High precision X-ray diffraction studies of polycrystalline materials on synchrotron radiation

The review is devoted to application of synchrotron radiation (SR) for studying the structure of polycrystalline materials. The main emphasis is made on the equipment and techniques for acquiring high precision structural information — high angular resolution powder diffractometry and the use of anomalous scattering effect in structural studies. Various schemes of recording the high resolution X-ray patterns are presented, diffractometers operating in the world’s leading synchrotron radiation centers are described, and examples of particular applications are reported.     

Optimal design and experimental validation of synchronous, asynchronous and flow-modulated, simulated moving-bed processes using a single-column setup

The performance of asynchronous (Varicol) and flow-modulated (PowerFeed) simulated moving-bed processes, as well as their combination into a single hybrid scheme, are studied both experimentally and by numerical simulation. A recently developed single-column experimental setup is employed to demonstrate the feasibility of the various schemes, explore the effect of their major operating parameters, and illustrate the performance enhancements that are obtained when these schemes are properly optimized. The experimental feasibility and effectiveness of the various schemes are assessed by running and comparing optimized configurations for the linear separation of two nucleosides on a high-performance reversed-phase stationary phase.     

Causes of error in analytical chemistry: results of a web-based survey of proficiency testing participants

Results of a voluntary-response survey of respondent-identified causes of unacceptable results in nine proficiency testing schemes are reported. The PT schemes were predominantly environment and food analysis schemes.?111 respondents reported 230 identified causes of error. Sample preparation (16?% of causes reported), Equipment failures (13?%), ??Human error?? (13?%) and Calibration (10?%) were the top four general causes of poor analytical results. Among sample preparation errors, sample extraction or recovery problems were the most important causes reported. Most calibration errors were related to errors in calculation and dilution and not in availability or quality of calibration materials. No failures were attributed to failures in commercial software; software-related problems were largely associated with user input errors. Corrective actions were generally specific to the particular problem identified. Review of all reported causes indicated that about 44?% could be attributed to simple operator errors.     

Mixed ferrocene-glucose oxidase-carbon-paste electrode for amperometric determination of glucose

The simultaneous incorporation of ferrocene derivatives and glucose oxidase into a carbon-paste matrix results in an effective microelectrode for sensing glucose. The close proximity of the enzymatic, redox mediating and sensing sites offers extremely short response times (t_95%=18 s) compared with early ferrocene-based glucose sensors. Several ferrocene derivatives are evaluated, with 1,1′-dimethylferrocene yielding the best results. The influence of the paste composition, operating potential, glucose concentration and other variables is described. The incorporation of stearic acid into the enzyme-containing paste greatly reduces the interference due to ascorbic acid. The microelectrode is easily fabricated, as time-consuming multi-step immobilization schemes are eliminated. Flow-injection measurements at a rate of 90 samples per hour and relative standard deviations of 3% are also reported.     

External quality assessment schemes for clinical analysis in Russia

 The history and the present condition of external quality assessment (EQA) schemes for clinical laboratories in Russia are described briefly. The creation of EQA programmes started in Russia in the 1980s. Now almost 20 years later these schemes have been transformed. The National External Quality Assessment Scheme ensures quality control in the clinical chemistry sector (more than 2000 laboratories) and is the most powerful scheme in Russia. The (Sistema Vneshnego Kontrola Katchestva, *) (BKK) system, covering about 120 Russian laboratories, and a lot of local regional programmes (mainly in Siberia), is also very active. The purposes and design of the operating programs, reference materials used, algorithms of estimation, modes of result representation and development prospects are considered. The basic obstacle to the development of EQA schemes in Russia is financial restriction.     

Optimization of detection of atomic absorption lines in intracavity laser spectroscopy

An intracavity laser spectrometer equipped with a graphite furnace electrothermal atomizer and two alternative types of narrow atomic lines detection schemes (high resolution diffraction spectrograph with optical multichannel analyzer or a resonant detector based on a hollow-cathode lamp) is described. Such system was used to determine ultra-trace amounts of lithium and strontium in aqueous solutions. A significant reduction in the measurable absorbance was demonstrated for both elements. Careful optimization of the operating conditions of the detection systems and a comparison of their typical features and advantages were performed.     

