Characterization of electrically conductive vanadate glass containing tungsten oxide

New conductive glass with a composition of 20BaO·10Fe₂O₃·xWO₃·(70 ? x)V₂O₅ (x = 10–50) was investigated by means of Mössbauer spectroscopy. A marked decrease in quadrupole splitting (Δ) was observed after the isothermal annealing at 500 °C for 1,000 min, due to the structural relaxation of 3D-network composed of FeO₄, VO₄, and VO₅ units. After the isothermal annealing, a marked increase in the electrical conductivity (σ) was observed from 1.7 × 10^?5 to 1.0 × 10^?1 S cm^?1 when “x” was 10, whereas comparable σ values of 1.1 × 10^?4 and 2.0 × 10^?4 S cm^?1 were observed when “x” was 40. These results evidently show that structural relaxation of 3D-network structure involved with a marked increase in σ is intrinsic of “vanadate glass”. XRD pattern indicated several weak peaks due to needle-like BaFe₂O₄ and α-Fe₂O₃ when the glass sample with “x” of 20 was annealed at 500 °C for 1,000 min. SEM study proved the formation of needle-like BaFe₂O₄ just on the surface of the sample, whereas hexagonal BaFe₁₂O₁₉ were observed in the annealed sample with “x” of 40. Chemical durability of WO₃-containing vanadate glass was investigated by immersing each glass sample into 20 %-HCl solution for 72 h.     

Thermodynamics of formation of β-cyclodextrin inclusion complexes with four series of surfactant homologs

We report on a titration microcalorimetric study of the formation of β-cyclodextrin inclusion complexes with the members of series of anionic, cationic, and nonionic surfactant homologs containing even numbers of carbon atoms in the alkyl chains. n-Alkyltrimethylammonium bromides (C_xTAB, x = 6–16), sodium n-alkyl sulfates (SC_xS, x = 6–12), sodium n-alkanesulfonates (SC_xSN, x = 6–12), and N,N-dimethylalkylamine-N-oxides (DC_xAO, x = 8–12) were selected for use. The stoichiometry, the binding constant, and the changes in enthalpy, entropy, and Gibbs free energy of the complexation reactions were determined at 298 K. It was found in each case that the complexation is favored by both the enthalpy and the entropy changes and that the thermodynamics of the process is affected far more strongly by the length of the alkyl chain than by the nature of the headgroup.     

“Demonstration” vs. “designation” of measurement competence: the need to link accreditation to metrology

Formal acceptance of the results of chemical laboratories is increasingly organized through a) accreditation of measuring laboratories nationally and b) mutual recognition of accreditation internationally (through formal Multilateral Recognition Agreements, MRAs). However, real comparability of results of measurements is realized by using common (internationally agreed) measurement scales which make these results traceable to this scale, i.e. “traceable” to the same (internationally agreed) value of the unit of that scale. In addition, the criterion against which the evaluation is done, should be “external” to the measurement laboratories which are being evaluated. This is realized in IRMM’s International Measurement Evaluation Programme (IMEP) where evaluation is performed against values which are anchored using “metrology”, the science of measurement with its own rules, which offers a sound foundation for measurement in all scientific disciplines. It is argued in this paper that the demonstration of measurement capability against values on such scales provides a result-oriented rather than a procedure-oriented evaluation. Thus, competence can be “demonstrated” rather than just “designated” and this can be shown to both customers and regulators. It inspires more confidence.     

Neutron Diffraction Study on the Structure of Aqueous LiNO3 Solutions

Neutron diffraction measurements were carried out at 25 °C for aqueous LiNO₃ heavy water solutions, (*LiNO₃) _x (D₂O)_1?x where x = 0.1, 0.05 and 0.01, in which the ⁶Li/⁷Li isotopic ratios were varied. Structural information on intermolecular nearest neighbor Li⁺···D₂O interactions in the extensive concentration range was derived from the first-order difference function, ?_Li(Q), obtained from the difference in scattering cross sections between ⁶Li- and ⁷Li-enriched sample solutions. The nearest neighbor Li⁺···O distance and coordination number for sample solution with x = 0.1 were determined to be r _LiO = 1.969 (8) Å and n _LiO = 4.12 (6), respectively, corresponding to the four-coordinated Li⁺ ion in the solution. On the other hand, those obtained for the solution with x = 0.01 are r _LiO = 2.00 (2) Å and n _LiO = 6.0 (2), respectively, indicating that hexaaqua Li⁺ is dominant in the dilute solution. These results clearly indicate that a concentration dependence of the hydration number of Li⁺ occurs in the aqueous solutions.     

