Estimation of kinetic rate constants by turbidity and nephelometry techniques in a homocoagulation process with different model colloids

 In this work turbidimetric and nephelometric techniques have been used to study the homocoagulation of aqueous dispersions of uniform spherical particles of surfactant-free latexes. Cationic and anionic latexes of similar particle sizes (361 and 370 nm) and different surface charge densities (+16.4 and −3.6 μC/cm²) were used throughout. The kinetic constants which control the aggregation processes when the electrical repulsion disappears were estimated by both techniques at different particle concentration and wavelength in order to establish the experimental conditions which provided reliable and similar values for the coagulation rate constant. Both experimental techniques (turbidity and nephelometry) and two ways of fitting the data have been used with both latexes. For the first method, the initial slope of turbidity or total scattered intensity versus time curves were used to calculate the kinetic constants. In the second method, the whole turbidity or total scattered intensity versus time curves were fitted and the kinetic constants calculated. An unambiguous experimental value for the doublet rate constant in diffusion conditions is obtained by turbidity and nephelometry techniques. By nephelometry both data treatments have permitted a distinction between the doublet rate constant and the global rate constant in diffusion conditions. Received: 2 June 1997 Accepted: 14 August 1997     

Microanalysis of solid surfaces by Secondary Neutral Mass Spectrometry

Summary The application of Secondary Neutral Mass Spectrometry (SNMS) for high resolution microanalysis of solid surfaces is a rapidly evolving field. Significant progress which has recently been made, as the different SNMS techniques are further developed, includes two important aspects. First the outstanding capability of SNMS for depth profiling with high depth resolution, which in the past was essentially restricted to electrically conducting samples, has been extended towards the analysis of insulating materials with dielectric constants approaching unity. Second, great effort has been made to develop a secondary neutral microprobe which allows SNMS surface and in-depth analysis with high lateral resolution. Here two promising approaches exist, which are based on different methods for post-ionization of sputtered neutral particles. The present state-of-the-art of both techniques is shown and a comparison in respect to detection limits and image acquisition times is attempted.     

Alpha particle absorption and inclined incidence track parameters evaluation in plastic detectors

In this work the use of our recently constructed irradiation chamber was involved in the current experiments. The absorption of alpha particle in air has been studied through a set of experiments in which the stopping power has been measured. A comparison between the calculated values and the present experimental results is given and a good agreement has been found. Critical angle (θ_c) determination has been carried out using two different techniques, via indirect and direct measurements, under different etching conditions and at various alpha energies. An empirical fit of θ_c−h (h is the removal thickness layer) dependence has been calculated and found to work well in the studied h ranges. Also, the inclined alpha tracks parameters of energies between 1.0 and 5.0 MeV have been studied. Results can be successfully applicable in alpha autoradiography studies and detector efficiency determination for track registration in plastic recorders.     

Determination of diffusion coefficients by gas chromatography

Gas chromatography (GC), apart from the qualitative and quantitative analysis of gaseous mixtures, offers many possibilities for physicochemical measurements, among which the most important is the determination of diffusion coefficients of gases in gases and liquids and on solids. The gas chromatographic techniques used for the measurement of diffusion coefficients, namely the methods based on the broadening of the chromatographic elution peaks, and those based on the perturbation of the carrier gas flow-rate, are reviewed from the GC viewpoint, considering their running though the history, the experimental arrangement and procedure, the appropriate mathematical analysis and the main results with brief discussions. The experimental data on diffusion coefficients, determined by the various gas chromatographic techniques, are compared with those quoted in the literature or estimated by the known empirical equations predicting diffusion coefficients. This comparison permits the calculation of the precision and accuracy of the techniques applied to the measurement of diffusion coefficients.     

A discussion on mass resolution in secondary ion mass spectrometry

Mass resolution is a very important parameter for mass spectrometry. It is necessary to compare the mass resolution between the newly developed TOF-SIMS and the conventionally high-performance magnetic SIMS. However, the definitions of mass resolution for these two types of instruments are quite different. Whether it is possible to compare mass resolution and how to do such comparison is a challenge. This problem was raised officially during the 2012 ISO/TC 201 meeting at Tampa, Florida, the United States and the long-term cooperation with ISO started afterwards. The definition of mass resolution is one of the most important and fundamental problems for mass spectrometry and should attract significant attention. Here, some detail discussions on mass resolution as well as the related experimental studies in the past few years, including the collaborations with ISO/TC 201/SC6 and SC1 are summarized. This summary covers the common problem for almost all the current existing and still used definitions of mass resolution. A reasonable new definition for mass resolution considering the peak shape or resolution function has been proposed, which has also been confirmed by using experimental studies of the mass resolution comparison between TOF and magnetic SIMS. This study lays a foundation for the future mass resolution comparisons between different mass spectrometry.     

