Vol 72, No 7 (2017)

A survey of the capabilities of electrochemical methods for the separation (capillary electrophoresis) and determination (amperometry, the versions of voltammetry, and potentiometry) of narcotic and psychotropic drugs and their metabolites, which are of interest in criminological practice, as the constituents of biological materials (hair, blood, and urine) and medicinal preparations is presented.

The suitability of the determination of the asymmetry factor of chromatographic peaks by the ratio of areas of two components separated by a perpendicular dropped from the maximum of the peak to the base-line, A_s* = S_b/S_a, where symbol a corresponds to the leading edge of the peak and b is for its tailing slope, is discussed. It is demonstrated that this method enables the estimation of the asymmetry of even partially separated chromatographic signals, including those eluted “in the tail” of intense peaks of solvents. The concepts of the asymmetry index I(A_s*) and its increment ΔI(A_s*) = (A_s*)–I(A_s*) are introduced, which ensures the characterization of the asymmetry of peaks of polar analytes with respect to the asymmetry of nonpolar reference components, that is, the separation of the effects of the polarity of analytes and their quantities injected into the chromatographic column on this parameter. For the first time we revealed a correlation of the asymmetry factors of compounds of different chemical nature with such a characteristic of their polarity as the difference in chromatographic separation temperature and the normal boiling point of analytes.

Possibility of using chemically modified silica (CMS) with covalently immobilized sulfonic and ethylenediaminetriacetate (ED3A) groups for the adsorption preconcentration and extraction of tetracycline (TC) from aqueous solutions is studied. The conditions of complex formation by europium(III) ions on the surface of these adsorbents are optimized. The effect of citrate and Eu³⁺ ions on the luminescence intensity of the Eu–TC complex is shown. The luminescence properties of SiO₂ED3AEu and SiO₂SO₃HEu systems with tetracyclines are studied depending on the acidity of the medium, time of phase contact, the ratio of the volume of the solution to the weighed portion of the adsorbent, and concentrations of the adsorbed substances. It is found that tetracycline is quantitatively extracted by CMS as a complex with europium(III) ions in pH range 6.5–8.0; adsorption capacity to tetracycline in the Henry region is as high as 0.07–0.09 mmol/g and partition coefficients are 10³–10⁴ mL/g. A procedure is developed for the solid-phase luminescence determination of tetracycline using SiO₂SO₃HEu and SiO₂ED3AEu systems with limits of detection of 0.8 and 2.0 nM, respectively; linearity range is 1 × 10^–9–1 × 10^–5 M. The procedure is tested in the analysis of model mixtures and samples of bottled water.

Products of reaction between the organoselenium xenobiotic, diacetophenonyl selenide (1,5-diphenyl-3-selenapenta-1,5-dione), and reduced glutathione at different molar ratios and pH values were studied by HPLC and TLC. Reaction intermediates, S-(acetophenylselenyl)glutathione and glutathione selenodisulfide, and reaction products, acetophenone and hydroselenide anion, were detected. The reaction scheme proposed earlier was confirmed.

To evaluate the oxidative stress under clinical conditions, a procedure is developed for the chemiluminescence determination of the total concentration of lipid hydroperoxides based on their oxidation in the presence of microperoxidase and chemiluminescence activator isoluminol in a borate buffer solution (pH 10.0). The limit of detection for linoleic acid hydroperoxide is 16 nM. The procedure is used to determine lipid hydroperoxides in follicular fluid lipoproteins and in plasma of patients undergoing extracorporeal fertilization.

The aim of this study was to investigate the level of organochlorine pesticides use for treatment of tomatoes, eggplants and cucumbers in Kirklareli, Turkey. Eighteen organochlorine pesticides were identified in vegetable samples using microwave or Soxhlet extraction, and results were obtained by gas chromatography–mass spectrometry. The optimized conditions were 1 mL/min for flow rate in the mobile phase, 1 μL for injection volume and 70 V for fragmentation potential. The analytical parameters show that the microwave oven extraction procedure provided the best results when compared to the Soxhlet extraction procedure. Samples were prepared for analysis with hexane‒dichlormethane (1: 1, v/v, 40 mL) using a solid-phase extraction method. The limits of detection and quantitation for the eighteen analytes were between 0.02–0.26 and 0.06–0.87 μg/L, respectively, and the relative standard deviations of the migration time ranged from 2.4 to 8.9%. The recoveries of surrogate spiked in vegetable samples ranged from 70 to 116%, respectively. The obtained concentrations of pesticides in all vegetables studied were proved in the range of ND–123 μg/kg. The organochlorine pesticide sum was below the legal limit, except for Endrin and Methoxychlor, which requires a further elucidation of the organochlorine pesticides pollution sources in the region. These studies on accumulation of organochlorine pesticides were necessary for accomplishing a comprehensive ecological risk assessment.

An ion-selective potentiometric sensor with an ionophore is developed based on the ion associate of artificial food colorant E133 and a cetylpyridinium cation. The main electroanalytical parameters of the sensor are evaluated: linearity range of the response, pH effect, and the effect of temperature on the electrode performance and selectivity. The sensor is used to determine E133 in the Powerade beverage. The accuracy of the determination is confirmed by an extraction–photometric method.

Experimental data are compared with the results of calculations by the finite difference technique within the dynamic diffusion model of the interphase potential on an example of a picrate-selective electrode in real scenarios corresponding to the conditions of the determination of selectivity coefficients by the methods recommended by IUPAC. It was found that, in the majority of the considered cases, the calculated values of the potential and selectivity coefficients and also the dynamics of potential change at particular steps well agree with the experimental data. The model has principal restrictions, leading the failure of calculations, when the concentration of potential-determining ions in the near-electrode layer of the solution performed is low according to the algorithm of measurements, whereas the instant increase in its concentration in the surface membrane layer due to the replacement of the sample solution induces a flux of these ions from the surface deep into of the membrane.

A procedure is developed for the quantitative determination of diterpene acids in garden sage leaves by UV spectrophotometry at the wavelength 285 nm. The target group of compounds was selectively extracted by petroleum ether 40/70. It was shown that the completeness of extraction is determined mainly by the number of portions of the pure solvent: at the optimum ratio of the mass of the weighed portion to the volume of solvent 1 g/200 mL, double extraction is sufficient. The duration of each extraction is 20 min. The procedure was used in the analysis of samples of garden sage leaves from various producers. It was found that the concentration of diterpene acids in samples varied from 2.1 to 3.6 wt % (in terms of carnosic acid). The error of a single determination of the sum of diterpene acids in garden sage leaves is ±2.38% (P = 0.95).