Evaluation of blood plasma changes by differential scanning calorimetry in psoriatic patients treated with drugs

Psoriasis is a chronic inflammatory skin disease, most commonly resulting in the occurrence of red and silver scaly plaques. Application of differential scanning calorimetry (DSC) should be used as a new method to detect the different stages of the disease and to monitor medications with different anti-psoriatic drugs using patient’s blood plasma. The study included 72 white adults (35 men and 37 women; median age 56 years) with diagnosed psoriasis. According to the psoriasis area severity index (PASI) patients were selected into three groups: symptomless (PASI: 0), mild (PASI: 1–15), and serious symptoms (PASI: >15). According to medication patients were divided into untreated (n = 39) and treated (n = 33) groups. For systemic drug treatment cytostatic therapy (methotrexate, n = 12), retinoid treatment (acitretin, n = 10), and biologic response modifiers (adalimumab, n = 5; infliximab, n = 5; ustekinumab, n = 1) were applied. Denaturation of human plasma components were detected in Setaram Micro DSC II calorimeter. The patients had no third denaturation peak in the untreated mild and serious symptoms groups. In mild symptoms all the thermal parameters altered significantly, while in serious symptoms only the first melting and the calorimetric enthalpy altered significantly compared with symptoms-free states. In case of systematic cytostatic and retinoid drug treatment (methotrexate, n = 12; acitretin, n = 10) cases the DSC scans of patients with symptoms exhibited significant differences (p < 0.05) in melting temperatures and in calorimetric enthalpy compared with the untreated symptoms-free patients. Using biologic response modifier agents (adalimumab, infliximab, and ustekinumab) we had no enough samples for a statistical evaluation for each one, but after the intervention a stronger effect can be seen as in case of systematic drug treatment. In this study blood plasma measurement in psoriatic patients by DSC showed differences between untreated, conventional systemic drug treatment, and application of biologic response modifier agents, but further studies are needed to elucidate these relationships (supported by grant OTKA CO-272).     

Densities, Heat Capacities and Asymmetric Criticality of Coexistence Curves for Binary Mixtures {Dimethyl Adipate + n-Heptane or n-Octane}

Densities of binary mixtures {x dimethyl adipate + (1 ? x) n-heptane} and {x dimethyl adipate + (1 ? x) n-octane} were measured at various temperatures. The excess molar volumes were calculated from the density data and fitted with the Redlich–Kister equation. The critical anomaly of density was detected for {x dimethyl adipate + (1 ? x) n-octane} binary solutions with the critical compositions in a narrow temperature range of the near-critical one-phase region. However, the density anomaly and the excess properties were taken into account in a test of the complete scaling theory and found to be negligible. The isobaric heat capacities per unit volume of the {x dimethyl adipate + (1 ? x) n-heptane} and {x dimethyl adipate + (1 ? x) n-octane} binary solutions at the critical compositions were also determined over the temperature range both near and far away from the critical points. It was found that the heat capacity plays an important role in describing the asymmetry of the coexistence curves.     

Sintering kinetic study of the nano-crystalline 3-mol% yttria-samaria codoped tetragonal zirconia polycrystal ceramics

Dilatometric shrinkage data was utilized to study the sintering kinetics of the in-house synthesized nano-crystalline 3-mol% yttria-samaria codoped tetragonal zirconia polycrystal (TZP) ceramics. The objective was to determine activation energy (Q) of sintering and the sintering mechanism (n) relevant to the initial stage of sintering. The product of activation energy and sintering parameter, i.e., “nQ” was calculated from the shrinkage data acquired from the constant rate of heating experiment. The apparent activation energy of sintering (Q) was calculated using modified-“Dorn” method. Modified Johnson’s equation was used to determine value of “n” using the activation energy obtained from the Dorn method. Stepwise isothermal dilatometry technique was utilized as an independent method to determine the “n” value. The activation energy of sintering was in the range of 400–525 kJ mol^?1 and found to be dependent on the dopant concentration. The value of “n” was found to be ~0.33 for both 3 mol% yttria-doped (3Y-TZP) and yttria-samaria codoped (3(Y,S)-TZP) TZP, whereas for 3 mol% samaria-doped tetragonal zirconia (3S-TZP), the value of “n” was ~0.40. From the obtained “n” values, it may be concluded that grain boundary diffusion (GBD) was the dominant sintering mechanism in 3Y-TZP and 3(Y,S)-TZP, whereas an intermediate of GBD and volume diffusion influences the initial sintering stage in the 3S-TZP.     

