Some new aspects of the theory of radioanalytical methods based on the partial solvent extraction separation of the element to be determined

Interrelationship between the error of the radioanalytical methods and the concentration of the element to be determined has been found for extraction systems with different parameters K_ex, pH, a concentration of the extractant. Based on a mathematical discussion of this interrelationship, the criterion of the estimation of sensitivity has been proposed for the different radioanalytical methods based on the substoichiometric principle as well as some deviations from it.     

Some aspects of colloids in photography

The principles of colloid and interface science underlie the successful formulation and manufacture of photographic products. The colour-forming components are usually delivered in colloidal form. Rapid and stable manufacture depends on the dynamic surface properties and the rheology of the coated fluids.     

Sulphur tracer experiments in laboratory animals using 34S-labelled yeast

We have evaluated the use of ³⁴S-labelled yeast to perform sulphur metabolic tracer experiments in laboratory animals. The proof of principle work included the selection of the culture conditions for the preparation of sulphur labelled yeast, the study of the suitability of this labelled yeast as sulphur source for tracer studies using in vitro gastrointestinal digestion and the administration of the ³⁴S-labelled yeast to laboratory animals to follow the fate and distribution of ³⁴S in the organism. For in vitro gastrointestinal digestion, the combination of sodium dodecyl sulphate-polyacrylamide gel electrophoresis and high-performance liquid chromatography and inductively coupled plasma mass spectrometry (HPLC-ICP-MS) showed that labelled methionine, cysteine and other low molecular weight sulphur-containing biomolecules were the major components in the digested extracts of the labelled yeast. Next, in vivo kinetic experiments were performed in healthy Wistar rats after the oral administration of ³⁴S-labelled yeast. The isotopic composition of total sulphur in tissues, urine and faeces was measured by double-focusing inductively coupled plasma mass spectrometry after microwave digestion. It was observed that measurable isotopic enrichments were detected in all samples. Finally, initial investigations on sulphur isotopic composition of serum and urine samples by HPLC-ICP-MS have been carried out. For serum samples, no conclusive data were obtained. Interestingly, chromatographic analysis of urine samples showed differential isotope enrichment for several sulphur-containing biomolecules.     

Some new aspects of the Boyer reaction

[reaction: see text] The reaction outcome of 2-azidoethanol and aliphatic aldehyde is found to be dependent on the catalyst and the structure of the azido alcohol. Under the catalysis of Cu(II) triflate, the corresponding acetal is obtained. A similar reaction between 2-aryl-2-azidoethanol and aldehyde catalyzed by BF3 yields a mixture of 3-oxazoline and 2-oxazoline. The latter reaction has been used for the preparation of 3-oxazolines in good enantioselectivity.     

Some aspects of the living isobutylene polymerization

The possibilities of increasing the livingness in cationic isobutylene polymerizations has been investigated. It has been assumed that the living chain-end is polarized but non-dissociated and relatively stable, therefore, i) shifting of the dissociation equilibrium by adding salts with common or non-common anion in excess, and ii) increasing of the stability of the chain-end by complexing it with electrondonors, may increase the livingness of the system. Indeed, the addition of n-Bu₄NCl or n-Bu₄NI to systems with BCl₃ or TiCl₄ coinitiators, as well as the addition of dimethyl sulphoxide as electrondonor in a broad concentration range, improved the living character. The possibility of complexation of the chain-end by the monomer has also been supported     

Some stereochemical aspects of the pellizzari rearrangement

Variable temperature nmr spectroscopy and X-ray crystallography have been employed to study the stereochemistry of 2-cyano-3,3-dimethyl-1-phenylpyrazolidin-5-one which thermally rearranges to 2,3-dihydro-2,2-dimethylpyrimido[1,2-a]benzimidazol-4(1H)-one.     

Some aspects of the mercuriation of ferrocene

The kinetics of mercuriation of ferrocene with Hg(OAC)₂ have been reinvestigated and the data interpreted in terms of rapid complex formation followed by rate determining conversion of the complex to products. The nature of analogous complexes with HgCl₂ was investigated by an NMR method which suggested the formation of a 1:1 iron-bound mercury species. Product analyses of the mercuriation reaction revealed evidence for homoannular disubstitution. The homoannular derivative is subsequently converted to the 1,1'-disubstituted product. Improved syntheses ot the acetatomercuri ferrocenes is also reported.     

