Solvent Mass Research Articles

Solvent-Dependent Cage Dynamics of Small Nonpolar Radicals: Lessons from the Photodissociation and Geminate Recombination of Alkylcobalamins

Time-resolved transient absorption spectroscopy was used to investigate the primary geminate recombination and cage escape of alkyl radicals in solution over a temperature range from 0 to 80 degrees C. Radical pairs were produced by photoexcitation of methyl, ethyl, propyl, hexylnitrile, and adenosylcobalamin in water, ethylene glycol, mixtures of water and ethylene glycol, and sucrose solutions. In contrast to previous studies of cage escape and geminate recombination, these experiments demonstrate that cage escape for these radical pairs occurs on time scales ranging from a hundred picoseconds to over a nanosecond as a function of solvent fluidity and radical size. Ultrafast cage escape (<100 ps) is only observed for the methyl radical where the radical pair is produced through excitation to a directly dissociative electronic state. The data are interpreted using a unimolecular model with competition between geminate recombination and cage escape. The escape rate constant, k(e), is not a simple function of the solvent fluidity (T/eta) but depends on the nature of the solvent as well. The slope of k(e) as a function of T/eta for the adenosyl radical in water is in near quantitative agreement with the slope calculated using a hydrodynamic model and the Stokes-Einstein equation for the diffusion coefficients. The solvent dependence is reproduced when diffusion constants are calculated taking into account the relative volume and mass of both solvent and solute using the expression proposed by Akgerman (Akgerman, A.; Gainer, J. L. Ind. Eng. Chem. Fundam. 1972, 11, 373-379). Rate constants for cage escape of the other radicals investigated are consistently smaller than the calculated values suggesting a systematic correction for radical size or coupled radical pair motion.

Programmed temperature vaporizer based method for the sensitive determination of trihalomethanes and benzene, toluene, ethylbenzene and xylenes in soils

A methodology based on the coupling of a headspace autosampler with a GC and a MS detector operating in SIM mode has been developed for the determination of volatile organic compounds (THMs and BTEX) in soils. The GC device used is equipped with a programmable temperature vaporizer (PTV) packed with Tenax-TA ® to introduce the samples (the injection mode used was solvent vent), and a modular accelerated column heater (MACH™) to control column temperature. The proposed measurement procedure reduces the sample pretreatment step to a minimum. Combined use of solvent vent injection mode and mass spectrometry detection allows a highly sensitive method to be proposed, with limits of detection of the order of ng/kg for all the target compounds. Furthermore, the capillary column used allows rapid separations of compounds in less than 4.60 min, affording a very short total analysis cycle time of 9 min.

Optimization of solid-phase extraction using developed modern sorbent for trace determination of ametryn in environmental matrices

In recent years, there has been a significant increase in molecularly imprinted solid-phase extraction (MISPE) technique for the purification and clean-up of environmental samples. In this study, solid-phase extraction using the imprinted polymer has been optimized with the experimental design approach for a triazine herbicide, named ametryn with regard to the critical factors such as sample pH, sample concentration, sample flow-rate, sample volume, elution solvent, washing solvent and sorbent mass. These factors were evaluated statistically and also validated with spiked drinking water samples and showed a good reproducibility over six consecutive days as well as six within-day experiments. Also, in order to the evaluate efficiency of the optimized MISPE protocols, enrichment capacity, reusability and cross-reactivity of cartridges have been studied. Finally, a selective MISPE was successfully demonstrated for ametryn with a recovery of above 90% for spiked drinking water samples. It was concluded that the central composite design could prove beneficial for aiding the MIP and MISPE development.

