Hydrogen bonded NHO chains formed by chloranilic acid (CLA) with 4,4′-di-t-butyl-2,2′-bipyridyl (dtBBP) in the solid state

In crystalline state 2,5-dichloro-3,6-dihydroxy-p-benzoquinone (chloranilic acid, CLA) forms with 4,4′-di-t-butyl-2,2′-bipyridyl (dtBBP) the hydrogen bonded chains along the b-axis. From one side of the CLA molecule the proton transfer takes place and the hydrogen bond length is very short (2.615 Å). A continuous infrared absorption is observed for dtBBP·CLA in the wavenumber range between 3100 and 800 cm⁻¹ also indicating the strong hydrogen bonds. The DSC measurements show a weak, close to continuous, phase transition at 414 K. The complex dielectric permittivity for a single crystal sample was measured in the temperature range 100-440 K and at frequencies between 200 Hz and 2 MHz. The dielectric response is a combination of semiconducting properties and a relaxation process most probably connected with the proton dynamics in the hydrogen bonds. The mechanism of the structural phase transition is discussed.     

Structurally-driven metal-insulator transition in Ca2Ru1−xCrxO4 (0≤x<0.14): A single crystal X-ray diffraction study

Correlation between structure and transport properties are investigated in high-quality single-crystals of Ca₂Ru_1−xCr_xO₄ with 0<x<0.14 using single crystal X-ray diffraction and by electronic studies. The parent compound was known to exhibit an intriguing first-order structurally driven metal-insulator (MI) transition at 357 K. Upon chromium doping on the ruthenium site, the metal-insulator transition temperature (T_MI) was drastically reduced, and is related to the competition between structural changes that occur upon Cr doping and with decreasing temperature. A strong suppression of structural distortions with increasing Cr substitution was identified. No clear T_MI can be observed when x>13.5% and the system behaves as an insulator. Such a large, sharp metal-insulator transition and tuneable transition temperature may have potential applications in electronic devices.     

Improvement of microwave-assisted digestion of milk powder with diluted nitric acid using oxygen as auxiliary reagent

The feasibility of using diluted HNO₃ solutions under oxygen pressure for decomposition of whole and non-fat milk powders and whey powder samples has been evaluated. Digestion efficiency was evaluated by determining the carbon content in solution (digests) and the determination of Ca, Cd, Cu, Fe, K, Mg, Mn, Mo, Na, Pb and Zn was performed by inductively coupled plasma optical emission spectrometry and Hg by chemical vapor generation coupled to inductively coupled plasma mass spectrometry. Samples (up to 500 mg) were digested using HNO₃ solutions (1 to 14 mol L^− 1) and the effect of oxygen pressure was evaluated between 2.5 and 20 bar. It was possible to perform the digestion of 500 mg of milk powder using 2 mol L^− 1 HNO₃ with oxygen pressure ranging from 7.5 to 20 bar with resultant carbon content in digests lower than 1700 mg L^− 1. Using optimized conditions, less than 0.86 mL of concentrated nitric acid (14 mol L^− 1) was enough to digest 500 mg of sample. The accuracy was evaluated by determination of metal concentrations in certified reference materials, which presented an agreement better than 95% (Student's t test, P < 0.05) for all the analytes.     

Characterisation and ac-electrical investigation of sublimated bis(dimethylglyoximato)palladium(II) thin films

Thin films of bis(dimethylglyoximato)palladium(II) complex of polycrystalline structure were prepared by sublimation in a vacuum at 140 °C, on glass and p-Si substrates. The films were characterised by spectral optical absorption, energy dispersion X-ray fluorescence (EDXRF), and X-ray diffraction (XRD) methods. After characterisation, metal-insulator (complex)-semiconductor MIS devices were fabricated to measure the frequency dependence of ac-conductivity in a range of 5-100 kHz. Data of ac-measurements follow the correlated barrier-hopping CBH model, from which one of the fundamental absorption peaks, the minimum hopping distance, and other parameters of the CBH model were determined, connecting and relating the optical, structural, and electrical measurements. The dielectric properties of the complex were studied through Debye model, from which the relaxation time for the dipoles (2.45 × 10⁻⁶ s) and the molecular dipole moment (3.63 × 10⁻³⁰ C m ) were determined.     

