A shot cut method for the determination of isoniazid in a solid dosage formulation (DF) has been developed. The method is based on isoniazid titration with a solution of photogenerated iodine obtained as a result of irradiation of an auxiliary solution containing potassium iodide, a mixture of sensitizers (sodium eosinate, fluorescein, auramine taken in a molar ratio of 1:1:1) and phosphate buffer solution (pH 7.5). Since the titrant content in the cell was controlled using the voltammetric method (amperometric titration with two polarized electrodes), the interaction of a physiologically active compound with the latter was accompanied by a decrease in the amount of titrant in the cell and, hence, in the current in amperometric circuit. Stabilization of the current in the circuit of the amperometric setup indicated the completeness of the reaction, and, therefore, provided estimation of the content of a physiologically active compound in the dosage formulation. Further irradiation of the solution and measurement of the generation time required to replenish the loss of titrant in the cell also made it possible to regulate the content of isoniazid in the preparation. The technique was tested on the samples of solid dosed formulations. It was shown that the components of the tablet mass (calcium stearate monohydrate, polysorbate, crospovidone and potato starch) do not affect the results of the determination of physiologically active compound provided that the analyzed form is obtained at room temperature. The determined content of isoniazid in a solid dosage formulation varies in the range of 286.0 – 296.0 mg and falls within the range recommended by the General Pharmacopoeia Monograph 1.4.2.0009.15 (285 – 315 mg), which indicates that the quality of the drug meets the GMP standards. The linear dependence of the analytical signal on the concentration of physiologically active compound is observed in the range of 161 – 1610 mg for the drug «Isoniazid. Tablets, 300 mg». The calculated detection limits and quantitative determination are 13.5 and 41.0 mg (both in terms of change in the current strength and in the time of titrant generation), respectively. The developed photochemical method for the determination of isoniazid in solid dosed formulation is easy to use, meets the requirements set out in the guidelines for validation of bioanalytical methods, and does not require expensive equipment. The method can be recommended for routine control of the DF quality indicators in any analytical laboratory.

A technique for the determination of dissolved forms of silicon in water using high-resolution continuum-source electrothermal atomic absorption spectrometry (HR-CS-ETAAS) is proposed. The quantitative determination of the dissolved forms of silicon was performed using an atomic absorption spectrometer ContrAA 700 with a graphite cross-heating cuvette. Natural water was selected to optimize the temperature-time program of the atomizer. To eliminate chemical interference during the silicon determination by HR-CS-ETAAS, the graphite cuvettes were modified with a permanent modifier to form a carbide coating. A solution of sodium tungstate was used as a permanent modifier. Thermal stabilization of silicon in a graphite furnace was achieved with a mixed palladium-magnesium modifier present in the nitrate form. The developed method was used for determination of the content of the dissolved forms of silicon in water. The developed technique was certified proceeding from the results of the research and the metrological examination by an organization accredited for this type of the activity and registered in Federal information Fund for ensuring the uniformity of measurements (FIF).

Current development of applied ionometry requires focusing of theoretical studies both on revealing the nature of the selectivity of electrode membranes and on the developing the new methods of membrane synthesis and their modification with the goal of obtaining more perfect structural units with improved functional properties. Elucidation of the relationship between the structural characteristics of the membranes and their effect on the electro-analytical properties is a rather important task. The interaction of organic cation levamisole with bromophenol blue was studied to meet the goals. Levamisole-selective sensor with a plasticized polyvinyl chloride (PVC) membrane has been developed. The electrode contains an ionic associate of levamisole with bromophenol blue. PVC was used as a matrix to model the membrane composition. Membranes plasticized with dibutyl phthalate (DBP), diethyl phthalate (DEP), dioctyl phthalate (DOP), dinonyl phthalate (DNP), dibutyl sebacate (DBP), tricresyl phosphate (TCP) were studied. It was shown that the nature of the plasticizer insignificantly affected the analytical characteristics of the electrode. The response is linear within the concentration range of 1 × 10^–5 – 1 ×10^–1 mole/liter with the slope of the electrode function 52.1 ± 1.0 mV/pC. The sensor has a quick response (10 sec) and can be used for at least 8 weeks without any divergence in the long run. The operation life of the membranes with a high plasticizer content is much longer. The electrode can be used within pH range of 3.0 – 8.0. Potentiometric selectivity coefficients of the electrode relative to a number of potentially interfering ions were determined. The developed electrode was tested in determination of levamisole in model solutions and pharmaceuticals («Decaris» and «Levamisole-Zdorovye»).