Simulation of dry‐spinning process of polyimide fibers

AbstractAs one type of high‐performance fibers, the polyimide fibers can be prepared from the precursor polyamic acid via dry‐spinning technology. Unlike the dry‐spinning process of cellulose acetate fiber or polyurethane fiber, thermal cyclization reaction of the precursor in spinline with high temperature results in the relative complex in the dry‐spinning process. However, the spinning process is considered as a steady state due to a slight degree of the imidization reaction from polyamic acid to polyimide, and therefore a one‐dimensional model based on White‐Metzer viscoelastic constitutive equation is adopted to simulate the formation of the fibers. The changes of solvent mass fraction, temperature, axial velocity, tensile stress, imidization degree, and glass transition temperature of the filament along the spinline were predicted. The effects of spinning parameters on glass transition temperature and imidization degree were thus discussed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Microwave-assisted extraction in toxicological screening of skeletal tissues

The use of microwave-assisted extraction (MAE) in screening of decomposed bone tissue for model drugs of abuse is described. Rats received 50 mg/kg (i.p.) pentobarbital ( n = 2), 75 mg/kg (i.p.) ketamine ( n = 2) or 16 mg/kg (i.p.) diazepam ( n = 1), or remained drug-free (control). Drug-positive animals were euthanized within 20 min of drug administration. Animal remains were allowed to decompose in a secure outdoor environment to the point of complete skeletonization. Bones (tibiae, femora, vertebrae, ribs, pelvi, humeri and scapulae) were collected and pooled (according to drug) in order to minimize effects due to inter-bone differences in drug distribution. Bones were crushed and cleaned of marrow and residual soft tissue in alkaline solution or phosphate buffer with ultrasonication. Cleaned bones were then ground and underwent MAE in phosphate buffer (pH 6), methanol or a methanol:water mixture (1:1, v/v) at atmospheric pressure in a domestic microwave oven, or passive extraction in methanol. Bone extracts (control and drug-exposed) containing methanol were evaporated to dryness before reconstitution in phosphate buffer (pH 6) and subsequent analysis by ELISA, while bone extracts containing only phosphate buffer were assayed directly by the same ELISA protocol. Measured absorbance values were expressed as the decrease in absorbance, measured as a percentage, relative to the corresponding drug-free control bone extract. The semi-quantitative nature of the ELISA assay allowed examination of the effects of extraction solvent and bone sample mass on the assay response for each drug examined, and subsequent comparison to assays of extracts obtained through passive methanolic extraction of various bone tissues. Overall, the time required for maximal extraction varied with extraction solvent and bone mass for each drug investigated, with significant extraction occurring with all solvent systems examined. MAE may represent a substantially faster extraction system than passive extraction, with significant extraction recovery observed within 1 min of exposure for all samples examined. The implications of these results in the context of the available literature on drug analysis in skeletal tissues are discussed.

Quantitative Analysis of Polar Lipids in the Nanoliter Level of Rat Serum by Liquid Chromatography/Mass Spectrometry/Mass Spectrometry

Polar lipids in serum, including lysophospholipids (LPLs) and free fatty acids (FFAs), have a broad range of biological activities and require a suitable method for their quantitative analysis. Conventional methods use multistep procedures to simultaneously purify and analyze polar lipids and non-polar lipids in serum. However, the methods could result in inaccurate quantifications of polar and/or non-polar lipids because compounds with different polarities have different behaviors in solvent extraction and mass spectrometric ionization. In this study, a method was designed to analyze polar lipids in serum based on the polarities of LPLs and FFAs. The method consisted of extraction without filtration and analysis of the crude extract without multistep purification. Fifty LPLs and 32 FFAs were detected in rat serum. The concentrations of LPLs (1272.1 micromole/L in female and 999.8 micromole/L in male) and FFAs (1910.9 micromole/L in female and 1651.4 micromole/L in male) were determined. Peak areas of MS ion in Extract Ion Chromatogram (EIC) were used for the quantification in this study. The approach of quantification should be perfectly suitable for precise quantification of a specific serum component by adding its isotope standard to the serum before extraction.

