The electrochemical behavior of disordered systems, such as high-entropy alloys, is a stochastic random process. To accurately predict and analyze the behavior of such systems under operating conditions, it is necessary to use new computational and experimental methods along with classical electrochemical methods. Using equimolar rare-earth alloys GdTbDyHoSc and GdTbDyHoY as an example, we demonstrate the efficiency of using fast Fourier transform and wavelet analysis to estimate the electrochemical behavior of stochastic systems. The time series of potential fluctuations of alloy samples are measured in 0.01 M NaCl solution within 12 h at a current density of 0.2–0.5 mA/cm2. Fast Fourier transform analysis of the obtained time series shows that the slope of the logarithm of spectral power density to the logarithm of frequency increases with the current density. In particular, coefficient β changes from –1.93 to –1.77 for a GdTbDyHoY sample and from –1.46 to –1.35 for a GdTbDyHoSc sample. In addition, wavelet analysis is used to process the time series obtained for both alloys at current densities from 0.2 to 0.5 mA/cm2. To illustrate the intensity of the electrochemical dissolution of the alloy surface, we construct scalograms for the obtained time series. The scalograms are used to calculate the global energy spectra distributed over frequency ranges and the total energies of the systems under study. The GdTbDyHoY alloy exhibits higher total energies as compared to the GdTbDyHoSc alloy. The total energy for the GdTbDyHoY alloy increases from 0.97 to 2.03 kV2 when the current density increases from 0.2 to 0.5 mA/cm2. For the GdTbDyHoSc alloy, the total energy increases from 0.50 to 0.84 kV2. Fast Fourier transform and wavelet analysis are found to be effective tools for understanding the electrochemical behavior of locally disordered chemical systems, such as high-entropy GdTbDyHoSc and GdTbDyHoY alloys, in addition to classical electrochemical methods.

The study considers a possibility of studying the manifestation of the major background ions derived from the main elements (H, N, O, and Ar) of inductively coupled plasma under low-temperature (“cold”) plasma conditions through thermodynamic simulation. These ions, known to induce significant spectral interferences, are always observed when aqueous samples are injected into inductively coupled plasma mass spectrometers (ICP–MS). Using thermodynamic simulation in the temperature range from 2000 to 5000 K, the quantitative composition of the major background ions in ICP–MS was determined as a function of plasma temperature. A comparison of the theoretical calculations and experimental data from mass spectral measurements of the major background ions was conducted, revealing a high degree of correlation between the two sets of the results. This agreement between the calculations and experiments confirms the validity of the thermodynamic model used for thermochemical processes in ICP–MS and its applicability to subsequent calculations in addressing analytical challenges. Additionally, a method is proposed for the unambiguous evaluation of the gas kinetic temperature of the plasma, while simultaneously considering practically all major background ions.

A significant improvement in the ability to remove ecotoxicants, hexavalent chromium and methylene blue dye, from aqueous solutions under the action of short-wave visible radiation was shown for anatase modification after mechanical activation.

Microcrystalline powders of rutile and anatase were milled in a high-energy planetary mill down to obtain nanosized TiO2 powders (the size of coherent scattering region (CSR) about 30 nm and 60 nm, respectively). The resulting powders were characterized by HRTEM, Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and the xi-potential of the aqueous suspensions was determined. High-energy milling made it possible to significantly increase the ability of TiO2 to remove chromium from aqueous solutions. The effectiveness of the powders for not only Cr(VI) removing but also total chromium adsorption under UV-irradiation and short wavelength visible light has been shown. This is important, since Cr(III) does not remain in the aqueous medium and cannot be oxidized back to Cr(VI) under the influence of some environmental factors. It is possible to remove more than 99.9 % of total chromium and 100 % of chromium hexavalent from a 50 mg center dot L-1 solution of Cr(VI) using milled anatase. XPS showed that, upon the photoadsorption, Cr(VI) is reduced to Cr(III). The presence of an acetate buffer in the solution promotes the most efficient removal of chromium. This work shows a simple way to obtain a highly effective material with potential applications for the removal of high toxic hexavalent chromium from industrial wastewater. The milled anatase sample was successfully tested to remove Cr (VI) from a real wastewater sample.

Spectrally pure graphite after mechanical activation demonstrates adsorption properties for Mo(VI), W(VI), Cr(VI), Ni(II), Fe(III) ions (more than 95% adsorption from solutions in the pH range from 4 to 6.5), which can be used to separate them from Re(VII) and As(V) and, in the future, be used for chemical analysis.