Some aspects of the model potential method

The theoretical justification of the model potential method is studied in some detail. The correct equations within the framework of Roothaan's open-shell scheme are derived and the approximations necessary to get a workable method are discussed. Analysis of the local part of the model potential suggests a new analytical form for it. The new expression is theoretically more consistent than the original one, and it can be determined in a more straightforward way. A basis set approximation, which is particularly suitable for approximate evaluation of two-electron integrals when only valence orbitals are involved, is discussed and tested with encouraging results. The ideas are tested on the Fe and I atoms.     

Some practical examples of method validation in the analytical laboratory

Method validation is a key element in both the elaboration of reference methods and the assessment of a laboratory's competence in producing reliable analytical data. Hence, the scope of the term method validation is wide, especially if one bears in mind that there is or at least should be a close relation between validation, calibration and quality control QA/QC. Moreover, validation should include more than the instrumental step only since the whole cycle from sampling to the final analytical result is important in the assessment of the validity of an analytical result. In this article validation is put in the context of the process of producing chemical information. Two cases are presented in more detail: the development of a European standard for chlorophenols and its validation by a full scale collaborative trial, and the intralaboratory validation of a method for ethylenethiourea using alternative analytical techniques.     

Publication activity on radioanalytical chemistry in the German Democratic Republic

The growth of the number of papers on radioanalytical methods and activation analysis, the distribution of the authorship and papers published in various periodicals are determined in the course of a scientometric analysis using the first complete National Bibliography of GDR on Radioanalytical Chemistry as a database.     

A new timescale dimension for migration experiments in clay: proof of principle for the application of miniaturized clay column experiments (MCCE)

Geological clay formations are often considered as a host rock for a future nuclear waste repository. Many studies concerning sorption or desorption experiments with metal ions like radionuclides or other relevant substances (e.g. metal complexing ligands) onto/from geological clay samples are performed with the batch techniques where only small amounts of the homogenized clay is in contact with the appropriate metals diluted in high volumes of aqueous solutions. This unnatural contact of clay with water can lead to high bias or not transferable results for a risk assessment study of a future repository. Diffusion experiments as an alternative and more natural experimental tool have the lack of huge time consuming when the migration of higher valent metal ions is considered. With the herein described new miniaturized clay column setup a linker between the unnatural batch techniques and the time consuming diffusion experiments is installed. The presented miniaturized clay column experiments (MCCE) derived and modified from high performance liquid chromatography can be applied in a lot of geochemical studies. Using MCCE, migration experiments of inert tracers (iodide), natural organic matter as complexing ligands (lactate and salicylate) as well as trivalent metal ions (europium) in compacted clay can be performed within a short time span of a few minutes or hours only in contrast to several months by use of classical diffusion or column methods. As preliminary results, typical migration times through miniaturized clay columns (20 × 3.5 mm, L × ID) of iodide as inert tracer are in the range of 145 min, meanwhile increasing retention times of salicylate from about 390 min in the absence of Eu to migration times in the range of 420–470 min in the presence of different Eu concentration can be observed.     

Some new aspects of bonding in cyclopropane

The peculiar properties of the three-membered ring in cyclopropane are partially due to characteristic relaxation effects of the carbon orbitals in the molecule. AO contraction in the two strongly C? C bonding MO's of A type is essential for the stability of the C₃ ring, whereas AO expansion in the E'-type HOMO contributes to the π character of the peripheral C? C bonds.     

Analysis of errors in the radioanalytical method of concentration dependent distribution

The precision of the title method is analyzed theoretically for a hypothetical case of solvent extraction involving the reaction. It was found that there exists a certain reagent concentration giving the lowest errors. If the error in the determination of distribution ratios is 2%, a broad range of conditions exists where the error of the result is near to or less than 1%. The ranges of the values _H ^1/N are found for N=1,2 3 for cases where the error of the results is 1%.     

Some aspects of the calculation of lattice energies

Some relations between lattice energies calculated from various simple equations are pointed out. It is found that these equations give values of the variation of compressibility with pressure that agree poorly with experiments, at least for sodium and cesium chloride, bromide, and iodide. Equations which take this variation into account are developed, and it is found that calculated values of the lattice energy vary very little with the exact equation used. On the whole these extended equations give better agreement between the calculated and observed lattice energies.