Extrusion freeforming of millimeter wave electromagnetic bandgap (EBG) structures

PurposeThe aim of this paper is to provide an easy method of extrusion freeforming to fabricate microwave electromagnetic bandgap (EBG) crystals. EBG crystals are periodic dielectric structures that can block wave propagation and generate a bandgap. These crystals can be used in high capability antennae, electromagnetic wave semiconductors, microresonators, high‐reflectivity mirrors and polarizing beam splitters.Design/methodology/approachThe effects of extrusion process parameters and paste characteristics were investigated. Finally, one‐period and two‐period woodpile EBG crystals with bandgaps in the frequency region of 90‐110 GHz were fabricated and the bandgap was measured.FindingsThe filament diameter is influenced by whether extrusion is carried out with or without a substrate and by the free fall‐distance from the nozzle. The quality of lattice structures is dependent on paste flow and properties. A ceramic paste with 60 vol. % (the fraction of ceramic powder based on solvent‐free polymer) was well suited to fabrication. The solvent content also influenced the fabrication. The experimental results show that under ∼12 per cent solvent mass fraction in the paste and relatively high extrusion ram velocity (more than 0.014 mm/s) at a pressure of 14 MPa, samples with high quality were fabricated.Originality/valueThis paper demonstrates that the rapid prototyping method of extrusion freeforming can be applied for the fabrication of EBG crystals from ceramic powders and the important factors which influence the product quality are identified.

Pressing and supercritical carbon dioxide extraction of walnut oil

The objective of this study was to evaluate the oil extraction process from walnut seeds by pressing followed by extraction with supercritical CO 2. In pressing experiments, a factorial arrangement was conducted in order to study the combined effects of seed moisture content (2.5%, 4.5% and 7.5%) and pressing temperature (25, 50 and 70 °C) on oil recovery and quality parameters. For all conditions tested, the oil quality compared well with that of cold-pressed walnut oil. Oil recovery increased significantly as moisture content raised. Highest oil recovery (89.3%) was obtained at 7.5% moisture content and 50 °C temperature. The cake resulting from pressing at these conditions was extracted with CO 2 in a high pressure pilot plant with single stage separation and solvent recycle. The effects of two different pressures (200 and 400 bar) and temperatures (50 and 70 °C) with regard to oil yield and quality, and time required for extraction were analyzed. At each condition, the extraction rate changed with the mass of solvent and extraction time. At first, the mass of oil extracted was determined by the oil solubility in CO 2 and a linear relationship was observed, where the slope results in the solubility of oil in CO 2 at the experiment conditions. After that, the extraction rate was governed by solubility and diffusion, and continuously decreased with time. The colour changed along the extraction from a whitish clear product to a yellow one. Tocopherol and carotenoid contents were significantly higher than those obtained by pressing. Extraction conditions did not affect significantly the fatty acid composition.

Acceleration of enzymatic hydrolysis of protein-bound selenium by focused microwave energy

This paper demonstrates for the first time that enzymatic hydrolysis of protein-bound selenium can be significantly accelerated by microwave energy. Extraction of selenomethionine from selenised yeast, used as the model sample, was performed using two-step enzymatic hydrolysis with protease/lipase/driselase in a focused microwave reactor. HPLC-ICP-MS with species-specific isotope dilution analysis (IDA) was used for species quantitation. To investigate enzymatic hydrolysis assisted by microwave energy the effect of parameters such as microwave power and extraction time on the extraction efficiency of SeMet from the Se-yeast CRM SELM-1 was investigated. The main chemical variables affecting enzymatic extraction of SeMet, such as pH, enzyme type, sample to enzyme mass ratio and sample to solvent mass ratio were set at the conditions used for conventional enzymatic hydrolysis (in a hybridisation oven). Using a power of 60 W and two consecutive extraction cycles, each of 15 min (total extraction time of 30 min) at 37 °C, the recovery of SeMet obtained by the proposed methodology and calculated based on the certified value of 3389 ± 173 mg kg−1SeMet was 99.6 ± 1.9% (n = 3). The major advantage of the newly proposed method is the dramatic reduction of extraction time in comparison with that of conventional enzymatic hydrolysis, which requires a two-step extraction, each cycle of approximately 20 h. This was achieved without compromising extraction efficiency. Application of the proposed method to the accurate quantification of SeMet in pharmaceutical yeast tablets with a total Se concentration of approximately 300 mg kg−1 was also addressed. The recovery of SeMet, which was calculated based on the mean of results [561.5 mg kg−1 (n = 11, with a standard deviation of 44.3 mg kg−1)] obtained for the yeast tablets in the international intercomparison CCQM-P86,1 was found to be 100.1 ± 3.3%.

