Vol 73, No 11 (2018)

A review of works performed by the authors and devoted to the development of new approaches to the preconcentration of organic compounds (phenols, phthalates, polycyclic aromatic hydrocarbons, and other toxic substances) on low-polar adsorbents is presented. Possibilities of the application of calculation methods to the selection of effective adsorbents and optimal concentration conditions and to the prediction of the behavior of analytes in flow adsorption chromatography systems of analysis are discussed. New methods of the adsorption preconcentration of analytes on fluoroplastic and carbon adsorbents, including the use of subcritical water for desorption, are proposed. A short list of procedures developed for water analysis using these preconcentration methods is presented.

Works of researchers of the Division of Analytical Chemistry of Moscow State University on the use of hypercrosslinked polystyrenes for the preconcentration and separation of organic compounds and ions of elements for the purpose of their subsequent determination are systematized. The works are devoted to the study of the adsorption of compounds of various classes on these materials and a possibility of combining the preconcentration of substances with modern methods of chemical analysis for the determination of amines, phenols, methylxanthines, sulfonamides, tetracyclines, and other compounds and ions of elements (gold, platinum, and rare-earth elements). The issues of using hypercrosslinked polystyrenes as stationary phases in chromatography and the creation of magnetic adsorbents based on them are also discussed.

The review systematizes the works of the researchers of the Division of Analytical Chemistry at the Moscow State University in the field of chemical colorimetry for the last 10 years. Various versions of the method, its possibilities, and prospects of use for solving many analytical problems are considered. The main ways of the development of chemical colorimetry are discussed.

A review of works of researchers of the Division of Analytical Chemistry of the Department of Chemistry of Moscow State University over the last 5 years in the total reflection X-ray fluorescence analysis of natural and drinking waters is presented. The advantages of the proposed methodological approaches to the sorption and extraction X-ray fluorescence determination of metal ions in waters are described. Various methods of the improvement of the performance characteristics of the results of analysis are discussed and compared (first of all, sensitivity of determination).

A flow injection method with chemiluminescence (CL) detection has been developed for hyoscine butylbromide (HBB) determination based on an enhancement of cerium(IV)–sulphite CL reaction in an acidic medium. The method enables HBB determination in the range of 0.005–15 ppm (R² = 0.9990, n = 10), with relative standard deviation of 2.5% (n = 12) for 0.25 ppm of HBB. The limit of detection (3s × blank) was 0.001 ppm with an injection throughput of 180 h^–1. The concentration of reagents involved in the CL reaction and the key physical variables were carefully studied and optimized. The proposed procedure offered high sensitivity, simplicity and rapidity, and was successfully applied to HBB determination in pharmaceutical preparations. The results obtained were in good agreement with the conventional spectrophotometric method. The mechanism of Ce(IV)‒Na₂SO₃‒HBB CL reaction is also discussed.

An effective method for the determination of four phthalate esters in plastic products for food usage was developed using the quick, easy, cheap, effective, rugged, and safe (QuEChERS) approach coupled with HPLC-diode array detection. Both the extraction and clean-up steps of the procedure were optimized using chemometrics methods. Under the optimized conditions, calibration model was linear from 10.0 to 500 μg/kg for benzyl butyl phthalate and from 5.0 to 500 µg/kg for dimethyl phthalate, dibutyl phthalate and diethylhexyl phthalate (R² ≥ 0.9859). The limits of detection and of quantification were less than 3 and 7 μg/kg, respectively. The repeatability and intermediate precision of the proposed method (relative standard deviations) were ≤6.4 and ≤9.2%, respectively. The proposed method is easy, precise, and accurate, and applicable for the determination of phthalic acid esters in plastics for food use classified as polyethylene terephthalate and polystyrene.

In an effort to reduce environmental pollution, the urea-selective catalytic reduction system is used to reduce NO_x emissions with urea additive diesel exhaust fluid (DEF) as reductant in the exhaust of diesel engines. ISO 22241-1:2006 specifies the quality characteristics of the DEF in order to maintain efficiency, and hence it is essential that the concentration of urea in DEF is accurately monitored. In this paper an online, four-electrode, temperature compensated, electrical conductivity measurement system based on Van der Pauw theory is proposed for measuring the variation in urea concentration in DEF. The equivalent circuit model of the measurement system is developed using the Randles circuit and the equivalent circuit parameters are determined from impedance analyses of system. The prototype of the measurement cell is fabricated with all associated electronics and tested for 0.25% change in urea concentration. The experimental results are compared with results obtained from the Randles equivalent circuit model of the measurement system. The temperature effect on the measurement system is abridged from 28.75 to 2.575 mV/grad with the design of simple electronic circuit.