Volume Fraction Of Modifier Research Articles

Modifier mass transfer kinetic effect in the performance of solvent gradient simulated moving bed (SG-SMB) process

The solvent-gradient simulated moving bed process (SG-SMB) is the new tendency in the performance improvement if compared to the traditional isocratic solvent conditions. In such SG-SMB separation process the modulation of the solvent strength leads to significant increase in the purities and productivity followed by reduction in the solvent consumption. A stepwise modelling approach was utilized in the representation of the interconnected chromatographic columns of the system combined with lumped mass transfer models between the solid and liquid phase. The influence of the solvent modifier was considered applying the Abel model which takes into account the effect of modifier volume fraction over the partition coefficient. The modelling and simulations were carried out and compared to the experimental SG-SMB separation of the amino acids phenylalanine and tryptophan. A lumped mass transfer kinetic model was applied for both the modifier (ethanol) as well as the solutes. The simulation results showed that such simple and global mass transfer models are enough to represent all the mass transfer effect between the solid adsorbent and the liquid phase. The separation performance can be improved reducing the interaction or the mass transfer kinetic effect between the solid adsorbent phase and the modifier. The simulations showed great agreement fitting the experimental data of the amino acids concentrations both at the extract as well as at the raffinate.

Retention prediction of highly polar ionizable solutes under gradient conditions on a mixed-mode reversed-phase and weak anion-exchange stationary phase

In the present work the retention of three highly polar and ionizable solutes – uric acid, nicotinic acid and ascorbic acid – was investigated on a mixed-mode reversed-phase and weak anion-exchange (RP/WAX) stationary phase in buffered aqueous acetonitrile (ACN) mobile phases. A U-shaped retention behavior was observed for all solutes with respect to the eluent organic modifier content studied in a range of 5–95% (v/v). This retention behavior clearly demonstrates the presence of a HILIC-type retention mechanism at ACN-rich hydro-organic eluents and an RP-like retention at aqueous-rich hydro-organic eluents. Hence, this column should be promising for application under both RP and HILIC gradient elution modes. For this reason, a series of programmed elution runs were carried out with increasing (RP) and decreasing (HILIC) organic solvent concentration in the mobile phase. This dual gradient process was successfully modeled by two retention models exhibiting a quadratic or a cubic dependence of the logarithm of the solute retention factor (lnk) upon the organic modifier volume fraction (φ). It was found that both models produced by gradient retention data allow the prediction of solute retention times for both types of programmed elution on the mixed-mode column. Four, in the case of the quadratic model, or five, in the case of the cubic model, initial HILIC- and RP-type gradient runs gave satisfactory retention predictions of any similar kind elution program, even with different flow rate, with an overall error of only 2.5 or 1.7%, respectively.

Rheological Behavior of Zinc-Oxide Nanolubricants

We report an experimental investigation of rheological properties of turbine oil–zinc-oxide nanoparticle dispersion with different nanoparticle weight fractions ranging from 0.1% to 4%. Rheological experiments were performed within the temperature range of 0–60°C. The results showed that nanolubricants and the base fluid behave like Bingham fluid. Nanolubricant viscosity enhancement as a function of nanoparticle volume fraction is well predicted by Bachelor equation with modified volume fraction. Thereby, rheological data revealed that nanoparticles make aggregates in the turbine oil with diameter about 3.6 of diameter of a single nanoparticle. Moreover, temperature effect on viscosity and yield stress of nanolubricants is shown and discussed.

Optimization strategies in the modelling of SG-SMB applied to separation of phenylalanine and tryptophan

The solvent-gradient simulated moving bed process (SG-SMB) is the new tendency in the performance improvement if compared to the traditional isocratic solvent conditions. In such SG-SMB process the modulation of the solvent strength leads to significant increase in the purities and productivity followed by reduction in the solvent consumption. A stepwise modelling approach was utilized in the representation of the interconnected chromatographic columns of the system combined with a lumped mass transfer model between the solid and liquid phase. The influence of the solvent modifier was considered applying the Abel model which takes into account the effect of modifier volume fraction over the partition coefficient. Correlation models of the mass transfer parameters were obtained through the retention times of the solutes according to the volume fraction of modifier. The modelling and simulations were carried out and compared to the experimental SG-SMB separation unit of the amino acids Phenylalanine and Tryptophan. The simulation results showed the great potential of the proposed modelling approach in the representation of such complex systems. The simulations showed great agreement fitting the experimental data of the amino acids concentrations both at the extract as well as at the raffinate. A new optimization strategy was proposed in the determination of the best operating conditions which uses the phi-plot concept.

