Some ideas on minimization in ultra micro elemental analysis

Summary The problems encountered in the development of ultra micro methods or trace methods of elemental analysis are generally discussed. It is shown that process analyses (e.g. titrations) are preferable to meet needs of accuracy and sensitivity. Moreover, continuous systems of chemical process analyses seem to give a solution to the generally stated problems.

---

Überlegungen zur Minimalisierung in der Ultramikroelementaranalyse

Zusammenfassung Die Probleme bei der Entwicklung von Ultramikro- oder Spurenmethoden in der Elementaranalyse werden allgemein diskutiert. Es wird gezeigt, daß Prozeßanalysen (z.B. Titrationen) den Anforderungen an Genauigkeit und Empfindlichkeit entsprechen. Darüber hinaus scheinen kontinuierliche Systeme chemischer Prozeßanalysen eine Lösung der aufgezeigten Probleme zu ermöglichen.

We thank the Czechoslovak Academy of Sciences, the Analytical Department of the Charles University of Prague and the High School for Chemical Technology of Pardubice for the possibility given to one of us (B.G.) to discuss with many colleagues in the SSR, the ideas presented in this article.     

The influence of solute-solvent interactions on the kinetics and stereospecificity of polymerization-the relevance of aromatic solvent shifts observed on the nmr spectrum of methyl methacrylate

The effect of certain aromatic compounds on the PMR spectrum of methyl methacrylate (MMA) was investigated. The magnitude of observed aromatic-induced shifts decreased in the order benzene ? styrene > chlorobenzene ≈ bromobenzene.Assuming that the interaction arises from a stoichiometric 1:1 complex, equilibrium parameters for the MMA-benzene interaction have been estimated. ΔH ± S.E. (ΔH) = ?(8 ± 4) kJ mol^?1. These effects are likely to have a small influence on the kinetics of copolymerization with aromatic monomers and polymerization in aromatic solvent. The stereochemistry of the solute-solvent interactions suggests that MMA takes a cis-conformation in solution, which is relevant to the mechanism of stereoregular polymerizations of this monomer.     

Photoreactions of aromatic compounds—XXXV: Nucleophilic photosubstitution of methoxy substituted aromatic compounds. Monophotonic ionization of the triplet

Methoxy groups exert an activating and ortho/para directing influence in light induced nucleophilic substitution reactions (cyanation, hydroxylation, etc) of aromatic compounds in aqueous media. The first chemical step in these processes is monophotonic ionization of the aromatic compound in its lowest triplet state, followed by reaction of the radical cation with the nucleophile Quantum yields of photocyanation of 4-fluoro- and 4-chloroanisole indicate that in 99% (mole fraction) water virtually all triplets formed undergo electron ejection.This hypothesis is in agreement with the results of charge density calculations for the radical cations. It is directly supported by the similarity of the product composition of these photochemical substitutions with that of anodic substitutions, where the intermediacy of an aromatic cation is generally accepted. The presence of an oxidizing agent (oxygen, or persulphate) is required only when a hydrogen is replaced. The nucleophilic photosubstitution at electron rich aromatic systems in solvents as water can therefore be classified as an S_r⁺n¹(³Ar^*) process.     

Use of thenoyltrifluoroacetone for the determination of manganese by activation analysis

A new procedure for the substoichiometric extraction of bivalent manganese by thenoyltrifluoroacetone into ethyl acetate has been developed and used in activation analysis. The value of the extraction constant has been found to be 3.1 x 10(-6); the pH range in which the extraction can be performed is 7.8-9.2. The influence of oxalate, citrate, tartrate, fluoride and cyanide ions has been studied. A selective substoichiometric extraction of manganese in the presence of Zr, Hf, Nb, Th, Fe and Sc is possible at pH 8-8.5, tartrate and fluoride being used as masking agents. Copper and cobalt can be screened by ammonia and cyanide respectively. The method has been used for the determination of manganese in biological materials, potassium fluoride and zirconium.     