Application of Experimental Design Methodologies in the Enantioseparation of Pharmaceuticals by Capillary Electrophoresis: A Review

Chirality is one of the major issues in pharmaceutical research and industry. Capillary electrophoresis (CE) is an interesting alternative to the more frequently used chromatographic techniques in the enantioseparation of pharmaceuticals, and is used for the determination of enantiomeric ratio, enantiomeric purity, and in pharmacokinetic studies. Traditionally, optimization of CE methods is performed using a univariate one factor at a time (OFAT) approach; however, this strategy does not allow for the evaluation of interactions between experimental factors, which may result in ineffective method development and optimization. In the last two decades, Design of Experiments (DoE) has been frequently employed to better understand the multidimensional effects and interactions of the input factors on the output responses of analytical CE methods. DoE can be divided into two types: screening and optimization designs. Furthermore, using Quality by Design (QbD) methodology to develop CE-based enantioselective techniques is becoming increasingly popular. The review presents the current use of DoE methodologies in CE-based enantioresolution method development and provides an overview of DoE applications in the optimization and validation of CE enantioselective procedures in the last 25 years. Moreover, a critical perspective on how different DoE strategies can aid in the optimization of enantioseparation procedures is presented.     

Ambient Mass Spectrometry Imaging: A Comparison of Desorption Ionization by Sonic Spray and Electrospray

Easy ambient sonic spray ionization (EASI) and desorption electrospray ionization (DESI) were used for imaging of a number of samples, including sections of rat brain and imprints of plant material on porous Teflon. A novel approach termed Displaced Dual-mode Imaging was utilized for the direct comparison of the two methods: Images were recorded with the individual rows alternating between EASI and DESI, yielding a separate image for each technique recorded under perfectly similar conditions on the same sample. EASI works reliably for imaging of all samples, but the choice of spray solvent and flow rate is more critical in tissue imaging with EASI than with DESI. The overall sensitivity of EASI is, in general, slightly lower than that of DESI, and the representation of the dynamic range is different in images of the two techniques for some samples. However, for abundant compounds, EASI works well, resulting in images of similar quality as DESI. EASI can thus be used in imaging experiments where the application of high voltage is impractical or undesirable. The present study is in its nature also a comparison of the characteristics of the two techniques, showing results also applicable for non-imaging work, with regards to sensitivity and experimental conditions.     

Estimating structure quality trends in the Protein Data Bank by equivalent resolution

The quality of protein structures obtained by different experimental and ab-initio calculation methods varies considerably. The methods have been evolving over time by improving both experimental designs and computational techniques, and since the primary aim of these developments is the procurement of reliable and high-quality data, better techniques resulted on average in an evolution toward higher quality structures in the Protein Data Bank (PDB). Each method leaves a specific quantitative and qualitative “trace” in the PDB entry. Certain information relevant to one method (e.g. dynamics for NMR) may be lacking for another method. Furthermore, some standard measures of quality for one method cannot be calculated for other experimental methods, e.g. crystal resolution or NMR bundle RMSD. Consequently, structures are classified in the PDB by the method used. Here we introduce a method to estimate a measure of equivalent X-ray resolution (e-resolution), expressed in units of Å, to assess the quality of any type of monomeric, single-chain protein structure, irrespective of the experimental structure determination method. We showed and compared the trends in the quality of structures in the Protein Data Bank over the last two decades for five different experimental techniques, excluding theoretical structure predictions. We observed that as new methods are introduced, they undergo a rapid method development evolution: within several years the e-resolution score becomes similar for structures obtained from the five methods and they improve from initially poor performance to acceptable quality, comparable with previously established methods, the performance of which is essentially stable.     

Synthesis and characterization of lanthanum chloranilate complex: application to spectrophotometric determination of anions

Lanthanum chloranilate complex has been synthesized and characterized using different techniques like Infrared spectroscopy and CHN analysis. It has been used for the development of spectrophotometric method of determination of anions like fluoride, EDTA and iodate. The determination is based on the reaction of these anions with the lanthanum ion in the chloranilate complex resulting in the liberation of an equivalent amount of chloranilate anion, the colour of which was measured. The experimental conditions, which affect the optical density, are studied to get maximum sensitivity. Interference studies were carried out with various ions. The method has been applied to the determination of these ions in actual samples viz. EDTA in detergents and iodate in salt.     

