High-density Solvent Research Articles

Molecular-level understanding of the rovibrational spectra of N2O in gaseous, supercritical, and liquid SF6 and Xe.

The transition between the gas-, supercritical-, and liquid-phase behavior is a fascinating topic, which still lacks molecular-level understanding. Recent ultrafast two-dimensional infrared spectroscopy experiments suggested that the vibrational spectroscopy of N2O embedded in xenon and SF6 as solvents provides an avenue to characterize the transitions between different phases as the concentration (or density) of the solvent increases. The present work demonstrates that classical molecular dynamics (MD) simulations together with accurate interaction potentials allows us to (semi-)quantitatively describe the transition in rotational vibrational infrared spectra from the P-/R-branch line shape for the stretch vibrations of N2O at low solvent densities to the Q-branch-like line shapes at high densities. The results are interpreted within the classical theory of rigid-body rotation in more/less constraining environments at high/low solvent densities or based on phenomenological models for the orientational relaxation of rotational motion. It is concluded that classical MD simulations provide a powerful approach to characterize and interpret the ultrafast motion of solutes in low to high density solvents at a molecular level.

Development of novel water equivalent liquid scintillator

Scintillation dosimeters are high efficiency and resolution devices for 3D dose radiotherapy measurement. Water is the best tissue equivalent material for most types of radiation, thus water-equivalent scintillator is the preferred scintillator for radiotherapy dose measurement. This research paper describes a new method of preparing water-equivalent liquid scintillators (LS). In this study, we first calculated the approximate ratio of each LS component by empirical formula and then used the Monte Carlo program Geant4 to optimize the concentration ratio of the water-equivalent LS. The newly prepared LS was doped with a high-density solvent containing silicon and oxygen. Experimental results showed that the newly developed LS had good water equivalence in different depths, both at high energy (6 MV) and low energy (50 kVp ~ 225 kVp). In addition, its luminous efficiency was superior compared to the commercial ULTIMA Gold™ LS. In conclusion, the Monte Carlo simulation was effective in predicting each component ratio in the water-equivalent LS. Furthermore, the newly prepared LS had excellent luminescence properties and water equivalence and is a potential 3D dose detector.

Surfactant‐enhanced spectrofluorimetric detection after magnetic nanoparticles‐based micro‐solid‐phase extraction coupled with dispersive liquid–liquid micro‐extraction for determination of ciprofloxacin in human plasma

A sensitive and fast micro-solid-phase extraction (μ-SPE) coupled with dispersive liquid–liquid micro-extraction (DLLME) was reported before micelle enhanced spectrofluorimetric detection for determination of ciprofloxacin antibiotic in human plasma samples. The DLLME was performed using methanol as disperser and 1-octanol as extracting solvent. Oleic acid-modified Fe3O4 nanoparticles (as hydrophobic adsorbents) were applied in μ-SPE step to extract the analyte from DLLME procedure. The method uses the advantageous of high surface area and strong superparamagnetism of these nanoparticles to many avoid labourhood column/cartridge-passing processes of traditional SPE. The major parameters affecting signal enhancement and analyte recovery were evaluated and optimised. Under the optimal conditions, the calibration curve (with calibration equation of I f = 2.5826 C + 10.273) was linear in the range 0.5–600 μg L−1 (R 2 = 0.997) with low limit of detection of 0.21 µg L−1 and limit of quantification of 0.63 µg L−1. The intra-day and inter-day precisions (as relative standard deviation) were in the range of 1.01–1.67% and high recoveries in the range of 93.5–102.4% were obtained. The results demonstrated that the proposed method is easy, low cost, and accurate. In addition, it confirms that choosing extraction solvent was not restricted to the high-density solvents which can extent the versatility of DLLME.

High Density Solvent Based Dispersive Liquid-Liquid Microextraction Technique for Simultaneous and Selective Extraction of Multiclass Pesticide Residues in Water and Sugarcane Juice Samples

In this study, a miniaturized analytical technique based on high density solvent based dispersive liquid-liquid microextraction (HD-DLLME) was developed for extraction of trace residues of multiclass pesticides including three striazine herbicides, two organophosphate insecticides and two organochlorine fungicides from environmental water and sugarcane juice samples. The analytical method was validated and found to offer good linearity: R2 ≥ 0.991; repeatability varied from 0.73% - 5.28%; reproducibility varied from 1.14% - 8.74% and limit of detection ranged from 0.005 to 0.02 μg/L. Moreover, accuracy of the optimized method was evaluated and the recovery was varied from 80.39% - 114.05%. Analytical applications of this method to environmental waters and sugarcane juice samples indicate the presence of trace residues of ametryn in the lake water and sugarcane juice samples. Atrazine and ametryn were also detected in irrigation water.