Oxygen nonstoichiometry and the thermodynamic properties of manganites Ca1 ? x ? ySrxLayMnO3 ? δ

The content of oxygen in Ca_{0.6 − y} Sr_0.4La _y MnO_{3 − δ}, where y = 0 and 0.05, was determined by coulometric titration over the temperature range 650–950°C at oxygen partial pressure in the gas phase varied from 10⁻⁴ to 1 atm. The results were used to calculate the partial molar enthalpy, Δ$ \bar H $ \bar H _O(δ), and entropy, Δ$ \bar S $ \bar S _O(δ), of oxygen in manganites. Changes in the Δ$ \bar H $ \bar H _O(δ) and Δ$ \bar S $ \bar S _O(δ) dependences caused by the introduction of lanthanum are evidence of the formation of local clusters of the double perovskite type in the Ca_0.6Sr_0.4MnO_{3 − δ} matrix.     

Highly selective and sensitive copper membrane electrode based on a new synthesized Schiff base

Bis(2-hydroxyacetophenone)butane-2,3-dihydrazone (BHAB) was used as new N-N Schiffs base which plays the role of an excellent ion carrier in the construction of a Cu(II) membrane sensor. The best performance was obtained with a membrane composition of 30% poly(vinyl chloride), 55% o-nitrophenyloctyl ether (NPOE), 7% BHAB and 8% oleic acid (OA). This sensor shows very good selectivity and sensitivity towards copper ion over a wide variety of cations, including alkali, alkaline earth, transition and heavy metal ions. The effect of membrane composition and pH and influence of additive anionic on the response properties of electrode were investigated. The electrode exhibits a Nernstian behavior (with slope of 29.6 mV per decade) over a very wide concentration range (5.0 × 10⁻⁸ to 1.0 × 10⁻² mol L⁻¹) with a detection limit of 3.0 × 10⁻⁸ mol L⁻¹ (2.56 ng mL⁻¹). It shows relatively fast response time, in whole concentration range (<15 s), and can be used for at least 12 weeks in the pH range of 2.8-5.8. The proposed sensor was successfully used to determination of copper in different water samples and as indicator electrode in potentiometric titration of copper ion with EDTA.     

Thermoelectric properties of HPHT sintered In-doped Pb0.5Sn0.5Te

The thermoelectric properties of Pb_0.5Sn_0.5Te doped with In at 1.0, 2.0, and 3.0×10¹⁹/cm³ and sintered at a high pressure and high temperature (HPHT) of 4.0 GPa and 800 or 900 °C, respectively, have been studied. All samples show p-type semiconducting behavior with positive thermopower. We find that HPHT sintering of conventionally synthesized materials improves their thermoelectric properties. The highest power factor is obtained for In doping of 2.0×10¹⁹/cm³ with 13.5 μW/cm K² at 230 °C. The corresponding figure of merit is 1.43×10⁻³/K. This represents a twofold improvement in thermoelectric figure of merit, compared to the conventionally sintered materials reported in the literature. When exposed to 400 °C for 10 days, samples sintered at 900 °C exhibit more stable thermoelectric properties, while the properties of those sintered at 800 °C deteriorated. These results demonstrate that HPHT sintering is a viable and controllable way of tuning the thermoelectric properties of PbTe-based materials.     

High-temperature electron-hole transport in PrBaCo2O5+δ

The oxygen content, conductivity and thermopower in the double perovskite-like cobaltite PrBaCo₂O_5+δ are reported in the oxygen partial pressure range 2×10⁻⁶-0.21 atm and temperatures between 650 and 950 °C. The electrical properties are shown to be continuous through the transition from δ>0.5 to δ<0.5. The variations of transport parameters with temperature and oxygen content reveal hole polaron hopping conduction within oxygen non-stoichiometry domain δ<0.5.     

Microwave-assisted digestion of organoarsenic compounds for the determination of total arsenic in aqueous, biological, and sediment samples using flow injection hydride generation electrothermal atomic absorption spectrometry

