bacterial particles can act as carriers and enhance the transport of hydrophobic contaminants in groundwater by reducing retardation effects. Because of their colloidal size and favorable surface conditions, bacteria act as efficient contaminant carriers. When such carriers exist in a water‐saturated porous medium, the system can be thought of as three phases: an aqueous phase, a carrier phase, and a stationary solid matrix phase. Contaminant may be present in either or all of these phases. In this study, a mathematical model based on mass balances is developed to describe the simultaneous transport and fate of a biodegradable contaminant and bacteria in a porous medium. The Monod model describes the relation between the growth rate of bacteria and concentration of the contaminant which serves as a growth substrate. The bacterial decay is assumed to be a first‐order reaction. The mechanisms of bacterial mass transfer between aqueous and solid matrix phases, and contaminant mass transfer between aqueous and bacterial phases are represented by kinetic models. Governing equations are nondimensionalized and solved to analyze the bacteria‐facilitated contaminant transport. The model is compared with a similar model obtained with local equilibrium assumption to understand the characteristics of kinetic and local equilibrium descriptions. Results show that the contaminant transport as well as bacterial transport can be described by local equilibrium assumption when Damköhler numbers are larger than 10. Significant sensitivities to model parameters, particularly bacterial growth rate and influent bacterial concentration, were observed. The numerical results of the bacteria carrier effect match favorably with experimental data reported in the literature.

Colloid-facilitated radionuclide transport in fractured porous rock

Numerical methods have been applied for the prediction of colloid-facilitated radionuclide transport through water-saturated fractured porous rock. The presence of colloids may enhance the transport of radionuclides in groundwater by reducing retardation effects. The colloids existing in the groundwater act as carriers, adsorbing radionuclides in their large surface area and moving faster than the average water velocity. With colloids present, the system consists of three phases, i.e. an aqueous phase, a carrier phase and a stationary solid phase. In the basic model, one-dimensional advection in a single planar fracture of infinite extent is coupled with diffusion in the rock matrix perpendicular to the fracture. In this study, a full-equilibrium model was developed to describe the transport and fate of the radionuclides in the fracture. Sorption onto the rock matrix, fracture surface and sorption onto mobile and immobile colloids are included. The effect of colloidal particle size was also considered. Mass partition mechanisms between the colloids and solid matrix and between colloid and contaminant are represented by local equilibrium. In the three-phase system, the three parameters, the retardation coefficient, the hydrodynamic dispersion coefficient and fracture width, are modified to include the equilibrium distribution coefficient of a contaminant with a carrier. In the three-phase model, much smaller retardation and hydrodynamic dispersion coefficients are obtained and the effect of the fracture width is larger. Much faster transport of contaminant has resulted mainly because the radionuclides attached to colloidal particles are not subject to retardation by diffusion into the rock matrix. With the additional consideration of colloidal particle sizes, these effects become ever larger. Numerical solutions for the model were obtained using a fully implicit finite difference scheme. A significant sensitivity to model parameters was discovered, and, in particular, the equilibrium distribution coefficients between a contaminant and the carrier were found to be the most important factors.

Modeling Facilitated Contaminant Transport by Mobile Bacteria

Introduction of exogenous biocolloids such as genetically engineered bacteria in a bioremediation operation can enhance the transport of contaminants in groundwater by reducing the retardation effects. Because of their colloidal size and favorable surface conditions, bacteria are efficient contaminant carriers. In cases where contaminants have a low mobility in porous media because of their high partition with solid matrix, facilitated contaminant transport by mobile bacteria can create high contaminant fluxes. When metabolically active mobile bacteria are present in a subsurface environment, the system can be treated as consisting of three phases: water phase, bacterial phase, and stationary solid matrix phase. In this work a mathematical model based on mass balance equations is developed to describe the facilitated transport and fate of a contaminant and bacteria in a porous medium. Bacterial partition between the bulk solution and the stationary solid matrix and contaminant partition among three phases are represented by expressions in terms of measurable quantities. Solutions were obtained to provide estimates of contaminant and bacterial concentrations. A dimensional analysis of the transport model was utilized to estimate model parameters from the experimental data and to assess the effect of several parameters on model behavior. The model results matched favorably with experimental data of Jenkins and Lion (1993). The presence of mobile bacteria enhances the contaminant transport. However, bacterial consumption of the contaminant, which serves as a bacterial nutrient, can attenuate the contaminant mobility. The work presented in this paper is the first three‐phase model to include the effects of substrate metabolism on the fate of groundwater contaminants.

