Rapid measurements of concentrations of natural uranium in process stream samples via gamma spectrometry at an extraction facility

A new application of gamma spectrometry in the efficient measurement of natural uranium in the process stream at an extraction plant is described here. The inherent nuclear properties of uranium viz. emanation of characteristic gamma rays (185.7 keV) has been exploited for the determination of concentrations ranging from 5 to 450 g l⁻¹ by passive photon counting of 185.7 keV gamma rays from ²³⁵U isotope for a maximum of 3-10 min per sample. This technique is totally matrix independent unlike other instrumental analytical techniques like wavelength dispersive X-ray fluorescence spectrometry and UV-vis spectrophotometry. Solution samples of aqueous and organic phase can be directly counted without the requirement of sample preparation. A MINIM-based gamma spectrometer consisting of a multichannel pulse height analyzer and a 3 in. × 3 in. well-type NaI(Tl) scintillation detector with an approximately 2 in. thick lead shield has been employed for the measurements. The results are compared with those obtained by potentiometry and wavelength dispersive X-ray fluorescence spectrometry (WD-XRF). Relative standard deviation of 1-5% has been obtained depending upon the concentration of uranium, which is more than adequate for routine process control samples. This paper also discusses in detail the problems associated with the determination of high concentrations of uranium in using 63 and 93 keV gamma rays emanating from ²³⁴Th (t_1/2 24 days) the immediate daughter of ²³⁸U isotope in samples that have attained secular equilibrium and the limitations of these energies in the routine analysis of freshly extracted uranium.     

Recent results of synchrotron radiation induced total reflection X-ray fluorescence analysis at HASYLAB,beamline L

At the Hamburger Synchrotronstrahlungslabor (HASYLAB), Beamline L, a vacuum chamber for synchrotron radiation-induced total reflection X-ray fluorescence analysis, is now available which can easily be installed using the adjustment components for microanalysis present at this beamline. The detector is now in the final version of a Vortex silicon drift detector with 50-mm² active area from Radiant Detector Technologies. With the Ni/C multilayer monochromator set to 17 keV extrapolated detection limits of 8 fg were obtained using the 50-mm² silicon drift detector with 1000 s live time on a sample containing 100 pg of Ni.Various applications are presented, especially of samples which are available in very small amounts: As synchrotron radiation-induced total reflection X-ray fluorescence analysis is much more sensitive than tube-excited total reflection X-ray fluorescence analysis, the sampling time of aerosol samples can be diminished, resulting in a more precise time resolution of atmospheric events. Aerosols, directly sampled on Si reflectors in an impactor were investigated. A further application was the determination of contamination elements in a slurry of high-purity Al₂O₃. No digestion is required; the sample is pipetted and dried before analysis. A comparison with laboratory total reflection X-ray fluorescence analysis showed the higher sensitivity of synchrotron radiation-induced total reflection X-ray fluorescence analysis, more contamination elements could be detected. Using the Si-111 crystal monochromator also available at beamline L, XANES measurements to determine the chemical state were performed. This is only possible with lower sensitivity as the flux transmitted by the crystal monochromator is about a factor of 100 lower than that transmitted by the multilayer monochromator. Preliminary results of X-ray absorption near-edge structure measurements for As in xylem sap from cucumber plants fed with As(III) and As(V) are reported. Detection limits of 170 ng/l of As in xylem sap were achieved.     

(E, E)S, S′-bis(2-benzimidazolylmethyl) dithioglyoxime, synthesis and characterization of heterotrinuclear complexes of and determination of their metal contents by EDXRF analysis

A vicinal dioxime ligand with two 2-benzimidazolylmethyl groups, namely S, S′-bis(2-benzimidazolylmethyl) dithioglyoxine (H₂L) and its axially pyridine and 2,6-dimethyl pyridine bonded Co(III) complexes were prepared according to prior literature [Y. Gök, S.Z. Y?ld?z, Synth. React. Inorg. Met-Org. Chem. 22 (9) (1992) 1327]. BF₂⁺ bridged Co(III) complexes have been synthesized via the hydrogen-bridged Co(III) complexes by using borontrifloride ethyl ether complex. Heterotrinuclear complexes have been prepared by the reaction of these more soluble BF₂-capped Co(III) complexes with stoichiometric amount of CdCl₂ · H₂O and NiCl₂ · 6H₂O salts. Using ¹H, ¹³C NMR, IR and MS spectral data and elemental analysis, the structures of the complexes were identified. Qualitative and quantitative determination of Co, Ni and Cd contents of the heterotrinuclear complexes have been investigated by energy dispersive X-ray fluorescence (EDXRF) method. An annular 50 mCi ²⁴¹Am radioactive source emitting 59.543 keV photons was used for excitation and Si(Li) detector having 157 eV FWHM at 5.9 keV was used for intensity measurements.     

