Cell morphology analysis of high density polymer foams

Polyolefin foams were produced by extrusion and injection molding in order to analyze their cellular morphology. This study proposes methods to calculate surface cell count as well as approaches for converting them into volumetric ones. Two methods of calculating surface cell count were examined. The first one considers an exact surface containing an undetermined number of cells, while the second considers an exact number of cells dispersed on a surface of undetermined area. Three approaches to calculate volumetric cell density were examined which are based on cell geometry: spherical, ellipsoids of revolution or true ellipsoids. It is found that both cell count methods are hampered by a 20% uncertainty but give similar results. All three methods of estimating cell density produce similar results when analyzing injected foams (spherical cells) but diverge significantly in the case of extruded foams (ellipsoidal cells).     

Acid-base titrations by stepwise addition of equal volumes of titrant with special reference to automatic titrations-III Presentation of a fully automatic titration apparatus and of results supporting the theories given in the preceding parts

This paper forms Part III of a series in which the first two parts describe methods for evaluating titrations performed by stepwise addition of equal volumes of titrant. The great advantage of these methods is that they do not require an accurate calibration of the electrode system. This property makes the methods very suitable for routine work. e.g., in automatic analysis. An apparatus for performing such titrations automatically is presented. Further, results of titrations of monoprotic acids, a diprotic acid, an ampholyte, a mixture of an acid with its conjugate base, and mixtures of two acids with a small difference between the stability constants are given. Most of these titrations cannot be evaluated by the Gran or Hofstee methods but yield results having errors of the order of 0.1% if the methods proposed in Parts I and II of this series are employed. The advantages of the method of stepwise addition of equal volumes of titrant combined with the proposed evaluation methods, in comparison with common methods such as titration to a preset pH, are that all the data are used in the evaluation, permitting a statistical treatment and giving better possibilities for tracing systematic errors.     

The application of data from proficiency testing to laboratory accreditation according to ISO 17025

Current methods of testing laboratories for their proficiency in reporting correct measurement results are liable to substantial errors of the second kind. This means that laboratories with deflated uncertainties are accepted as proficient, even though their reported measurement results pave the way for erroneous conclusions. Only by using E _n numbers based on an accepted reference value with the lowest possible uncertainty can the risk of recognising incorrect measurement results be kept at an acceptable level. Based on an actual set of proficiency test (PT)-data for the concentration of Pb in water, this paper compares PT results obtained by methods using E _n numbers with methods based on z-scores. Kaj Heydorn is a technical assessor at The Danish Accreditation and Metrology Fund (DANAK).     

New AMBER force field parameters of heme iron for cytochrome P450s determined by quantum chemical calculations of simplified models

The heme protein, cytochrome P450, is an oxidoreductase that plays an important role in drug metabolism. To model P450s using molecular mechanics methods and classical molecular dynamics simulations, force field parameters and atomic charges are required. Because these parameters are generally obtained by quantum chemical methods, an appropriate simplified model for the iron-porphyrin system was needed. In this study, two models with a five-coordinated Fe(III) mimicking the sextet spin state of P450s are proposed, which are optimized by semiempirical and ab initio unrestricted Hartree-Fock methods. The results produced using the simpler of the two models were similar to those of the more complex model; therefore, the more simplified model of P450 can be used without a loss of accuracy. Furthermore, several quantum chemical calculations were carried out on the simpler model to investigate which method was most suitable for iron-porphyrin systems. The results calculated by hybrid density functional theory (DFT), with the MIDI basis set for iron, reproduced the three-dimensional structures determined by X-ray diffraction and extended X-ray absorption fine-structure experiments. From these results, atomic charges and force-field parameters for molecular mechanics and molecular dynamics calculations were obtained.     

A comparison of the Kjeldahl and Dumas methods for the determination of protein in foods,using data from a proficiency testing scheme

Both the Kjeldahl and the Dumas methods for the determination of protein in foodstuffs are currently in use, but the empirical nitrogen factors used to convert the determined nitrogen content to protein content are based on the Kjeldahl method alone. Non-equivalence between the two methods could therefore result in some laboratories reporting an incorrect protein content. We report here a study using data accumulated over several years in the results of a proficiency testing scheme. On average the Dumas method provided results that were relatively higher by about 1.4% than the Kjeldahl method, but the difference between the methods depended on the type of foodstuff. The methodology of looking for bias between analytical methods is critically discussed.     