Dopant position of Co atom in Zn1−xCoxO nanoparticles studied by extended X-ray absorption fine structure

Zn_1?xCo_xO nanoparticles were prepared by sol–gel method. The microstructure and dopant position were studied by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and extended X-ray absorption fine structure (EXAFS). The XRD patterns did not show any signal of impurity in the Zn_1?xCo_xO nanoparticles with Co concentration from x = 0.01 to 0.08. Neither did the HRTEM image for the highest concentration sample with x = 0.08. The nanoparticles have also been investigated by the EXAFS measurements at Co k-edge. The radical distribution functions, the fitting result of bond length and coordination numbers, indicated there was an impurity in the highest Co concentration sample with x = 0.08. Although most of the Co atoms were substituted for Zn sites in ZnO with x = 0.08, a few of Co atoms formed a microstructure similar to Co₃O₄, which was not found in the XRD and HRTEM. The room temperature ferromagnetic behaviour was found for x = 0.01 sample by superconducting quantum interference device .     

Study on structures and electron affinities of small potassium–silicon clusters Si n K (n = 2–8) and their anions with Gaussian-3 theory

The neutral Si _n K (n = 2–8) clusters and their anions have been systematically studied by means of the higher level of Gaussian-3 schemes. Equilibrium geometries and electron affinities have been calculated and are discussed for each considered size. For neutral Si _n K clusters, the ground state structure is found to be “attaching structure”, in which the K atom is bound to Si _n clusters. The most stable isomer for their anions, however, is found to be “substitutional structures”, which is derived from Si_(n+1) by replacing the Si atom with a K. The dissociation energies of K atom from the lowest energy structures of Si _n K have also been estimated to examine relative stabilities.     

A global approach to method validation and measurement uncertainty

The enforcement of legal limits for food safety raises the question of decision-making in the context of uncertain measurements. It also puts the question of demonstrating that measurement technique that is used is fit for the purpose of controlling legal limits. A recent European Commision (EC) decision gives some indications how to deal with this question. In the meantime, the implementation of quality systems in analytical laboratories is now a reality. While these requirements deeply modified the organization of the laboratories, it has also improved the quality of the results. The goal of this communication is to describe how two fundamental requirements of ISO 17025 standard, i.e. validation of the methods and estimation of the uncertainty of measurements, can give a way to check whether an analytical method is correctly fit for the purpose of controlling legal limits. Both these requirements are not independent and it will be shown how they can be combined. A recent approach based on the “accuracy profile” of a method was applied to the determination of acrylamide and illustrates how uncertainty can be simply derived from the data collected for validating the method. Moreover, by basing on the β-expectation tolerance interval introduced by Mee [Technometrics (1984) 26(3): 251–253], it is possible to unambiguously demonstrate the fitness for purpose of a method. Remembering that the expression of uncertainty of the measurement is also a requirement for accredited laboratories, it is shown that the uncertainty can be easily related to the trueness and precision issuing from the data collected to build the method accuracy profile. The example presented here consists in validating a method for the determination of acrylamide in pig plasma by liquid chromatography–mass spectromery (LC–MS). Concentrations are expressed as mg/l and instrumental response is peak surface. The calibration experimental design included 5×5×2 measurements and namely consisted in preparing duplicate standard solutions at five concentration levels ranging from 10 to about 5000 mg/l. This was repeated for 5 days. The validation experimental design was similar.     

Using high-performance quantitative NMR (HP-qNMR®) for certifying traceable and highly accurate purity values of organic reference materials with uncertainties <0.1 %

Quantitative nuclear magnetic resonance (qNMR) in combination with metrological weighing is optimised to demonstrate the power of the qNMR measurement method. It is shown that with ¹H-qNMR it is possible to certify the purity of organic reference materials (expressed as mass fraction) with relative expanded uncertainties of <0.1 % for a 95 % confidence interval (k = 2). Following well-defined selection criteria, a set of twelve different chemical compounds is evaluated and certified to serve as internal references for ¹H-qNMR measurements. A series of comparison measurements is made amongst a subset of the selected compounds. The purity of maleic acid is determined by six different ¹H-qNMR measurement series, and all results show full consistency. All the six mean values are covered within the range of ±0.05 %. In two more measurement series, four different nuclei are analysed within the same sample against one calibrator. Even with non-optimised signal intensity ratios and varying signal pattern, a high consistency was obtained. Therefore, the validity and robustness of ¹H-qNMR measurement results are demonstrated. ¹H-qNMR measurement results are directly traceable to a variety of internationally accepted primary reference materials, and therefore, traceability to SI units is obtained. All experiments are performed under ISO/IEC 17025 and ISO Guide 34 accreditation.     