Long-term ground penetrating radar monitoring of a small volume DNAPL release in a natural groundwater flow field

An earlier field experiment at Canadian Forces Base Borden by Brewster and Annan [Geophysics 59 (1994) 1211] clearly demonstrated the capability of ground penetrating radar (GPR) reflection profiling to detect and monitor the formation of DNAPL layers in the subsurface. Their experiment involved a large volume release (770 L) of tetrachloroethylene into a portion of the sand aquifer that was hydraulically isolated from groundwater flow by sheet pile walls. In this study, we evaluated the ability of GPR profiling to detect and monitor much smaller volume releases (50 L). No subsurface confining structure was used in this experiment; hence, the DNAPL impacted zone was subjected to the natural groundwater flow regime. This condition allowed us to geophysically monitor the DNAPL mass loss over a 66 month period. Reflectivity variations on the GPR profiles were used to infer the presence and evolution of the solvent layers. GPR imaging found significant reflectivity increases due to solvent layer formation during the two week period immediately after the release. These results demonstrated the capacity of GPR profiling for the detection and monitoring of lesser volume DNAPL releases that are more representative of small-scale industrial spills. The GPR imaged solvent layers subsequently reduced in both areal extent and reflectivity after 29 months and almost completely disappeared by the end of the 66 month monitoring period. Total DNAPL mass estimates based on GPR profiling data indicated that the solvent mass was reduced to 34%–36% of its maximum value after 29 months; only 4%–9% of the solvent mass remained in the study area after 66 months. These results are consistent with independent hydrogeological estimates of remaining DNAPL mass based on the downgradient monitoring of the dissolved solvent phase. Hence, we have concluded that the long-term GPR reflectivity changes of the DNAPL layers are likely the result from the dissolution of chlorinated solvents residing in those layers. The long-term monitoring results demonstrated that GPR profiling is a promising non-invasive method for use at DNAPL contaminated sites in sandy aquifers where temporal information about immiscible contaminant mass depletion due to either natural flow or remediation is needed. However, our results also indicated that the GPR signature of older DNAPL impacted zones may not differ greatly from the uncontaminated background if significant mass reduction due to dissolution has occurred.

Solid Phase Extraction for 1-Hydroxypyrene as a Biomarker of Occupational Exposure to PAHs Prior to High Performance Liquid Chromatography

Urinary 1-hydroxypyrene is frequently used as a major metabolite and biological indicator of the overall exposure to polycyclic aromatic hydrocarbons. In this study, solid phase extraction was appropriately conditioned with regard to sample pH, sample concentration, loading flow rate, elution solvent, washing solvent, sample volume and sorbent mass. Octadecyl silica cartridge (C18) was used as solid phase adsorbent and showed to be an efficient phase in simplifying sample preparation for1-hydroxypyrene. Methanol extracted analyte from spiked urine gave a clean sample for reverse-phase HPLC-florescence. In the developed solid phase extraction conditions (sample pH: 5, sample concentration: 10 μg/l, washing solvent: distilled water, eluent: methanol, sample volume: 200 ml sample flow rate: 10 ml/min), the extraction recovery exceeded 99.96%, achieving detection limit of 0.02 μg/l. The extraction factors (sample pH, sample concentration, washing solvent , eluent , sample volume and sample flow rate), were evaluated statistically and also the procedure was validated with three different pools of spiked urine samples at low, medium , and high sample concentrations and showed a good reproducibility over six consecutive days as well as six within-day experiments. All coefficients of variations were less than 3.1%. Finally, urinary 1-hydroxypyrene of industrially exposed workers was also measured, using the appropriate conditions obtained in this study, in which, the amount of the compound of interest in the total exposed subjects was significantly higher than those of non-exposed.

