Total reflection X-ray fluorescence determination of rare earth elements in mineral water

A method is proposed for determination of lanthanum, cerium, praseodymium, neodymium, and samarium in mineral water by means of total-reflection X-ray fluorescence analysis. In this work, the combined technique of preconcentration of rare earth ions is used. This technique consists of coprecipitation of metal hydroxides on the collector (iron (III) hydroxide) and dispersive liquid–liquid microextraction of their complexes with 1-(2-pyridylazo)-2-naphthol by chloroform in the presence of ethanol. The use of the developed hybrid approach allows simultaneous determination of the mentioned metals in mineral water in the range n(10^–2–10¹) μg/L. The results of analysis of Arkhyz and Rychal-Su mineral waters by the proposed extraction–X-ray fluorescent method are confirmed by the literature data, obtained by inductively coupled plasma mass spectrometry.     

Application of microemulsions for the extraction of <Emphasis Type="Italic">o</Emphasis>-phthalate esters from soil with subsequent separation of microemulsions,simultaneous preconcentration,and gas chromatographic analysis of target components

The possible application of microemulsions as extractants for the extraction of o-phthalate esters from soils with the subsequent breakdown of microemulsions, simultaneous preconcentration of dialkhylphthalates in the organic phase, and their following gas chromatographic analysis with mass-spectrometric detection is demonstrated. The preconcentration factor was 18. The method is characterized by low detection limits, good selectivity, and reproducibility.     

Separation of rare earth elements in the tributyl phosphate–Ln(NO<Subscript>3</Subscript>)<Subscript>3</Subscript>–Ca(NO<Subscript>3</Subscript>)<Subscript>2</Subscript> system in the counter current process

The 40-step extraction process to separate rare earth elements (RЕEs) according to the praseodymium–cerium line with the use of mixer–settler extractors in a 100% TBP–Ln(NO₃)₃–Ca(NO₃)₂ system is implemented. A lanthanum–cerium concentrate containing less than 0.03 wt % of the remaining REEs is obtained. The flow diagram of the separation process of a rare earth (RE) concentrate isolated from phosphogypsum is considered.     

Direct Analysis of Natural Waters by Electron Spray Ionization and High-Resolution Time-of-Flight Mass Spectrometry Detection. Determination of Pesticides of Various Classes

The possibility of directly determining 36 pesticides (derivatives of urea, triazines, triazoles, imidazoles, carbamates, triazinones, benzamides, and pyridazinones and organophosphorus pesticides) by electrospray ionization with high-resolution quadrupole time-of-flight mass spectrometry in natural waters is demonstrated. A significant matrix effect is observed in the determination of pesticides in natural waters, and the use of the standard addition method is proposed for their determination in test samples, both undiluted and diluted with deionized water. The analytical range of the analytes was 0.5–50 ng/mL. The relative standard deviation of the results does not exceed 10%; the time required for the analysis is 10–15 min.     

Time‐Resolved Energetics of Photoprocesses in Prokaryotic Phytochrome‐Related Photoreceptors

Time‐resolved photoacoustics (PA) is uniquely able to explore the energy landscape of photoactive proteins and concomitantly detects light‐induced volumetric changes (ΔV) accompanying the formation and decay of transient species in a time window between ca. 20 ns and 5 μs. Here, we report PA measurements on diverse photochromic bilin‐binding photoreceptors of prokaryotic origin: (1) the chromophore‐binding GAF3 domain of the red (R)/green (G) switching cyanobacteriochrome 1393 (Slr1393g3) from Synechocystis; (2) the red/far red (R/FR) Synechocystis Cph1 phytochrome; (3) full‐length and truncated constructs of Xanthomonas campestris bacteriophytochrome (XccBphP), absorbing up to the NIR spectral region. In almost all cases, photoisomerization results in a large fraction of energy dissipated as heat (up to 90%) on the sub‐ns scale, reflecting the low photoisomerization quantum yield (<0.2). This “prompt” step is accompanied by a positive ΔV₁ = 5–12.5 mL mol^?1. Formation of the first intermediate is the sole process accessible to PA, with the notable exception of Slr1393g3‐G for which ΔV₁ = +4.5 mL mol^?1 is followed by a time‐resolved, energy‐conserving contraction ΔV₂ = ?11.4 mL mol^?1, τ₂ = 180 ns at 2.4°C. This peculiarity is possibly due to a larger solvent occupancy of the chromophore cavity for Slr1393g3‐G.     

Electronic properties of achiral and chiral gold nanotubes

The band structure of ten single-walled gold nanotubes of different radius and chirality angle have been calculated by the linearized augmented cylindrical wave method. For all tubes, the Fermi level crosses the half-filled band; therefore, the tubes are characterized by a metallic electronic structure. The band structure of the nanotubes changes relatively weakly with a change in nanotube structure. The valence band width for all the tubes is 9.1 eV. The density of states at the Fermi level remains unaltered with a change in chirality angle and decreases by 30% with an increase in radius from 3 to 12 Å.     

Effect of 3<Emphasis Type="Italic">d</Emphasis>-metal dopants on the electronic properties of hexagonal titanium dioxide nanotubes

The electronic structure of hexagonal TiO₂ nanotubes doped with 3d transition metals from Sc to Zn was calculated by the linearized augmented cylindrical wave method. The calculated densities of states demonstrate that the substitution of Sc, V, Co, Cu, or Fe atoms for a part of Ti atoms leads to the decrease in the band gap width of the material from 4 to 2 eV. Such nanotubes are promising materials for creation of electrodes for electrochemical photolysis of water.