Analytical approaches for the determination of cobalt, nickel and copper by aeration-assisted homogeneous liquid–liquid microextraction and flame atomic absorption spectrometry

ABSTRACTA new aeration-assisted homogeneous liquid–liquid microextraction using high-density solvent for determination of copper, nickel and cobalt, as a prior step to their determination, coupled to flame atomic absorption spectrometry is presented. Under the optimum conditions, the calibration graphs were linear in the range of 5.0–600.0 ng/mL for copper, 10.0–450.0 ng/mL for nickel and 8.0–500.0 ng/mL for cobalt. The limits of detection were 1.3, 3.6 and 2.7 ng/mL and the enrichment factor estimated to be 350, 340 and 360, for copper, nickel and cobalt, respectively. The proposed method was successfully applied for the determination of these cations in different samples.

A novel aeration-assisted homogenous liquid–liquid microextration for determination of thorium and uranium in water and hair samples by inductively coupled plasma-mass spectroscopy

A novel method based on aeration-assisted homogeneous liquid–liquid microextraction using high density solvent is presented, which is combined with inductively coupled plasma-mass spectroscopy in which simultaneous preconcentration and determination of thorium and uranium with arsenazo III as the chelating reagent is carried out. To achieve optimum conditions, several parameters such as pH, concentration of arsenazo III, extraction and homogenous solvent types and their volumes, salt concentration and extraction time were investigated. Under which, the calibration graphs were linear in the range of 0.5–600.0ngL−1 for thorium and 0.3–550.0ngL−1 for uranium. Good linearities were obtained for both analytes with R2 values larger than 0.9990. The limits of detection (LOD, 3Sb/m, n=5) of this method were 0.12 and 0.09ngL−1, and the enrichment factors were estimated to be 370 and 410 for thorium and uranium, respectively. The proposed method was applied to determine the thorium and uranium in human hair and different environmental water samples. Acceptable recoveries ranged from 99.4% to 100.7% with standard deviation of 0.05 to 0.17.

Dispersive liquid-liquid microextraction: trends in the analysis of biological samples.

Dispersive liquid-liquid microextraction (DLLME) is a recent microextraction technique that was first developed by Rezaee and co-workers in 2006. It allows the simultaneous extraction and preconcentration of analytes into a micro-volume of extracting solvent based on a ternary solvent system involving an aqueous phase, a nonpolar water immiscible high-density solvent that acts as extraction phase, and a disperser solvent, which is often polar and water miscible. This article presents an overview of DLLME applications in the analysis of biological samples (e.g., plasma and urine). Aside from the classical DLLME applications using high density extraction solvents, recent advances in the use of low density solvents and ionic liquids are also discussed. Although most of the applications deal with the analysis of organic target compounds, a few applications on the bioanalysis of inorganic substances are also included.

Time-averaged distributions of solute and solvent motions: exploring proton wires of GFP and PfM2DH.

Proton translocation pathways of selected variants of the green fluorescent protein (GFP) and Pseudomonas fluorescens mannitol 2-dehydrogenase (PfM2DH) were investigated via an explicit solvent molecular dynamics-based analysis protocol that allows for direct quantitative relationship between a crystal structure and its time-averaged solute-solvent structure obtained from simulation. Our study of GFP is in good agreement with previous research suggesting that the proton released from the chromophore upon photoexcitation can diffuse through an extended internal hydrogen bonding network that allows for the proton to exit to bulk or be recaptured by the anionic chromophore. Conversely for PfM2DH, we identified the most probable ionization states of key residues along the proton escape channel from the catalytic site to bulk solvent, wherein the solute and high-density solvent crystal structures of binary and ternary complexes were properly reproduced. Furthermore, we proposed a plausible mechanism for this proton translocation process that is consistent with the state-dependent structural shifts observed in our analysis. The time-averaged structures generated from our analyses facilitate validation of MD simulation results and provide a comprehensive profile of the dynamic all-occupancy solvation network within and around a flexible solute, from which detailed hydrogen-bonding networks can be inferred. In this way, potential drawbacks arising from the elucidation of these networks by examination of static crystal structures or via alternate rigid-protein solvation analysis procedures can be overcome. Complementary studies aimed at the effective use of our methodology for alternate implementations (e.g., ligand design) are currently underway.