Albumin is a nanoscale protein packed in a specific way into a polypeptide chain. Albumin maintains the osmotic pressure of the blood and protein reserve of the body, and provides an important transport function. We present the results of studying the structure of plasma albumin using a small-angle scattering of synchrotron radiation, one of the most effective analytical methods for analysis of the nanoscale structures. Moreover, the method provides studying the structures of liquid biological objects in a natural solution. It is shown that protein globules have the form of ellipsoids with semi axes 8, 8, and 3 nm and are formed by three domains consisting of α-spirals. The domains differ in the distance between ordered α-spirals. Albumin can be in the form of separate globules, dimers and oligomers surrounded by hydration membranes. Protein molecules in the studied plasma are arranged chaotically. The results obtained can be used to develop a method for assessing the quality of plasma based on the determination of the quantitative content of individual globules. Data on the protein structure are also valuable for the therapeutic applications of albumin.

Austenitic stainless steels are widely used in nuclear and thermal power engineering due to their high mechanical, corrosion and technological properties. We present the results of studying the effect of deformation martensite on the corrosion resistance of chromium-nickel steels of the austenitic class. Samples of heat exchange tubes of steam generators, tube bends, plates (constituents of steam turbines), safety valves used in NPP equipment were studied. The tests were carried out using metallographic, X-ray diffraction, atomic emission and atomic absorption spectral analyses. Electron microscopy was used to determine the content of the ferrite phase. It is shown that irregular dark gray spots located along a line parallel to the sample axis contain iron oxides. The appearance of such defects observed only on the outer surface of the products is attributed to the technology of their manufacture. It is also shown that severe plastic deformation which occurs during production or operation leads to formation of the deformation martensite which is subject to corrosion at this the corrosion cracking is accompanied by stress. The absence of δ-ferrite in the metal of samples is also revealed. The deformation martensite formed during operation of the product at the point of contact with a harder material leads to appearance of a large number of microcracks, which develop according to the fatigue mechanism under cyclic loading. The results obtained can be used to assess the probability of the formation of deformation martensite in chromium-nickel austenitic steels.

A net detrimental effect of acid vapors on human health and environment characteristic for chemical methods of descaling the surface of steel wire rod, as well as the difficulties in the disposal of pickling sludge dictate the need for developing a new methodology free of the aforementioned shortcomings. A metallographic method for determining the mass of scale on the surface of a steel wire rod subjected to two-stage cooling is proposed. The tests were carried out in accordance with the requirements of current standards for assessing the accuracy (correctness and precision) of methods and measurement results. The proposed metallographic approach appeared advantageous for proved reliability of the scale mass determination with the required accuracy at a confidence level of 95%; for significant reduction in the material consumption due to the absence of the need for special sample preparation; reduction of the test time due to determination of metallographic parameters in parallel with optimization of the descaling procedure through scale dissolution in a pickling solution and protection of the base metal with the inhibitors; for elimination of using acids and, as a result, the necessity of waste disposal. Apart from quantifying the scale content, the method provides for determination of the phase component ratio. It is shown that the metallographic method, including determination of the scale mass by measuring the thickness of the layers of the scale phases (wustite, magnetite), can be used as an alternative to the traditional standardized method for rapid determination of the scale amount and X-ray structural analysis of the phase composition.

Layered composites formed by unidirectional layers are widely used in aviation in the most loaded areas of the aircraft. Data on the elastic properties of the layers are required for the strength and stiffness calculation of structural elements made of such materials. There are two possible approaches to address the problem. The first approach is based on solving the problem of micromechanics using methods of the theory of elasticity. The second approach consists in developing a simplified model of a unidirectional layer. Analysis of the model can provide for fairly simple formulas for determination of the effective stiffness of a unidirectional layer. A comparative analysis of the results obtained in both approaches revealed the limits of applicability of approximate formulas derived for evaluating the effective characteristics of the different types of composites depending on the volume content of fibers. The effective elastic characteristics of unidirectional composites are determined by the finite element method in the framework of the linear theory of elasticity. The boundary value problem is solved for a characteristic representative element selected in accordance with the physical and geometric parameters of the medium of an ordered structure. A set of algorithm-programs has been developed under ANSYS environment which automates calculations of the elastic characteristics of materials depending on the volume content of fibers at different ratios of the elastic properties of fibers and binder, and on the parameters of the curvature of the fiber cross-sectional profile. The results obtained by the numerical method are compared with the data obtained experimentally and by approximate formulas.

The indicators of the brittleness and viscosity of metals calculated from their mechanical properties are considered with allowance for the stress state proceeding from the results of tensile testing of cylindrical smooth and notched samples of perlite 16KhSN, martensitic-aging (maraging) 03Kh11N10M2T, and austenitic 10Kh11N23T3MR steels. Tests were carried out on a UEM-10TM tensile strength testing machine, deformation diagrams developed on a scale of ~50:1 at a deformation rate of 5 mm/min. The sample size before and after testing were measured using a micrometer and an ISA-2 comparator with an accuracy of ±10^–3 mm. Pendulum impact bending tests were carried out on a MK15 with the same cylindrical notched samples used to plot the plasticity and viscosity diagrams depending on the Bridgman stress state stiffness index. The new indicators of the brittleness λ = ε_k/η and viscosity η = (S_k/σ_b) – 1 (where ε_k = ln(1/(1 – ψ_k)) is the true limit plasticity) are proposed proceeding from the testing data. The special feature of the brittleness index λ is growth of the index with increase in the metal strength, e.g., due to pre-deformation or strengthening heat treatment procedures. However, a decrease in the groove radius on the samples, i.e., an increase in the Bridgman stress state stiffness, has almost no effect on the brittleness value λ, but is accompanied by a correlation decrease in the values of the viscosity indices η and the ultimate ductility ε_k of steels. The curves of the temperature dependences of the mechanical properties of steels 16KhSN and 03Kh11N10M2T show that anomalies in the brittleness indices λ observed at elevated test temperatures can be attributed to the structural transformations like increase in the grain size of 16KhSN steel or in the amount of the residual austenite in 03Kh11N10M2T steel due to reverse martensitic transformation. In this case, the temperature dependences of the viscosity η and brittleness λindicators change in the opposite way.