Preconcentration sensitive determination of pyrethroid insecticides in environmental water samples with solid phase extraction with SiO2 microspheres cartridge prior to high performance liquid chromatography

Present study developed a new method for the sensitive determination of pyrethroid insecticides with solid phase extraction in combination with high performance liquid chromatography and UV detector. SiO₂ microspheres, a new SiO₂ based material, was investigated for the enrichment ability and applicability as the solid phase extraction sorbent. Four pyrethroid pesticides such as fenpropathrin, cyhalothrin, fenvalevate and biphenthrin were used as the target analytes. Parameters that maybe influence the extraction efficiency such as the eluent type and its volume, sample flow rate, sample pH, and the sample volume were optimized in detail, and the optimal conditions were as followed: sample volume, 100 mL; concentration of methanol, 30%; acetone volume, 5 mL; sample flow rate, 4.2 mL min⁻¹; sample pH, 7. The experimental results indicated that there was good linearity in the concentration range of 0.1–50 μg L⁻¹ except biphenthrin in the range of 0.05–25 μg L⁻¹. The detection limits for fenpropathrin, cyhalothrin, fenvalevate and biphenthrin were in the range of 0.02–0.08 μg L⁻¹. The intra-day and day to day precisions (RSDs, n = 6) were in the ranges of 2.6–4.4% and 5.3–7.2%, respectively. The method was validated with five real environmental water samples, and all these results proved that proposed method could be used as a good alternative for the routine analysis for such pollutants in environmental samples.     

Adsorption studies of Cd(II) onto Al2O3/Nb2O5 mixed oxide dispersed on silica matrix and its on-line preconcentration and determination by flame atomic absorption spectrometry

The present study describes the adsorption characteristic of Cd(II) onto Nb₂O₅/Al₂O₃ mixed oxide dispersed on silica matrix. The characterization of the adsorbent has been carried out by infrared spectroscopy (IR), scanning electronic microscopy (SEM), energy dispersive spectroscopy (EDS), energy dispersive X-ray fluorescence analysis (EDXRF) and specific surface area (S_BET). From batch experiments, adsorption kinetic of Cd(II) was described by a pseudo-second-order kinetic model. The Langmuir linear isotherm fitted to the experimental adsorption isotherm very well, and the maximum adsorption capacity was found to be 17.88 mg g⁻¹. Using the effective material, a method for Cd(II) preconcentration at trace level was developed. The method was based on on-line adsorption of Cd(II) onto SiO₂/Al₂O₃/Nb₂O₅ at pH 8.64, in which the quantitative desorption occurs with 1.0 mol L⁻¹ hydrochloric acid towards FAAS detector. The experimental parameters related to the system were studied by means of multivariate analysis, using 2⁴ full factorial design and Doehlert matrix. The effect of SO₄²⁻, Cu²⁺, Zn²⁺ and Ni²⁺ foreign ions showed no interference at 1:100 analyte:interferent proportion. Under the most favorable experimental conditions, the preconcentration system provided a preconcentration factor of 18.4 times, consumption index of 1.08 mL, sample throughput of 14 h⁻¹, concentration efficiency of 4.35 min⁻¹, linear range from 5.0 up to 35.0 μg L⁻¹ and limits of detection and quantification of 0.19 and 0.65 μg L⁻¹ respectively. The feasibility of the proposed method for Cd(II) determination was assessed by analysis of water samples, cigarette sample and certified reference materials TORT-2 (Lobster hepatopancreas) and DOLT-4 (Dogfish liver).     