Effect of macromolecular polydispersity on diffusion coefficients measured by Rayleigh interferometry

Rayleigh interferometry has been extensively used for the precise determination of diffusion coefficients for binary and ternary liquid mixtures. For ternary mixtures, the 2x2 matrix of multicomponent diffusion coefficients is obtained. Polydispersity adds complexity to the meaning of these measured diffusion coefficients. Here we discuss three important issues of polydispersity regarding the diffusion measurements extracted from this interferometric technique. First, we report novel equations for the extraction of diffusion moments from the Rayleigh interferometric pattern. These moments are used to define polydispersity parameters for macromolecular systems. We have experimentally determined mean diffusion coefficients and polydispersity parameters for aqueous solutions of poly(ethylene glycol) and poly(vinyl alcohol) at 25 degrees C. Aqueous solutions of poly(ethylene glycol) mixtures were used to examine the accuracy of the polydispersity parameters. Second, we compare Rayleigh interferometry to dynamic light scattering. Specifically, we have performed diffusion measurements on the same system using both techniques. To our knowledge, no direct experimental comparison between dynamic light scattering and classical methods for the measurements of diffusion coefficients has been previously reported in relation to polydispersity. We find that substantial discrepancies (i.e., 1 order of magnitude) between the mean diffusion coefficients obtained from these two different techniques can be observed when polydispersity is large. Third, for two-solute mixtures with one polydisperse solute, we report a novel corrective procedure for extracting accurate ternary diffusion coefficients from Rayleigh interferometry. Computer simulations were used to examine the accuracy of the extracted ternary diffusion coefficients.     

Monitoring enzymatic conversions by mass spectrometry: a critical review

This review highlights recent advances in the application of electrospray ionisation and matrix-assisted laser desorption/ionisation mass spectrometry (MS) to study enzymatic reactions. Several assay schemes for different fields of application are presented. The employment of MS as a means of detection in pre-steady-state kinetic studies by rapid-mixing direct analysis and rapid-mixing quench flow techniques is discussed. Several steady-state kinetic studies of a broad range of different enzymatic systems are presented as well as enzyme inhibition studies for various target enzymes. As a promising new development multiplex assays, which monitor the conversion of several substrates simultaneously in one experiment, are described. This assay type has been used for competition studies, enzymatic activity screenings and for diagnostic purposes in clinical chemistry. Generally, it can be concluded that mass spectrometry offers an intriguing alternative as detection methodology in enzymatic bioassays. Its applicability for the monitoring the conversion of naturally occurring substrates and its overall versatility make MS an especially promising tool for the study of enzyme-catalysed processes.     

Influence of crystal polymorphism on crystallinity calculation of poly(l-lactic acid) by infrared spectroscopy

Vibrational spectroscopic methods have been used to determine the crystallinity of poly(l-lactic acid) (PLLA), which is the most popular bio-plastic today. However, it is found that influence of crystal polymorphism of PLLA on the quantitative method proposed for crystallinity calculation based on IR technique has seldom been considered. Herein, by preparing a set of PLLA specimens with different crystallinity and crystal forms, the absorption coefficient ratios between amorphous and crystal bands for evaluating the absolute crystallinity of PLLA α and α′ crystal form have been derived, respectively. In addition, a comparison of the proposed IR method with other techniques used to analyze crystallinity of PLLA such as X-ray diffraction (XRD) and differential scanning calorimetry (DSC) is presented. The origin of the disagreement on the results of quantitative measurements of crystallinity by different methods is also discussed. This study provides a simple spectral method to determine the crystallinity of PLLA with various crystal modifications.     

Determination of Molecular Structure in Terms of Potential Energy Functions from Gas-Phase Electron Diffraction Supplemented by Other Experimental and Computational Data

Different approaches of equilibrium structure determinations by the gas-phase electron diffraction (ED) method or by its combination with other relevant techniques have been reviewed. Some problems and limitations of these approaches are discussed. Special attention is paid to various potential energy function models. Different types of equilibrium bond lengths obtained by the optimization of ED data or their combination with experimental and computational spectroscopic data are compared in tables. Relations between different types of vibrational corrections are discussed. Structure data determined by other methods or approaches are given for comparison.     

