Stalagmometric titrations

End-point detection in some precipitation titrations is achieved by measurement of the surface tension between mercury and the solution ("stalagmometric" titration). The drop-time of a polarographic dropping mercury electrode in open circuit is plotted against volume of surface-active titrant added, and shows a break or a peak at the end-point. The stalagmometric titration of sodium tetraphenylborate with Zephiramine (tetradecyldimethylbenzylammonium chloride) was satisfactory and made possible the determination of potassium by back-titration. Potassium was also titrated directly with tetraphenylborate and with calcium dipicrylaminate. Sodium dodecylbenzenesulphonate was titrated directly with Zephiramine and the results were compared with those obtained by the p-toluidine method and Epton's method.     

A simple operational relationship between drop-time and interfacial tension at a charged mercury/aqueous solution interface

This paper describes a simple operational relationship between the drop-time of a dropping mercury electrode and the interfacial tension at a charged mercury/aqueous solution interface. An apparatus and technique for measuring drop-times is reported, and examples are given of the fit of experimental drop-times to literature values of interfacial tensions. The operational relationship is independent of temperature in the range 293-313 K.     

The admittance of an electrochemical cell with adsorption of electroactive species at the DME

Equations for the electrode admittance in, the case of adsorption of electroactive species have been derived, considering both a.c. and d.c. aspects of adsorption. It was shown that due to the d.c. aspects the function also contains a drop-time dependent term f(t_m): =c_OD_O^1/2+c_RD_R^1/2 +f(t_m)?s Under normal polarographic conditions the value of is constant, so c_O and c_R are drop-time dependent and consequently also the value of the Warburg coefficient σ, as well as the adsorption parameters C_LF and C_HF.     

Determination of metals by second-harmonic alternating-current voltammetry with a semi-stationary mercury electrode

The simultaneous determination of tin(II) and lead(II) as well as of indium(III) and cadmium(II) by second-harmonic a.c. voltanunetry using a semi-stationary mercury electrode with a drop-time of 240-300 sec (the long-lasting sessile-drop mercury electrode) has been investigated. Under the best experimental conditions, concentration ratios in the ranges l:12 c(Sn):c(Pb) 15:1 and 1:15 c(In):c(Cd) 15:1 can be determined.     

Polarographic procedures without removal of oxygen, and other approaches to making the determinations more rapidly

One disadvantage of conventional d.c. polarography as an analytical method has always been its relative slowness. The possibility of simplifying and speeding up analyses by avoiding the necessity for removal of oxygen is demonstrated under suitable conditions with current-sampled d.c., pulse and a.c. polarography. In particular it is shown that high-frequency phase-selective a.c. polarography gives considerable discrimination against the oxygen electrode process in some aqueous media. Under these conditions, the high-frequency a.c. technique can be combined with the method of short drop-time, fast scan-rate rapid a.c. polarography to provide a most attractive method of routine analysis. Polarographic analysis in non-aqueous media without removal of oxygen is also discussed.     

Trace-metal determination by second-harmonic alternating-current anodic stripping voltammetry

Second-harmonic alternating-current voltammetry can be used for the sequential determination of two electroactive species having very similar half-wave potentials (deltaE(1 2 ) < 50 mV). Since the concentrations of such metals in samples of special interest are often at trace levels, for their determination second-harmonic a.c. voltammetry (extremely selective but not sufficiently sensitive) can usefully be combined with the anodic stripping method, which has a very high analytical sensitivity. The determination of tin and lead as well as of indium and cadmium in 1M hydrochloric acid is described. The half-wave potentials are only 35 and 45 mV apart, respectively, for these systems. A three-electrode cell was used with a long-lasting sessile-drop mercury electrode as the working electrode, with a drop-time of 240-300 sec. The detection limit was found to be 10(-8)M for all four elements studied. The precision expressed as the relative standard deviation was 2-3% and the relative error was 1-2%.     

Molecular adsorption-mediated control over the electrical characteristics of polycrystalline CdTe/CdS solar cells.

The effect of surface treatments on p-CdTe/n-CdS solar cell performance was examined. Adsorption of organic molecules with various magnitudes and directions of the dipole moment on p-CdTe resulted in controlled changes in electron affinity and surface bond bending. Similar adsorption on CdTe in state-of-the-art p-CdTe/n-CdS solar cells changes the cell performance, and we explain this by a combination of increased series resistance and changes in light absorption and in cell photovoltage. While at this stage no improvement in performance has been found with these cell structures, which are the result of years of empirical optimization, the molecular effect on the photovoltage shows that it is possible in this way to control the photovoltaic effect at this junction. Separate optimization may well lead to improvement by inserting a dipole layer near the photovoltaic interface. Our results also show that this is even possible when dipole adsorption is performed on the complete polycrystalline thin-film cell.     