Solvent selection in ultrasonic-assisted emulsification microextraction: Comparison between high- and low-density solvents by means of novel type of extraction vessel

There are numerous published reports about dispersive liquid phase microextraction of the wide range of substances, however, till now no broadly accepted systematic and purpose oriented selection of extraction solvent has been proposed. Most works deal with the optimization of available solvents without adequate pre-consideration of properness. In this study, it is tried to compare the performances of low- and high-density solvents at the same conditions by means of novel type of extraction vessel with head and bottom conical shape. Extraction efficiencies of seven basic pharmaceutical compounds using eighteen common organic solvents were studied in this work. It was much easier to work with high-density solvents and they mostly showed better performances. This work shows that although exact predicting the performance of the solvents is multifaceted case but the pre-consideration of initial selection of solvents with attention to the physiochemical properties of the desired analytes is feasible and promising. Finally, the practicality of the method for extraction from urine and plasma samples was investigated.

Development of on-line spectroscopic determination approach of dispersive liquid–liquid microextraction based on an effective device

A novel, rapid, simple, and low-cost on-line determination approach of dispersive liquid–liquid microextraction (DLLME) with low-density solvents was developed with the support of a specially designed effective homemade device. The proposed method surmounted the drawbacks of conventional DLLME of the need of high-density solvents as extractants, and the requirement of centrifugation operation to obtain phase separation, and the difficulties to realize on-line determination. The amount of sample utilized can conveniently change according to practical needs by varying the volume of the extraction tube of the device to perform a more effective DLLME. A case study was carried out to assess this method utilizing the dye rhodamine B as the model analyte. The experiment parameters influencing the extraction were systematically investigated. Under optimum conditions, the linearity was obtained in the range of 0.015–1.000μg/mL with the correlation coefficient (r2) of 0.9980. The limit of detection and quantification were 6.1 and 20.4μg/L, respectively. Good repeatability was achieved with the relative standard deviations (RSD) for five replicate measurements of different concentration samples less than 4.06%, and the presented method was successfully employed to quantify rhodamine B in three real samples.

High-density solvent-based de-emulsification microextraction technique combined with fiber optic-linear array detection spectrometry for fast determination of ppb-level phenol index

In this work, a simple, rapid, and efficient solvent-based de-emulsification microextraction technique using high-density solvent has been developed for determining phenol index in water samples for the first time. The extraction of phenolic compounds in the aqueous sample solution was performed by using chloroform (as extraction solvent) and acetone (as dispersive solvent) in the presence of 4-aminoantipyrine (4-AAP) as chromogenic reagent. A de-emulsification solvent (ACN) was then injected into the sample solution to break up the emulsion, and then obtained emulsion cleared into two phases quickly, with no centrifugation step. The lower layer organic phase transferred into a microcell of a fiber optic-linear array detection spectrophotometry. The effect of various parameters on the extraction recovery was investigated. Under the optimized conditions and preconcentration of 10 mL of sample, the enhancement factor of 140 and the detection limit of 0.6 μg L−1 were obtained. Validation of the method was performed by spiking recovery method and comparison of results with those obtained by American Society for Testing and Materials standard method.

Magnetic nanoparticle assisted dispersive liquid–liquid microextraction for the determination of 4-n-nonylphenol in water

A fast extraction technique involving dispersive liquid–liquid microextraction (DLLME) coupled with magnetic nanoparticle-based dispersive solid-phase microextraction (D-μ-SPE) was developed. For preliminary study, this method was applied for the extraction of 4-n-nonylphenol (4-NP) in water. In this method, n-octyl-triethoxysilane surface-modified magnetic iron oxide nanoparticles (C8MNPs) were first synthesized. The DLLME was performed by injecting 1 mL of methanol (disperser) containing 10 μL of 1-octanol (extraction solvent) into 15 mL of water sample. To this solution, C8MNPs were immediately added for the retrieval of the extraction solvent and of the extracted 4-NP by sonication. Subsequently, a magnet was held next to the vial to attract and isolate the C8MNPs. Then, the water sample was decanted, the nanoparticles were freeze-dried, and the 4-NP was extracted from nanoparticles by sonication with methanol. The detection of 4-NP was performed using a HPLC coupled with a fluorescence detector. Under optimal extraction conditions, a low method of detection limit (13.9 ng L−1), good linearity (R2 = 0.9958), and repeatability (1.7–2.2%) were achieved during 4-NP extraction. This method was also successfully used to analyze the real water samples such as drinking water and secondary wastewater. Generally, this sample preparation method offered an alternative to the conventional DLLME, because, in this method, centrifugation is not required and the retrieval of the extraction solvent is based on the adsorption process by magnetic nanoparticles (MNPs). Also, this two-step method improved the versatility of DLLME because the selection of the extraction solvent was no longer limited to the high density solvents. Because MNPs can be surface-modified for the extraction of different organic solvents, this method could have great prospects in the future.