Kinetics and mechanism of solid decompositions — From basic discoveries by atomic absorption spectrometry and quadrupole mass spectroscopy to thorough thermogravimetric analysis

This paper sums up the evolution of thermochemical approach to the interpretation of solid decompositions for the past 25 years. This period includes two stages related to decomposition studies by different techniques: by ET AAS and QMS in 1981–2001 and by TG in 2002–2007. As a result of ET AAS and QMS investigations, the method for determination of absolute rates of solid decompositions was developed and the mechanism of decompositions through the congruent dissociative vaporization was discovered. On this basis, in the period from 1997 to 2001, the decomposition mechanisms of several classes of reactants were interpreted and some unusual effects observed in TA were explained. However, the thermochemical approach has not received any support by other TA researchers. One of the potential reasons of this distrust was the unreliability of the E values measured by the traditional Arrhenius plot method. The theoretical analysis and comparison of metrological features of different methods used in the determinations of thermochemical quantities permitted to conclude that in comparison with the Arrhenius plot and second-law methods, the third-law method is to be very much preferred. However, this method cannot be used in the kinetic studies by the Arrhenius approach because its use suggests the measuring of the equilibrium pressures of decomposition products. On the contrary, the method of absolute rates is ideally suitable for this purpose. As a result of much higher precision of the third-law method, some quantitative conclusions that follow from the theory were confirmed, and several new effects, which were invisible in the framework of the Arrhenius approach, have been revealed. In spite of great progress reached in the development of reliable methodology, based on the third-law method, the thermochemical approach remains unclaimed as before.     

Calculation of the (29)si NMR chemical shifts of aqueous silicate species

A DFT methodology for calculating (29)Si NMR chemical shifts of silicate species typically present prior to nucleation in zeolite synthesis solutions, incorporating solvent effects through an implicit representation is presented. We demonstrate how our methodology can reproduce the experimentally observed spectra and, by comparison to well characterized peaks in two different experimental studies, demonstrate the transferability and robustness of the methodology. We discuss certain cases in which caution must be exercised when implicit solvent representations are used for calculating silicate cluster geometries: those cases in which intramolecular hydrogen bonding can play a significant role in the geometry. A number of reassignments of previous tentative experimental assignments are proposed, and we also make assignments for the challenging substituted four-ring species. We present all of our computed chemical shift for previously observed species together with a number of other viable silicate clusters to serve as a reference point for future experimental studies.     

Computational methods for remote homolog identification

As more and more protein sequences are available, homolog identification becomes increasingly important for functional, structural, and evolutional studies of proteins. Many homologous proteins were separated a very long time ago in their evolutionary history and thus their sequences share low sequence identity. These remote homologs have become a research focus in bioinformatics over the past decade, and some significant advances have been achieved. In this paper, we provide a comprehensive review on computational techniques used in remote homolog identification based on different methods, including sequence-sequence comparison, and sequence-structure comparison, and structure-structure comparison. Other miscellaneous approaches are also summarized. Pointers to the online resources of these methods and their related databases are provided. Comparisons among different methods in terms of their technical approaches, their strengths, and limitations are followed. Studies on proteins in SARS-CoV are shown as an example for remote homolog identification application.     

Comparison of multivariate preprocessing techniques as applied to electronic tongue based pattern classification for black tea

In an electronic tongue, preprocessing on raw data precedes pattern analysis and choice of the appropriate preprocessing technique is crucial for the performance of the pattern classifier. While attempting to classify different grades of black tea using a voltammetric electronic tongue, different preprocessing techniques have been explored and a comparison of their performances is presented in this paper. The preprocessing techniques are compared first by a quantitative measurement of separability followed by principle component analysis; and then two different supervised pattern recognition models based on neural networks are used to evaluate the performance of the preprocessing techniques.     

Improved g-level calculations for coil planet centrifuges

Calculation of the g-level is often used to compare CCC centrifuges, either against each other or to allow for comparison with other centrifugal techniques. This study shows the limitations of calculating the g-level in the traditional way. Traditional g-level calculations produce a constant value which does not accurately reflect the dynamics of the coil planet centrifuge. This work has led to a new equation which can be used to determine the improved non-dimensional values. The new equations describe the fluctuating radial and tangential g-level associated with CCC centrifuges and the mean radial g-level value. The latter has been found to be significantly different than that determined by the traditional equation. This new equation will give a better understanding of forces experienced by sample components and allows for more accurate comparison between centrifuges. Although the new equation is far better than the traditional equation for comparing different types of centrifuges, other factors such as the mixing regime may need to be considered to improve the comparison further.     

Potassium Concentration Alters Calibration Sensitivities of Dopamine but not Serotonin

The use of carbon fibre microelectrodes and amperometric techniques for measurement of biological molecules has been widely studied. The use of calibrations to translate biological data is common practice between labs. Tris buffer is commonly used for conducting calibrations, where potassium ion concentrations are varied in buffers. However, little is known about how changes in this ion alter the calibration sensitivity of neurotransmitters. This work showcases that dopamine calibrations are highly dependent on the concentration of potassium ions, whilst serotonin is less affected. Our findings have implications on interpretation and comparison of measurements between different studies.