A comparison of neutron activation and alpha spectroscopy analyses of thorium in crystalline rocks

The concentrations of Th in samples of crystalline rock from three drillcore sections were analysed independently by instrumental neutron activation analysis and by chemical separation and alpha spectroscopy. The two methods show good general agreement over an approximate concentration range of 1 to 100 ppm Th. Variations in results between the two methods are not of a systematic nature and probably arise from sample heterogeneity. The results confirm the reliability of both methods and provide a useful comparison of the standards and reference materials used. The study indicates that, in cases where Th isotopic information is not required, the simpler and more rapid neutron activation analysis provides a satisfactory method.     

Expanding the analytical toolbox for identity testing of pharmaceutical ingredients: Spectroscopic screening of dextrose using portable Raman and near infrared spectrometers

In the pharmaceutical industry, dextrose is used as an active ingredient in parenteral solutions and as an inactive ingredient (excipient) in tablets and capsules. In order to address the need for more sophisticated analytical techniques, we report our efforts to develop enhanced identification methods to screen pharmaceutical ingredients at risk for adulteration or substitution using field-deployable spectroscopic screening. In this paper, we report our results for a study designed to evaluate the performance of field-deployable Raman and near infrared (NIR) methods to identify dextrose samples. We report a comparison of the sensitivity of the spectroscopic screening methods against current compendial identification tests that rely largely on a colorimetric assay. Our findings indicate that NIR and Raman spectroscopy are both able to distinguish dextrose by hydration state and from other sugar substitutes with 100% accuracy for all methods tested including spectral correlation based library methods, principal component analysis and classification methods.     

The BIOREMA project—Part 2: International interlaboratory comparison for biodiesel test methods

The results of an interlaboratory comparison, using various measurement methods to carry out biodiesel testing, are presented and the findings are discussed. The interlaboratory comparison was organised within the framework of an EU-funded project called BIOREMA. A general overview of the project and results of an interlaboratory comparison on bioethanol are published as Part 1 and 2 of this series of papers. In the study presented here, reference values, provided by national metrology institutes and expert laboratories, were used for evaluating the results. Consensus values, derived from the results of all participants, were used to assess any bias between the results from the national metrology institutes and testing laboratories. The emphasis in this interlaboratory comparison was not the performance rating of the individual laboratories, but recognising and interpreting differences caused by the measurement methods applied. For most biodiesel parameters, a good agreement of measurement results was found among different methods, and between the consensus and reference values. The study material was a rapeseed oil fatty acid methyl ester, for which it was demonstrated that it is feasible to prepare and characterise reference materials for biodiesel with well-established reference values for many parameters.     

Vergleich von anionenanalysenergebnissen aus der bestimmung mittels ionenchromatographie und klassischen analysenmethoden

(Comparison of analytical results for common anions obtained by ion chromatography and classical methods.)The concentrations of chloride, nitrate, and sulphate were determined in ground-water samples by ion chromatography and by the classical titrimetric, photometric, and gravimetric methods. The results were compared by an orthogonal regression procedure. The criteria established and the tests of the confidence intervals of the orthogonal regression function indicate that the results obtained by the different analytical methods are similar for chloride and sulphate but not for nitrate.     

Quantum-chemical method for determination of effective structure-energy parameters of multiparticle interaction in solutions of polar substances

A new method is developed for the determination of equilibrium value of effective structure-energy parameter of multiparticle interaction (Onsager radius of a molecule) in solutions of polar compounds. The method is based on the results of quantum-chemical calculations of the dependence of an electric dipole moment of the studied molecule in the ground state on the dielectric properties of the individual solvents that are applied. Additinal data were obtained that confirmed an opinion that by its physical sense the Onsager radius of a molecule was a value close to van der Waals radius of the same molecule which can be found using known methods of quantum chemistry and structural chemistry for isolated molecules (gas phase). It was shown by an example of solutions of 4-dimethylaminochalcone and several phthalimide and N-methylphthalimide derivatives that the results of determination of Onsager and van der Waals radii of all the studied molecules using three independent methods are in good quantitative agreement confirming their validity.     

