mL Of Aqueous Phase Research Articles

Enantioseparation of 2-(4-chlorophenyl)succinic acid by countercurrent chromatography and investigation of injection volume on resolution.

2-(4-Chlorophenyl)succinic acid was successfully enantioseparated by countercurrent chromatography using hydroxypropyl-β-cyclodextrin as chiral selector. A two-phase solvent system composed of n-hexane-ethyl acetate-0.1mol/L phosphate buffer with pH 2.65 (5:5:10, v/v) was selected. Enantioselective liquid-liquid extraction was used to optimize the enantioseparation conditions. Meanwhile, the influence of injection volume on resolution in countercurrent chromatography was investigated and a linear relationship between the inflection point of injection volume and sample loading was tentatively obtained. The peak resolution will decrease significantly when the injection volume over the inflection point was used. In addition, it could be found that the smaller amount of sample loading, the larger impact of injection volume on resolution could be observed, which might serve as a good reference for the selection of sample volume in enantioseparations by countercurrent chromatography. Under optimized conditions, 20mg of 2-(4-chlorophenyl)succinic acid racemate dissolved in 10mL of aqueous phase was successfully enantioseparated by countercurrent chromatography. The recovery for both of the enantiomer of (±)-2-(4-chlorophenyl)succinic acid reached within 70-75% with a purity of 99.0%.

Selective separation of cobalt and nickel using a stable supported ionic liquid membrane

The selective separation of cobalt from nickel is of major importance for the recovery of cobalt from primary or secondary sources, as well as for analytical purposes. In this paper, the extraction of cobalt from the mixtures was examined using a supported liquid membrane employing the undiluted hydrophobic ionic liquid, namely tri(hexyl)tetradecyl phosphonium chloride [P66614][Cl], as a carrier and polyvinylidene difluoride (PVDF) as a membrane material.In the preliminary study, the efficiency of this supported ionic liquid membrane (SILM) for the cobalt extraction was evaluated by conventional static mode sorption experiments. Up to 86% of cobalt can be recovered under optimal conditions (by contacting SILM with 9.8 cm2 in 5 mL of aqueous phase for 1 h at 100 rpm, with 9 mol·L−1 HCl in the aqueous phase).Next, metal ion transport through a flat sheet SILM was investigated with pure water as a receiving phase. Permeation coefficients values of 2.2 × 10−6 m·s−1 and 8.0 × 10−6 m·s−1 were obtained with a hydrophobic and a hydrophilic membrane, respectively. The SILM showed selectivity for cobalt over nickel with separation factors as high as 218. Membrane stability was proven to be excellent, since the same SILM was used three times without losses of performances.

The Effectiveness of Nitrate-Mediated Control of the Oil Field Sulfur Cycle Depends on the Toluene Content of the Oil.

The injection of nitrate is one of the most commonly used technologies to impact the sulfur cycle in subsurface oil fields. Nitrate injection enhances the activity of nitrate-reducing bacteria, which produce nitrite inhibiting sulfate-reducing bacteria (SRB). Subsequent reduction of nitrate to di-nitrogen (N2) alleviates the inhibition of SRB by nitrite. It has been shown for the Medicine Hat Glauconitic C (MHGC) field, that alkylbenzenes especially toluene are important electron donors for the reduction of nitrate to nitrite and N2. However, the rate and extent of reduction of nitrate to nitrite and of nitrite to nitrogen have not been studied for multiple oil fields. Samples of light oil (PNG, CPM, and Tundra), light/heavy oil (Gryphon and Obigbo), and of heavy oil (MHGC) were collected from locations around the world. The maximum concentration of nitrate in the aqueous phase, which could be reduced in microcosms inoculated with MHGC produced water, increased with the toluene concentration in the oil phase. PNG, Gryphon, CPM, Obigbo, MHGC, and Tundra oils had 77, 17, 5.9, 4.0, 2.6, and 0.8 mM toluene, respectively. In incubations with 49 ml of aqueous phase and 1 ml of oil these were able to reduce 22.2, 12.3, 7.9, 4.6, 4.0, and 1.4 mM of nitrate, respectively. Nitrate reduced increased to 35 ± 4 mM upon amendment of all these oils with 570 mM toluene prior to incubation. Souring control by nitrate injection requires that the nitrate is directed toward oxidation of sulfide, not toluene. Hence, the success of nitrate injections will be inversely proportional to the toluene content of the oil. Oil composition is therefore an important determinant of the success of nitrate injection to control souring in a particular field.

