An indirect simple and rapid cloud point extraction is proposed for separation and preconcentration of sulfadiazine and its determination by flow injection‐flame atomic absorption spectroscopy (FI‐FAAS). The sulfadiazine from 35 mL of solution was readily converted to silver sulfadiazine upon addition of silver nitrate (9.7 × 10‐5 mol/L). Then, Triton X‐114 a non ionic surfactant was added and the solution was heated to 60 °C. At this stage, two separate phases was formed and silver sulfadiazine enters the surfactant rich phase of non‐ionic micelles of Triton X‐114. The surfactant‐rich phase (~50 μL) was then separated and diluted to 300 μL with acidic methanol. The concentration of silver in the surfactant‐rich phase which is proportional to the concentration of sulfadiazine in sample solution was determined by FI‐FAAS. The parameters affecting extraction and separation were optimized. Under the optimum conditions (i.e. pH 2‐10, silver concentration (9.7 × 10 ‐5 mol/L), Triton X‐114 (0.075% v/v) and temperature 60 °C) a preconcentration factor of 117 and a relative standard deviation of 4.9% at 37 μg L‐1 of sulfadiazine was obtained. The method was successfully applied to analysis of milk, urine and tablet samples and accuracy was determined by recovery experiments. 相似文献
We have studied the phase behavior of homologous series of diglycerol fatty acid esters (Qn‐D, for n=10, 12, 14, and 16, where n represents the carbon number in the alkyl chain length of amphiphile) in aqueous solution as a function of temperature and surfactant concentration. The different equilibrium phases present over a wide range of composition and temperature studied were characterized by means of visual observation under normal and polarized light, and x‐ray scattering techniques at small (SAXS) and wide angle (WAXS) regions. In diglycerol monocaprate (Q10‐D) and diglycerol monolaurate (Q12‐D)/H2O systems, lamellar liquid crystal (Lα) phase is present in the surfactant rich region and it swallows an appreciable amount of water. The amount of water swallowed by the Lα phase was determined by plotting the interlayer spacing, d, as a function of reciprocal of the surfactant weight fraction Ws. In the dilute regions, dispersion of Lα phase in water is observed over a wide range of temperature. At higher temperatures, the Lα phase melts to isotropic two‐liquid phases in water rich region whereas to isotropic reverse micellar solution (Om) in surfactant rich region. The Lα‐Om transition temperature is increased on increasing the hydrocarbon chain length of the surfactant from Q10‐D to Q12‐D. There is surfactant solid phase in equilibrium with water up to 25°C in diglycerol monomyristate (Q14‐D)/H2O system and the solid phase could solubilize 25 wt% water. The melting temperature of solid phase is practically constant in a wide range of compositions. Both the solid present region and the extent of water solubilization are increased in diglycerol monopalmitate (Q16‐D)/H2O system. At lower surfactant concentrations, excess water appears and dispersion of solid in water is formed. The structure of the solid is identified by WAXS measurement and it is confirmed to α‐solid. Normal vesicular aggregates are formed in Lα+W regions in the Q14‐D/H2O system at 25°C. 相似文献
Complementary techniques had to be applied to investigate the binary system tetradecanedioic acid (C14H26O4)–hexadecanedioic acid (C16H30O4), because all the forms observed have the same space group (P21/c; Z = 2). We studied the polymorphism of the two single compounds and of their mixtures by X‐ray powder diffraction, differential‐scanning calorimetry (DSC), infrared spectroscopy (IR), scanning electron microscopy (SEM), and thermo‐optical microscopy (TOM). The two diacids were found to be isopolymorphic. At low temperature, they crystallize in the same ordered C‐form, and, on heating, adopt the ordered Ch‐form, 1° below their melting point. In contrast to similar compounds (unbranched alkanes, alkanols, and fatty acids), the solid–solid and solid–liquid phase‐transition temperatures decrease with increasing chain length. At low temperature, a new monoclinic form, Ci, appears as a result of the disorder of composition in the mixed samples. There are two [C + Ci]‐type solid–solid domains. On heating, the solid domains are related to solid–liquid domains by a peritectic invariant for compositions rich in C14H26O4, and by a eutectic invariant for compositions rich in C16H30O4. At higher temperature, there appears a second peritectic invariant for compositions rich in C14H26O4, together with a metatectic invariant for compositions rich in C16H30O4. All the solid forms observed in this binary system are isostructural. Nevertheless, the equilibrium between them is complex near the melting point, and their miscibility in the solid state is reduced. 相似文献