The Vapor Extraction Process: Review

The high viscosity of Canadian crude oil is a serious challenge for the recovery efficiency of this resource by conventional methods. Since 1991, the vapor extraction process (VAPEX) has emerged as a promising technology that has gained considerable attention within the oil industry. This article presents a current review of this process and its variations, as well as describing important factors affecting the process such as solvent requirements, mass transfer, asphaltene precipitation, oil rate, and wettability. Recent research has shown that VAPEX is an efficient alternative for the recovery of heavy oil.

Modelling the fluid phase behaviour of polydisperse polyethylene blends in hydrocarbons using the modified Sanchez–Lacombe equation of state

One or more polyethylene (PE) samples with different molecular configurations can be mixed together to produce a blend with different physical characteristics. The blending of multiple polyethylenes from different reactors, each with their own molar mass distribution and degree of branching, can be carried out in a hydrocarbon solvent. Modelling the fluid phase behaviour of polydisperse polyethylene blends would be an important tool for the design, optimization and operation of the production process. The modified Sanchez–Lacombe equation of state (MSL-EOS) was used to calculate the cloud points of a blend of two polydisperse linear low-density polyethylenes (LLDPEs) in a hydrocarbon solvent. The type of linear low-density polyethylenes considered were hydrogenated polybutadienes (hPBDs). The calculated cloud points were compared to experimental data that were available for the systems: hPBD-1 + hPBD-2 + n-hexane and hPBD-3 + hPBD-4 + n-pentane. The four hPBD samples have considerably different molar mass distributions (MMDs) though the other properties of the samples are unknown (degree, type and frequency of branching in the polyethylene molecule). The polyethylene molar mass distributions were approximated using probability distribution functions that match the reported number- and weight-average molar masses. The molar mass distributions were represented in the model using 100 pseudocomponents. The temperature-dependent LLDPE + hydrocarbon binary interaction parameters had been previously adjusted to correlate the cloud points of the binary mixtures. Previous investigations have demonstrated that for the same LLDPE parameters, the magnitude of the binary interaction parameter is in part related to the branch content of the polyethylene sample. The cloud point isotherms calculated exhibit a distinctive bend when the solvent mass fraction is held constant and the ratio of the two polymers is allowed to vary. The model predicts a three-liquid phase region inside the two-liquid phase region for the LLDPE-1 + LLDPE-2 + n-pentane system although none was observed experimentally. The molar mass distributions of both of the polyethylenes in each of the three liquid phases will be presented.

A Novel Experimental Technique for Studying Solvent Mass Transfer and Oil-Swelling Effect in the Vapour Extraction (VAPEX) Process

Abstract In this paper, a new experimental technique is presented to study the solvent mass transfer in heavy oil and the resultant oil-swelling effect by applying dynamic pendant drop volume analysis (DPDVA). In the experiment, a pendant drop of heavy oil is formed inside a visual high-pressure cell, which is initially filled with a solvent (e.g. propane). As the solvent gradually dissolves into heavy oil, the volume of the pendant oil drop keeps increasing due to the oil-swelling effect. The sequential digital images of the dynamic pendant oil drop are acquired and analyzed to determine its volumes at different times. Theoretically, a previously formulated mathematical model is applied to describe the solvent mass transfer in heavy oil and the oil-swelling effect. The diffusion coefficient of the solvent in heavy oil and the oil-swelling factor are determined by finding the best fit of the theoretically predicted volumes of the dynamic pendant oil drop to the experimentally measured data. Experimental tests are conducted for the heavy oil-propane system at constant pressures of P = 0.4 − 0.9 MPa and a constant temperature of T = 23.9 °C. It is found that both the diffusion coefficient and the oil-swelling factor of the heavy oil-propane system increase with pressure. The major advantage of this new technique is that simultaneous measurements of the solvent diffusivity in heavy oil and the oil-swelling factor can be completed within two hours at the pre-specified constant pressure and temperature. Introduction In the vapour extraction (VAPEX) process, a solvent (e.g. methane, ethane, propane, butane or carbon dioxide) is injected into a heavy oil reservoir at a pressure close to its vapour pressure(1). Previous studies have already shown that molecular diffusion of the injected solvent in heavy oil plays a vital role in the VAPEX process(2–4). Thus the diffusion coefficient of the solvent in heavy oil under the actual reservoir conditions becomes an important parameter in the reservoir simulation and field design of the VAPEX process. In the literature, there are several experimental methods for measuring solvent diffusivity in heavy oil. These experimental methods can be roughly categorized into conventional and non-conventional methods. Conventional methods involve compositional analysis of liquid samples taken from the heavy oil-solvent mixture at different times and locations during a diffusion test(5). These methods are expensive, intrusive and time-consuming, especially if the diffusion test is conducted at a high pressure. In addition, compositional analysis of the heavy oil-solvent mixture is prone to large experimental error. Non-conventional methods measure the change of a property of the heavy oil-solvent system during the molecular diffusion process. This property can be the gas volume(6), oil-gas interface position inside a capillary(7), laser light intensity of the heavy oil-gas mixture(8), gas pressure(9) and shape of a pendant heavy oil drop surrounded by a gaseous solvent(10). In particular, the decaying gas pressure is measured while the molecular diffusion of the solvent into heavy oil proceeds within a closed high-pressure diffusion cell. This is referred to as the pressure decay method, which has been applied to measure the diffusivities of methane, ethane, propane, nitrogen and carbon dioxide in crude oils(11–14).

