Micellar extraction preconcentration of silver with thiazolylazo reagents into a nonionic surfactant phase at the cloud point

The effect of the main factors on the extraction of the silver complexes of 4-(2-thiazolylazo)resorcinol and 1-(2-thiazolylazo)-2-naphthol into a micellar phase of a nonionic surfactant at the cloud point was studied. Conditions were found for the atomic absorption determination of silver with micellar extraction preconcentration into an OP-7 phase upon heating.     

Atomic-Absorption Determination of Zinc in Water with Micellar-Extraction Preconcentration with Phases of Nonionic Surfactants

Effects of various factors on the extraction of zinc with carboxylic acids and their mixtures with amines into a micellar phase of a nonionic surfactant at the cloud point were studied. The conditions for the atomic-absorption determination of zinc preconcentrated into an OP-10 phase on heating with capric acid and n-octylamine were developed.     

Preconcentration of Cadmium with OP-10 Nonionic Surfactant Phases at the Cloud Point

The effect of the main parameters on the extraction of cadmium with carboxylic acids into the micellar phase of the OP-10 nonionic surfactant at the cloud point was studied. Conditions were found for the atomic absorption determination of cadmium in natural and waste waters using the micellar-extraction preconcentration with capric acid and n-octylamine into the surfactant phase.__________Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 5, 2005, pp. 458–462.Original Russian Text Copyright © 2005 by Doroshchuk, Kulichenko.     

The cloud point extraction of copper(II) with monocarboxylic acids into non-ionic surfactant phase

The possibility to use monocarboxylic acids and their mixtures with amines for copper concentrating by the way of micellar extraction at cloud point temperature, and later atomic absorption spectrometry (AAS) determination was investigated. Under the optimum conditions, preconcentration of 100 ml of water sample in the presence of 1% non-ionic surfactant OP-10, 0.005 M capric acid and 0.01 M octylamine permitted the detection of 0.01 μg ml⁻¹ copper. The proposed method has been applied to the AAS determination of copper in water samples after cloud point extraction.     

Application of a chemical equilibrium model to thermodynamic functions of transfer of alcohols from water to aqueous surfactants

In ternary aqueous solutions, hydrophobic solutes such as alcohols tend to aggregate with surfactants to form mixed micelles. These systems can be studied by meas of the functions of transfer of hydrophobic solutes from water to aqueous solutions of surfactant. These thermodynamic functions often go through extrema in the critical micellar concentration (CMC) region of the surfactant. A simple model based on interactions between surfactant and hydrophobic solute monomers, on the distribution of the hydrophobic solute between water and the micelles and on the shift in the CMC induced by the hydrophobic solute, can simulate the magnitude and trends of the transfer functions using parameters which are mostly derived from the binary systems. In order to check the model more quantitatively, volumes and heat capacities of transfer of alcohols from water to aqueous solutions of a nonionic surfactant, octyldimethylamine oxide, were measured. A quantitative agreement was achieved with three adjustable parameters. Good fits are also obtained for the transfers to the ionic surfactants, octylamine hydrobromide and sodium dodecylsulfate. When the equilibrium displacement contribution is small, the distribution constants and the partial molar properties of the alcohols in the micellar phase agree well with the parameters obtained with similar models.     

Determination of furosemide in urine by HPLC with preconcentration by micellar-extraction

The micellar extraction of furosemide by the nonionic surfactant (NS) Triton X-100 at the cloud point was studied; it was performed in a conventional heating mode and upon induction with phenol. It was shown that the quantitative recovery of the preparation was attained using hydrophobic micellar phases of NS modified with phenol. A procedure was developed for determining furosemide in urine by reversed-phase HPLC with preconcentration by micellar extraction in the presence of phenol. The preconcentration ratio was 80 and the detection limit for furosemide, 3 mg/L. The procedure was used to analyze urine samples by the standard addition method.     

Photoinduced phase separation

A novel approach of photoinduced phase separation has been demonstrated with a photolabile anionic surfactant, mixed with an inert nonionic surfactant in the presence of salting-out electrolyte. Breakdown of the photolyzable surfactant results in hydrophobic photoproducts, which are emulsified by the remaining inert surfactant; added electrolyte resolves the emulsion into macroscopic oily and aqueous phases. The initial micellar systems can disperse an insoluble additive marker dye (shown), which may be spatially segregated from the aqueous environment by the action of UV light.     