Mechanical activation of spectrally pure graphite was carried out in a high-energy planetary mill. Changes in the structure and physicochemical properties caused by this modification are shown by SEM, XRD, Raman spectroscopy, XPS, N-2 adsorption-desorption, and inert gas fusion methods. Because of the mechanical activation, a decrease in crystallite size of the graphite and the oxidation occurred; it began to exhibit sorption properties with respect to Cr(VI) ions. The optimal conditions were found for removing more than 99% of Cr(VI) from the 50 mg.l(-1) aqueous solutions. In an acetate buffer solution with pH 6.3 after 1 h of heating at 90 degrees C, the Langmuir adsorption capacity for chromium on this sorbent is 14.7 mg.g(-1). Thermodynamic characteristics of the adsorption were determined; they show that the process is spontaneous and endothermic. It was found that only incomplete desorption of chromium from the surface of the modified graphite is possible using concentrated NaOH solutions. An assumption was made about a mixed mechanism of chromium adsorption, including partial reduction of Cr(VI) to Cr(III), anionic adsorption of Cr(VI) ions through electrostatic interaction, and the formation of an insoluble chemical compound of Cr(III) on the surface of the mechanically activated graphite. The sorbent was tested on a real sample of wastewater from bichromate production, after adsorption hexavalent chromium was not detected in the water.

For the first time, chi-Al2O3 was investigated as a sorbent for the simultaneous separation of copper and molybdenum from rhenium. This work finds the optimal conditions of the process. In an acetate buffer solution with a pH of 5.5 under the action of ultrasound for 30 min, the Langmuir adsorption capacity for copper and molybdenum on this sorbent was 46 mg.g(-1) and 44 mg.g(-1), respectively, rhenium remained in the solution. The adsorption corresponded to the pseudo-second-order kinetics model. It has been shown that under the indicated conditions, over 80% of molybdenum and 95% of copper can be removed from synthetic solutions containing 100- and 1000-fold mass excess of copper and molybdenum. In nitric acid or sulfuric acid solutions, the same results can be achieved at a pH of 2.5-3.0. It was found that the recovery of rhenium by inductively coupled plasma atomic emission spectrometry after matrix separation was improved; on average, a threefold reduction in the relative standard deviation (n = 5) was achieved. The mechanism of adsorption of Cu, Re, and Mo ions on the surface of chi-Al2O3 was proposed, based on the interaction of ions with an electric double layer of sorbent particles.

Thermochemical processes of gaseous molecules SrI and HaI formation, which are used in the electrothermal molecular absorption determination of iodine, were studied using the method of thermodynamic simulation. The calculations made it possible to establish that gaseous molecules SrIg and BaIg are formed during the course of the thermal decomposition of gaseous SrI2g or BaI2g, respectively.

Influence of magnesium nitrate used as chemical modifier on the temperature of pyrolysis for Al, Ag, Cr, Cu, Sn determination was estimated by theoretical calculations and experiments. Theoretical results were confirmed by the experimental data. The mechanism of the modifier action was determined.

The possibility of chromium(VI) removing from water by adsorption on mechanically activated rutile was demonstrated. Degree of adsorption of the pollutant was studied as a function of pH, sorbent load, time, solution composition, and also when the aqueous solution was illuminated with various radiation sources.

The effect of Mg(NO3)2 used as chemical modifier on the temperature of pyrolysis for indium determination was determined. Thermodynamic simulation of thermochemical process at the pyrolysis stage with and without Mg(NO3)2 was carried out. Theoretical results were confirmed by experimental runs.

