Radiometric control of analytical separation procedures

Summary Different analytical separation procedures were investigated by radioactive tracer techniques.By liquid-liquid extraction with isoamylacetate it was found possible to eliminate traces of chromium from a great excess of iron. The iron thus purified was tested for residual Cr by thermal neutron irradiation. A corresponding extraction technique, using cuproïne in isoamylalcohol as extractant, was used for the separation of traces of copper from irradiated zinc.The quantitative extraction of zinc with methyldioctylamine in xylol and the quantitative character of the Zn[Hg(SCN)₄] precipitation were furthermore proved.The separation of nickel and cobalt by dimethylglyoxime precipitation was investigated with⁶⁵Ni and⁶⁰Co tracers. About 0.6% cobalt was coprecipitated.Coprecipitation of sodium with potassium dipicrylaminate and with potassium tetraphenylborate was found to be about 0.5%. As this decontamination was sufficient to permit selective-counting of⁴²K in presence of²⁴Na, no double precipitation purification step was attempted.

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Zusammenfassung Verschiedene analytische Trennungsverfahren wurden mit Hilfe radiometrischer Indikatormethoden überprüft.Durch Flüssig-flüssig-Extraktion mit Isoamylacetat lassen sich Chromspuren aus großen Eisenüberschüssen entfernen. Das so gereinigte Eisen wurde durch Bestrahlung mit thermischen Neutronen auf Chromreste geprüft. Ein analoges Extraktionsverfahren mit isoamylalkoholischer Cuproinlösung wurde zur Abtrennung von Kupferspuren aus bestrahltem Zink verwendet. Weiters wurden die quantitative Extraktion von Zink mit Methyldioctylamin in Xylol und die Vollständigkeit der Fällung von Zink-Thiocyanatomercuriat überprüft. Die Trennung von Nickel und Kobalt mittels Dimethylglyoxim wurde mit Spuren⁶⁵Ni und⁶⁰Co untersucht. Ungefähr 0,6% Kobalt wurden mitgefällt. Die mit Kaliumdipikrylaminat und Kaliumtetraphenylborat mitgefällte Natriummenge beträgt etwa 0,5%. Da diese Reinigung zur selektiven Messung der-Aktivität des⁴²K in Gegenwart von²⁴Na ausreicht, wurde keine weitere Reinigung durch wiederholte Fällung versucht.

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Résumé Plusieurs méthodes de séparations analytiques furent contrôlées à l'aide de traceurs radioactifs. Il s'avéra possible d'éliminer des traces de chrome d'un excès de fer en employant une technique d'extraction liquide-liquide à base d'acétate d'isoamyle. Le degré de purification du fer fut contrôlé par irradiation dans un flux de neutrons thermiques.Le 2-2 dichinolyle fut employé pour l'extraction sélective de traces de cuivre d'un échantillon de zinc irradié. Il fut ensuite prouvé que le zinc peut être isolé quantitativement par extraction au méthyle-dioctylamine ou en le précipitant sous la forme de Zn[Hg(SCN)₄].La séparation nickel-kobalt à l'aide du diméthyleglyoxime fut contrôlée à l'aide de⁶⁵Ni et de⁶⁰Co. Environ 0,5% du cobalt présent fut coprécipité dans les conditions expérimentales données. Enfin, la coprécipitation du sodium avec le dipicrylaminate ou le tetraphénylborate de potasse fut déterminée; en moyenne elle fut de l'ordre de 0,5%.

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Dedicated to Prof. Dr. Ing.Fritz Feigl on occasion of his 70th birthday.

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Research Fellow I. I. K. W. (Belgium).     

Radiometric measurements of fallout under accidental conditions

Empirical expression for experimentally obtained functional dependence between the results of total -activity and integral -activity activity of fallout, measured during May, 1986, at a control point: 44°47 northern latitude and 20°32 eastern longitude, has been established in order to enable estimation of the level of fallout contamination by -emitters when total -activity values are known.     