A microwave assisted wet digestion method for organoarsenic compounds and subsequent determination of total arsenic in aqueous, biological and sediment samples by means of flow injection hydride generation electrothermal atomic absorption spectrometry (FI-HG-ETAAS) is described. Sodium persulfate, sodium fluoride and nitric acid serve as digestion reagents, which allow a quantitative transformation of organoarsenic compounds to hydride forming species in a commercial microwave sample preparation system. The maximum operating pressures of the applied tetrafluorometoxil (TFM) liners are 75 bar (high pressure vessels) and 30 bar (medium pressure vessels), corresponding to maximum solution temperatures of 300 and 260 °C. For the investigated samples, digestion temperatures of 210-230 °C (medium pressure vessels) and 240-280 °C (high pressure vessels) were obtained.In medium pressure vessels, arsenic recovery from aqueous testing solutions of dimethylarsinic acid (DMA), phenylarsonic acid (PAA) and tetraphenylarsonium chloride (TPA) at initial concentrations of 100 and 10 μg l⁻¹ is complete, even in the presence of an excess of organic carbon (potassium hydrogen phthalate, 2000 mg l⁻¹) or fatty acids (linolenic acid 70%; linoleic acid ≈20-25%; Oleic acid ≈3%, 900-4500 mg l⁻¹).Arsenic recovery from aqueous arsenobetaine (ASB) solutions with the same initial concentrations is also complete if high pressure vessels and a higher concentration of fluoride ions are used, whereas the addition of organic carbon (potassium hydrogen phthalate, 2000 mg l⁻¹, fatty acids, 900-4500 mg l⁻¹) leads to a decrease in arsenic recovery of about 2-5%. In all cases, residual carbon contents are close to the limit of detection for the applied analytical method (15 mg l⁻¹).Results of arsenic analysis in reference standard materials revealed a significant dependence on the material’s nature (sediment samples, plant materials and seafood samples). Sediment samples and plant materials show recoveries for arsenic around 100% after a single-step digestion in medium pressure TFM liners. Seafood (fish/lobster/mussel samples) usually require either the use of high pressure vessels or a second digestion step, if medium pressure vessels are used.     

Valence and origin of metal-insulator transition in Mn doped SrRuO3 studied by electrical transport, X-ray photoelectron spectroscopy and LSDA+U calculation

We have studied the valence and electronic properties of Mn doped SrRuO₃ using electrical transport measurement, X-ray photoelectron spectroscopy (XPS) and local (spin) density approximation plus Coulomb interaction strength calculation (LSDA+U). The resistivity data revealed that the system undergoes transition from metal to insulator at the critical Mn doping level, x∼0.2, which is accompanied by the structural transition from orthorhombic to tetragonal crystal symmetry. Besides, the significant reduction of the spectral weight at the coherent zone (0.8 eV) of the valence band is observed for x>0.2. The core XPS spectra suggest that both the transition elements exist in the mixed ionic pair, Ru⁺⁴/Ru⁺⁵↔Mn⁺³/Mn⁺⁴. The detail analysis of the results suggests that the Coulomb correlation effect in conjugation with localization of the charge carriers predominate over the mixed ionic pair effect and responsible for the metal-insulator transition in the series.     

Quantitative millimetre wavelength spectrometry at pressures approaching atmospheric: II. Determination of oxygen at atmospheric pressure

A millimetre wavelength (MMW) Fabry-Perot cavity spectrometer described in earlier work has been applied to the measurement of oxygen absorption at 60 GHz and atmospheric pressure in a gas matrix of nitrogen. The spectrometer has also been modified such that the MMW source is stabilised by a sub-harmonic microwave signal transmitted by an infrared carrier on a single mode telecommunications fibre optic. This is a step towards developing an instrument comprising minimal electronic components that can perform MMW spectrometry remotely. Oxygen determinations were achieved by monitoring the change in the quality factor (Q) of a resonant Fabry-Perot cavity due to the presence of an absorbing sample. The MMW absorption of the sample was determined by incrementing the frequency modulation (FM) deviation of the source frequency scanning the cavity resonance profile. The response curve of absorption signal versus fraction of oxygen in nitrogen was found to be linear throughout the working range of 1-100% O₂ (v/v) in N₂ with a slope of (1.407±0.007)×10⁻⁴ m⁻¹ (% O₂)⁻¹. The detection limit (3× standard deviation of the background) was found to be ∼0.8% (v/v). The MMW technique employed is advantageous since, unlike common MMW techniques, there is no vacuum requirement. Application of this method, to the monitoring of oxygen in gas mixtures of practical importance, is proposed. Values of the oxygen spectral absorption coefficients of lines between 55 and 60 GHz were measured at reduced pressure and found to be within ±2% of previous literature values. A pressure correction coefficient for O₂ absorption at 60 GHz in the 45-121 kPa range was obtained and found to be (1.354±0.014)×10⁻⁴ m⁻¹ kPa⁻¹.     

A fluorescent chemical sensor for Fe based on blocking of intramolecular proton transfer of a quinazolinone derivative

In this paper, 2-(2′-hydroxy-phenyl)-4(3H)-quinazolinone (HPQ), a typical compound that exhibits excited state intramolecular proton transfer (ESIPT) reaction and possesses good photophysical properties, is synthesized and used as fluoroionophore for Fe³⁺ sensitive optochemical sensor. The decrease of fluorescence intensity of HPQ membrane upon the addition of Fe³⁺ was attributed to the blocking of ESIPT reactions of HPQ and quenching its fluorescence. The effect of the composition of the sensing membrane was studied, and experimental conditions were optimized. The sensor shows a linear response toward Fe³⁺ in the concentration range of 7.1 × 10⁻⁷ M to 1.4 × 10⁻⁴ M with a limit of detection of 8.0 × 10⁻⁸ M, and a working pH range from 2.5 to 4.5. It shows excellent selectivity for Fe³⁺ over a large number of cations such as alkali, alkaline earth and transitional metal ions. The proposed sensor is applied to the determination of the content of iron ions in pharmaceutical preparations samples with satisfactory results.     