Thermodynamic properties, namely standard molar enthalpy of formation (Δ H f ° 298 ), standard molar entropy ( S ° 298 ), and temperature dependence of heat capacity ( С р ( Т )) of crystalline metal perrhenates, were assessed by the semi-empirical methods. In this work, Δ H f ° 298 , S ° 298 and coefficients a , b and c for C p = а + 0.001× b × T + 10 5 × c × T – 2 equation were calculated using several methods and averaged. These thermodynamic properties were calculated for the following perrhenates metals: Li, N, K, Rb, Cs, Cu, Ba, Fe, Ca, Cd, Co, Mg, Mn, Pb, Sr, Zn, Al, Crи Fe. The calculated values of the thermodynamic properties were in good accordance with the known literature data. New data were applied to the thermodynamic simulation of rhenium-containing sample pretreatment processes for the chemical analysis. The thermodynamic simulation of the sintering sample with the magnesium oxide with/without oxidizing agents was carried out using HSC 6.1 software with new data about the perrhenates. According to the calculated results, the addition of the oxidizing agent (NaNO 3 or K 2 S 2 O 7 ) to the magnesium oxide was needed and its presence ensured the rhenium transition into the solution without losses. In this case, rhenium was present at the temperature of the sintering predominantly as NaReO 4 c or KReO 4 c . Calculation results and estimation of perrhenates thermodynamic properties could be used for the thermodynamic simulation of different processes as well as in analytical chemistry and in metallurgy. Keywords : perrhenates, thermodynamic properties, thermodynamic simulation, sintering, oxidizing agent, rhenium (Russian) DOI: http://dx.doi.org/10.15826/analitika.2019.23.4.015 O.V. Melchakova 1 , P.V. Zaitceva 1 , A.V. Maiorova 1,2 , T.V. Kulikova 1,2 , N.V. Pechishcheva 1 , K.Yu. Shunyaev 1,2 1 Institute of Metallurgy of the Ural Branch of the Russian academy of Sciences, 101, Amundsen street, Ekaterinburg, 620016, Russian Federation, 2 Ural Federal University named after the first President of Russia B.N. Yeltsin, 19, Mira street, Ekaterinburg, 620002, Russian Federation

The analytical technique has been developed for the determination of valuable trace components, namely gold, silver and cobalt in materials containing high concentrations of sulfur, copper, iron and nickel by inductively coupled plasma atomic emission spectrometry (ICP-AES). For this purpose, the effect of the major components on the atomic emission of target analytes in solutions after the acid decomposition of the samples was studied. Also the method for calibrating the spectrometer and the optimal operating parameters were chosen, as well as the optimum wavelengths for observing the analytes emission. The quality of the procedure was verified using certified reference materials of copper, copper-nickel, goldsilver sulfide ores, matte and their mixtures.

The determination of low phosphorus content in different samples is most commonly carried out by the various spectroscopic methods with electrothermal vaporization (ETV) and electrothermal atomization (ETA). The thermochemical processes of converting substances from the initial sample to particle are the same for these methods. In this work, we have compared the conditions of analysis and analytical characteristics (limit of detection and characteristic mass) of a large quantity of spectroscopic methods for the phosphorus determination. Atomic absorption analysis with ETA and molecular absorption analysis with ETV, with and without different chemical modifiers in ETA and ETV, are the ones that have been studied in most detail. The possible causes of phosphorus losses during the stage of pyrolysis, mechanisms of phosphorus atomization and molecules formation with ETA and ETV were considered. A special attention was paid to the effectiveness (temperature increase of the pyrolysis stage, improvement of the sensitivity and determination accuracy, reduction of the background interference, etc.) of the following chemical modifiers: lanthanum and palladium nitrates, fluoride (HF, NaF, KF, CsF, and NH4F) and several other chemicals. Both experimentally proven and proposed action mechanisms of various chemical modifiers manifesting themselves during the phosphorus determination were considered. The prospects of the use of high-resolution continuum source atomic absorption spectrometers for the phosphorus determination by atomic and molecular absorption and for the effective registration of the background absorption are noted. Key words : phosphorus, atomic absorption analysis, molecular absorption analysis, spectroscopic methods of analysis, the stage of pyrolysis, atomization, vaporization, chemical modifier. DOI: http://dx.doi.org/10.15826/analitika.2016.20.4.010 Alexander A. Pupyshev 1 , Polina V. Zaitceva 1 , Maria V. Zaitceva 2 1 Federal State Autonomous Educational Institution of Higher Education «Ural Federal University named after the first President of Russia B.N. Yeltsin», ul. Mira, 19, Ekaterinburg, 620002, Russian Federation 2 The Zavaritsky Institute of Geology and Geochemistry of the Ural Branch of the Russian Academy of Sciences (IGG UB RAS), ul. Akademika Vonsovskogo, 15, Ekaterinburg, 620016, Russian Federation