A method to characterize the greenness of solvents used in pharmaceutical manufacture

This paper describes the development of a method to calculate the overall “greenness” of a pharmaceutical process that uses multiple solvents. This calculation is made by taking into account various environmental parameters and determining an overall greenness index. Through this method a scientist or engineer can effectively determine alternative, “greener” solvents or processes based on the use of a solvent database and greenness score. The objective is to develop a means to improve the process of drug development through solvent replacement/reduction. A solvent selection table, using a common spreadsheet software routine, was developed for the purpose of allowing a user to compare the greenness between two different process routes. This table includes over 60 solvents and associated chemicals common in the pharmaceutical and chemical industries. The comparison was made possible by the creation of a user-defined, weighted-solvent, greenness index that is an overall weighted factor taking into consideration solvent type, quantity used, and environmental impact. A given process or solvent receives an index ranking based on a variety of environmental and health parameters. The index values, along with the mass of solvents used in the given process, are used to compute the index, which allows for a quick and easy quantitative environmental comparison between two potential process routes.

Basicities of Aquo + Alcoholic (Mono-ol) mixtures

Gibbs energies of transfer of H+ion [ΔG0t(w→s)(H+)] from water (w) to different aquo + alcoholic mixtures (s) were calculated using no extrathermodynamic assumptions. ΔG0t(w→s)(H+) values with and without interactions are given.ΔG0t(w→s)(H+) values (without interaction terms) compare well with the selected values of ΔG0t(w→s)(H+) in different aquo + alcoholic mixtures recommended by Marcus from compilations of data reported by various workers using different extrathermodynamic assumptions. Suitable conversion was made to bring the data into the range of the TATB scale.ΔG0t(w→s)(H+) values in binary mixtures (without interaction terms) are lower and qualitatively to some extent close to the values reported in the literature at least at low percentages.The results show that ΔG0solv(H+) and ΔG0t(w→s)(H+) values are increasingly positivei.e.less basic as the mass% of organic solvents increases and the sequence of basicities are in the orderi.e.the organic solvent and solvent mixtures are less basic than water contrary to the prevalent conceptions. The main factor appears to be the number of O-atoms with lone-pair of electrons responsible for H+acceptance, H-bonding and other structural modifications of the solvent mixtures. Obviously, the lower the molar mass of the organic solvent, the greater will be the basicity of the solvent and solvent mixtures.