We have investigated the phase behavior of diglycerol monomyristate (DGM) in a variety of organic solvents over a wide range of temperatures and compositions. At lower temperature, there exists a surfactant solid, which solubilize different amounts of oils depending on the oil nature. The melting temperature of the solid phase is virtually constant in a wide range of composition. In all the systems, a lamellar liquid crystal (Lα) is formed in surfactant‐rich regions at intermediate temperatures between the solid‐melt and isotropic two‐ or single‐phase regions. In the dilute regions reverse vesicles are formed in the Lα+O regions mainly in the case of linear hydrocarbon type oils. In the aromatic and cyclic aliphatic oils, there are isotropic solutions at 25°C. However, there is dispersion of α‐solid in the case of liner hydrocarbon oils. Two liquid‐phase regions above the Lα phase are observed in the case of tetradecane and hexadecane. In the shorter chain oil systems, such as octane and decane, no two liquid‐phase appear above Lα region. That is the two liquid‐phase region is largely dependent on the chain length of the oils, and becomes wider in longer hydrocarbon oil. 相似文献
Recent theoretical calculations predict that megabar pressure stabilizes very hydrogen‐rich simple compounds having new clathrate‐like structures and remarkable electronic properties including room‐temperature superconductivity. X‐ray diffraction and optical studies demonstrate that superhydrides of lanthanum can be synthesized with La atoms in an fcc lattice at 170 GPa upon heating to about 1000 K. The results match the predicted cubic metallic phase of LaH10 having cages of thirty‐two hydrogen atoms surrounding each La atom. Upon decompression, the fcc‐based structure undergoes a rhombohedral distortion of the La sublattice. The superhydride phases consist of an atomic hydrogen sublattice with H?H distances of about 1.1 Å, which are close to predictions for solid atomic metallic hydrogen at these pressures. With stability below 200 GPa, the superhydride is thus the closest analogue to solid atomic metallic hydrogen yet to be synthesized and characterized. 相似文献
A novel cellulose tris(N‐3,5‐dimethylphenylcarbamate) (CDMPC) chiral stationary phase (CSP) was prepared by coating CDMPC on TiO2/SiO2, which was prepared by coating titania nanoparticles on silica through a self‐assemble technique. At first, 2‐hydroxyl‐phenyl acetonitrile and α‐phenylethanol were separated on this new CSP to evaluate the chiral separation ability. Then, two pesticides, matalaxyl and diclofop‐methyl were separated. The influence of the mobile phase composition on the enantioselectivity was discussed, and the repeatability and stability of the CSP were studied too. 相似文献
Summary: The effects of viscosity asymmetry of the components on morphology and dynamics of phase‐separating AB fluids are investigated numerically based on a modified Model H. For critical mixtures, in the early stage of phase separation the co‐continuous morphology with droplets of A in B and B in A is observed. In the late stage of phase separation, the viscosity asymmetry leads to morphological change from co‐continuous structure to completely dispersed structure where the less viscous component forms droplet. The pathway of this transformation is accompanied by the breakdown of balance of volume fraction between droplets with different viscosity. Domain growth is characterized by a crossover from a faster growth at intermediate time under the influence of hydrodynamics to Lifshitz–Slyozov behavior at late times. For off‐critical mixture, viscosity asymmetry only plays an important role for domain growth in the intermediate stage of phase separation and the domain growth depends on whether the more viscous phase is dispersed or continuous, and the late stage of domain growth follows Lifshitz–Slyozov power law independent of which phase is dispersed.
Result for the evolution of phase‐separating domains for critical fluid mixtures = 0.5 for t = 1 500 with viscosity asymmetry: ηA = 0.8, ηB = 0.2. A‐rich regions and B‐rich regions are represented by white and black, respectively. 相似文献
Here, task‐specific ionic liquid solid‐phase extraction is proposed for the first time. In this approach, a thiourea‐functionalized ionic liquid is immobilized on the solid sorbent, multiwalled carbon nanotubes. These modified nanotubes packed into a solid‐phase extraction column are used for the selective extraction and preconcentration of ultra‐trace amounts of lead(II) from aqueous samples prior to electrothermal atomic absorption spectroscopy determination. The thiourea functional groups act as chelating agents for lead ions retaining them and so, give the selectivity to the sorbent. Elution of the retained ions can be performed using an acidic thiourea solution. The effects of experimental parameters including pH of the aqueous solution, type and amount of eluent, and the flow rates of sample and eluent solutions on the separation efficiency are investigated. The linear dependence of absorbance of lead on its concentration in the initial solution is in the range of 0.5–40.0 ng/mL with the detection limit of 0.13 ng/mL (3sb/m, n = 10). The proposed method is applicable to the analysis of red lipstick, pine leaves, and water samples for their lead contents. 相似文献