Optimization of detection of atomic absorption lines in intracavity laser spectroscopy

An intracavity laser spectrometer equipped with a graphite furnace electrothermal atomizer and two alternative types of narrow atomic lines detection schemes (high resolution diffraction spectrograph with optical multichannel analyzer or a resonant detector based on a hollow-cathode lamp) is described. Such system was used to determine ultra-trace amounts of lithium and strontium in aqueous solutions. A significant reduction in the measurable absorbance was demonstrated for both elements. Careful optimization of the operating conditions of the detection systems and a comparison of their typical features and advantages were performed.     

Synthesis of thiophene/phenylene co‐oligomers. III . thienyl‐capped oligophenylenes

The author reports the synthesis of thienyl‐capped oligophenylenes via improved synthetic schemes. These schemes are based on either the Grignard or Suzuki coupling reaction and enable the author to obtain the target compounds at appreciably high yields. Regarding several of these compounds, their synthesis and characterization are believed to be reported for the first time. The resulting materials have been fully characterized through the nmr and ir spectroscopy. The ir analysis is particularly useful in characterizing the materials of higher molecular weight, since those materials are difficult to dissolve in organic solvents.     

不同常压流化床煤气化方案的模型预测 Ⅰ. 模型建立及验证

为评价不同气化方案对常压流化床气化的影响，从化学动力学角度并结合化学平衡建立了流化床气化模型，该模型考虑了煤热解和气化所经历的各反应过程。模型预测结果与文献报道的试验数据吻合较好，气化组分的平方误差和在10%左右，表明该模型可以用来预测各种气化方案对常压流化床气化的气化过程、生成煤气组分和气化效率等方面的影响。     

Quantification of the intensity enhancements for the double-pulse laser-induced breakdown spectroscopy in the orthogonal beam geometry

Simple- and double-pulse laser-induced breakdown spectroscopy was studied on aluminum samples at atmospheric pressure in air. The double-pulse experiments were carried out in the orthogonal beam geometry in two different ways: the reheating scheme and the pre-ablation spark dual-pulse scheme. An ablation laser emitting at 532 nm was combined with a second laser operating at 1064 nm according to the orthogonal geometry. For both schemes, the influence of the delay between the two laser pulses was investigated. In particular, different optima of interpulse delays were determined, underlying the differences of physical mechanisms involved in both processes. The estimation of the plasma temperatures provided explanations on the signal increases for both schemes. Whatever the configuration developed in the orthogonal geometry, a correlation between the increases in emission lines intensities and their excitation energy levels was established in the double-pulse approach. Besides, the effect of laser energy for both pulses was studied so as to make comparisons of the different configurations at the same total laser energy.     

Application of monofluorophosphate/alkaline phosphatase system in flow injection analysis

Monofluorophosphate was found to be a specific substrate for alkaline phosphatase (EC 3.1.3.1) forming novel biosensing schemes with potentiometric detection. Several utilities of this substrate/enzyme system in analytical chemistry will be demonstrated. The system is useful for direct detection of enzymes and substrates as well as for indirect determination of enzyme inhibitors and cofactors using common potentiometric instrumentation. The analytical values of reported biosensing schemes are significantly improved by their implementation into flow injection analysis. This paper presents recent developments in this area and suggests important prospects for further investigations and applications.     

Modelling of addressing schemes in surface stabilized ferroelectric liquid crystal cells using a three variable model in one dimension

The 'Three-Variable Model in One Dimension' has been successfully used to model the domain switching process for simple monopolar and bipolar pulses. In this paper, we discuss the development of this model to describe the switching process due to more complicated addressing waveforms. We have taken two contrasting addressing schemes: the Seiko scheme which is a simple example of a low voltage addressing scheme, and the Joers Alvey scheme, a high voltage addressing scheme which utilizes the high biaxiality properties of a ferroelectric liquid crystal (FLC) material. We experimentally simulate the voltage sequence 'seen' by a pixel subject to these addressing schemes, and take into consideration the worst case combinations of voltages that could cause switching and non-switching conditions. We show that the 'Three Variable Model in One Dimension' is in excellent agreement with experimental data for the Seiko addressing scheme, and can be used to predict the operating regime for the Joers Alvey addressing scheme.     