Methylmercury determination using a hyphenated high performance liquid chromatography ultraviolet cold vapor multipath atomic absorption spectrometry system

The present work investigates the use of a multipath cell atomic absorption mercury detector for mercury speciation analysis in a hyphenated high performance liquid chromatography assembly. The multipath absorption cell multiplies the optical path while energy losses are compensated by a very intense primary source. Zeeman-effect background correction compensates for non-specific absorption. For the separation step, the mobile phase consisted in a 0.010% m/v mercaptoethanol solution in 5% methanol (pH = 5), a C₁₈ column was used as stationary phase, and post column treatment was performed by UV irradiation (60 °C, 13 W). The eluate was then merged with 3 mol L^− 1 HCl, reduction was performed by a NaBH₄ solution, and the Hg vapor formed was separated at the gas–liquid separator and carried through a desiccant membrane to the detector. The detector was easily attached to the system, since an external gas flow to the gas–liquid separator was provided. A multivariate approach was used to optimize the procedure and peak area was used for measurement. Instrumental limits of detection of 0.05 µg L^− 1 were obtained for ionic (Hg²⁺) and HgCH₃⁺, for an injection volume of 200 µL. The multipath atomic absorption spectrometer proved to be a competitive mercury detector in hyphenated systems in relation to the most commonly used atomic fluorescence and inductively coupled plasma mass spectrometric detectors. Preliminary application studies were performed for the determination of methyl mercury in sediments.     

Determination of itopride hydrochloride by high-performance liquid chromatography with Ru(bpy)3 electrogenerated chemiluminescence detection

In this work, a stable electrogenerated chemiluminescence (ECL) detector was developed. The detector was prepared by packing cation-exchanged resin particles in a glass tube, followed by inserting Pt wires (working electrode) in this tube and sealing. The leakage of Ru(bpy)₃²⁺ can be compensated by adding a small amount of Ru(bpy)₃²⁺ into solution phase. Coupled with high-performance liquid chromatography separation, the detector has been used for determination of itopride hydrochloride in human serum. Under the optimal conditions, the ECL intensity has a linear relationship with the concentration of itopride hydrochloride in the range of 1.0 × 10⁻⁸ g mL⁻¹ to 1.0 × 10⁻⁶ g mL⁻¹ and the detection limit was 3 × 10⁻⁹ g mL⁻¹ (S/N = 3). The as-prepared ECL detector displayed good sensitivity and stability.     

On-line electrochemical preconcentration and flame atomic absorption spectrometric determination of manganese in urine samples

A sensitive and selective method was developed for the determination of traces of manganese in urine using on-line electrochemical preconcentration followed by flame atomic absorption spectrometry detection. A home made flow-through polypropylene cell (4.5 cm long × 0.8 cm diameter filled with glass marbles) with an effective inner volume of 0.5 ml containing a working and a counter electrode, both of glassy carbon and a Pt pseudo reference electrode was located in a flow injection manifold specially designed for the purpose of this work. The manganese was deposited from buffer solution of NH₃/NH₄Cl at pH 9.00 through an oxidizing process at a current of 400 mA during 7 min. A flow of HCl 0.1 mol l⁻¹ at 4 ml min⁻¹ through the cell, chemically dissolved the deposit. A small portion (15 μl) of the concentrate was introduced in a continuously flowing system by means of a timing device and was then carried to the detector for the manganese quantification. All electrochemical and spectroscopic variables as well as possible interferences in both systems were systematically studied. The relative standard deviations for ten consecutive measurements of manganese solutions of 2.0 and 20 μg l⁻¹ were of 2.3 and 1.5%, respectively, while for a sample processed five times was less then 5%. The accuracy of the developed procedure was evaluated by adding known amounts of manganese standard to urine samples and following the whole procedure. Recoveries within the range 97.2-102.8% were obtained. To further prove the accuracy, a Seronorm Trace Elements in Urine, Batch 403125 sample with a reported concentration of 13 μg Mn l⁻¹ was also analyzed. The experimental value obtained was of 12.7 ± 0.1 μg l⁻¹, which does not differ significantly from the reported amount (p < 0.05). A preconcentration factor of 40, a linear range between 0.015 and 60 μg l⁻¹ and a limit of detection of 15 ng l⁻¹ permitted the determination of manganese in real urine samples from non-exposed subjects in the range 0.5-2.8 μg l⁻¹.     