Combination of Directly Suspended Droplet Microextraction and Flame Atomic Absorption Spectrometry for Determination of Trace Amounts of Iron and Copper

A miniaturized liquid-phase extraction procedure based on directly suspended droplet microextraction combined with flame atomic absorption spectrometry was developed for determination of trace amounts of iron and copper, without any need for the centrifugation step for phase separation. The method was based on the extraction of the iron and copper complexes with 2-mercaptopyridine-N-oxide onto a microdrop of methyl isobutyl ketone (MIBK) as extractant solvent. The factors influencing the extraction were optimized. Under optimum conditions, an enrichment factor of ~25 was obtained for both iron and copper from only 6.5 mL of aqueous phase. The analytical curves were linear between 40-800 μg L-1 and 25-1200 μg L-1 for iron and copper, respectively. The limits of detection were 3.76 μg L-1and 1.84 μg L-1 for iron and copper, respectively. The developed method has been successfully applied for the determination of iron and copper ions in environmental waters, fruits, vegetables and also certified reference materials, with high efficiency.

Ionic liquid-based dispersive liquid–liquid microextraction for determination of trace amounts of iron in water, rock and human blood serum samples

A green and sensitive dispersive liquid-phase microextraction procedure based on room-temperature ionic liquid (1-hexyl-3-methylimidazolium hexafluorophosphate) for preconcentration and determination of total iron in real samples prior to flame atomic absorption spectrometry was developed. 2-Mercaptopyridine-N-oxide (pyrithione) and ethanol were used as complexing agent and dispersive solvent in the proposed method, respectively. The factors influencing the extraction were optimized. Under optimum conditions, the enhancement factor of 15 was obtained from only 11.35 mL of aqueous phase. The linear dynamic range and the detection limit were 10.0–700 and 2.4 μg L−1, respectively. The relative standard deviation (RSD) for ten replicate measurements of 500 μg L−1 of iron is 3.1 %. The developed method has been successfully applied for the determination of iron in water samples, human blood serum and rock certified reference material with high efficiency.

Surfactant mediated sulfide estimation at trace level: Application to environmental samples

A simple spectrophotometric method has been developed for the quantification of dissolved sulfide based on its reaction with ferric iron and the subsequent reaction of ferrous iron with 1-nitroso-2-naphthol in alkaline medium. The insoluble iron(II)-ligand complex has been solubilized in micellar medium using neutral surfactant which facilitates the non extraction step. The method obeys Beer’s law in the concentration range 0.5–8 μg in 10 mL of aqueous phase. The complex showed an absorption maximum at 710 nm with e value of 4.11 × 104 L/mol cm. The detection limit has been found to be 0.0036 μg/mL. The interference of common cations and anions has been studied and the proposed method has been successfully applied to determine the sulfide in different sewage water samples.

Development of ultrasound-assisted emulsification solidified floating organic drop microextraction for determination of trace amounts of iron and copper in water, food and rock samples

A simple and efficient liquid-phase microextraction technique was developed using ultrasound-assisted emulsification solidified floating organic drop microextraction combined with flame atomic absorption spectrometry, for the extraction and determination of trace amounts of iron and copper in real samples. 2-Mercaptopyridine n-oxide was used as chelating agent and 1-dodecanol was selected as extraction solvent. The factors influencing the complex formation and extraction were optimized. Under optimum conditions, an enrichment factor of ~13 was obtained for both iron and copper from only 6.7 mL of aqueous phase. The analytical curves were linear between 40–800 and 20–1,200 μg L−1 for iron and copper respectively. Based on three SD of the blank, the detection limits were 8.6 and 4.1 μg L−1 for iron and copper respectively. The relative SDs for ten replicate measurements of 500 μg L−1 of metal ions were 2.9 and 1.2 for iron and copper respectively. The proposed method was successfully applied for determination of iron and copper in environmental waters and some food samples including chess, rice, honey and powdered milk. Finally, method validation was made using rock certified reference material. A student’s t test indicated that there was no significant difference between experimental results and certified values.