Activity coefficients of electrolytes from the E.M.F. of liquid membrane cells. I. The method—Test measurements on KCl

A new electrochemical cell is described, in which two permselective liquid membranes, one anionic the other cationic, are interposed between the subsidiary electrodes and the solution of the electrolyte under examination By means of this kind of cell it is possible to measure activity coefficients of salts of cations and anions for which reversible electrodes are not available, with great accuracy even at high dilutions never accessible before (down to ≊10⁻⁴ mol-dm⁻³). The cell performance has been tested by measuring the activity coefficients of KCl for which accurate data are available in literature.     

Miniaturized sample preparation and separation methods for environmental and drug analyses.

Miniaturized extraction and separation media have been successfully developed from precisely controlled technologies. In this article, recent developments in these high performance analytical methods, such as miniaturized sample preparation methods and the coupling of these techniques with microscale separation systems, have been reviewed, along with some applications to environmental and biological analysis. The advantage of the miniaturization is not only for the environmental compatibility but also for the developments of the high performance analytical systems. Down-sizing also makes it possible to investigate and introduce various compounds and materials as novel media (such as tailor-made materials and devices) in separation science. As a typical example of the novel miniaturized sample preparation system, the applications of fibrous materials for microcolumn liquid-phase separation methods are described.     

Unknown identification using reference mass spectra. Quality evaluation of databases

The high success of the “uncertified” mass spectrometry spectral collection started in 1956 demonstrated qualitatively that a partial reference mass spectrum, even one measured routinely, can be of real value. Correct matchings were still possible despite reference errors, which almost never led to close matches that were incorrect. This study shows quantitatively that the number of different compounds, not the number of peaks in a spectrum, is by far the most important determinant of database efficiency for identifying a “global” unknown. A statistical evaluation of matching performance shows that only 6, 12, and 18 peaks in a reference spectrum are 13%, 67%, and 96%, respectively, as valuable as hundreds of peaks. Also, a separately measured second spectrum of the same compound is 50% as valuable as the first. Database expansion that tripled the number of possible wrong answers only reduced the proportion of correct identifications by 5%. Corrections of a mass or abundance error in each of six reference spectra increase the database matching performance by as much as the addition of one spectrum of a new compound. A new “matching quality index” based statistically on these values indicates that the largest database is also by far the most effective for matching unknowns.     

High resolution separation methods for the determination of intact human erythropoiesis stimulating agents. A review

Human erythropoietin (hEPO), a hormone involved in the formation of red blood cells, is a 30 kDa glycoprotein with a high carbohydrate content. The production of recombinant hEPO has made possible its widespread therapeutic use and its banned use in competition sports. Methods to analyze EPO and other erythropoiesis stimulating agents (ESAs) are necessary for the characterization and quality control of these biopharmaceuticals and also for doping control. In this paper, high resolution separation methods, namely high performance liquid chromatography (HPLC) and capillary electrophoresis (CE), with special attention to CE-coupled mass spectrometry, are reviewed. The usefulness of these techniques when applied in different modes to separate the glycoprotein isoforms, aggregates or excipients are detailed. In addition, sample preparation methods that have been applied to ESA samples for subsequent determination by HPLC or CE, as well as the potential compatibility of other preparation methods, are discussed. Applications of the HPLC and CE methods regarding regulatory considerations for biopharmaceuticals analysis, with emphasis on biosimilars, and doping control are also included. Finally, limitations of the present methods and their possible solutions are considered.     

Phase-space overlap measures. II. Design and implementation of staging methods for free-energy calculations

We consider staged free-energy calculation methods in the context of phase-space overlap relations, and argue that the selection of work-based methods should be guided by consideration of the phase-space overlap of the systems of interest. Stages should always be constructed such that work is performed only into a system that has a phase-space subset relation with the starting system. Thus multiple stages are required if the systems of interest are not such that one forms a phase-space subset with the other. Three two-stage methods are possible, termed umbrella sampling, overlap sampling, and funnel sampling. The last is appropriate for cases in which the subset relation holds, but only in the extreme, meaning that one system's important phase space constitutes a very small portion of the others. Umbrella sampling is most suitable for nonoverlap systems, and overlap sampling is appropriate for systems exhibiting partial phase-space overlap. We review recently introduced metrics that characterize phase-space overlap, showing that the performance of the single- and two-stage methods is consistent with the phase-space picture. We also demonstrate that a recently introduced bias-detection measure is effective in identifying inaccuracy in single- and multistage calculations. The examples used are the chemical-potential calculation for a Lennard-Jones liquid at moderate and at high densities, the same for model water at ambient conditions, and a process of charging a neutral ion in water.     