Flow-through optosensing of 1-naphthaleneacetic acid in water and apples by heavy atom induced-room temperature phosphorescence measurements

A sensitive and selective phosphorimetric method for the determination of 1-naphthaleneacetic acid (1-NAA) based on a flow-injection system connected to a flow cell packed with a solid support and placed in the sample compartment of a conventional luminescence spectrometer is described. A non-ionic solid polymeric resin Amberlite XAD-7 is used for the packing. After injection of the sample, 1-NAA is on-line retained in the packed resin and measurements of the heavy atom induced (HAI)-room temperature phosphorescence (RTP) emission (λ_ex/λ_em = 292/490 nm) from this native luminescent compound are taken.The optimum experimental conditions were investigated by injecting 2 ml samples of an aqueous solution of 1-NAA in the flow system. A concentration 0.15 mol l⁻¹ of thallium(I) ions, as heavy atom, both in the samples and the carrier flow, was finally selected. Also, a concentration of 6 mmol l⁻¹ of sulphite was optimal for ensuring the necessary deoxygenation of the system at the selected flow rate of 0.8 ml min⁻¹. After measurement, the solid support was efficiently regenerated by injecting 1 ml of a mixture water:acetone in a ratio 1:1 (v/v) into the flow.The detection limit (3σ criterion) was 1.2 ng ml⁻¹ of 1-NAA. The repeatability (R.S.D.) for five replicates of a sample containing 50 ng ml⁻¹ of analyte turned out to be ±3% and the calibration graphs proved to be linear up to 500 ng ml⁻¹ of 1-NAA (maximum concentration assayed). The effect of potential interferences from other organic species which can be also used as plant growth regulators, as well as from various inorganic cations and anions, has been investigated as well.The method was successfully applied to the determination of low levels of this plant growth regulator in natural waters (river and fountain waters) and apples.     

The viscosity of the binary vapor mixture methanol-triethylamine at low densities and in the saturated vapor phase of the vapor-liquid equilibrium

For the first time, results of precision measurements of the viscosity coefficient of the binary vapor mixture methanol-triethylamine at low densities are reported. The relative measurements with an all-quartz oscillating-disk viscometer were carried out for nearly equimolar mixtures along five isochores at densities from 0.010 to 0.033 mol dm⁻³ as well as for a mixture of the mole fraction y_meth = 0.3322 at a density 0.016 mol dm⁻³ in the temperature range between 298 and 498 K. The uncertainty is estimated to be ±0.2% at ambient temperature, increasing to ±0.3% at higher temperatures. Isothermal values of a mixture with the averaged mole fraction y_meth = 0.5002 were recalculated from the original experimental data and evaluated with a first-order expansion for the viscosity, in terms of density. A so-called individual correlation on the basis of the extended theorem of corresponding states was employed to describe the interaction viscosity in the limit of zero density. Some data points at low temperatures had to be excluded from this calculation, since the measurements were performed in the saturated vapor phase. For these data points the vapor-liquid equilibrium had to be evaluated to assign the correct mole fraction in the vapor to the measured viscosity.     

Modified mesoporous silica materials for on-line separation and preconcentration of hexavalent chromium using a microcolumn coupled with flame atomic absorption spectrometry

A modified SBA-15 mesoporous silica material NH₂-SBA-15 was synthesized successfully by grafting γ-aminopropyl-triethoxysilane. The material was characterized using transmission electron microscopy (TEM) and Fourier transform infrared/Raman (FT-IR/Raman) spectroscopy, and used for the first time in a flow injection on-line solid phase extraction (SPE) coupled with flame atomic absorption spectrometry (FAAS) to detect trace Cr (VI). Effective sorption of Cr (VI) was achieved at pH 2.0 with no interference from Cr (III) and other ions and 0.5 mol L⁻¹ NH₃·H₂O solution was found optimal for the complete elution of Cr (VI). An enrichment factor of 44 and was achieved under optimized experimental conditions at a sample loading of 2.0 mL min⁻¹ sample loading (300 s) and an elution flow rate of 2.0 mL min⁻¹ (24 s). The precision of the 11 replicate Cr (VI) measurements was 2.1% at the 100 μg L⁻¹ level with a detection limit of 0.2 μg L⁻¹ (3 s, n = 10) using the FAAS. The developed method was successfully applied to trace chromium determination in waste water. The accuracy was validated using a certified reference material of riverine water (GBW08607).     