Efficient charge separation and light absorption are crucial for solar energy conversion over solid photocatalysts. This paper describes the construction of Pt@TiO2@In2O3@MnOx mesoporous hollow spheres (PTIM‐MSs) for highly efficient photocatalytic oxidation. TiO2–In2O3 double‐layered shells were selectively decorated with Pt nanoparticles and MnOx on the inner and outer surfaces, respectively. The spatially separated cocatalysts drive electrons and holes near the surface to flow in opposite directions, while the thin heterogeneous shell separates the charges generated in the bulk phase. The synergy between the thin heterojunctions and the spatially separated cocatalysts can simultaneously reduce bulk and surface/subsurface recombination. In2O3 also serves as a sensitizer to enhance light absorption. The PTIM‐MSs exhibit high photocatalytic activity for both water and alcohol oxidation. 相似文献
A procedure for zinc flotation separation from fresh water prior to its determination by atomic absorption spectrometry (AAS) has been developed. Hexamethyleneammonium hexamethylenedithiocarbamate (HMA-HMDTC) added to the first precipitate collector of hydrated Fe(III) oxide (Fe2O3· xH2O) gives the second precipitate collector of Fe(HMDTC)3. After addition of a surfactant, the precipitate of collectors is separated from the water phase by a stream of air bubbles, dissolved by strong acid and the solution then tested by AAS. The experimental parameters (amount of collector used, pH, ionic strength, type of foaming reagent, ζ potential, induction time etc.) affecting the flotation efficiency were optimized. At a pH of 6, Zn is separated quantitatively (98.5%) by addition of 5 mg Fe(III) and 3 mL 0.1 mol/L HMA-HMDTC to the sample. Results are compared with those obtained by ammonium tetramethylenedithiocarbamate. 相似文献
RP‐HPLC coupled with fluorescence detection for separation of carbon nanoparticles (CNP) synthesized with microwave‐assisted pyrolysis of citric acid and 1,2‐ethylenediamine is presented. The influence of methanol content and pH of mobile phase on the separation of CNP has been investigated. Under optimal mobile phase and elution gradient conditions, the effect of mole ratio of amine to carboxylic groups (NH2/COOH) in the initial reagents on CNP product is studied. At NH2/COOH = 0.67, the strongest fluorescence CNP sample is obtained. The separated CNP fractions are collected and further characterized by UV‐visible absorption and photoluminescence (PL) spectroscopy, CE, transmission electron microscopy (TEM), and MALDI‐TOF MS. The absorption and PL emission bands of the fractions are bathochromatically shifted with the elution order of CNP on RP‐HPLC. The TEM images prove that CNP are eluted from the smallest to the largest. The MS data show that CNP undergo fragmentations, closely relating to their surface‐attached carboxylic acid and amide/amine moieties. This work highlights the merit of RP‐HPLC coupled with fluorescence detection, TEM, and MS for isolation and characterization of individual CNP species present in a CNP sample. 相似文献
An analytical method for the simultaneous determination of 13 mycotoxins in feed by magnetic dispersive solid‐phase extraction combined with ultra‐high performance liquid chromatography and tandem mass spectrometry was developed. The samples were extracted with acetonitrile/water (80:20, v/v, containing 3% acetic acid), and separated by centrifugation after salting‐out, and then treated with magnetic adsorbents to remove interferences. The separation of target mycotoxins was performed on an ACQUITY UPLC HSS T3 column using a mobile phase consisting of 1 mmol/L ammonium acetate with 0.1% formic acid and methanol by gradient elution. Good linearities for the 13 mycotoxins were achieved with correlation coefficients over 0.99, and the recoveries of mycotoxins were in the range of 89.3–112.6% at spiking at levels of 5, 20, and 100 μg/kg, with relative standard deviations of 0.9–10.4%. Based on the functional magnetic materials (MDN@Fe3O4, PSA@Fe3O4, ZrO2@Fe3O4) applied in dispersive solid‐phase extraction, the pretreatment process is more convenient and it is beneficial to reduce the experimental cost by reusing the recycled magnetic materials. It is a simple, rapid, and environmentally friendly analytical method for the determination of mycotoxins in feed. 相似文献
A highly efficient Z‐scheme photocatalytic system constructed with 1D CdS and 2D CoS2 exhibited high photocatalytic hydrogen‐evolution activity of 5.54 mmol h?1 g?1 with an apparent quantum efficiency of 10.2 % at 420 nm. More importantly, its interfacial charge migration pathway was unraveled: The electrons are efficiently transferred from CdS to CoS2 through a transition atomic layer connected by Co–S5.8 coordination, thus resulting in more photogenerated carriers participating in surface reactions. Furthermore, the charge‐trapping and charge‐transfer processes were investigated by transient absorption spectroscopy, which gave an estimated charge‐separation yield of approximately 91.5 % and a charge‐separated‐state lifetime of approximately (5.2±0.5) ns in CdS/CoS2. This study elucidates the key role of interfacial atomic layers in heterojunctions and will facilitate the development of more efficient Z‐scheme photocatalytic systems. 相似文献