Thermotropic Liquid Crystalline Side Group Polymers as Stationary Phases in High Performance Liquid Chromatography. II. the Mechanism of Separation

Abstract

Liquid crystalline side group polymers support coated on silica gels have been applied as stationary phases in high performance liquid chromatography. It has been possible to show that also in liquid chromatography, separations based on the mesophase structure can be observed in analogy to gas chromatography. From results of separations in which temperature, flow rate, sample concentration and the solvent strength of the mobile phase were varied, this work derives views on the fundamental mechanisms involved. In addition, it will be shown that different mechanisms are probably involved in the separation of steroids and dinitrobenzene isomers on these stationary phases.     

Calibration transfer for excitation-emission fluorescence measurements

The main part of the wide array of different calibration transfer methods found in literature is dedicated to two-way data arrangements (m×n matrices). Less work has been done within the area of calibration transfer for three-way data structures (m×n×l tensors) such as calibrations made for excitation-emission-matrix (EEM) fluorescence spectra. There are two possible ways to attack the problem for EEM transfer. Either the tensors are unfolded to two-way data, whereby the existing methods can be applied, or new methods dedicated to three-way calibration transfer have to be developed. This paper presents and compares both. It was possible to make a local linear pixel-based model that could be used for transfer of EEM's. This new method has a similar performance to the classical methods found in literature, direct- and piecewise direct standardization. The three-way advantages made it possible to use as few as four samples to build useable transfer models. Care has to be taken though when choosing the samples. When subset recalibration of the systems is compared to calibration transfer, better performance is seen for the transferred calibrations. Overall the three-way calibration transfer methods have a slightly better performance than the two-way methods.     

Electrode materials and reaction mechanisms in solid oxide fuel cells: a brief review. III. Recent trends and selected methodological aspects

Continuing previous reviews on mixed-conducting electrodes for intermediate-temperature solid oxide fuel cells (IT SOFCs), this work presents a short overview of novel cathode and anode materials, their electrochemical performance in contact with oxygen anion- and proton-conducting solid electrolytes, and specific features determining possible applications. Priority was given mainly to recent research reports published during the last 2–5 years. Particular emphasis is focused on the relevant methodological aspects, potential limitations and drawbacks, and factors affecting electrode polarization and durability. Typical ranges of the polarization resistances, overpotentials, power densities in the cells with various current collectors, and the electrode materials total conductivity and thermal expansion are compared. The electrode compositions appraised in single-chamber and micro-SOFCs, hydrocarbon- and carbon-fueled cells, high-temperature electrolyzers, and other solid-electrolyte appliances are briefly covered in light of their similarity to the common SOFC materials discussed in the previous parts.     

Faster isolation of recombinant factor VIII SQ, with a superporous agarose matrix.

A superporous agarose matrix was compared with a corresponding homogenous matrix in the isolation of recombinant factor VIII SQ (r-VIII SQ) by immunoaffinity chromatography. As a reference, the commercially available Sepharose FastFlow, used for a similar purification in the industry, was also evaluated. Breakthrough curves are described for flows between 50 and 400 cm/h with pre-purified r-VIII SQ and with cell culture broth. The superporous gel gave the best performance and a 1000-fold purification was obtained in a one-step procedure. The superporous matrix made it possible to increase the throughput about four-fold, presumably due to its better mass transfer properties. The importance of the ligand distribution profile is discussed based upon immunofluorescence microscopy data.     

A formulation of multiple-reference CI with terms linear in the interelectronic distances. II. An alternative ansatz

An alternative ansatz for r₁₂-MR -CI is given. The final formulas are much more easily obtained than was possible previously. The numerical performance is demonstrated with a model calculation of the ground state of helium using three different Gaussian basis sets (5s, 10s, 16s). With the two largest basis sets, the energies obtained with the new formulas, the formulas of Part I of this series of articles, and the formulas of the original formulation agree within 2 μE_H. Since the new ansatz is much easier to handle mathematically, we recommend its usage for future work. © 1995 John Wiley & Sons, Inc.     

小型燃料电池的研究现状与应用前景分析

本文评述了小型燃料电池的研究现状,详细分析了小型燃料电池的电性能、燃料方案与排放物三方面存在的问题,指出了其可能的应用范围。最后展望了小型燃料电池进一步发展所需要继续研究的课题。