Determination of hormones in milk by hollow fiber-based stirring extraction bar liquid–liquid microextraction gas chromatography mass spectrometry

The hollow fiber-based stirring extraction bar liquid–liquid microextraction was applied to the extraction of hormones, including 17-α-ethinylestradiol, 17-α-estradiol, estriol, 17-β-estradiol, estrone, 17-α-hydroxyprogesterone, medroxyprogesterone, progesterone and norethisterone acetate, in milk. The present method has the advantages of both hollow fiber-liquid phase microextraction and stirring bar sorptive extraction. The stirring extraction bar was used as both the stirring bar of microextraction, and extractor of the analytes, which can make extraction, clean-up and concentration be carried out in one step. When the extraction was completed, the stirring extraction bar was easy isolated from the extraction system with the magnet. Several experimental parameters, including the type of extraction solvent, the number of hollow stirring extraction bar, extraction time, stirring speed, ionic strength, and desorption conditions were investigated and optimized. The analytes in the extract were derived and determined by gas chromatography mass spectrometry. Under optimal experimental conditions, good linearity was observed in the range of 0.20–20.00 ng mL⁻¹. The limits of detection and quantification were in the range of 0.02–0.06 ng mL⁻¹ and 0.07–0.19 ng mL⁻¹, respectively. The present method was applied to the analysis of milk samples, and the recoveries of analytes were in the range of 93.6–104.6% with the relative standard deviations ranging from 1.6% to 6.2% (n = 5). The results showed that the present method was a rapid and feasible method for the determination of hormones in milk samples.     

Effect of the pre-treatment of the samples on the natural substances extraction from Helianthus annuus L. using supercritical carbon dioxide

The extraction of bioactive compounds from sunflowers (Helianthus annuus L.) with supercritical carbon dioxide has been studied. The samples were treated in four different ways and the effects of two factors (pressure and temperature) were investigated at 100, 500 bar and 35, 50 °C. The best yields were obtained using a high temperature and a high pressure (50 °C and 500 bar). The dry samples produced better extraction yields than the moist samples. The bioactivities of the extracts were compared for the samples treated in different ways. The best activity profiles were obtained for the moist samples extracted at 35 °C and 500 bar.     

High pressure Raman scattering study on the phase stability of LuVO4

High pressure Raman spectroscopic investigations have been carried out on rare earth orthovanadate LuVO₄ upto 26 GPa. Changes in the Raman spectrum around 8 GPa across the reported zircon to scheelite transition are investigated in detail and compared with those observed in other vanadates. Co-existence of the zircon and scheelite phases is observed over a pressure range of about 8-13 GPa. The zircon to scheelite transition is irreversible upon pressure release. Subtle changes are observed in the Raman spectrum above 16 GPa which could be related to scheelite ↔ fergusonite transition. Pressure dependencies of the Raman active modes in the zircon and the scheelite phases are reported.     

Development of selective and chemically stable coating for stir bar sorptive extraction by molecularly imprinted technique

A novel stir bar coated with molecularly imprinted polymer (MIP) as selective extraction phase for sorptive extraction of triazine herbicides was developed. The stir bar was prepared by chemically bonding the MIP to the glass bar to improve its stability. A homogeneous and porous structure was observed on the stir bar surface. Extraction performance shows that the MIP-coated stir bar has stronger affinity to the template molecule terbuthylazine as compared with that of the reference stir bar without addition of template. Owning to the shape and structural compatibility, the obtained stir bar also demonstrated specific selectivity to the structural related-compounds of nine triazines, and thus can be applied to simultaneous determination of these compounds from complex samples coupled with high performance liquid chromatography. Four complex samples with different matrix, including rice, apple, lettuce and soil were used to evaluate this proposed method. The limits of detection obtained are in the range of 0.04-0.12 μg L⁻¹, and the recoveries for the spiked rice, apple, lettuce and soil samples were 80.8-107.7%, 80.6-107.8%, 72.0-109.8% and 89.0-114.8% with RSD from 1.2 to 7.9%, respectively. Moreover, this MIP-coated stir bar was firm, durable and can be prepared simply and reproducibly. The developed coating method would be useful to prepare a range of selective stir bars in order to extend the applicability of stir bar sorptive extraction (SBSE) in complex sample analysis.     