Constituents of cannabis sativa L. XII—mass spectral fragmentation patterns for some. Cannabinoid acid as their TMS derivatives

Fragmentation schemes for a number of TMS derivatized cannabinoid acids are described. Specific fragmentation pathways and rearrangement mechanisms were determined based on the ion composition of deuterium labeled derivatives. Significant differences in the mode of fragmentation of the two isomeric Δ⁹-tetrahydrocannabinolic acids are described. These results are based on information obtained from deuterium labeling and high resolution data or by the extension of previously reported mechanisms for neutral cannabinoids. Comparisons of the fragmentation schemes between the neutral and acidic cannabinoids are used to confirm many of the fragmentation mechanisms.     

An analysis of the vibrational frequencies and amplitudes of the H5O+2 ion in H4SiW12O40·6H2O (TSA·6H2O) and H3PW12O40·6H2O (TPA·6H2O)

The infrared, Raman and inelastic neutron scattering (INS) spectra of TSA·6H₂O and TPA·6H₂O are in agreement with those expected for the presence of H₅O⁺₂ ions. Force fields for different assignment schemes are compared with the observed vibrational frequencies and the INS spectral profile. All but two schemes are eliminated. Whilst low-resolution INS spectroscopy cannot distinguish between these two schemes, the orientations of the vibrational ellipsoids for one scheme are in better agreement with those reported from low-temperature crystallographic studies of the H₅O⁺₂ ion.     

Logic circuit upon angiogenic response controlled by enzyme-linked iron oxide microparticles--towards biocomputing in human cells

In the present study, we designed a logic circuit upon angiogenic response controlled by a combination of enzyme-functionalized magnetic microparticles operating in human umbilical vein endothelial cells (HUVECs). The reported results represent the first example of a biocomputing system operating in controlling angiogenesis.     

On the impossibility of double focusing in combined electric and magnetic fields homogeneous in Euler’ terms

The use of Euler’s homogeneous electric and magnetic fields can be a good basis for designing static mass spectrometers capable of operating in a spectrographic mode and enabling recording of mass spectra with a wide mass range in one measurement. It is proved mathematically that, when combined Euler’s homogeneous electric and magnetic fields are used to design a single-cascade mass-spectrometer, the double focusing mode cannot be achieved practically along the entire focal line. It is demonstrated that the use of mass spectrographic schemes in which the electric stage and the magnetic stage are separated is an inevitable solution in the creating of a mass spectrograph with high analytical performance.     

Ylures sans sel,evolution en phosphoranes et equilibre ylure ⇌ phosphorane : II. Stéréochimie et mécanismes

In the previous work, we reported the synthesis of ylids and phosphoranes obtained from an addition reaction between a phosphhite or an aminophosphine and dimethylacetylene dicarboxylate in presence of a protic trapping reagent. This present work is devoted to the elaboration of the various mechanistic schemes involved in these reactions in connection with their stereochemical aspect.     

Characterization of a microscale cyclical electrical field flow fractionation system

A microscale cyclical electrical field flow fractionation (CyElFFF) channel is characterized with regard to the effect of various operating parameters and comparison made to recent theoretical developments. Challenges associated with various operating conditions are reported along with some of the optimized operating parameters. The effect of retention wall choice, an offset voltage, relaxation steps, and flow rates, along with the basic operating parameters of voltage, frequency, and electrophoretic mobility are reported. Retention of polystyrene nanoparticle standards is accomplished and the first separations using this technique in a microscale system are also demonstrated. Relaxation steps and offset voltages are found to be effective in eliminating early peaks and in improving plate heights. Plate heights were also found to decrease with increasing flow rates, which is the opposite of the behavior seen in most existing chromatographic systems. The experimental results are compared to the analytical and empirical models of CyElFFF and found to be compatible. Suggestions are made for improving the separation and analysis methods used with CyElFFF.     

Efficient functionalization of aqueous CdSe/ZnS nanocrystals using small-molecule chemical activators

Small molecular reagents that can efficiently functionalize water soluble CdSe/ZnS nanocrystals (NCs) are reported. These reagents do not cause quenching or precipitation of NCs as seen with commercially available activators. The results demonstrate that controlling the electrostatic character of the materials is critical in the design of functionalization schemes.     

Evaluation of positron annihilation in Beryllium

A band theoretical calculation of angular distribution of annihilation photons (ADAP ) and the positron lifetime, up to and including higher momentum components is reported. The results obtained using biquadratic quasianalytic integration schemes for all Brillouin zone integrals, compare favorably with existing experimental data. There are, however, significant structures in the ADAP curve obtained than in the experimental curves.