Thermometrische Schnellanalyse von Martin- und Hochofenschlacken sowie anderen Silicaten

Summary A novel method has been developed for the rapid analysis of silicates. Each component is determined from the temperature variation of the solution resulting from the addition to the test solution of a selectively reacting reagent. By suitable construction of the instrument the concentration of the component to be determined can be read directly in per cent. The determination of a component takes usually 4 to 8 minutes.In the test solution a temperature change proportional to the concentration of the component to be determined has been produced by the following reagents: sulphuric acid for barium, ammonium peroxodisulphate for iron, hydrogen peroxide for titanium, hydrofluoric acid for silicic acid, potassium permanganate for sulphur, ammonium molybdate and hydrogen peroxide for phosphate, potassium permanganate for manganese, potassium oxalate for calcium, diammonium hydrogenphosphate for magnesium, ascorbic acid for chromium. The above components can be determined without any separations. Only in the case of aluminium a separation of silicic acid from aluminium by dehydrating with perchloric acid in necessary. Thereafter the aluminium can be determined with hydrofluoric acid.The precision of the determinations is practically identical with the precision of the usual plant methods.     

The simulated ab-initio molecular orbital (SAMO) method for polymers. Polyethylene and polyene

The application of the simulated ab-initio molecular orbital (SAMO) method — a new non-empirical technique — to the band structure of polymers is reported. The method uses full ab-initio results on small molecules to construct for polymers molecular orbitals which simulate those obtained from full ab-initio treatments. Results are compared with those obtained from published ab-initio and semi-empirical calculations.     

Effects of complex-valued electronic wave functions on nuclear motions

Moleculer species and colliding groups of atoms are considered for which the electronic wave functions are complex-valued, having arguments that depend parametrically on the nuclear coordinates. The effective Hamiltonian for nuclear motions in the adiabatic approximation that arises in the present case differs from the ordinary Born–Oppeneheimer Hamiltonian, the latter being obtained when restriction to real-valued electronic functions is made. The asymptotic boundary conditions imposed in collision theory lead to in- and out- states [8], and hence to complex-valued wave functions in the coordinate representation. The study of the influence of electron–molecule scattering on nuclear motions therefore necessitates the use of the new effective Hamiltonian, which leads to results differing from those predicted on the basis of the Born–Oppenheimer operator. It is shown that momentum-dependent potentials occurring in the new Hamiltonian might cause “distortions” to the vibrational patterns of some electron–molecule metastable states. Also, these terms can give rise to non-Born–Oppenheimer resonances when motions in an internuclear coordinate become unbounded. We derive expressions for the relevant level widths and line shapes, showing them to be subject to an isotope effect. Even when real-valued electronic functions may be used, the selections of complex-valued functions in their linear span is still optional. Although exact treatments lead to the same results in both real and complex cases we show how the choice of the argument of the electronic function to be non-zero and dependent on nuclear coordinates may be useful for the application of certain approximation schemes. It is demonstrated that for certain systems a suitable choice of the argument assures convergence when the related Lippmann–Schwinger Equation is iterated. It is also shown that in this way an nth order term in the series expansion of the T matrix [8] for moleculer systems can be made negligibly small.     

Energetic calculations of the chain conformation of isotactic polymers of olefins in the crystalline state

Energetic calculations have been carried out on a correlated series of isotactic aliphatic polymers (polypropylene (PP), poly-α-butene (PB), poly-3-methylbutene (P3MB), poly-(S)-3-methylpentene-1 (P(S)3MP) and isotactic polystyrene (PS). The possible variation of the CCC bond angles and of all the internal rotation angles (no group of atoms being taken as a unit) was considered.The possibility to predict the experimental helical parameters without any previous assumption is discussed. The differences in the shape of the minima for polymers with aliphatic and aromatic branched chains have been critically evaluated.For the P(S)3MP the results have shown how the asymmetric configuration of the side group influences the chain conformation of the polymer.     

The influence of the mercury and thallium atoms in organomercury and organothallium nitroxyl radicals on their reactivity

An increase is found in the reactivity of organomercury and organothallium nitroxyl mono- and biradicals of the imidazoline type in comparison with the analogous compounds without organometallic fragments. This is explained by the formation of coordination bonds NHg, NTl, and NOHg.Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 224–226, January, 1993.