Ultrasound Assisted Emulsification Microextraction Based on dimetyl (E)‐2‐[(Z)‐1‐acetyl)‐2‐hydroxy‐1‐propenyl]‐2‐butenedioate for Determination of Total Amount of Iron in Water and Tea Samples

AbstractAn ultrasound assisted emulsification microextraction (USAEME) is successfully used for extraction and determination of trace amount of iron in water and tea samples, followed by flame atomic absorption spectroscopy (FAAS). In this approach, a new synthetic ligand dimetyl (E)‐2‐[(Z)‐1‐acetyl)‐2‐hydroxy‐1‐propenyl]‐2‐butenedioate (DAHPB) is used as chelating agent and chloroform is selected as an extraction solvent. The factors influencing the complex formation and extraction by USAEME method are optimized. These factors are extraction solvent type as well as extraction volume, time, temperature, pH, and the amount of chelating agent. Under optimum conditions, an enrichment factor of 202.9 is obtained from only 7.1 mL of aqueous phase. The calibration graph using the preconcentration system for iron is linear between 40.0 and 800.0 μg L−1 with a detection limit of 7.4 μg L−1. The relative standard deviation (R.S.D) for ten replicate measurements of 500.0 μg L−1 of iron is 2.5%.

Nitrite/nitrate speciation through arsenomolybdenum blue complex at trace level: application to biological and environmental samples

A novel and simple method has been proposed for the estimation of nitrite/nitrate based on the reduction of arsenomolybdic acid to arsenomolybdenum blue using ascorbic acid. The obtained arsenomolybdenum blue complex has been oxidized by the addition of nitrite and the decrease in the absorbance of blue color is directly proportional to the nitrite quantity. The absorbance of the arsenomolybdenum blue complex has been measured at 840 nm. All the reaction variables have been optimized and Beer's law has been obeyed in the concentration range 2–10 μg in 25 mL of aqueous phase with a molar absorptivity 4.37 × 104 L mol−1 cm−1. The relative standard deviation of the method has been found to be 1.7% for five measurements with a detection limit of 0.003 μg mL−1. The method has been applied to determine nitrite/nitrate levels in biological samples as well as environmental samples.

Spectrophotometric Determination of Malachite Green Residue in Water Samples After Preconcentration on Surfactant-Coated Alumina

ABSTRACT A new, simple, and reliable method for rapid preconcentration of trace levels of malachite green from water samples is developed using a sodium dodecyl sulfate coated alumina solid phase. The effects of pH, flow rate of sample solution, and foreign ions on the sorption of malachite green have been investigated. Two micrograms of malachite green from 250 mL of aqueous phase could be quantitatively extracted into a 500 mg of SDS coated alumina. The collected malachite green molecules were eluted with 2 mL of acetonitrile and determined spectrophotometrically at 617 nm. The detection limit corresponding to three times of the standard deviation of the blank was found to be 3.2 µg L−1. The proposed method was used for the separation and preconcentration of malachite green with high enrichment factor (about 250) from water samples.