Molecular dynamics simulations of the effect of the volume fraction on unidirectional polyimide–carbon nanotube nanocomposites

Molecular dynamics (MD) simulations were used to predict the effect of the reinforcement volume fraction on a unidirectional nanocomposite comprised of a polyimide and multi-walled carbon nanotubes (MWCNTs). We derived a modified volume fraction equation that takes the interface into account, and thus can precisely calculate the volume fraction of the reinforcement. From the MD simulations, both the stress and the modulus are predicted to increase with increasing number of MWCNTs as a function of a constantly applied strain, although some interesting observations were made in comparison to a pure polyimide system that is ordered, akin to the pre-nucleated crystalline system. In addition, we developed an approach to indirectly predict the change in the degree of order in the matrix with the addition of the CNT reinforcements. The results suggest that the degree of ordering increases with an increase in the volume fraction of MWCNTs, especially at the polymer–CNT interface according to number density plots of the polymer, which is consistent with the hypothesis that CNTs can act as nucleation sites for the crystallization of the polymer matrix.

Study on Solvent Extraction of Citric Acid from Fermentation Broth

Extraction of citric acid from aqueous solutions with tertiary amine, dissolved in mixtures of kerosene and phase modifier have been studied as a function of exaction yield at different phase modifier volume fraction, temperatures, stirring speed and exaction time. The optimal experimental conditions of extraction were obtained: reaction temperature 303K, reaction time 3 min, the kerosene volume fraction 20%, and 45% 1−octanol as phase modifier, stirring speed 450rpm/min. Under these conditions, the extraction yield could reach 75%. The complex of citric acid and tertiary amine was a surfactant that makes surface tension decrease. The composition of the citric acid complex is (R3N) · (H3A). The formation of complex was exothermic reaction that the standard enthalpy change and standard entropy change are obtained: ΔHθ=-10.17kJ/mol, ΔSθ=-11.86J/(mol·K).

New theoretical equation for effective thermal conductivity of two-phase composite materials

A new theoretical equation that describes the thermal conductivity of a two-phase composite is proposed. The Cheng–Vachon equation has been modified, and a new parameter, i.e. the modified volume fraction, is introduced. The modified volume fraction is a function of the physical volume fraction and thermal conductivity ratio of constituent phases. It was found that the new equation can describe the thermal conductivity of different two-phase composites, such as Cu/solder, Al/water, Al/air and cellular concrete, very accurately.

Effective medium theory for random media composed of two-layered spheres

We study the effective index of random media composed of two-layered spheres by using the energy-density coherent potential approximation method. As expected from the Ewald-Oseen extinction theorem, in the long-wavelength limit, the optical properties of a random medium composed of two-layered spheres are identical to those of a random medium composed of the corresponding pure spheres, while in the Mie-scattering region, the single-scattering resonances lead to an overall shift of the effective refractive index with the modified volume fraction.

Toughening of polycarbonate by core‐shell latex particles: Influence of particle size and spatial distribution on brittle‐ductile transition

AbstractThe impact toughness of polycarbonate modified with acrylic core‐shell latex particles was investigated. Addition of impact modifiers with size ranging from 115.7 to 231.4 nm can result in maximum impact strength. Equations for spatial distribution of modified particles were proposed to associate the interparticle distance with particle size and modifier volume fraction in terms of two possible morphologies, given by T = d[0.91/(φ)1/3 − 1] or T = d[0.88/(φ)1/3 − 1]. The influence of particle size on brittle‐ductile transition was also studied. The results indicated that critical interparticle distance was not a definitive value and had a narrow region. Moreover, there existed a linear relationship between critical interparticle distance and modifier size, that is, critical interparticle distance would enlarge with the increasing of core‐shell particle size. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1970–1977, 2010

Density isotherms of binary solvents hexane-modifier for liquid chromatography

Isothermic dependences of density of binary mobile phases on volume fraction of modifiers for normal-phase liquid chromatography are studied by the example of hexane-modifier systems (dioxane, diethyl ester, ethyl acetate). The influence of temperature on density and deviations of density of mobile phases from additivity are discussed.