Ultrasound-assisted emulsification microextraction using low density solvent for analysis of toxic nitrophenols in natural waters

An ultrasound-assisted emulsification microextraction (USAEME) based on low-density solvents was successfully applied for the extraction and pre-concentration of four toxic nitrophenols in water samples. The extracted analytes were analyzed by high-performance liquid chromatography-UV detection. The important parameters influencing the extraction efficiency were studied and optimized utilizing two different optimization methods: one variable at a time (OVAT) and central composite design (CCD). The results showed that the emulsification process can be completed in a few seconds using low-density solvents, but almost 10–20 min is necessary for high-density solvents. Under the optimum conditions (extraction solvent, 1-octanol; extraction solvent volume, 40 µL; sample pH, 3.0; salt concentration, 20% (w/v) NaCl; extraction temperature, 40 (±3)°C), limits of detection of the method were in the range of 0.25 to 1 µg L−1 and the repeatability and reproducibility of the proposed method, expressed as relative deviation, varied in the range of 2.2–4.2% and 4.7–6.9%, respectively. Linearity was found to be in the range of 1 to 200 µg L−1 and the preconcentration factors (PFs) were between 77 and 175. The relative recoveries of the four nitrophenols from water samples at spiking level of 10.0 µg L−1 were in the range of 92.0 to 115.0%.

Sensitive determination of 2,4,6-trichloroanisole in water samples by ultrasound assisted emulsification microextraction prior to gas chromatography–tandem mass spectrometry analysis

A novel application of an ultrasound assisted emulsification microextraction (USAEME) technique is proposed for the extraction and preconcentration of 2,4,6-trichloroanisole (2,4,6-TCA) from water samples prior to its determination by gas chromatography-tandem mass spectrometry (GC-MS/MS). USAEME employs a non-polar high-density solvent (extractant solvent), which forms an oil-in-water emulsion (O/W) in the aqueous sample bulk assisted by ultrasonic radiation. Several factors including, solvent type and volume, extraction time, extraction temperature, shaking mode and matrix modifiers were studied and optimized over the relative recovery of the target analyte. An aliquot of 5mL water sample was conditioned by adding 150microL 6.15molL(-1) sodium chloride and 300microL 0.05molL(-1) phosphate buffer (pH 6), and finally extracted with 40microL chloroform by using USAEME technique. Under the optimal experimental conditions 2,4,6-TCA was quantitatively extracted achieving an enrichment factor (EF) of 555. The detection limit (LOD), calculated as three times the signal-to-noise ratio (S/N), was 0.2ngL(-1) and the RSD was 6.3% (n=5) when 1ngL(-1) 2,4,6-TCA standard mixture was analyzed. The coefficients of estimation of the calibration curves obtained following the proposed methodology was >or=0.997 and the linear working range was 1-5000ngL(-1). Finally, the proposed technique was successfully applied for extraction and determination of the 2,4,6-TCA in water samples. Recovery studies lead values >or=94%, which showed a successfully robustness of the analytical methodology for determination of nanogram per liter of 2,4,6-TCA in water samples.

Low temperature metal oxide film deposition and reaction kinetics in supercritical carbon dioxide

An effective method is developed for low temperature metal oxide deposition through thermal decomposition of metal diketonates in supercritical carbon dioxide (scCO 2) solvent. The rates of Al(acac) 3 (Aluminum acetyl acetonate) and Ga(acac) 3 (Gallium acetyl acetonate) thermal decomposition in scCO 2 to form conformal Al 2O 3 and Ga 2O 3 thin films on planar surfaces were investigated. The thermal decomposition reaction of Al(acac) 3 and Ga(acac) 3 was found to be initialized at ∼ 150 °C and 160 °C respectively in scCO 2 solvent, compared to ∼ 250 °C and 360 °C in analogous vacuum-based processes. By measuring the temperature dependence of the growth rates of metal oxide thin films, the apparent activation energy for the thermal decomposition of Al(acac) 3 in scCO 2 is found to be 68 ± 6 kJ/mol, in comparison with 80–100 kJ/mol observed for the corresponding vacuum-based thermal decomposition reaction. The enhanced thermal decomposition rate in scCO 2 is ascribed to the high density solvent which effectively reduces the energy of the polar transition states in the reaction pathway. Preliminary results of thin film deposition of other metal oxides including ZrO x , FeO x , Co 2O 3, Cr 2O 3, HfO x from thermal decomposition of metal diketonates or fluorinated diketonates in scCO 2 are also presented.