Comparison of different types of filters for atmospheric trace element analysis by three analytical methods

Different atmospheric aerosol samples were collected on three types of filters. From both of the loaded and clean areas of each kind of filter, different disks were cut and investigated by XRF, PIXE and scanning electron microscopy (SEM). The blank concentration values of the elements Al, Si, P, S, Cl, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Br and Pb in the three types of filter are discussed. It is found that for trace elemental analysis, the Nuclepore membrane filters are the most suitable for sampling. These filters have much lower blank element concentrations than the glass fiber and ash free filters. It was found also that PIXE is a more reliable analytical technique for atmospheric aerosol particles than the other methods used.     

Investigation of different types of filters for atmospheric trace elements analysis by three analytical techniques

Different atmospheric aerosol samples were collected on three types of filters. Disks of both loaded and clean areas of each kind of filter were investigated by XRF, PIXE and Scanning Electron Microscope (SEM) methods. The blank concentration values of the elements Al, Si, P, S, Cl, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Br and Pb in the three types of fiters are discussed. It is found that for trace elemental analysis, the Nuclepore membrane filters are the most suitable for sampling. These have much lower blank element concentration values than the glass fibres and ash free filters. It was found also that the PIXE method is a more reliable analytical technique for atmospheric aerosol particles than the other methods.     

Information efficiency of analytical methods

The concepts of information efficiency and profitability are discussed in relation to analysis.     

Excess electron in water at different thermodynamic conditions

A hydrated electron in water at different densities and temperatures is studied via a set of density functional based molecular dynamics simulations, showing that a localization of an excess electron is still present even at very low densities. Space variations of the molecular dipole moments are analyzed, proposing a simple algorithm to identify the region of localization of the wavefunction relative to the solvated electron in terms of orientation of the H2O molecular dipole moments. Finally, the effects of the self-interaction corrections on the optical absorption spectra are analyzed and compared with both available experimental data and path integral molecular dynamics calculations, showing that a weighted subtraction of the self-interaction yields a systematic improvement in the position of the absorption peak.     

Principles and analytical applications of acousto-optic tunable filters, an overview

Advantages of acousto-optic tunable filters have been exploited to develop novel analytical instruments which are not feasible otherwise. The instrumentation development and unique features of such AOTF based instruments including the multidimensional fluorimeter, the multiwavelength thermal lens spectrometer, the near-infrared spectrometer based on erbium doped fiber amplifier (EDFA), and detectors for high performance liquid chromatography (HPLC) and flow injection analysis (FIA), will be described.     

Supramolecular assembly of lysine-b-glycine block copolypeptides at different solution conditions

Here we report the supramolecular assembly of poly(l-lysine)-b-polyglycine diblock copolypeptides at different solution conditions. Light scattering and confocal microscopy indicate that the supramolecular aggregates initially formed in solution are vesicles with a broad size distribution, depending strongly on the initial processing conditions. The vesicles formed after multiple pH cycles appear independent of the initial processing conditions and are related to the thermodynamic nature of the assembled supramolecular aggregates. Circular dichroism results verify that this change in size observed over pH cyclings tracks with the conformation changes of the lysine block confined in the vesicle membranes. This appears interesting for peptosome-based materials, implying a high level of fluidity in the membrane that allows the supramolecular aggregates formed in solution to respond to changes in pH. The results also show that the external stimulus, which is the change of pH in this study, provides an additional means to regulate polypeptide vesicle size and size distribution.     