Lipophilicity Evaluation of the Products Obtained in the Reaction of N3-Substituted Amidrazones with cis-1,2-Cyclohexanedicarboxylic Anhydride

The lipophilicity of the novel 12 products of the reaction of N3-substituted amidrazones with cis-1,2-cyclohexanedicarboxylic anhydride (4 linear, 4 triazole-like and 4 isoindole ones) with potential pharmacologic activity was evaluated by thin layer and liquid chromatography. Using organic-aqueous eluent systems (with methanol or acetonitrile) on RP18 plates and C18 column, a linear relationship between the volume fraction of modifiers and the retention indices was obtained. The retention values, log k or RM were extrapolated to zero organic modifier content to obtain the log kw or RMW values. 12 compounds with known literature lipophilicity were used as a calibration dataset. The results were compared in a multivariate way with in silico methods (ALOGPs, AC_logP, AB/LogP, COSMOFrag, miLogP, ALOGP, MLOGP, KOWWIN, XLOGP3).

Vertical Free Convective Boundary-Layer Flow in a Bidisperse Porous Medium

In this article, we study the effect of adopting a two-temperature and two-velocity model, appropriate to a bidisperse porous medium (BDPM), on the classical Cheng–Minkowycz study of vertical free convection boundary-layer flow in a porous medium. It is shown that the boundary-layer equations can be expressed in terms of three parameters: a modified volume fraction, a modified thermal conductivity ratio, and a third parameter incorporating both thermal and BDPM properties. A numerical simulation of the developing boundary layer is guided by a near-leading-edge analysis and supplemented by a far-field analysis. The study is completed by a presentation of numerical simulations of the elliptic equations in order to determine how the adoption of the BDPM model affects the thermal fields in the close vicinity of the origin.

An unexpected observation concerning the effect of anionic additives on the retention behavior of basic drugs and peptides in reversed-phase liquid chromatography

Anionic species with ion pair forming ability are commonly used to enhance the retention and efficiency of basic analytes in RPLC separations. However, little is known about the interactions between organic mobile phase modifiers and such ion pairing anions. In this work, we measured the magnitude of the retention increase of basic drugs and peptides upon addition of strong inorganic ion pairing anions (e.g. perchlorate) as a function of the volume fraction of modifier in acidic water-acetonitrile mobile phases on two different stationary phases. We found that the increase in retention upon addition of various salts depended strongly on the eluent strength. In general, larger retention increases upon addition of the anion were observed at higher organic fractions. Regression of retention against the volume fraction of organic modifier indicated that the ion pair forming anions substantially decreased S values while only slightly changing ln k ′ w values. The decrease in S is the major cause of the retention increase of basic drugs and peptides when such anions are added to the mobile phase.

Surface tension of binary mobile phases for liquid chromatography

The dependences of the surface tension of some binary mobile phases for normal and reversed-phase liquid chromatography on the volume fraction of modifiers are considered. The dependences are described by polynomial functions containing surface tensions of the initial components along with empirical coefficients. The compositions with extrema of surface tension deviations from additive values were determined.

The retention behavior of some atypical antipsychotic drugs in normal-phase TLC

Chromatographic behavior in normal-phase thin-layer chromatography has been investigated for six atypical antipsychotic drugs (amisulpride, clozapine, olanzapine, quetiapine, risperidone, and ziprasidone). The drugs were separated on silica gel, alumina, NH 2 , CN, diol, and polyamide plates with mixtures of n -hexane and six polar modifiers (acetone, dioxane, diethylamine, ethanol, isopropanol, and tetrahydrofuran) as mobile phases. The linearity of relationships between R M and volume fraction of modifier, the logarithm of the volume fraction, the molar fraction, and the logarithm of the molar fraction was tested. The results usually fitted the Snyder-Soczewinski equation, with r > 0.9. The best separation was achieved on silica gel plates with ethanol- n -hexane, 1 + 1 ( v/v ), containing 1.5% aqueous ammonia, as mobile phase.