Dependence of computed copolymer reactivity ratios on the calculation method. I. Effect of experimental setup

Five calculation methods for estimating reactivity ratios are compared. Two of these methods are only valid at low conversion, two methods are assumed to be valid up to high conversion, and the fifth method is the integrated form of the copolymer equation. Data were simulated for selected couples of r-values and two conversion levels. The data were randomly disturbed by normal error with mean zero. As (the) monomer feed ratio(s) will be drifting during the course of reaction, the influence of an approximated monomer feed ratio on the r-values calculated was also examined. When conversion is low, all methods give estimates with low precision. High conversion results in larger precision, however, for several methods bias appears. For calculation methods that need information about an approximated monomer feed ratio, the influence of this approximation appears to be rather important especially if the r-values are dissimilar or conversion is high.     

Multidimensional separations of ubiquitin conformers in the gas phase: Relating ion cross sections to H/D exchange measurements

Investigating gas-phase structures of protein ions can lead to an improved understanding of intramolecular forces that play an important role in protein folding. Both hydrogen/deuterium (H/D) exchange and ion mobility spectrometry provide insight into the structures and stabilities of different gas-phase conformers, but how best to relate the results from these two methods has been hotly debated. Here, high-field asymmetric waveform ion mobility spectrometry (FAIMS) is combined with Fourier-transform ion cyclotron resonance mass spectrometry (FT/ICR MS) and is used to directly relate ubiquitin ion cross sections and H/D exchange extents. Multiple conformers can be identified using both methods. For the 9+ charge state of ubiquitin, two conformers (or unresolved populations of conformers) that have cross sections differing by 10% are resolved by FAIMS, but only one conformer is apparent using H/D exchange at short times. For the 12+ charge state, two conformers (or conformer populations) have cross sections differing by <1%, yet H/D exchange of these conformers differ significantly (6 versus 25 exchanges). These and other results show that ubiquitin ion collisional cross sections and H/D exchange distributions are not strongly correlated and that factors other than surface accessibility appear to play a significant role in determining rates and extents of H/D exchange. Conformers that are not resolved by one method could be resolved by the other, indicating that these two methods are highly complementary and that more conformations can be resolved with this combination of methods than by either method alone.     

Polypropylene oxidation kinetics

Differential thermal analysis methods have been used to investigate the kinetics of oxidation of isotactic polypropylene. The interpretation of results is based on an oxidation mechanism that emphasizes the role of hydroperoxide production. The mechanism has been simulated by computer methods, and the rate constants for the abstraction of labile hydrogen atoms as well as an apparent energy of activation are obtained.     

Thin-layered electrolysis in molten electrolytes

Generalized results of research in the field of high-temperature electrochemistry that are devoted to solving applied problems of metallurgy of nonferrous metals by methods of thin-layered electrolysis are presented. It is demonstrated that, by applying thin porous dielectric materials, it is feasible to realize electrolysis at an interelectrode distance equal to the thickness of the porous dielectric and that the electrolyte amount contained in the pores of the dielectric is sufficient enough to ensure stable mass exchange between liquid electrodes. Thin-layered electrolysis ensures not only the reduction of the specific energy and electrolyte consumption. It also ensures better quality of refined nonferrous metals. Model notions that make it possible to predict the results of thin-layered electrolysis as a function of its parameters and the porous-material characteristics are offered. The refinement indicators are presented for assorted metals. Various methods are compared.     