In order to select the temperature-time heating program, the calibration method, the prediction of matrix interference and to increase the sensitivity and accuracy of the halogens determination using the electrothermal molecular absorption spectrometry it is essential to know the formation mechanism of the measured molecules. Thermochemical processes of gaseous molecules CaF formation, which are used in the electrothermal molecular absorption determination of fluorine, were studied using the method of the thermodynamic simulation. All calculations were performed using the HSC 6.1 software package with its own database of thermodynamic data. For calculations, the non-equilibrium thermodynamic system, which was realized in the graphite furnace, was divided into the thermodynamic subsystems that correspond to the main stages of time-temperature program: drying of the sample, pyrolysis, vaporization and formation of gaseous diatomic molecules. The composition of the condensed sample residues after drying and pyrolysis stages, the composition of the gas phase in the analytical zone of the graphite furnace during vaporization and the formation of molecules stages were determined by the calculations. This study theoretically describes thermochemical processes of the formation of gaseous CaF molecules using thermodynamic simulation for electrothermal molecular absorption determination of fluorine. The calculations make it possible to establish that gaseous molecules CaF g  are formed during the course of the thermal decomposition of the condensed fluoride (CaF 2 c ).  The correct execution of thermodynamic simulation was confirmed by the comparison of the theoretical temperature curves of pyrolysis and the formation of molecules CaF g  with the experimental curves. The developed procedure of the thermodynamic simulation can be applied to study the formation of other dimeric molecules used for molecular absorption analysis with electrothermal atomization. Keywords:  high-resolution continuum source molecular absorption spectrometry, thermodynamic simulation, fluorine, calcium mono-fluoride, temperature of drying, pyrolysis and vaporization. Polina V. Zaitceva*, Alexander A. Pupyshev Ural  Federal University named after the fist President of Russia B.N.Yeltsin (UrFU), ul. Mira, 19, Ekaterinburg, 620002, Russian Federation DOI: http://dx.doi.org/10.15826/analitika.2015.20.1.003

Thermochemical processes accompanying the formation of gaseous molecules SrF g at the electrothermal determination of fluorine via the molecular absorption were investigated using equilibrium thermodynamic modeling. The algorithm of modeling was developed. For carrying out the calculations non-equilibrium thermodynamic system realized in graphite furnace was divided into serial quasi-equilibrium thermodynamic subsystems. These subsystems correspond to the major stages of temperature-time program: drying of the sample, pyrolysis, vaporization and gaseous dimer molecule formation. Original chemical compound of thermodynamic subsystems during modeling, method for its realization and treatment of calculated data were recommended for each stage. The evaluation of modeling accuracy was carried out using published experimental data and the results of our own experiments. Theoretically according to our experimental cases of mixed and separated injection of Sr(NO 3 ) 2 and NaF solutions on different area platform of graphite furnace were examined. The carried out calculations made it possible to establish the composition of condensed residues after stages of drying and pyrolysis, gas phase composition of the analytical zone of graphite furnace at the stage of evaporation and molecules formation. It has been established that molecules SrF g formation happens due to thermal decomposition of condensed SrF 2 c for the mixed injection of solutions and interaction gaseous compounds of fluorine with Sr g for the separated injection of solutions. The proposed algorithm may be used for research of other dimer molecules formation in a graphite furnace. The results of modeling may be useful for the selection of temperature-time program of heating, method of calibration, increasing the sensitivity and accuracy of halogens determination. Key words: fluorine, strontium, dimer molecules, molecular absorption, graphite furnace, thermodynamic modeling, interference gallium, temperature of drying, pyrolysis and evaporation . (Russian) DOI: http://dx.doi.org/10.15826/analitika.2014.18.3.005 P.V. Zaitceva, A.A. Pupyshev, I u. А . Kurmachev Federal State Autonomous Educational Institution of Higher Professional Education «Ural Federal University named after the first President of Russia B.N. Yeltsin» (UrFU) , Ekaterinburg, 620002, Russian Federation

The ICP-AES technique was developed for rhenium determination in the range of 0.00002 - 0.05 % in copper and molybdenum ores along with their concentrates. The sample pretreatment method by sintering with magnesium oxide and oxidizing agents was offered for analysis; optimum conditions for samples digestion were established. These conditions enabled to pass rhenium into solution with no losses. Matrix influence on rhenium emission spectral lines was studied and methods were investigated to eliminate matrix effects. The analysis results of rhenium-containing ores and concentrates certificated reference materials and mixtures on their basis, obtained by the developed procedure, agreed well with the certified rhenium content values.