SOLUBILIZATION IN MIXED REVERSE MICELLAR SYSTEMS OF AOT/NONIONIC SURFACTANTS/n-HEPTANE

Solubilization of water and aqueous NaCl solutions in mixed reverse micellar systems of anionic surfactant AOT and nonionic surfactants in n-heptane was studied. It was found that the maximum solubilization capacity of water was higher in the presence of certain concentrations of NaCl electrolyte, and these concentrations increased with the increase of nonionic surfactant content and their EO chain length. Soluibilization capacity was enhanced by mixing AOT with nonionic surfactants. The observed phenomena were interpreted in terms of the stability of the interfacial film of reverse micellar microdroplet and the packing parameter of the surfactant that formed mixed reverse micelles.     

Extraction of lanthanide ions from acidic and strongly acidic media by phosphine oxide derivatives using temperature-induced phase separation

A composite for the extraction of lanthanide ions from strongly acidic media by temperature-induced phase separation was designed based on the nonionic surfactant Triton X-100 and new phosphine oxide derivatives. The dependence of the efficiency and selectivity of micellar extraction on the length of the hydrophobic substituent at the P=O group is determined by both the influence of hydrophobic substituents on the electron-donor capacity of the P=O group and the solubility of phosphine oxides in aqueous and micellar phases. The nitric acid concentration was found to influence the efficiency of extraction of lanthanide ions by phosphine oxides with different structures. An increase in the concentration of nitric acid in an aqueous medium from 0.1 to 1 mol L⁻¹ leads to a decrease in the degree of extraction by water-soluble derivatives and a substantial increase in the degree of extraction by phosphine oxides, which are soluble only in the micellar phase of Triton X-100.     

An NMR study of translational diffusion and structural anisotropy in magnetically alignable nonionic surfactant mesophases

The diffusion of both water and surfactant components in aqueous solutions of the nonionic surfactant "C12E6"--which includes hexagonal, cubic, lamellar, and micellar mesophases--has been studied by pulsed-field-gradient NMR. Diffusion coefficients were measured in unaligned samples in all of these phases. They were also obtained in the hexagonal and lamellar phases in oriented monodomain samples that were aligned by slow cooling from the micellar phase in an 11.7 T magnet. Measured water and soap diffusion coefficients in the NMR-isotropic cubic and (high-water-content) micellar phases as well as diffusion anisotropy measurements in the magnetically aligned hexagonal phase were quantitatively consistent with the constituent structures of these phases being identical surfactant cylinders, with only the fraction of surface-associated water varying with the water-soap molar ratio. The values of the water and soap diffusion coefficients in the oriented lamellar phase suggest an increase in defects and obstructions to soap diffusion as a function of increasing water content, while those in the low-water-content micellar phase rule out the presence of inverse micelles.     

Role of the Surfactant Structure in the Behavior of Hydrophobic Ionic Liquids within Aqueous Micellar Solutions

The behavior of an ionic liquid (IL) within aqueous micellar solutions is governed by its unique property to act as both an electrolyte and a cosolvent. The influence of the surfactant structure on the properties of aqueous micellar solutions of zwitterionic SB‐12, nonionic Brij‐35 and TX‐100, and anionic sodium dodecyl sulfate (SDS) in the presence of the “hydrophobic” IL 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([bmim][PF₆]) is assessed along with the possibility of forming oil‐in‐water microemulsions in which the IL acts as the “oil” phase. The solubility of [bmim][PF₆] within aqueous micellar solutions increases with increasing surfactant concentration. In contrast to anionic SDS, the zwitterionic and nonionic surfactant solutions solubilize more [bmim][PF₆] at higher concentrations and the average aggregate size remains almost unchanged. The formation of IL‐in‐water microemulsions when the concentration of [bmim][PF₆] is above its aqueous solubility is suggested for nonionic Brij‐35 and TX‐100 aqueous surfactant solutions.     

Lattice Monte Carlo simulations of phase separation and micellization in supercritical CO2/surfactant systems: effect of CO2 density

Lattice Monte Carlo simulations are used to study the effect of nonionic surfactant concentration and CO2 density on the micellization and phase equilibria of supercritical CO2/surfactant systems. The interaction parameter for carbon dioxide is obtained by matching the critical temperature of the model fluid with the experimental critical temperature. Various properties such as the critical micelle concentration and the size, shape, and structure ofmicelles are calculated, and the phase diagram in the surfactant concentration-CO2 density space is constructed. On increasing the CO2 density, we find an increase in the critical micelle concentration and a decrease in the micellar size; this is consistent with existing experimental results. The variation of the micellar shape and structure with CO2 density shows that the micelles are spherical and that the extension of the micellar core increases with increasing micellar size, while the extension of the micellar corona increases with increasing CO2 density. The predicted phase diagram is in qualitative agreement with experimental phase diagrams for nonionic surfactants in carbon dioxide.     