Analytical derivation of the Hückel “4n + 2 rule”

The “4n + 2 rule” is derived analytically at the level of the simple Hückel theory for neutral even-membered chains, their double ions, as well as cations and anions of the odd-membered chains, by determining the first order energetic effect of the ring closure. The topological background of the “4n + 2 rule” is also briefly discussed.     

Extraction of Astaxanthin from Shrimp Waste Using Pressurized Hot Ethanol

An efficient and environmentally sustainable extraction method is proposed for the enrichment of a high-value pigment, astaxanthin, from a low-value raw material, shrimp waste. Ethanol at elevated temperature and pressure was used as a “green” extraction solvent. An experimental design approach based on central composite design was used to investigate the dependence of pressurized liquid extraction (PLE) operating variables (pressure, temperature, extraction time) on the recovered astaxanthin concentration from shrimp waste. The results show that at a 95% confidence level, the most significant PLE operating variables were extraction temperature and time. Extraction pressure had only a minor effect on the astaxanthin recovery in the studied experimental conditions. The maximum astaxanthin recovery obtainable by PLE was calculated from the chemometrics results and then appraised by experiments. Our results show astaxanthin yields of around 24 mg kg^?1 shrimp waste. The reproducibility of the developed PLE method is good, showing a relative standard deviation of 3.5% (n = 6) for astaxanthin.     

An Improved and Validated LC Method for Resolution of Panthenol

An improved LC method was developed and validated for determination of enantiomeric purity of panthenol in bulk drugs. The method is based on derivatization of panthenol with 3,5-dinitrobenzoyl chloride. Baseline separation with resolution >2.7 was achieved within 20 min on Kromasil CHI-DMB (250 × 4.6 mm) column using n-hexane:ethanol (95:5 v/v) as mobile phase at a flow rate of 1.5 mL min^?1. The analytes were detected by their UV absorbance at 265 nm. The effects of ethanol, 2-propanol and temperature on enantioselectivity and resolution of enantiomers were evaluated. The method was extensively validated and proved to be robust. The recoveries were between 98.3 and 101.4% with <1.6% relative standard deviation. The regression equations for the derivatives of d-panthenol and l-panthenol were y ₁ = 18.01x ₁ ? 32.56 (r ₁ ²  = 0.9984) and y ₂ = 17.855x ₂ ? 28.16 (r ₂ ²  = 0.9990), respectively. The LOD and LOQ for the derivative of d-panthenol were 10.6 and 37.4 μg mL^?1 and for the derivative of l-panthenol were 12.1 and 40 μg mL^?1, respectively. The improved method was found to be simple, rapid, and sensitive for the determination of enantiomeric purity of panthenol in bulk drugs.     

Simultaneous quantification of 28 synthetic cathinones and metabolites in urine by liquid chromatography-high resolution mass spectrometry

Synthetic cathinones are novel stimulants derived from cathinone, with amphetamines or cocaine-like effects, often labeled “not for human consumption” and considered “legal highs”. Emergence of these new designer drugs complicate interpretation of forensic and clinical cases, with introduction of many new analogs designed to circumvent legislation and vary effects and potencies. We developed a method for the simultaneous quantification of 28 synthetic cathinones, including four metabolites, in urine by liquid chromatography coupled to high resolution mass spectrometry (LC-HRMS). These cathinones include cathinone, methcathinone, and synthetic cathinones position-3’-substituted, N-alkyl-substituted, ring-substituted, methylenedioxy-substituted, and pyrrolidinyl-substituted. One mL phosphate buffer pH 6 and 25 μL IStd solution were combined with 0.25 mL urine, and subjected to solid phase cation exchange extraction (SOLA SCX). The chromatographic reverse-phase separation was achieved with a gradient mobile phase of 0.1 % formic acid in water and in acetonitrile in 20 min. We employed a Q Exactive high resolution mass spectrometer, with compounds identified and quantified by target-MSMS experiments. The assay was linear from 0.5–1 to 100 μg/L, with limits of detection of 0.25–1 μg/L. Imprecision (n?=?20) was <15.9 % and accuracy (n?=?20) 85.2–118.1 %. Extraction efficiency was 78.9–116.7 % (CV 1.4–16.7 %, n?=?5), process efficiency 57.7–104.9 %, and matrix effects from ?29.5 % to 1.5 % (CV 1.9–13.1 %, n?=?10). Most synthetic cathinones were stable at 4 °C for 72 h (n?=?27) and after 3 freeze-thaw cycles (n?=?26), but many (n?=?19) were not stable at room temperature for 24 h (losses up to ?67.6 %). The method was applied to authentic urine specimens from synthetic cathinone users. This method provides a comprehensive confirmation method for 28 synthetic cathinones in urine, with good selectivity and specificity.     

