Vol 72, No 10 (2017)

The results of determination of Henry’s coefficients for an equilibrium vapor containing trace concentrations of acetone, benzene, toluene, and xylenes over their aqueous solutions are presented. Continuous gas extraction is used.

Based on a property that in dilute hydrochloric acid hydrogen peroxide oxidizes Ponceau S to fade and cerium(IV) has a catalytic effect on the reaction, a new spectrophotometric method was developed for the determination of trace cerium(IV). At 450 nm, the cerium(IV) concentration presents a good linear relationship over the range of 0.08‒4 μg/mL with the fading degree ΔA. Its linear regression equation is ΔA = 0.0475c (μg/mL) + 0.0007, with a correlation coefficient of 0.9991. The detection limit of method is 0.05 μg/mL. The method has been successfully applied to the determination of cerium in water and molecular sieve samples with good results. The relative standard deviations of eleven determinations were 0.97‒1.11 and 0.19‒1.01%, respectively. The recoveries of standard additions were 99.4‒99.9 and 99.2‒101.0%, respectively. The reliability of this method was certified by parallel determination against the dibromo-p-chlorochlorophosphonazo spectrophotometry.

A series of 7-hydroxy-2-aryl-3-(2-aryldiazenyl)-4H-chromen-4-one derivatives was synthesized in quantitative yields. Herein, we demonstrate the antioxidant potential of the synthesized substituted azo flavones using 1,1-diphenyl-2-picryl-hydrazyl assay method along with the evaluation of their redox behaviour by cyclic voltammetry. The synthesized compounds manifested good antioxidant potential as compared to standard antioxidant ascorbic acid, which especially pertains to the compounds having methoxy and hydroxyl groups. A good correlation between minimum inhibitory concentration (IC₅₀) and deduced electrochemical parameter, i.e., half peak oxidation potential (E_p/2) values, was established.

A simple procedure is proposed for determining the concentration of maleimide and acrylate groups in organic compounds based on the addition of morpholine to the activated double bond by the Michael reaction, followed by the potentiometric titration of the reaction mixture with 1 M HCl in ethanol. The applicability of the method to N-substituted maleimides with aromatic, aliphatic, and oligomeric substituents, as well as to acrylates and acrylonitrile, is verified. It is demonstrated that maleimides and acrylates can be determined simultaneously.

The coordination of the results of different works for the systematization of the structures of products previously detected in the complex samples is an important stage in the interpretation of the results of the identification of the components of complex samples of natural origin by chromatography–mass spectrometry with the low reproducibility of their mass spectra under the conditions of electrospray ionization and limited reference information. The data processing of this kind was carried out for the products of the oxidation of the most common natural flavonoid quercetin (3,5,7,3',4'-pentahydroxyflavone) by atmospheric oxygen in weakly alkaline aqueous alcohol solutions. For the correlation of peaks in chromatograms with the structures of oxidation products, their reversed-phase HPLC retention indices in the scale of reference n-alkyl phenyl ketones were determined for the first time. It was confirmed that not all of the oxidation products are stable in solution; some of them can accumulate or disappear during the storage of the samples.

A pneumovacuum circuit of a Tsvet-800-2 gas chromatograph with a helium ionization detector (HID) in the ionization amplification mode is proposed for controlling limiting trace impurities in ammonia, arsine, monosilane, and phosphine of grade 6N4. The conditions for the preparation and reliable operation of the chromatograph with the HID are systematized. The effect of an additive of (0.0–17.6) × 10^–4 mol % of hydrogen in the carrier gas of the detector on the polarity of its signal on the impurities of oxygen and nitrogen at a level of (0.5–20.0) × 10^–5 mol % is studied. Methods are proposed for eliminating systematic errors in the determination of the concentration of oxygen and nitrogen in the range from 0.5 × 10^–5 to 1 × 10^–3 mol % in 6N4 volatile hydrides, caused by “counter” impurities in the carrier gas, the mechanism of the heteropolar sensitivity of the HID, and irreversible chemical reactions of oxygen traces with phosphine and products of its decomposition on a CaA–ShM zeolite in a separating column of a chromatograph. Gas chromatography analysis of ammonia, arsine, monosilane, and phosphine of grade 6N4 was carried out.

A procedure is developed for the determination of more than 60 individual sulfur-containing compounds (SCC) in liquid hydrocarbon raw materials and in liquid fuels using gas chromatography on a 25-m WCOT column, inner diameter 0.32 mm, with a nonpolar dimethylpolysiloxane stationary phase (layer thickness 5 μm) and chemiluminescence detection. SCC were identified by individual standard substances and published data. Quantitative determination was carried out by the internal standard method. The results of determination of individual SCC in petrol and stable gas condensate are presented. The most high-boiling SCC found in significant amounts (more than 0.005 wt % of sulfur) were C₂-benzothiophenes (in petrol) and C₄-dibenzothiophenes (in gas condensate).

A comparative study of the batch and dynamic extraction methods used to evaluate the physicochemical “mobility” of element species in environmental samples was carried out using samples of contaminated soils and technogenic sands of the Dzhida Tungsten–Molybdenum Factory. In determining the total concentration of mobile species of Cu, Zn, Pb, Cd, Mn, and Mo, they were extracted with an acetate–ammonium buffer solution (pH 4.8) in the batch mode. Fractionation of the most mobile and environmentally relevant element species, that is, exchange and acid-soluble, was carried out in a dynamic extraction mode in a rotating coil column using calcium nitrate and acetic acid. Element concentrations in the initial samples and extracts were determined by inductively coupled plasma atomic emission spectrometry and mass spectrometry. It is shown that the concentrations of mobile species of Cd, Mn, and Mo, isolated with an acetate–ammonium buffer solution, correspond to the sum of these elements in the exchange and acid-soluble fractions, while the concentration of lead in the acetate–ammonium extract is 2–4 times higher. The convergence of the results of dynamic and batch extraction of copper and zinc depends on the type of sample: for sand, the results are in satisfactory agreement, while for soil, the concentration of copper and zinc in the acetate–ammonium extract is 2–4 times lower than their concentration in the exchange and acid-soluble forms. Nevertheless, the data obtained confirm that the conventional method of batch extraction with an acetate–ammonium buffer solution (pH 4.8) can be considered acceptable for the rapid assessment of the physicochemical mobility and potential bioavailability of elements in soil and technogenic sand. For a more detailed study of highly contaminated samples and the assessment of their danger to the environment, it is advisable to separate exchange and acid-soluble fractions.