Submicron hard X-ray fluorescence imaging of synthetic elements

Synchrotron-based X-ray fluorescence microscopy (XFM) using hard X-rays focused into sub-micron spots is a powerful technique for elemental quantification and mapping, as well as microspectroscopic measurements such as μ-XANES (X-ray absorption near edge structure). We have used XFM to image and simultaneously quantify the transuranic element plutonium at the L₃ or L₂-edge as well as Th and lighter biologically essential elements in individual rat pheochromocytoma (PC12) cells after exposure to the long-lived plutonium isotope ²⁴²Pu. Elemental maps demonstrate that plutonium localizes principally in the cytoplasm of the cells and avoids the cell nucleus, which is marked by the highest concentrations of phosphorus and zinc, under the conditions of our experiments. The minimum detection limit under typical acquisition conditions with an incident X-ray energy of 18 keV for an average 202 μm² cell is 1.4 fg Pu or 2.9 × 10⁻²⁰ moles Pu μm⁻², which is similar to the detection limit of K-edge XFM of transition metals at 10 keV. Copper electron microscopy grids were used to avoid interference from gold X-ray emissions, but traces of strontium present in naturally occurring calcium can still interfere with plutonium detection using its L_α X-ray emission.     

Automated stopped-in-dual-loop flow analysis system for catalytic determination of vanadium in drinking water

An automated stopped-in-dual-loop flow analysis (SIDL-FA) system is proposed for the determination of vanadium in drinking water. The chemistry is based on the vanadium-catalyzed oxidation reaction of p-anisidine by bromate in the presence of Tiron as an activator to produce a dye (λ_max = 510 nm). A SIDL-FA system basically consists of a selection valve, three pumps (one is for delivering of standard/sample, and others are for reagents), two six-way injection valves, a spectrophotometric detector and a data acquisition device. A 100-μL coiled loop around a heated device is fitted onto each six-way injection valve. A well-mixed solution containing reagents and standard/sample is loaded into the first loop on a six-way valve, and then the same solution is loaded into the second loop on another six-way valve. The solutions are isolated by switching these two six-way valves, so that the catalytic reaction can be promoted. The net waste can be zero in this stage, because all pumps are turned off. Then each resulting solution is dispensed to the detector with suitable time lag. A touchscreen controller is developed to automatically carry out the original SIDL-FA protocol. The proposed SIDL-FA method allows vanadium to be quantified in the range of 0.1-2 μg L⁻¹ and is applied to the determination of vanadium in drinking water samples.     

A novel solid-state electrochemiluminescence detector for capillary electrophoresis based on tris(2,2'-bipyridyl)ruthenium(II) immobilized in Nafion/PTC-NH2 composite film

A new electrochemiluminescence (ECL) detector for capillary electrophoresis (CE) based on tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) immobilized in Nafion/PTC-NH₂ (an ammonolysis product of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA)) composite film was presented for the first time. The Nafion/PTC-NH₂ composite film could effectively immobilize tris(2,2′-bipyridyl)ruthenium(II) via ion-exchange and electrostatic interaction. Cyclic voltammetric and ECL behavior of Nafion/PTC-NH₂/Ru composite film was investigated compared to Nafion/Ru composite. The Nafion/PTC-NH₂/Ru composite film exhibited good ECL stability and simple operability. Then the CE with solid-state ECL detector system was successfully used to detect sophora - a quinolizidine type - alkaloids as sophoridine (SR) and matrine (MT). The CE-ECL parameters that affected separation and detection were optimized. Under the optimized conditions, the linear range was from 2.5 × 10⁻⁸ to 2 × 10⁻⁶ mol/L for SR, 1.0 × 10⁻⁸ to 1.0 × 10⁻⁶ mol/L for MT. The detection limit (S/N = 3) was estimated to be 5 × 10⁻⁹ and 10⁻⁹ mol/L for SR and MT, respectively. It was shown that the CE coupling with solid-state ECL detector system exhibited satisfying sensitivity of analysis.     