Retention behavior of new oral antidiabetic drugs in reversed-phase chromatography

The thin-layer chromatographic behavior of three of the newest oral antidiabetic agents, pioglitazone, rosiglitazone, and repaglinide, has been studied in reversed-phase systems. Chromatography was performed on RP-8 as adsorbent with buffer-organic modifier binary mobile phases of widely different composition. Phosphate buffers of pH 2.4, 4.4, 6.0 and 7.9 were used with three organic mobile-phase modifiers, acetonitrile, 2-propanol, and methanol; the concentration of organic modifier was varied between 20 and 80% ( v/v ). Plates were developed in horizontal chambers, visualized by UV illumination at λ = 254 nm, and scanned with a densitometer. The effect of the mobile phase on retention was studied. The selectivity of the chromatographic systems is discussed. The linearity of relationships between R M and modifier volume fraction, molar fraction, and logarithm of the molar fraction was calculated.

Reversed-phase chromatographic retention behavior of some fibrate-type antihyperlipidemic drugs

Relationships between R M values and mobile phase composition have been examined for six fibrate-type drugs — bezafibrate, ciprofibrate, clofibrate, clofibric acid, fenofibrate, and gemfibrozil. They were separated in horizontal chambers on RP18 plates by use of mobile phases containing phosphate buffer and different amounts of six modifiers — acetone, acetonitrile, dioxane, isopropanol, methanol, and tetrahydrofuran. Plates were visualized under UV irradiation at λ = 254 nm, and scanned with a densitometer in multi-wavelength scan mode. Optimum modifier concentrations were also investigated on RP8 and CN plates for comparison. The linearity of relationships between R M and modifier volume fraction, molar fraction, and the logarithm of the molar fraction was calculated. Most results fitted the Snyder-Soczewinski equation with r > 0.95; for almost half r > 0.99. Separation of all the drugs was achieved on RP18 plates with mobile phase containing 70% dioxane in pH 7.60 phosphate buffer.

Use of binary and ternary mobile phases in reversed-phase high performance liquid chromatographic separation of chiral compounds.

The influence of the nature of typical organic modifiers, used in reversed-phase systems diluted with water, on retention and selectivity of chiral acetylated diamines and acetonitriles possessing pharmacological activity was investigated. Linear, semi-logarithmic relationships between the logarithm of the retention factor, k, of the enantiomer and the volume fraction, phi, of the organic modifier in the binary aqueous-organic eluent were established for chiral stationary phases. The slope of a plot of log k vs. the modifier volume fraction depends not only on the chemical structure of the chromatographed enantiomers, but also on the nature of the modifier. Moreover, the enantioselectivity of the studied racemates also depends on the nature and concentration of the modifier and is higher for a methanol mobile phase than for acetonitrile.

The retention behavior in normal-phase chromatographic systems of some fibrate-type antihyperlipidemic drugs

Relationships between R M values and mobile phase composition have been determined for the six antihyperlipidemic agents-bezafibrate, ciprofibrate, clofibrate, clofibric acid, fenofibrate, and gemfibrozil. The drugs were separated on silica gel, CN, and Diol plates using mobile phases containing n -hexane as weakly polar diluent and five polar modifiers: acetone, dioxane, ethyl methyl ketone, ethyl acetate, and tetrahydrofuran. The optimum mobile phases were also investigated on alumina, NH 2 , and polyamide phases for comparison. The linearity of relationships between R M and modifier volume fraction, molar fraction, and logarithm of molar fraction was calculated. Plates were developed in horizontal chambers, visualized under UV irradiation at λ = 254 nm, and scanned with a densitometer in the multi-wavelength scan mode. Most results fitted the Snyder-Soczewinski equation with r > 0.9; for approximately half r > 0.99. Separation of all the drugs was achieved on Diol plates with mobile phases containing 2...

Influence of the mobile-phase modifier on the retention of somepara-substituted amides; correlation with compound lipophilicity

The chromatographic behavior of para -substituted amides of α -phenylacetic, benzoic, propanoic, and 2,2-dimethylpropanoic acid has been studied in reversed-phase thin-layer chromatography on silica gel impregnated with paraffin oil. Mobile phases used were acetone-water, methanol-water, and dioxane-water. R M 0 values were calculated by linear extrapolation of retention to 0% organic modifier for each mobile phase. The relationships between R M 0 values obtained with different organic modifiers in the mobile phases are discussed. C 0 values were obtained from the slopes and intercepts of linear relationships between retention and volume fraction of modifier. Correlation between partition coefficient, log P , and R M 0 and between log P and C 0 was examined. Results show that C 0 is a better measure of the lipophilicity of the amides than R M 0 .