Micellar-Mediated Extractive Spectrophotometric Determination of Hydrogen Sulfide/Sulfide through Prussian Blue Reaction: Application to Environmental Samples

A sensitive surfactant-mediated extractive spectrophotometric method has been developed, based on the reaction of ferric iron with sulfide to form ferrous iron and its subsequent reaction with ferricyanide to form Prussian Blue, to quantify trace levels of hydrogen sulfide/sulfide in environmental samples. The method obeys Beer's law in the concentration range 2-10 microg of sulfide in 25 mL of aqueous phase with molar absorptivity (epsilon) of 3.92 x 10(4) L mol(-1) cm(-1). The colored species has been extracted into isoamyl acetate in the presence of a cationic surfactant i.e. cetylpyridinium chloride, to enhance the sensitivity of the method with epsilon value 5.2 x 10(4) L mol(-1) cm(-1). The relative standard deviation has been found to be 0.69% for 10 determinations at 4 microg of sulfide and the limit of detection was 0.009 microg mL(-1). The interference from common anions and cations has been studied. The proposed method has been applied to the determination of residual hydrogen sulfide in the laboratory fume hood as well as ambient atmospheric hydrogen sulfide in the vicinity of open sewer lines after fixing the analyte in ionic form using suitable trapping medium.

Separation and preconcentration of U(VI) on XAD-4 modified with 8-hydroxy quinoline

Amberlite XAD-4 adsorber resin was modified with 8-hydroxy quinoline (Oxine) by equilibrating with methanol solution of the reagent and the modified resin was used as a support material for the solid phase extraction and preconcentration of UO 2 2+ from aqueous solution at pH between 4 and 5.5. Ten micrograms of uranium from 300 ml of aqueous phase could be quantitatively extracted in to 1 g of the modified resin giving an enrichment of 200. Uranium collected in the column could be eluted out with methanol–HCl mixture and determined spectrophotometrically using arsenazo(III) as the chromogenic reagent. The preconcentration could be made selective to uranium by using EDTA as a masking agent for transition metal ions and Th(IV).

X-ray fluorescence analysis of trace metal ions following a preconcentration of metal-diethyldithiocarbamate complexes by homogeneous liquid-liquid extraction.

A homogeneous liquid-liquid extraction method for 36 metal ions with diethyldithiocarbamate was studied. As a result, 11 metal ions were extracted as metal-chelates. Under the experimental conditions, the maximum concentration factor was 500 (i.e., 0.1 mL of sedimented liquid phase was produced from 50 mL of aqueous phase). Moreover, the proposed method was utilized as a preconcentration method for X-ray fluorescence analysis of these metals. The recovery of each metal was ca. 97-100%. All calibration curves were linear over the range of 5.0 x 10(-7) mol L-1 to 1.0 x 10(-5) mol L-1. The detection limits were at the 10(-8) mol L-1 levels and the relative standard deviations were below 5% (5 determinations). When the proposed method was used for the determination of contaminants in a synthetic sample (Al-based alloy model) and of components in an Au-Pd alloy, the results were satisfactory.

Adsorption Parameters of Cd(II), Pb(II), and Hg(II) on Zirconium(IV) Phosphate Chemically Grafted onto Silica Gel Surface

Adsorption properties of metallic ions not essential for human metabolism, such as cadmium, lead, and mercury, on silica chemically modified with zirconium(IV) phosphate, SiZrP, were investigated using batch systems. The immobilization procedure was efficient and the functionalization degree was 2.82% for zirconium (0.31 mol g−1) and 2.54% for PO3−4(0.27 mol g−1). These results indicate that phosphate reacted with zirconium in a 1:1 ratio. The equilibrium is reached very quickly (15 min), indicating that the adsortion sites are well exposed. The best adsorption parameters were evaluated using 50 mL of aqueous phase at pH 4.5, an adsorption time of 15 min, and 0.2000 g of adsorbent. From adsorption isotherms obtained for the metals ions and distribution coefficients the affinity of SiZrP for the metal ions studied increases in the order Cd(II) < Pb(II) < Hg(II). Twice as much lead was adsorbed by the SiZrP surface (Nf = 10.0 μmol g−1) as cadmium (Nf = 5.0 μmol g−1). For mercury, the capacity was greater; nevertheless an adsorption plateau was not observed.