Combination of micellar extraction and GC-ECD for the determination of polychlorinated biphenyls (PCBs) in water

 The application of the solvent-free micellar extraction as an alternative method to the liquid–liquid extraction for the enrichment of polychlorinated biphenyls (PCBs) from ultrapure and natural water is presented. A nonionic surfactant was used to preconcentrate the PCBs. After a clean-up consisting of two columns (silica gel and Florisil) the analytes were identified and quantified by GC-ECD. Recoveries for spiked water were up to 100%. For highly contaminated seepage water of landfills liquid–liquid extraction is involving great problems with the phase separation of water and solvent. According to our results, the micellar extraction is superior to the liquid–liquid extraction for this difficult kind of aqueous matrix. Received: 20 February 1996/Revised: 20 May 1996/Accepted: 30 May 1996     

Combination of micellar extraction and GC-ECD for the determination of polychlorinated biphenyls (PCBs) in water

 The application of the solvent-free micellar extraction as an alternative method to the liquid–liquid extraction for the enrichment of polychlorinated biphenyls (PCBs) from ultrapure and natural water is presented. A nonionic surfactant was used to preconcentrate the PCBs. After a clean-up consisting of two columns (silica gel and Florisil) the analytes were identified and quantified by GC-ECD. Recoveries for spiked water were up to 100%. For highly contaminated seepage water of landfills liquid–liquid extraction is involving great problems with the phase separation of water and solvent. According to our results, the micellar extraction is superior to the liquid–liquid extraction for this difficult kind of aqueous matrix. Received: 20 February 1996/Revised: 20 May 1996/Accepted: 30 May 1996     

The microstructure of di-alkyl chain cationic/nonionic surfactant mixtures: observation of coexisting lamellar and micellar phases and depletion induced phase separation

The evolution of the microstructure and composition occurring in the aqueous solutions of di-alkyl chain cationic/nonionic surfactant mixtures has been studied in detail using small angle neutron scattering, SANS. For all the systems studied we observe an evolution from a predominantly lamellar phase, for solutions rich in di-alkyl chain cationic surfactant, to mixed cationic/nonionic micelles, for solutions rich in the nonionic surfactant. At intermediate solution compositions there is a region of coexistence of lamellar and micellar phases, where the relative amounts change with solution composition. A number of different di-alkyl chain cationic surfactants, DHDAB, 2HT, DHTAC, DHTA methyl sulfate, and DISDA methyl sulfate, and nonionic surfactants, C12E12 and C12E23, are investigated. For these systems the differences in phase behavior is discussed, and for the mixture DHDAB/C12E12 a direct comparison with theoretical predictions of phase behavior is made. It is shown that the phase separation that can occur in these mixed systems is induced by a depletion force arising from the micellar component, and that the size and volume fraction of the micelles are critical factors.     

Use of surfactant-mediated phase separation (cloud point extraction) with affinity ligands for the extraction of hydrophilic proteins

The feasibility of utilizing a zwitterionic surfactant, 3-(nonyldimethylammonio)propylsulfate, or nonionic surfactant, Triton X-114, mediated phase separation in conjunction with affinity ligands was studied for hydrophilic protein extractions. Below (or above) its critical temperature (so-called cloud point), aqueous solutions of zwitterionic (or nonionic) surfactants separate into two immiscible phases, a surfactant-rich phase and an aqueous phase. Avidin was successfully extracted into the zwitterionic surfactant-rich phase when a small amount of the affinity ligand, N- biotinoyl)dipalmitoyl- l -alpha- phosphatidyl ethanolamine, was added to the system. It was not possible to extract hexokinase into the surfactant-rich phase of the nonionic surfactant, Triton X-114, even if a considerable amount of octyl-beta-d-glucoside was added to the solution as an affinity ligand. In contrast, the use of the zwitterionic surfactant and octyl-beta-d-glucoside as an affinity ligand proved to be effective for the extraction of hexokinase. The hexokinase extraction efficiency was found to depend upon the solution pH and the concentration of the affinity ligand in the system. The results clearly indicate that hydrophilic proteins can be successfully extracted with surfactant mediated phase separations (cloud point extractions) via use of the zwitterionic surfactant, 3-(nonyldimethylammonio)propylsulfate, and appropriate affinity ligands. Some advantages of zwitterionic surfactants in such extractive processes relative to that of nonionic surfactants are delineated.     