不同彬县焦的水蒸气气化反应动力学研究

在常压,900℃～1050℃考察了彬县煤的三种焦样（常规方法制焦、快速热解焦和脱灰快速热解焦）在热天平上的水蒸气气化反应。考察了温度和焦种对水蒸气气化反应的影响。对比了三种焦的动力学参数和比表面积。结果表明,气化温度是影响煤焦气化反应速率的主要因素,提高50℃,反应速率增加一倍。快速热解焦的反应速率在相同反应条件下明显大于慢速焦。三种焦的表观活化能以快速焦最大,因而反应速率受温度的影响也最大,快速脱灰焦次之,慢速焦最小。     

Thermal characterization of the bromopride recrystallized from different solvents and at different temperature conditions

Polymorphism is the ability of a substance to crystallize into different crystalline states. Different polymorphs vary according to their physical and chemical properties, and therefore, the presence of different crystalline forms of a drug may change some physicochemical properties of certain medicines. The goal of this work was to detect polymorphic forms of a compound used as a drug, bromopride. For the purpose of this study, recrystallizations were carried out from different solvents and at distinct temperatures, with the aim of obtaining different crystalline forms, which were characterized by dynamic thermal analysis (DTA) and X-ray powder diffraction. The samples obtained through recrystallization in different temperature conditions and solvents showed peculiar DTA curves and diffractograms profiles, indicating the presence of crystalline forms distinct from each other.     

PAH-losses from glass fiber filters under the conditions of different air volume sampling: results of field evaluations in occupational atmospheres

Summary The estimation of the occupational medical and toxicological risks to workers exposed to PAH depends on sampling these compounds, some of which are carcinogenic, with as little loss as possible in the air of the working environment.A sampling system for the collection of air samples for PAH in field investigations consisting of a glass fiber filter followed by a suction pump has been tested for its efficiency at various suction rates using n=19 specially selected reference substances. The variability of the suction rate obtainable with the pump employed is to be regarded as being of particular significance.A total of 60 determinations made in areas devoted to the manufacture of artificial coal and at road paving operations revealed greatly reduced and pumping rate-dependent recoveries, i.e. correspondingly high losses. With an air throughput of 22 500 l/h an average of 47.8% of the total of 19 PAH was recovered on the glass fiber filter; when a suction pump with a throughput of 2840 l/h was employed 28% of the PAH was not collected and the losses amounted to 15% at a pumping rate of 120 l/h. The losses of 5 PAH compounds chosen for their carcinogenicity were of the same order of magnitude with ca. 51%, 22% and 11%.The influence of the number of rings in the PAH, i. e., its increasing boiling point, plays a decisive role in its recovery rate. Thus, when sampling at a throughput of 120 l/h, the recovery rates of various members of the 4, 5, 6 and 7-ring PAH systems were on average 77.1%, 88.4%, 95.6% and 99.1%, respectively.Glass fiber filters are not suitable for use as the sole collection phase for PAH air sampling, particularly when pumps having a high throughput are employed. A combination of filters as the collection phase for particulate PAH followed by adsorbent tubes of Tenax or XAD-2 for gaseous PAH must be regarded as necessary for the collection of representative samples for determination of the total concentration of polycyclic aromatics.

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PAH-Verluste an Glasfaserfiltern unter den Bedingungen der Probenahme bei unterschiedlichen Luftdurchsätzen: Ergebnisse von Feldauswertungen in Arbeitsbereichen

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Dedicated to Prof. Dr. G. Hesse on the occasion of his 80th birthday     

Radiometric determination of sulfate

A radiometric procedure for the determination of sulfate based upon the precipitation of barium sulfate is described with a sensitivity of about 0.01 μg/ml. Carrier-free³⁵SO₄ is added to the sample to measure the chemical recovery. The sulfate is precipitated with an excess of barium having a known specific activity of¹³³Ba. The amount of¹³³Ba determined by gamma counting is directly related by stoichiometry to the amount of sulfate in the precipitate.     

A closer look at analytical signals

Analytical chemistry will be considered here as the measurement science of chemistry that generates, treats, and evaluates signals which contain information about the composition and structure of samples. Analytical information is always obtained from signals. Characteristics and peculiarities of analytical signals will be considered from a very general point of view. A mathematical model of the influencing of signals will be given from which essential performance characteristics of analytical methods can be derived, e.g. sensitivity, cross-sensitivity, specificity, selectivity, and ruggedness (robustness).     