Pervaporation membranes highly selective for solvents present in fermentation broths

Pervaporation is an energy-efficient alternative to distillation for removing volatile organic compounds (VOCs) from water especially solvents from their dilute solutions in a fermentation broth. Polymeric, ceramic and liquid membranes have been used in the pervaporation process for removing such solvents; however, polymeric and ceramic membranes have rather poor solvent selectivity compared to liquid membranes even though they achieve reasonable solvent mass fluxes. Liquid membranes have stability problems due to various losses. The loss of liquid membrane (LM) to the feed solution leads to toxicity for the organisms in a fermentation broth. A new liquid membrane-based pervaporation technique has been developed to achieve high selectivity, ensure stability and prevent contamination of the fermentation broth. Trioctylamine (TOA) as a liquid membrane was immobilized in the pores of a hydrophobic hollow fiber substrate having a nanoporous coating on the broth side and studied for pervaporation-based removal of solvents (acetone, ethanol, and butanol) from their dilute aqueous solutions. The LM of TOA in the coated hollow fibers demonstrated high selectivity and reasonable mass fluxes of solvents in pervaporation. The selectivities of butanol, acetone, and ethanol achieved were 275, 220, and 80, respectively with 11.0, 5.0, and 1.2 g/m 2 h for the mass fluxes of butanol, acetone and ethanol, respectively at a temperature of 54 °C for a feed solution containing 1.5 wt% butanol, 0.8 wt% acetone, and 0.5 wt% ethanol. The mass fluxes were increased by as much as five times with similar selectivity of solvents when an ultrathin liquid membrane was used. However, acetic acid in the feed solution reduced the selectivities of the solvents without reducing the solvent fluxes due to coextraction of water which increases the rate of water permeation to the vacuum side. The TOA-based LM present throughout the pores of the coated substrate demonstrated excellent stability over many hours of experiment and essentially prevented the loss of liquid membrane to the feed solution and the latter's contamination by the liquid membrane.

Fluorometric investigations on the transition from reverse micelles to microemulsions in non-aqueous microemulsions

The fluorescent probes auramine-O (Au O) and 8-anilino-1-napthalene sulfonic acid, ammonium salt (ANS) were employed to determine the transition value for the conversion of reverse micelle to microemulsions in non-aqueous microemulsion systems containing diisooctylsodium sulfosuccinate (AOT) as the surfactant, n-alkanes as oil and various polar solvents. The n-alkanes used were hexane, heptane, octane and isooctane. The polar solvents employed were ethylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol and their aqueous mixtures. The effect of the oil's chain length and the mass of polar solvent on the transition values were investigated.

Solubility of β-Carotene in Binary Solvents Formed by Some Hydrocarbons with 2,5,8-Trioxanonane, 2-Propanone, and Cyclohexanone

Experimental results are reported for the solubility of β-carotene in six binary mixed solvents formed by 2,5,8-trioxanonane with 1-hexene, cyclohexane, hexane, and toluene and by 1-hexene with 2-propanone and cyclohexanone at 293.15 K. A spectral colorimeter was used for analysis of β-carotene concentration. The β-carotene solubility in the pure solvents increases in the order: 2-propanone < hexane < 2,5,8-trioxanonane < 1-hexene < cyclohexane < cyclohexanone < toluene. The solubility data as a function of the binary solvent mass fractions were smoothed by the Myers and Scott equation for asymmetric functions. The Flory and Huggins theory of non-athermal mixtures and the Acree and Rytting model were used for prediction of experimental data for the solubility of β-carotene in the six binary above listed mixed solvents.

Hydrodistillation–Headspace Solvent Microextraction: An Efficient Method for Analysis of the Essential Oil from the Seeds of Foeniculum vulgare Mill.

Hydrodistillation–headspace solvent microextraction (HD–HSME) has been used for isolation and preconcentration of the essential oil from the seeds of Foeniculum vulgare Mill. The effect on extraction efficiency of different conditions, for example sample mass, extraction time, microdrop volume, and choice of solvent, was studied and all were optimized. The results were compared with those from hydrodistillation, as reference method. Fourteen compounds were identified; the main components were trans-anethole (70.4%), fenchone (9.3%), and p-allylanisole (8.8%). The results were in good agreement with those obtained by hydrodistillation.