Micellar medium effects on the hydrolysis of phenyl chloroformate in ionic,zwitterionic, nonionic,and mixed micellar solutions

The spontaneous hydrolysis of phenyl chloroformate was studied in various anionic, nonionic, zwitterionic, and cationic aqueous micellar solutions, as well as in mixed anionic–nonionic micellar solutions. In all cases, an increase in the surfactant concentration results in a decrease in the reaction rate and micellar effects were quantitatively explained in terms of distribution of the substrate between water and micelles and the first‐order rate constants in the aqueous and micellar pseudophases. A comparison of the kinetic data in nonionic micellar solutions to those in anionic and zwiterionic micellar solutions makes clear that charge effects of micelles is not the only factor responsible for the variations in the reaction rate. Depletion of water in the interfacial region and its different characteristics as compared to bulk water, the presence of high ionic concentration in the Stern layer of ionic micelles, and differences in the stabilization of the initial state and the transition state by hydrophobic interactions with surfactant tails can also influence reactivity. The different deceleration of the reaction observed in the various micellar solutions studied was discussed by considering these factors. Synergism in mixed‐micellar solutions is shown through the kinetic data obtained in these media. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 445–451, 2002     

Physicochemical characterization of PEG1500-12-acyloxy-stearate micelles and liquid crystalline phases

PEG 12-acyloxy-stearates are used as drug delivery carriers that have low cell damage effects. The mechanical and physical properties surrounding these processes and surfactants are still however not known. In this study, the physicochemical micellar properties of PEG 12-acyloxy-stearates were characterized by optical microscopic, nuclear magnetic resonance, and small-angle X-ray scattering techniques. We determined the phase diagrams of the surfactants as a function of surfactant concentration and temperature, the micellar size and shape, and micellar dynamics. We found that each surfactant has a micellar, cubic Im3m, and hexagonal phase. The aggregation number in the discrete cubic phase, as determined by small-angle X-ray scattering, was approximately 150 for each surfactant, and showed no measurable chain-length dependence. The diffusion coefficients of the surfactant showed a discontinuity between the micellar and cubic phases, where the cubic phases gave very low values on the order of 10(-)(16) m(2) s(-)(1): this value indicates a non-bicontinuous cubic structure. In summary, these surfactants behave to a large extent as nonionic poly(ethylene glycol) surfactants with extended PEG headgroups.     

Pyrene solubilization capacity in octaethylene glycol monododecyl ether (C12E8) micelles

We used fluorescence quenching, vibronic band ratios and excimer fluorescence techniques to quantify the statistics of pyrene solubilization in nonionic octaethylene glycol monododecyl ether (C₁₂E₈) micelles. Using a two-phase model (aqueous and micellar pseudophases) to interpret fluorescence results, we found that all three of these experimental methods provide consistent information about pyrene partitioning between aqueous and micellar pseudophases. From dynamic quenching experiments we determined the pyrene partition coefficient and the average number of pyrene molecules solubilized per micelle over a range of surfactant concentrations. The pyrene partition coefficient increases with increasing surfactant concentration. We confirmed the partitioning results by excimer fluorescence measurements. Quenching results indicate that pyrene is accessible to Cu²⁺ quenchers even in the limit of high surfactant concentration where solubilized pyrene is in the infinite dilution limit in the micellar pseudophase. This suggests that solubilized pyrene resides in the micellar palisade layer. We determined the maximum number of pyrene solubilizates allowed per micelle (micellar solubilization capacity) by applying a three-phase model to fluorescence experiments conducted in the presence of solid phase pyrene. The estimated maximum capacity is 6 pyrene molecules per micelle. The three phase partitioning model successfully predicted the excimer fluorescence in the presence of solid pyrene.     

Microstructure of un-neutralized hydrophobically modified alkali-soluble emulsion latex in different surfactant solutions

At low pH conditions and in the presence of anionic, cationic, and nonionic surfactants, hydrophobically modified alkali-soluble emulsions (HASE) exhibit pronounced interaction that results in the solubilization of the latex. The interaction between HASE latex and surfactant was studied using various techniques, such as light transmittance, isothermal titration calorimetry, laser light scattering, and electrophoresis. For anionic surfactant, noncooperative hydrophobic binding dominates the interaction at concentrations lower than the critical aggregation concentration (CAC) (C < CAC). However, cooperative hydrophobic binding controls the formation of mixed micelles at high surfactant concentrations (C > or = CAC), where the cloudy solution becomes clear. For cross-linked HASE latex, anionic surfactant binds only noncooperatively to the latex and causes it to swell. For cationic surfactant, electrostatic interaction occurs at very low surfactant concentrations, resulting in phase separation. With further increase in surfactant concentration, noncooperative hydrophobic and cooperative hydrophobic interactions dominate the binding at low and high surfactant concentrations, respectively. For anionic and cationic surfactant systems, the CAC is lower than the critical micelle concentration (CMC) of surfactants in water. In addition, counterion condensation plays an important role during the binding interaction between HASE latex and ionic surfactants. In the case of nonionic surfactants, free surfactant micelles are formed in solution due to their relatively low CMC values, and HASE latexes are directly solubilized into the micellar core of nonionic surfactants.