Vol 72, No 6 (2017)

The article covers factors that determine fundamental difficulties of chemical phase analysis of a mixture of solid phases of inorganic compounds. Stoichiographic principles and methods, novel for analytical chemistry and leading to the efficient solution of the problems of phase analysis, are discussed. Conditions of the selective separation of mixtures of multiphase multielement solid compounds and principles of the new method, fan-like separation, ensuring the extraction of individual phases from unseparated mixtures, are considered. An idea of a complex method of solving analytical problems by stoichiography methods in proposed. The problem of the multiplicity of objects of analysis is discussed and general principles of the efficient solution of problems of the detection and identification of components of complex mixtures of unknown chemical composition are considered.

A test method is developed for determining benzo[a]pyrene in natural water, based on the use of a polyethylene filter (frit) with adsorbed specific antibodies, placed within a transparent column. In passing a test solution, the analyte is adsorbed on the frit similarly to the process implemented in immunoaffinity preconcentration. The added conjugate of a labeled analyte takes the remained vacant binding sites of antibodies. Luminescent semiconductor nanoparticles (quantum dots) CdSe/ZnS, used as labels, enable visual determination under irradiation with UV light. The limit of detection for benzo[a]pyrene in water is ~0.5 ng/mL.

Total external reflection X-ray fluorescence spectrometry is a promising method for the highly sensitive determination of heavy metals in seawater, offering such advantages as the mobility of the used equipment and the low cost of analysis. Various methods of sample preparation to the analysis of seawater aimed at the elimination of interferences with the salt matrix were compared. It was shown that the method based on the preliminary extraction of metals as diehyldithiocarbamate complexes followed by back extraction is characterized by the highest efficiency. A procedure was developed for the determination of Ni, Cu, and Co in seawater with limits of detection at a level of 0.16–0.26 μg/L.

The products of conversion of 1,1-dimethylhydrazine after contact with the surface of AMg-6 alloy, which is a model of construction materials that contact with rocket fuel components, were characterized by use of chromatographic and mass-spectrometric methods. Alkyl phthalates, the homologues of triphenyl phosphate, and numerous polymer-homologues related to acetone condensation products were detected in acetone extracts taken from the test surfaces. The presence of such products makes it possible to identify fuel components that contacted with the construction materials; this is important for the utilization of the detachable parts of launch vehicles.

A procedure is developed for the determination of benzothiophene, dibenzothiophene, and 4,6-dimethyldibenzothiophene in high-purity sulfur, including liquid-phase microextraction preconcentration, identification by gas chromatography−mass spectrometry, and gas chromatographic determination with flame photometric detection. The rate of microextraction recovery was from 16 to 78%. The limits of detection were 8 × 10^–5 wt % for benzophiophene and 2 × 10^–5 wt % for dibenzothiophene and 4,6-dimethyldibenzothiophene.

Method of sorption–atomic-absorption determination of Co, Cr, Cu, Fe, Mn, and Ni in samples of high-purity Nb₂O₅ with heterochain S,N-containing sorbents was developed. The method is based on the sorption preconcentration of trace impurities followed by their determination by high-resolution continuum source graphite furnace atomic absorption spectrometry (HR CS GFAAS). Selectivity of three original inhouse synthesized S,N-containing heterochain sorbents was studied. The recoveries of Co, Cr, Cu, Fe, Mn, and Ni using heterochain sorbents OKS, MTH, and GLSH were 100, 80, and 76%, correspondingly. Sorbent “OKS”, which provided the quantitative recovery of trace impurities, was chosen for further research. The sorption conditions for chloride solutions of different acidities (0.1–3 M HCl) were studied and optimized. Using the conditions established for the sorption and HR CS GFAAS analysis, trace Co, Cr, Cu, Fe, Mn, and Ni were determined in high purity Nb₂O₅ with a relative error less than 5%. The trueness control of the obtained results is confirmed by the “added–found” method. The developed method allows us to determine concentrations of analytes: 0.02–0.20 ppm Co, 2.0–3.3 ppm Cr, 0.2–1.5 ppm Cu, 6.0–21.0 ppm Fe, 0.6–0.8 ppm Mn, and 2.8–3.5 ppm Ni. The proposed methodology can be successfully extended to the determination of various trace elements in other high-purity inorganic materials.

A possibility of identification of the oxidation state of iron by wavelength dispersive X-ray fluorescence spectroscopy using both the position and intensity of L_α and L_β spectral lines of iron and by principal component analysis score data obtained by the decomposition of the spectral region corresponding to spectral L-series lines of iron is demonstrated. The application of scores ensures a more reliable identification in comparison with line parameters (position and intensity). Two approaches based on projection on latent structures (PLS) regression for the determination of the concentration of iron in different oxidation states are proposed. The first approach consists in using reference models with compositions similar to those of analyzed samples. In the second approach, PLS regression was build using model spectra obtained from spectra of readily available iron compounds.

Electrochemically modified electrodes based on gallium arsenide (GaAs) were designed for the potentiometric determination of mercaptans in raw hydrocarbons. The main electrochemical characteristics (linearity range of the electrode function, limit of detection, and slope of electrode function) were studied. The argentometric titration of mercaptans in a gas condensate was performed using the GaAs electrodes prior to and after modification. The use of the electrochemically modified electrode ensures a more reliable determination of the titration end-point.

A nanocomposite system based on coumarin derivative and graphene sheet was used to prepare a new electrochemical sensor. The objective of the mentioned nanocomposite was to investigate novel electrochemical properties enabling the quantification of epinephrine (Ep). Cyclic voltammetry was used to study the redox properties of the mentioned modified electrode at different scan rates. Henceforward, the electrocatalytic oxidation of Ep at the surface of the modified electrode was considered. The data has shown excellent catalytic activity of the modified electrode for the electrooxidation of Ep, which leads to a reduction of overpotential for more than 238 mV. According to differential pulse voltammetry (DPV), the oxidation of Ep showed a dynamic range between 0.1 and 1000.0 μM and the detection limit (3s) of 0.011 μM. Besides, DPV was used for the determination of Ep at the mentioned modified electrode in the presence of serotonin.