Synthesis and thermal properties of NiSbS–As doped phase

The substitution of Sb with As in the NiSbS intermetallic compound was studied in the framework of evaluating a possible increase of the thermoelectric properties. Different NiSb_1?xAs_xS samples were synthesized with increasing amounts of As (0 < x < 0.66) employing a simple synthetic route using a muffle furnace. Scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy was used to investigate the microstructure. X-ray powder diffraction techniques were employed in order to study the possible existence of a solid solution between NiSbS and NiAsS compounds, as well as to identify the crystal structure and determine the lattice parameters. All compounds were found to crystallise with the NiSbS prototype (cP12-P2₁3), with lattice parameters varying from a = 0.59341(7) nm (x = 0) to a = 0.56849(6) nm (x = 1). Good agreement with Vegard’s law was evidenced. Thermal measurements on NiSb_1?xAs_xS samples were carried out using DTA instruments to evaluate the thermal stability and the melting temperatures.     

Properties of PAN-TBP extraction chromatographic material

Three production routes of the preparation of a solid extractant based on tributylphosphate (TBP) embedded in the polyacrylonitrile matrix (PAN) have been studied. The method of direct PAN coagulation with TBP was found to be not viable due to the significant TBP solubility in the coagulation bath. The most suitable PAN-TBP solid extractant was prepared by the well-known impregnation method of ready-made neat PAN beads. The kinetics of uranium extraction from 3 mol L^?1 HNO₃, the effect of nitrate and nitric acids concentrations on the value of weight distribution coefficients D _g as well as the uranium “extraction isotherm” were determined for this material. Uranium extraction was rather fast, approximately 1 h was sufficient for the equilibrium achievement. Capacity for the uranium uptake, measured in batch experiments on PAN-TBP for 0.048 mol L^?1 of uranium in 3 mol L^?1 nitric acid, was found to be q = 0.363 mmol g^?1 (58 % of the theoretical capacity). It was concluded that PAN-TBP material behaves like TBP in liquid–liquid extraction. Extraction capacity determined in column experiments was lower (by about 23 %) than expected from the “extraction isotherm” due to the TBP leaching out of the column. The thus prepared material is therefore not very suitable for multicycle extraction and stripping and can be used once, particularly for the analytical purposes.     

Non-isothermal crystallisation kinetics study on Se90−xIn10Sbx (x = 0, 1, 2, 4, 5) chalcogenide glasses

The non-isothermal crystallisation kinetics of Se_90?xIn₁₀Sb_x (x = 0, 1, 2, 4, 5) chalcogenide glasses prepared by a conventional melt quenching technique was studied using the differential scanning calorimetry (DSC) measurement at different heating rates 5, 7, 10 and 12 °C min^?1. The values of the glass transition temperature T _g and the crystallisation temperature T _c are found to be composition and heating rate dependent. The activation energy of glass transition E _g, Avrami index n, dimensionality of growth m and activation energy of crystallisation E _c have been determined from different models.     

Synthesis and characterisation of Ni(II), Cu(II), and Zn(II) complexes with an acyclic Mannich base functionalised with thioglycolate moiety

New complexes ML(CNS)·nH₂O [M = Ni, n = 0.5; M = Cu, n = 4.5; M = Zn, n = 0.5, HL: 6-mercapto-(1,4,8,11-tetraazaundecanyl)-6-carboxylic acid)] have been synthesised, chemical analysed, and characterised by different spectroscopic techniques (IR, UV–Vis–NIR, ¹H NMR, EPR, ESI–MS), and magnetic measurements. Based on the IR spectra a dinuclear structure with the 1,3-CSN coordination was proposed for Ni(II) and Cu(II) complexes. The dinuclear structure of Cu(II) complex is also consistent with both magnetic behaviour and EPR spectrum. According to TG, DTG and DTA curves the thermal transformations are complex processes, including dehydration, Mannich base oxidative degradation and thiocyanate decomposition. The final product of decomposition is the most stable metallic oxide, as XRD data indicates. The new complexes were also screened for their microbicidal and antibiofilm properties.