Generalized CC-TDSCF and LCSA: The system-energy representation

Typical (sub)system-bath quantum dynamical problems are often investigated by means of (approximate) reduced equations of motion. Wavepacket approaches to the dynamics of the whole system have gained momentum in recent years and there is hope that properly designed approximations to the wavefunction will allow one to correctly describe the subsystem evolution. The continuous-configuration time-dependent self-consistent field (CC-TDSCF) and local coherent-state approximation (LCSA) methods, for instance, use a simple Hartree product of bath single-particle-functions for each discrete variable representation (DVR) state introduced in the Hilbert space of the subsystem. Here we focus on the above two methods and replace the DVR states with the eigenstates of the subsystem Hamiltonian, i.e., we adopt an energy-local representation for the subsystem. We find that stable and semiquantitative results are obtained for a number of dissipative problems, at the same (small) computational cost of the original methods. Furthermore, we find that both methods give very similar results, thus suggesting that coherent-states are well suited to describe (local) bath states. As a whole, present results highlight the importance of the system basis-set in the selected-multiconfiguration expansion of the wavefunction. They suggest that accurate and yet computationally cheap methods may be simply obtained from CC-TDSCF/LCSA by letting the subsystem states be variationally optimized.     

定量解析差热分析曲线的计算方法

对于有特征热效应发生的化学反应,本文根据合理的动力学模型提出了二元线性回归解析DTA曲线,求取动力学参数的方法。该法的特点在于仅通过一次DTA实验及一次回归即得到多个动力学参数。结合实例详细说明了截取DTA数据的三次样条插值函数法及D-M分布函数法,并指出这两种计算方式求出的基本数据按二元线性回归法得到结果的一致性,可做为所求动力学参数正确与否的判据。     

Determination of nanocrystal sizes: a comparison of TEM, SAXS, and XRD studies of highly monodisperse CoPt3 particles

One of the most fundamental tasks in nanoscience is the accurate determination of particle sizes. Various methods have been developed to elucidate the mean particle diameter and the standard deviation for an ensemble of nanocrystals. However, good agreement between the results from different methods is not always encountered in the literature. In this study, we investigate colloidally prepared, highly monodisperse CoPt3 nanoparticles by transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and powder X-ray diffraction (XRD). The results are compared in order to examine to which extent agreement is obtained by the different techniques when applied to small nanocrystals in the size range below 10 nm. In particular, the applicability of the simple Scherrer formula for size determination from the broadening of XRD reflections is checked. When the different techniques are correctly applied, the results from all methods are in good agreement.     

Stability constants: comparative study of fitting methods. Determination of second-order complexation constants by (23)Na and (7)Li NMR chemical shift titration

NMR chemical shift titration has been widely used as a method for the determination of stability constants. Systems involving metal-ligand complexation have been investigated using a number of methodologies. There are significant differences in the values reported for stability constants obtained by different experimental methods, such as calorimetry and ion selective electrode (ISE) titrations; nor has NMR chemical shift titration always yielded consistent results. Different researchers have obtained different results for the same system with results differing by as much as an order of magnitude. The chemical shift data are generally plotted against the concentration ratio of the metal and ligand for a set of solutions. A nonlinear least squares fitting method using an analytical solution of the cubic equation for the equilibrium concentration of the free ligand is used in this study and compared with methods used in the literature. Second-order association constants for the LiClO(4):12-crown-4 system in acetonitrile and the NaClO(4):12-crown-4 system in methanol are reported. Formation of both 1:1 and 1:2 metal-ligand complexes are considered. The LiClO(4):12-crown-4 acetonitrile system had been investigated previously by NMR titration but only 1:1 complexation was considered in that study. This study provides convincing evidence that both 1:1 and 1:2 complexes are important, at least, in the lithium system. A Monte Carlo investigation of the propagation of errors from the chemical shifts to the stability constants shows that the choice of data analysis methods may, in part, contribute to discrepancies and that the nonlinear nature of the model can dramatically affect the error limits on the stability constants.     

Interlaboratory Study to Improve the Quality Control of Methylmercury Determination in Sediment

The results are presented of an interlaboratory study on methylmercury (MeHg) in sediment carried out by a group of European laboratories within the framework of a project managed by the EC Standards, Measurements and Testing Programme (formerly BCR). The aim of this exercise was to evaluate the performance of current methods used for MeHg determination in sediment in order to improve the state-of-the-art prior to the certification of a candidate reference material. The paper describes the organization of the interlaboratory study, the preparation of the sediment material used, the techniques evaluated and the results obtained by the participating laboratories. The outcome of the collaborative project showed that certification could be contemplated, providing that certain analytical techniques were optimized, especially with regard to extraction methods.