Thermal mechanical equipment or the pipelines of the second circuit of a VVER type NPP are mainly subject to two degradation mechanisms that reduce the strength of structural elements: flow-accelerated corrosion and fatigue damage. As a rule, the aforementioned degradation mechanisms bear no combined impact as they affect different zones of the object. However, welded joints are subjected to the impact of both mechanisms which results in initiation and development of cracks in welded joints and in their local thinning due to the low content of alloying elements or due to hydrodynamic features of the flows arising in back of taps, throttling devices, cone transitions and similar pre-connected sections. The goal of the study is to elucidate the effect of flow-accelerated corrosion on the development of fatigue cracks in welded joints. We used the formulas of fracture mechanics to describe the time-dependent undergrowth of cracks and empirical data to describe the dependence of flow-accelerated corrosion on the operation time and postulated residual defect structure. The proposed approach provided estimation the effect of flow-accelerated corrosion on the rate of crack developing in the equipment or pipeline. It is shown that flow-accelerated corrosion can both reduce and significantly increase the crack growth rate. The distribution of defects versus the operating time is obtained, taking into account the entire set of possible missed defects. The distribution obtained provides for more correct assessing of the reliability and safety of welded joints of the NPP equipment and pipelines.

A mathematical model for studying temperature-time conditions of arc surfacing upon manufacturing of steel-aluminum compositions has been developed and verified. During simulation, the dependences of the thermophysical properties of the materials under study (thermal conductivity and heat capacity of a unit mass of the substance at constant pressure and volume) on the heating temperature were added to the database of the «SVARKA» software to solve the thermal problem. When simulating the arc surfacing, the geometric model of the object was set in the form of a single body, which, e.g., in case of formation of functional coatings based on non-ferrous alloys on steel substrates, can consist of various materials. The parameters of the heat loads of the heating source are: the advance speed, power, distribution along and across the weld, as well as the presence and grade of the filler material. The calculation of heat propagation upon argon-arc surfacing with a non-consumable electrode was carried out according to the scheme with a normal-circular heat source located on the surface of a flat layer with the limiting effect of the bottom plane of the sheet. The considered calculation scheme includes all the main features of the argon-arc surfacing process, i.e., introduction of the heat of the welding arc into a massive body from the surface; small pressure of the welding arc; slight immersion of the active arc spot in the liquid metal. It is shown that allowance for the thermophysical properties of the intermetallic layer of the Fe – Al system located in the diffusion zone, provided determination of the heating temperature with the uncertainty of no more than 8 % not only at the steel-aluminum interface, but also at any point of the samples both in the transitional bimetallic steel-aluminum elements joined with aluminum or steel structures, and in functional aluminum coatings formed by surfacing, including those made of composite materials.

A problem of optimizing the configuration of a navigation measuring system is considered in terms of the experimental design using a distance navigation problem for position of the object location. It is shown that the stated problem is equivalent to the problem of A-optimal experimental design for a regression function (nonlinear in parameters) and can be reduced to a trigonometric model. The response function, Fisher’s information and the sensitivity factor of the navigation system in case of two and three beacons and correlated measurements are presented in an explicit form. Using the equivalence theorem for A-criterion in the case of two-dimensional (plane) distance problem we confirm again the Barabanovs’s result that matrixes of A-optimal designs are the Kolmogorov – Maltsev matrixes. A similar result holds for the D-optimality criterion in the considered case. The effect of the measurement correlation in a distance navigation problem with two and three reference points is considered. The formulas for the sensitivity factors expressed in terms of bearings on the reference points and intersection angle of object are derived. In addition to a problem of optimizing the network configuration, the data processing problem in two-dimensional distance navigation problem with two reference points is also considered. The location of the object is determined in two ways, i.e., using the geometrical method and method of resultants. In the first method the solution of a distance navigation problem comes to the consideration of two independent quadratic equations for determination of the first and the second coordinates of the object. The equations are obtained in the explicit form. The second method also leads to two quadratic equations for determination of the object location. This is an option of the exclusion method which provides for an explicit form of conditions ensuring the solution of the considered problem for determination of the object location. Examples are considered that confirm the stated conclusions.