Solute–solute potential of mean force in supercritical solvents: A nonlocal integral equation study

We employ Monte Carlo simulations and two versions of integral equation theory to study the potential of mean force between two dilute solutes in a supercritical solvent. The nonlocal integral equation theory is shown to be far superior compared to its homogeneous counterpart. Important differences in the behavior of the potential of mean force between medium and high density solvents are pointed out.

Predicting the ‘missing cone’ in protein crystallography – Amplitudes from a structure with high-density solvent

Abstract Published 6 Å X-ray diffraction data from rubredoxin were used to base trial phase extensions within a ‘missing cone’ of the reciprocal lattice. The intensities from a protein with a high ammonium sulfate in the solvent space were used as if they had been collected by tomographic sampling within a ± 45° planar tilt restriction from the hk0 net. These amplitudes within the permitted sample space, combined with crystallographic phases from a protein backbone model, were used as a basis for the Sayre equation to predict missing amplitude and phase values. The Sayre expansion with amplitudes (but not phases) partially representing a reverse contrast structure was found to give a reasonable prediction of missing phase terms, with a mean difference of 68.6° for 36 reflections within the data set of 127 reflections, or 49.4° for the 12 most intense reflections. Oddly enough, the overall phase accuracy is better than if ±60° tilt data are used for the extension but the prediction of missing amplitudes is worse for the ±45° experiment.

Theory of transport in dilute solutions, suspensions, and pure fluids. II. Intrinsic shear and bulk viscosities

We evaluate the intrinsic shear and bulk viscosities of a solution or suspension of hard-sphere solute in a hard-sphere solvent. We use the ideas, developed in the preceding paper, of the generalized boundary condition descriptive of the solute–solvent binary collision in the presence of the solvent treated as a continuum. Via an appropriate choice of the effective core radius and effective mass of the binary collision, we obtain analytically simple expressions that yield the correct hydrodynamic results in the limit K=l/σ11→0 as well as a reasonable approach to the Enskog result when K is large. Here l and σ11 are the mean free path in solvent and size of the solute particle, respectively. Our results also show for the case of a high-density solvent remarkable agreement with hydrodynamic results over a wide range of solute particle size.

Interaction of phosphatidylcholine with bovine serum albumin. Specificity and properties of the complexes

Phosphatidylcholine dispersed on Celite was rapidly solubilized by neutral bovine serum albumin solutions. Stable protein-lipid complexes were isolated by Agrose gel filtration or by ultracentrifugal flotation in high density solvents, and the physicochemical properties of the complexes were investigated in terms of the stoichiometry of binding, effect of fatty acid ligands on phosphatidylcholine binding, effect of high ionic strength on the stability of the complexes, intrinsic fluorescence and circular dichroism spectra, and sedimentation velocity coefficients. Complexes containing from 2 to 30 phosphatidylcholine molecules per protein molecule were observed; however, no saturation of binding sites could be detected in this range of molar ratios. Oleic acid binding by serum albumin prevents interaction of the protein with phosphatidylcholine, indicating possible competition of these ligands at low contents of the phospholipid. For molar ratios of up to 10 phosphatidylcholine molecules per serum albumin, binding is primarily due to hydrophobic interactions that have no effect on the overall shape and secondary structure of the native protein except for local modifications at tryptophan residues, whose fluorescence becomes quenched and blue shifted on phosphatidylcholine binding. Similar phosphatidylcholine uptake experiments performed with a series of globular proteins indicated that the lipid extraction from Celite surfaces is a non-specific process, accelerated by several other proteins (e.g. aldolase, egg albumin, chymotrypsinogen, soybean trypsin inhibitor, and the major apolipoprotein from bovine serum high density lipoprotein). Formation of stable protein-lipid complexes, however, was only observed with bovine serum albumin, which in contrast to the other proteins is known to have high affinity binding sites for anions with hydrophobic side chains.