Simultaneous determination of CFC-11, CFC-12 and CFC-113 in seawater samples using a purge and trap gas-chromatographic system

We have optimized the analytical parameters of a homemade instrument for the simultaneous measurement of the chlorofluorocarbons CCl₂F₂ (CFC-12), CCl₃F (CFC-11) and C₂Cl₃F₃ (CFC-113) in seawater. Seawater samples are flame sealed into 60 ml glass ampoules avoiding any contact with the atmosphere and stored in cold, dark condition until analysis. In the laboratory, after cracking the ampoule in an enclosed chamber filled with ultra-pure nitrogen, the seawater sample is transferred to a stripping chamber, where ultra-pure nitrogen is used to purge the dissolved CFCs from the seawater. The extracted gases are then cryogenically trapped, subsequently the trap is isolated and heated and the CFCs are transferred by a carrier gas stream into a precolumn and then are separated on a gaschromatographic packed column. To separate adequately CFC-12 from N₂O, during the early part of the chromatographic run, the gas stream passes through a molecular sieve, which is then isolated and backflushed. The CFCs are detected on an electron capture detector (⁶³Ni ECD). After a careful choice of the experimental conditions, the performances of the system were evaluated. The detection limits for seawater samples are: 0.0081 pmol kg⁻¹ for CFC-12, 0.0073 pmol kg⁻¹ for CFC-11 and 0.0043 pmol kg⁻¹ for CFC-113. The reproducibility of replicate samples lies within 5% for the three CFCs. The system has been successfully employed for CFC measurements in seawater samples collected in the Ross Sea (Antarctica) in the framework of the Italian Antarctic research project.     

Novel reductive–reductive mode electrochemical detection of Rohypnol following liquid chromatography and its determination in coffee

Rohypnol (flunitrazepam) has been successfully determined in coffee by high performance liquid chromatography dual electrode detection (LC-DED) in the dual reductive mode. Initial studies were performed to optimise the chromatographic conditions and these were found to be 50% acetonitrile, 50% 50 mM pH 2.0 phosphate buffer at a flow rate of 0.75 mL min⁻¹, employing a Hypersil C₁₈, 5 μm, 250 mm × 4.6 mm column. Cyclic voltammetric studies were made to ascertain the redox behaviour of Rohypnol at a glassy carbon electrode over the pH range 2–12. Hydrodynamic voltammetry was used to optimise the applied potential at the generator and detector cells; these were identified to be −2.4 V and +0.8 V for the redox mode and −2.4 V and −0.1 V for the dual reductive mode respectively. A linear range of 0.5–100 μg mL⁻¹, with a detection limit of 20 ng mL⁻¹ was obtained for the dual reductive mode. Further studies were then performed to identify the optimum conditions required for the LC-DED determination of Rohypnol in beverage samples. A convenient and rapid method for the determination of Rohypnol in beverage samples was developed using a simple sample pre-treatment procedure. A recovery of 95.5% was achieved for a sample of white coffee fortified at 9.6 μg mL⁻¹ Rohypnol.     

New method for the quantification of dequalinium cations in pharmaceutical samples by absorption and fluorescence diode array thin-layer chromatography

A diode array HPTLC method for dequalinium chloride in pharmaceutical preparations is presented. For separation a Nano TLC silica gel plate (Merck) is used with the mobile phase methanol—7.8% aqueous NH₄⁺CH₃COO⁻ (17:3, v/v) over a distance of 6 cm. Dequalinium chloride shows an R_F value of 0.58. Pure dequalinium chloride is measured in the wavelength range from 200 to 500 nm and shows several by-products, contour plot visualized in absorption, fluorescence and using the Kubelka–Munk transformation. Scanning of a single track in absorption and fluorescence measuring 600 spectra in the range from 200 to 1100 nm takes 30 s. As a sample pre-treatment of an ointment it is simply dissolved in methanol and can be quantified in absorption from 315 to 340 nm. The same separation can also be quantified using fluorescence spectrometry in the range from 355 to 370 nm. A new staining method for dequalinium chloride, using sodium tetraphenyl borate/HCl in water allows a fluorescence quantification in the range from 445 to 485 nm. The linearity range of absorption and fluorescence measurements is from 10 to 2000 ng. Sugar-containing preparations like liquids or lozenges with a reduced sample pre-treatment can be reliably quantified only in fluorescence. The total for the quantification of an ointment sample (measuring four standards and five samples), including all sample pre-treatment steps takes less than 45 min!     

