Vol 74, No 4 (2019)

A living organism is a biochemically unique system, and its vital functions can be investigated using analytical measurements. Characteristic chromatographic or electrophoretic profiles of biologically active substances have been the objects of active biomedical research for more than 15 years because of the possibility of rapidly obtaining diagnostically important information. In this review, targeted and untargeted metabolomic studies performed by chromatography and capillary electrophoresis are considered.

In this study, nickel ferrite magnetic nanoparticles adsorbent was synthesized and developed for solid phase extraction and spectrophotometric determination of trace amounts of lead ions in aqueous media. The adsorbent was characterized by X-ray diffraction, transmission electron microscopy and vibrating sample magnetometry. The magnetic separated lead ions were eluted and quantified based on the complex formation of lead ions with 1,5-diphenylthiocarbazone at pH 8.5. The influence of variables affecting the efficiency of the extraction system, such as sample pH, amount of adsorbent, type and volume of desorption solvent and contact time, was evaluated and optimized. Under the optimal conditions, a linear calibration curve in the range from 0.004 to 0.6 μg/mL was obtained with a preconcentration factor of 80. The limit of detection for lead was found to be 0.27 ng/mL. The developed method was successfully applied for the determination of trace amounts of lead ions in various water samples with satisfactory results.

A nanocomposite acrylamide tin(IV) silicomolybdate (AC/TSMNC) was chemically synthesized by the sol–gel technique in surfactant medium at room temperature. The synthesis conditions, such as reactant concentrations, pH and temperature were varied to optimize the ion exchange properties of the nanocomposite ion exchange material. The ion exchange capacity was found to be 1.92 meq/g for Na⁺. The nanocomposite was characterized on the basis of chemical composition, Fourier-transform infrared spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies. The interpretation of the XRD pattern indicated its semi-crystalline nature. The diamond shape morphology was observed in SEM studies. The particle size of the material was in the range of 50‒100 nm as indicated by TEM. Sorption studies were performed in a number of solvent systems showing high selectivity for Pb(II) and Ni(II) in synthetic mixtures. On the basis of distribution coefficient studies several binary separations of metal ions, viz. Mg²⁺–Pb²⁺, Mg²⁺–Ni²⁺, Sr²⁺–Pb²⁺, Sr²⁺–Ni²⁺, Zn²⁺–Pb²⁺, Zn²⁺–Ni²⁺ were achieved quantitatively on acrylamide tin(IV) silicomolybdate columns. The quantitative separation of Ni²⁺ and Zn²⁺ was also achieved on a commercially available pharmaceutical formulation (Rxplus). Photocatalytic degradation of methylene blue dye onto AC/TSMNC was investigated for 3.5 h under solar light at a wavelength of 664 nm. The rate of methylene blue dye photodegradation onto AC/TSMNC was found to follow the pseudo-first-order kinetic model.

A carbon paste electrode was prepared and modified with 3-(4'-amino-3'-hydroxy-biphenyl-4-yl)-acrylic acid and graphene nanosheets. In phosphate buffer solution, the modified electrode showed an excellent electrocatalytic effect on the oxidation of epinephrine. This was further used to determine epinephrine in the presence of uric acid by square wave voltammetry. The oxidation peak current showed a linear relationship with the concentration of epinephrine in the range of 1.0 × 10^–7 to 5.0 × 10^–5 M, with the detection limit of 5 × 10^–8 M. The method has high sensitivity, selectivity, stability, and has been successfully applied to determining epinephrine and uric acid in real samples.

A method is developed for preparing of nanosized ion exchangers (nano ion exchangers, NIEX) as water-stable sols of a given ionic form of two types: nano cation exchangersand nano anion exchangers. According to their physicochemical properties, nano ion exchangers are simultaneously dissolved hypercharged ions and microscopic solid ion exchangers capable of solid-phase ion exchange. In chromatographic and other methods of analysis, can serve as modifiers of stationary and mobile phases, providing a high capacity of the first one and special buffer properties of the second one. Some results of using for the creation of polymodal phases for ion chromatography, as a modifier in capillary electrophoresis, and in a luminescence method for the determination of heavy metals (using copper as an example) in aqueous solutions are presented.

We demonstrate that the method based on supercritical fluid extraction (SFE) using supercritical carbon dioxide (SC-CO₂) as a basis of a solvent can be used, in principle, to fractionate a sample of heavy oil into narrow fractions. Studies are conducted using heavy oil of the Ashalchinskoye field as an example. The composition and yield of the fractions extracted from heavy oil depend on the concentration of the organic modifier (toluene) added to SC-CO₂. Supercritical fluid extraction was carried out in a semiperiodic mode at 50°C and a pressure of 100 bar with a gradual increase in the concentration of toluene from 0 to 40 wt %. This resulted in nine fractions extracted with a total extract yield of 83.4 wt %. The use of SFE can significantly decrease the amount of the residue after the fractionation of heavy oil. The composition and properties of narrow fractions extracted from heavy oil are determined. The distribution of group hydrocarbon components, metals, sulfur, and Conradson carbon residue (CCR) between the extract fractions and the residue is found.