Vol 73, No 1 (2018)

Four methods of correction and three methods of calculation of absorption coefficients are tested in electron probe microanalysis of rock-forming minerals. Experimental data by Pouchou and Pichoir, Sewell–Love–Scott, and Armstrong are attracted in tests. It is shown that the correction factor can be calculated with the error no more than 1 rel. % if a short-wave line (matrix effect is determined mainly by the effect of atomic number) is used as an analytical line or the analytical line belongs to the absorption K-edge of elements present in the sample. In the presence of binary matrix effect, when the analytical line absorbs in the K–L₁ region, the situation is more complex and additional studies are required.

A magnetic sorbent with a multilayer shell of the composition Fe₃O₄@TEOS@CTAB@TEOS + MPTEOS designed for the simultaneous or sequential preconcentration of components of various nature is obtained. The conditions of microwave synthesis and modification of a new magnetic sorption material are described; its composition and particle sizes are characterized. The sorption capacity of the sorbent is provided by creating a mesoporous silica layer filled with cetyltrimethylammonium bromide (CTAB) micelles and additionally modified with an S-containing polymer (MPTEOS) on the surface of the magnetic carrier. The properties of the obtained material with respect to the regulated substances from two groups of priority pollutants are studied: phenols of various structures and heavy metals. The main sorption characteristics (effect of pH, phase contact time, nature of eluent, V: m, salt background) are studied and the conditions for extracting ecotoxicants at their concentration in the solution at a level of μg/L are optimized. The data obtained under the conditions of separate and simultaneous extraction of analytes of different nature confirmed a possibility of the quantitative determination of various types of natural water pollutants at the levels significantly lower than the MPC using a single sorption material. In using HPLC methods and electrothermal atomic absorption spectrometry, a complete analysis of a single sample takes 40−50 min and of a series of samples, 2–3 h. Such characteristics, combined with the simplicity of material preparation make it promising for routine analytical studies.

In this study, in-situ ionic liquid based dispersive liquid−liquid microextraction method for enrichment of tetracyclines before liquid chromatographic analysis has been improved. A 1-benzyl-3- methylimidazolium chloride was used as an ionic liquid. To increase extraction efficiency, some optimization parameters (amount of ammonium hexafluorophoshate, extraction time, centrifugation time, ratio of ionic liquid/salt) were investigated. At optimized conditions, enrichment factors of four tetracycline antibiotics (tetracycline, chlortetracycline, methacycline, doxycycline) were between 25 and 98. The residues of tetracyclines were not found in the studied real samples. For the accuracy of the method, the concentration of 50 and 250 μg/L of standard tetracycline mixture solutions were spiked to the blank real milk, honey and egg samples and the percentage recoveries were obtained in the range of 75.8–109.7%.

In this work, phenol reacted with 4-aminoantipyrine (4-AAP) reagent in presence of potassium hexacyanoferrate(III) and then was extracted using ultrasound-assisted emulsification microextraction via 1-hexyl-3-methyl imidazolium hexafluorophosphate as an environmentally friendly solvent. Effects of the main experimental variables were investigated and optimized by central composite design. Under the optimum conditions (pH 9.5, 100 mg/L 4-AAP, 100 μL of ionic liquid as extraction solvent, 0.2 g/L K₃Fe(CN)₆ and 0.2 M NH₄Cl) the dynamic linear range, limit of detection and relative standard deviation were obtained as 0.2‒25 μg/L, 0.07 μg/L and 2.6%, respectively. Finally, the applicability of the proposed ultrasoundassisted emulsification microextraction was examined and very good results were obtained. The results confirmed the applicability of the proposed method as a versatile, low cost and sensitive preconcentration method for determination of very low concentrations of phenol in aqueous solutions.

The application of mass spectrometry to the detection of m-nitrobenzoic and 3,5-dinitrobenzoic acids and their salts on the surface of construction materials used in rocketry is described. Analytes are washed with acetonitrile from the studied surface and then analyzed by HPLC−MS with electrospray ionization or the matrix assisted laser desorption/ionization (MALDI). For electrospray ionization, the limit of detection is 6 μg/L and for MALDI ionization, 2 μg/L. The MALDI technique also ensures the direct investigation of samples without washing out; in this case, mass spectra can be visualized by constructing 2D diagrams of the distribution of nitrobenzoic acids over the surface.

The present paper describes the fabrication of a new polyvinylchloride (PVC) membrane electrode for the determination of Nd(III) ion based on 4-hydroxypyrrolidine-2-carboxylic acid (LHP) as an active material along with sodium tetraphenyl borate (NaTPB) as an anionic additive and acetophenone (AP) as solvent mediator. The optimum composition (%, w/w) of the best performing membrane contained 66 AP, 30 PVC, 2 NaTPB and 3 LHP. The basic analytical parameters of this electrode such as slope characteristics, detection limit, response time, selectivity and pH effect were assessed. The electrode displayed a Nernstian response in terms of slope (20.5 ± 0.4 mV per decade) and response time (~8 ± 1 s) over a wide neodymium ion concentration range of 10^–6 to 10^–2 M with a detection limit of 7.5 × 10⁻⁷ M. The potentiometric response of the electrode was constant in the pH range of 3.2‒8.9. According to the selectivity coefficients determined by the matched potential method, the interference of many common alkaline, alkaline earth, transition, heavy metals and specially lanthanide ions in determination of Nd(III) ion was very low. The proposed electrode has been successfully used as an indicator electrode in the potentiometric titration of Nd(III) ion with EDTA and applied for determination of Nd(III) ion in mixtures of different ions.

A review of new approaches and solutions in the development and application of enantioselective voltammetric sensors for the recognition of optical isomers of biologically active compounds and medicines is presented. The main methods of electrode modification by enantioselective selectors are discussed, i.e., the application of inclusion complexes, molecularly imprinted polymers, elements of living systems and their analogs, inorganic and organic materials with the effect of chirality, and also supramolecular structures. The main analytical characteristics of some sensors and sensor systems of the electronic tongue type for the recognition and determination of enantiomers in various samples are presented. Methods of processing of voltammetric data for the elimination of the effect the memory of measurements and the cleanup of analytical signals at low concentrations of enantiomers are considered.

A serial analyzer of dissolved oxygen, Expert-009, based on the optical detection method is created. The sensitive element of the sensor is a polymer film with a dye—a metal complex of fluorine-substituted porphyrin—distributed in it. The method is based on the quenching of the phosphorescence of the dye by molecular oxygen, which the analyzer recounts to the concentration value by the calibration curve method. The metrological characteristics of the analyzer are determined.