Desorption of tefluthrin insecticide from soil in simulated rainfall runoff systems—Kinetic studies and modelling

The sorption and subsequent desorption from soil particles, of tefluthrin, a widely used soil-active pyrethroid insecticide, were studied in a simulated rainfall runoff system. Experimentation was facilitated by use of the 14C-labelled compound. The desorption of such highly hydrophobic organic compounds from soils has rarely been reliably determined previously. Sorption results showed that the partition coefficients ( K p and K oc) were determined with good precision, although the resultant coefficients were shown to be underestimates of true adsorption to soil due to non-attainment of true equilibrium and the presence of colloidal material in the aqueous phase supernatants analysed. Once the adsorption slurries were diluted (30 ml of aqueous phase to 3.51) to simulate transport of soil to a larger water body after heavy rainfall, kinetic studies, using a centrifugation method, indicated that the soil phase concentration decreased once more, whilst at the same time a biphasic re-equilibration process occurred in the aqueous phase. A direct particle counting method was used to rapidly and reproducibly measure desorption of 14C-tefluthrin from soil under contrasting experimental conditions. Initial re-equilibration was shown to be rapid when soil-to-water ratios were changed significantly, temperature having a pronounced effect on this desorption. The results are important for the accurate modelling of tefluthrin behaviour in the environment.

Simultaneous determination of copper, mercury and lead by first-order derivative spectrophotometry using dithizone as reagent

A first-order derivative spectrophotometric method has been developed for the simultaneous determination of copper, mercury and lead at μg/L levels using dithizone as reagent. The procedure involves the simultaneous extraction of these elements by dithizone in chloroform from weakly alkaline solutions. Linear calibration curves were obtained in the ranges 0.5–10 (Cu), 1–10 (Hg) and 1–10 (Pb) μg present in 40 ml of aqueous phase with detection limits of 5 μg/L (Cu) and 20 μg/L (Hg and Pb). The R.S.D.s for 100 μg/L of copper, mercury and lead were 2.5, 2.6 and 3.1% respectively, for 5 determinations. The method is applicable for the determination of copper and lead in marine sediment samples with good precision and accuracy.

Spectrophotometric determination of trace amounts of iron(III) in salicylates by extraction of the mixed-ligand iron-salicylate-purpurin complex

A sensitive method is described for the determination of microgram amounts of iron(III) by means of its reaction at pH 9.0 with salicylate and purpurin (1,2,4-trihydroxyanthraquinone) and extraction into 4-methylpentan-2-one. The molar absorptivity of the 1:1:2 iron(III)-salicylate-purpurin complex is 4.7 × 104 l mol–1 cm–1 at 590 nm. Beer's law is obeyed up to a concentration of 10 µg of iron in 40 ml of aqueous phase. Iron contents in salicylate, acetylsalicylate and pharmaceutical products containing these compounds can be determined at levels of the order of 10–5%.

A simple method for the separate estimation of labelled drugs and their metabolites by liquid scintillation counting. Some practical examples

A simple method is described for the separate determination in plasma of lipophilic drugs and their more hydrophilic metabolites by liquid scintillation counting. This is done by measuring the radioactivity after adding biological specimens to a scintillation liquid which takes up both the unchanged drug and its hydrophilic metabolites (Bray's solution), and by mixing further aliquots of the specimen with a scintillation fluid which only takes up unchanged drug (Toluene+PPO=TSC). The amount of hydrophilic substances dissolved in TSC, as well as irradiation from the aqueous phase, were shown to be less than 13% for both of the isotopes3H and14C, employing 0.5 ml of aqueous phase added to 10 ml toluene scintillant. Checking the method by thin layer chromatography showed that the concentrations of fentanyl and haloperidol in plasma were determined accurately. After taking account of a special procedure used to dissolve a greater proportion of morphine in toluene, the ratio of TSC and BSC measurements was in agreement with data obtained by thin layer chromatography. Experiments with chlorpromazine showed that lipophilic degradation products were formed which could not be separated from the original drug by liquid-liquid partition. In such cases, therefore, the method cannot be employed. Etorphine is an example of how reliable results were obtained despite low dosage and relatively low specific activity of this drug.