Simulierte Gegenstromchromatographie

AbstractSimulated Countercurrent Chromatography. This paper reviews simulated countercurrent chromatography, a separation process that has received only little attention. In contrast to standard batchwise operated chromatography, a periodical mode of operation is used. The feed and collection lines are shifted along the column, thus simulating countercurrent operation of the liquid phase and the stationary solid phase. As a result, higher product yield and higher product purity are obtained. At the same time the amount of solid phase and solvent phase required in comparison to discontinuous chromatography is reduced. Industrial applications have been developed since 1964 by Universal Oil Products (UOP). Large scale separation processes in the petrochemical and the sugar industries are already in operation. On the bench scale this process is used to separate biotechnological products and pharmaceuticals. The need to solve difficult separation problems (isomeric or racemic mixtures, biomolecules, polymers) will encourage further developments. Together with improved process‐simulation tools and process control, simulated countercurrent chromatography will be established as a powerful separation technique with widespread industrial applicability.

Determination of the surface properties of two batches of salbutamol sulphate by inverse gas chromatography

The surface properties of two batches of salbutamol sulphate, demonstrated to be chemically and structurally equivalent by FT-Raman spectroscopy and X-ray powder diffraction, were measured using a gas-solid chromatography technique, inverse gas chromatography (IGC). IGC was undertaken using polar and non-polar adsorbates (probes) at infinite dilution with salbutamol sulphate as the solid stationary phase. The retention behaviour of the probes was found to differ markedly between the two batches, implicating a profound difference in surface energetics. This was reflected in the differences in calculated dispersive component of surface free energy ( γ S D) and acid-base parameters.

Verification of the mathematical modeling of bio-physico chemical processes in activated carbon columns

Plug-flow stationary solid phase upflow and completely mixed recycle fluidized adsorber experiments were conducted to test the predictive models developed earlier. Model parameters were determined independently from adsorption equilibrium, kinetic investigations, biokinetic experiments and correlation techniques. Two ideally adsorbable and biodegradable compounds, glucose and sucrose, as well as two actual wastewaters, a dairy waste and a landfill leachate, were used to compare the model profiles and experimental data of non-bioactive and bioactive adsorber systems. The performance prediction by the models satisfactorily described the experimental data.

Colloid‐facilitated groundwater contaminant transport

Colloidal particles or dissolved organic matter (DOM) can act as carriers to enhance the transport of contaminants in groundwater by reducing retardation effects. When either of these materials is present, the system can be treated as consisting of three phases: an aqueous phase, a carrier phase, and the stationary solid matrix phase. The contaminant may be present in either or all of these phases. In the work reported, a mathematical model was developed to describe the transport and fate of the contaminant and carrier material in a porous medium. The model is based on mass balance equations describing the transport and fate of the contaminant and carrier in a three‐phase medium. Colloid/contaminant and colloid/matrix mass transfer mechanisms are represented by first‐order kinetics. Equilibrium partitioning of DOM acting as a carrier of the contaminant introduces a significant simplification in the model formulation. For a constant DOM concentration a much smaller retardation coefficient can be obtained in the three‐phase system than the coefficient obtained in a conventional advective/dispersive transport equation for a two‐phase system. The modified retardation coefficient reflects the presence of the mobile carrier by incorporating both the sorption of the contaminant and capture of the carrier on the solid matrix. Numerical solutions for the model were obtained by using a finite difference scheme to provide estimates of contaminant and carrier concentrations. Significant sensitivities to model parameters, particularly the rate constants of carrier capture and sorption were discovered. The numerical results of the DOM carrier effect matched favorably with experimental data reported in the literature.