Layer-by-layer self-assembly of polyelectrolyte complexes and their multilayer films for pervaporation dehydration of isopropanol

Two negatively charged polyelectrolyte complex colloidal nanoparticles (PEC⁻) and one positively charged nanoparticle (PEC⁺) were prepared and used as novel layer-by-layer (LbL) building blocks. These PEC nanoparticles include poly(2-methacryloyloxy ethyl trimethylammonium chloride)/sodium carboxymethyl cellulose (PDMC/CMCNa PEC⁻), poly(diallyldimethylammonium chloride)/CMCNa (PDDA/CMCNa PEC⁻) and PDDA/poly(sodium-p-styrenesulfonate) (PDDA/PSS PEC⁺). LbL multilayer films based on (PEC⁺/PEC⁻) were constructed on both quartz slides and modified polyamide (MPA) reverse osmosis support membranes. UV–vis spectroscopy, quartz crystal microbalance (QCM), field emission scanning microscopy (FESEM) and atomic force microscopy (AFM) were utilized to follow the thickness growth and morphology evolution of these multilayer films with increasing bi-layer numbers. LbL multilayer films deposited on MPA support membranes were subjected to pervaporation dehydration of 10 wt% water–isopropanol and effect of bi-layer numbers and feed temperature on pervaporation performance was studied. Generally, PEC⁺/PEC⁻ can be LbL self-assembled successfully on both substrates with a thickness growth rate ca. 200 nm/bi-layer. Moreover, PEC⁺/PEC⁻ multilayer films show high pervaporation performance with film thickness up to several micrometers. For example, performance of the multilayer films in dehydrating 10 wt% water–isopropanol at 50 °C is J = 1.18 kg/m² h, α = 1013 for (PEC⁺/PDMC-CMCNa PEC⁻)₂₄ and J = 1.36 kg/m² h, α = 938 for (PEC⁺/PDMC-CMCNa PEC⁻)₂₅, respectively.     

The ionic conductivity and local environment of cations in Bi9ReO17

The influence of temperature on the structure of Bi₉ReO₁₇ has been investigated using differential thermal analysis, variable temperature X-ray diffraction and neutron powder diffraction. The material undergoes an order-disorder transition at ∼1000 K on heating, to form a fluorite-related phase. The local environments of the cations in fully ordered Bi₉ReO₁₇ have been investigated by Bi L_III- and Re L_III-edge extended X-ray absorption fine structure (EXAFS) measurements to complement the neutron powder diffraction information. Whereas rhenium displays regular tetrahedral coordination, all bismuth sites show coordination geometries which reflect the importance of a stereochemically active lone pair of electrons. Because of the wide range of Bi-O distances, EXAFS data are similar to those observed for disordered structures, and are dominated by the shorter Bi-O bonds. Ionic conductivity measurements indicate that ordered Bi₉ReO₁₇ exhibits reasonably high oxide ion conductivity, corresponding to 2.9×10⁻⁵ Ω⁻¹ cm^-1 at 673 K, whereas the disordered form shows higher oxide ion conductivity (9.1×10⁻⁴ Ω⁻¹ cm⁻¹ at 673 K).     

Energy resolved X-ray fluorescence imaging based on a micropattern gas detector

A simple system for energy resolved X-ray fluorescence imaging using a room temperature, 2-D sensitive Micro-Hole and Strip Plate (MHSP) operating in pure xenon is proposed. The Micro-Hole and Strip Plate is an electron multiplier with two stages of avalanche production, one of them in the holes and another one in the anode strips. The X-ray interaction via photoelectron absorption in the xenon produces a number of electrons proportional to the incoming X-ray energy. The electron cloud is, then, amplified in the two amplification stages, resulting in a charge pulse that is also proportional to the detected X-ray energy. The 2-D capability is achieved in the Micro-Hole and Strip Plate by using two orthogonal resistive lines, one connecting the anode strips on the bottom face of the Micro-Hole and Strip Plate and the other one connecting the strips structured on the Micro-Hole and Strip Plate top surface. This low cost detector has an active area of 28 × 28 mm², an intrinsic position resolution of σ∼ 125 µm, an energy resolution of about 825 eV (Full Width at Half Maximum) at 5.9 keV and a count rate capability as high as 0.5 MHz. Fluorescence images were obtained by irradiating the sample with X-rays and using a pinhole placed between the sample and the detector window. Elemental map discrimination for different samples, image amplification and detector parameters, are presented.