Packing density,permeability, and separation efficiency of packed microchips at different particle-aspect ratios

HPLC microchips are investigated experimentally with respect to packing density, pressure drop–flow rate relation, hydraulic permeability, and separation efficiency. The prototype microchips provide minimal dead volume, on-chip UV detection, and a 75 mm long separation channel with a ca. 50 μm × 75 μm trapezoidal cross-section. A custom-built stainless-steel holder allowed to adopt optimized packing conditions. Separation channels were slurry-packed with 3, 5, and 10 μm-sized spherical, porous C8-silica particles. Differences in interparticle porosity, permeability, and plate height data are analyzed and consistently explained by different microchannel-to-particle size (particle-aspect) ratios and particle size distributions.     

Deposition efficiency of fractal-like aggregates in fibrous filters calculated using Brownian dynamics method

Nonspherical particles, such as fractal-like aggregates emitted by diesel engines, are commonly met in the ambient air. Some of them are believed to be carcinogenic to humans, thus their efficient removal is of crucial practical importance. A fibrous filter is the device commonly used for aerosol purification but the literature lacks experimental data concerning aggregates filtration. Effect of aggregates' parameters (fractal dimension, primary particle radius) as well as fiber diameter and air velocity on the filtration efficiency is investigated theoretically using the modified Brownian dynamics method. Three different expressions for the friction coefficient evaluation for the aggregates were examined. The results obtained indicate that structure of an aggregate, filter structure and process conditions strongly influence the aggregates deposition efficiency, which significantly differs from the values determined for mass-equivalent spherical particles. The results determined using the Brownian dynamics approach were compared with the values calculated using classical single fiber theory and noticeable discrepancy was observed for the most penetrating particles, while both approaches agree for the limiting cases of small or large particles. Peclet number based on the mobility radius and the interception parameter based on the outer radius are the proper criteria to describe diffusional and deterministic deposition of aggregates.     

Effect of chromatographic conditions on the separation and system efficiency for HPLC of selected alkaloids on different stationary phases

Retention parameters of alkaloid standards were determined on different stationary phases, i.e., octadecyl silica, base-deactivated octadecyl silica, cyanopropyl silica, preconditioned cyanopropyl silica, and pentafluorophenyl, using different aqueous eluant systems: acetonitrile-water mixtures; buffered aqueous mobile phases at pH 3 or 7.8; and aqueous eluants containing ion-pairing reagents (octane-1-sulfonic acid sodium salt and pentane-1-sulfonic acid sodium salt) or silanol blockers (tetrabutyl ammonium chloride and diethylamine). Improved peak symmetry and separation selectivity for basic solutes was observed when basic buffer, ion-pairing reagents, and, especially, silanol blockers as mobile phase additives were applied. The best separation selectivity and most symmetric peaks for the investigated alkaloids were obtained in systems containing diethylamine in the mobile phase. The influence of acetonitrile concentration and kind and concentration of ion-pairing reagents or silanol blockers on retention, peak symmetry, and system efficiency was also examined. The most efficient and selective systems were used for separation of the investigated alkaloids and analysis of Fumaria officinalis and Glaucium flavum plant extracts.     

Hydration of hydrogentungstate anions at different ph conditions: a car-parrinello molecular dynamics study

Standard density functional theory calculations with a continuous model of solvation as well as Car-Parrinello molecular dynamics simulations with explicit solvent molecules are carried out to analyze the effect of the pH of the solution on the coordination sphere of the W (VI) ion. Both methodologies agree in predicting an expansion of the coordination sphere of the W (VI) ion upon a decrease in the pH. Continuous solvation models, however, are unable to predict as stable some structural isomers of a hydrated hydrogentungstate anion and tungstic acid.     

Thermal performances of porous snow by a hydronic heating system at different weather conditions

Journal of Thermal Analysis and Calorimetry - The snow on the road in the cold regions is easy to cause slippery conditions, which are dangerous for vehicles and people. To remove the slippery...