Novel platinum(II) selective membrane electrode based on 1,3-bis(2-cyanobenzene)triazene

A plasticized poly (vinyl chloride) membrane electrode based on 1,3-bis(2-cyanobenzene)triazene (CBT) for highly selective determination of platinum(II) (in PtCl₄²⁻ form) is developed. The electrode showed a good Nernstian response (29.8 ± 0.3 mV decade⁻¹) over a wide concentration range (1.0 × 10⁻⁶ to 1.0 × 10⁻² mol L⁻¹). The limit of detection was 5.0 × 10⁻⁷ mol L⁻¹. The electrode has a response time of about 40 s, and it can be used for at least 1 month without observing any considerable deviation from Nernstian response. The proposed electrode revealed an excellent selectivity toward platinum(II) ion over a wide variety of alkali, alkaline earth, transition, and heavy metal ions, and it could be used in the pH range of 3.2-5.1. The practical utility of the electrode has been demonstrated by its use in determination of platinum ion in, alloy, tap, mineral and river water samples.     

A cobalt(II)-selective PVC membrane based on a Schiff base complex of N,N′-bis(salicylidene)-3,4-diaminotoluene

A new PVC membrane electrode for Co²⁺ based on N,N′-bis(salicylidene)-3,4-diaminotoluene, an excellent neutral carrier, has been fabricated using sodium tetraphenylborate (NaTPB) as an anionic excluder and dioctylphthalte (DOP) as a solvent mediator. The electrode exhibits a linear potential response in the concentration range of 7.9 × 10⁻⁸ to 1.0 × 10⁻¹ M with a slope of 30 ± 0.2 mV per decade. The detection limit of the proposed sensor is 5.0 × 10⁻⁸ M and it can be used over a period of 5 months. The proposed sensor revealed good selectivity over a wide variety of other cations including alkali, alkaline earth, heavy and transition metals and could be used in the pH range of 2.0-9.0. This electrode was successfully applied for the determination of Co²⁺in real samples and as an indicator electrode in potentiometric titration of cobalt ions.     

Determination of diclofenac from paediatric urine samples by stir bar sorptive extraction (SBSE)-HPLC-UV technique

A novel stir bar sorptive extraction (SBSE) method coupled with high performance liquid chromatography (HPLC) and UV detection for the extraction of diclofenac (DIC) from paediatric urine samples has been developed and validated. Selectivity and sensitivity being the prime objectives of the bioanalytical method for clinical samples, an optimised SBSE protocol was developed that selectively extracted DIC from various concurrently administered drugs. The validated assay was found to be linear (r = 0.9999) over a concentration range of 100-2000 ng mL⁻¹. SBSE showed consistent recoveries (∼70%) of DIC across the validated linearity range. Overall, the method exhibited excellent accuracy and precision across all QC concentrations, tested over three days. Calculated LOD and LOQ were found to be 12.03 ng mL⁻¹ and 36.37 ng mL⁻¹, respectively, however, for the experimental purposes, 100 ng mL⁻¹ was considered as the validated LOQ (accuracy and precision at this LQC was <20%). Further, studies on various attributes of the stir bar/SBSE, showed no significant inter- and intra-stir bar variability for DIC extraction. There was no carryover effect with re-use of conditioned stir bars and for the first time, a systematic investigation on the effect of ageing of stir bars on their extraction efficiency was carried out. Results showed that, for the present study, stir bars which were used 150 times were still functional based on in-house acceptance criteria and extraction efficiency. The validated method was successfully applied to the analysis of DIC in paediatric clinical trial samples.     

Structural and mechanical characterizations of microporous silica–boron membranes for gas separation

This paper presents structural and mechanical characterizations of microporous silica membranes for gas separation. The membrane separative layer is made of microporous silica–B₂O₃ produced via a sol–gel process. This layer of about 200 nm of thickness is deposited on the internal surface of a tubular asymmetric γ-alumina/α-alumina support. FTIR and Raman analyses indicate the presence of the boron in the silica net and the above methods in conjunction with ¹¹B MAS NMR analyses of the samples indicate that boron is located mainly in the tetrahedral framework position. Such membranes present interesting gas separation properties at temperatures up to 500 °C and transmembrane pressures lower than 8 bar. He permeance values close to 10⁻¹⁰ kmol m⁻² s⁻¹ Pa⁻¹ are obtained, associated with ideal selectivity α(He/CO₂) which can reach 55. Mechanical properties of separative silica-modified layers are measured by nanoindentation and the coefficient of thermal expansion is obtained from pure material.