Variational principles of magnetostatics of superconductors. I

Fundamental and dual variational principles of magnetostatics of superconductors are formulated. It is shown how test fields can be expressed in terms of vector and scalar potentials. General consequences of the variational magnetostatic formulation are discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 97–102, September, 1991.     

On-line coupling of sorption preconcentration to liquid-chromatographic methods of analysis

Methods of analysis combining the on-line sorption preconcentration of analytes with their subsequent separation and determination by high-performance liquid chromatography are considered. Approaches to the selection of sorbents, the sizes of preconcentration columns, and the sorption and desorption conditions are discussed along with the corresponding instrumentation. Many examples of the determination of organic compounds of different polarity and organic and inorganic ions are presented.     

Sorption–Atomic Absorption Determination of Trace Elements in Natural Waters with Dynamic Preconcentration in Electrothermal Atomizers

A sorption–atomic absorption method was proposed for the determination of ultratrace amounts of suspended and soluble forms of Ag, Cd, Bi, Pb, and Tl in natural waters using a dynamic preconcentration of these forms (separately or simultaneously) on the DETATA sorbent placed in a crucible atomizer and the subsequent direct atomic absorption analysis of the concentrate. This method is characterized by high a sensitivity and provides for the determination of elements in small volumes of unique samples. The accuracy of the determination of element species was verified by different methods in the analysis of sea and river water, atmospheric precipitation, and suspensions.     

Filters for the Preconcentration of Elements from Solutions

The main techniques for the preconcentration of elements on thin-layer filters are considered: sorption on filters with noncovalently immobilized reagents, bonded groups, and mechanically fixed sorbents and the extraction of elements on filters as poorly soluble and polymeric forms previously formed in solution. The matrix of the filters is cellulose, synthetic polymers of the linear and branched structures, synthetic fibers, reversed-phase silica gels, foamed polyurethanes, etc. The variation of the nature of the bonded group or the reagent introduced into the solution, the matrix material, and the technique for the immobilization of groups provides the preconcentration of elements with regard to the peculiarities of test materials and the method for the subsequent determination of elements. Methods for the determination of elements in different samples including preconcentration on filters are considered.     

Analytical chemistry: The day today

The author considers the expanding possibilities of analytical chemistry and the lines of development of present-day analytical methods and tools. Examples of practically important solutions are presented. Some unsolved specific problems are listed and an attempt is made to outline the nearest prospects for analytical chemistry.     

Preconcentration of Polycyclic Aromatic Hydrocarbons on Polyurethane Foams and Their Determination in Waters with the Use of Luminescence and High-Performance Liquid Chromatography

A technique was developed for the sorption preconcentration of polycyclic aromatic hydrocarbons on polyurethane foams in the batch and dynamic modes providing their simultaneous quantitative extraction. A procedure was proposed for screening waters for polycyclic aromatic hydrocarbons based on the preconcentration of these compounds with polyurethane foam, determination of their total amount by the luminescence method, desorption of adsorbed compounds with acetonitrile, and determination of individual compounds in the eluate by high-performance liquid chromatography with fluorescence detection. The procedure was tested with model and real samples of water.     

Formation of mixed complexes in the extraction of indium with 1-(2-pyridylazo)-2-naphthol

A detailed study has been made of the extraction of indium into chloroform by 1-(2-pyridylazo)-2-naphthol (PAN). The rate of extraction is maximal if the PAN is added to the aqueous phase and is not added as its chloroform solution. The ratio of indium to PAN is 1:1 and the cationic complex can be extracted only if a suitable anion is present, such as acetate or chloride.