Vol 72, No 3 (2017)

Contemporary nonenzymatic methods for the qualitative and quantitative determination of hydrogen peroxide and reactive oxygen species, preceding to hydrogen peroxide or resulting from it, are reviewed. Many of these procedures can be applied to the detection and determination of reactive oxygen species, for example, anions, peroxide radical anions, hydroxide radicals, etc., in both model and real samples that are of practical importance in biochemistry and medicine. The main direction of development in this area includes the target formation of a surface layer of a sensing element at the nanoscale level, including using nanoparticles. In some cases, higher selectivity can be achieved, and the analytical and performance characteristics of the procedures, such as minimum detectable concentration, analytical range, or sensitivity, can be improved. Most of the cited papers were published after 2010.

A polyaniline–multiwalled carbon nanotubes composite fiber was electrodeposited onto a platinum wire using cyclic voltammetry. This fiber was used for headspace solid-phase microextraction combined with gas chromatography and flame ionization detector of trace levels of benzaldehyde in some injectable pharmaceutical formulations. Three solid-phase microextraction parameters including temperature, time and stirring rate were investigated simultaneously using a three-level-three-factor Box–Behnken as experimental design on the extraction capability. The as-made fiber has a lifetime of over 300 extractions without any obvious decline in extraction efficiency. At the optimum conditions (extraction temperature 60°C, extraction time 15 min, stirring rate 700 rpm), the method displays excellent linearity over the concentration range of 25–1000 ng/mL of benzaldehyde with RSD values ranging from 1.0 to 6.8%. The limits of quantitation and detection were 25 and 10 ng/mL, respectively.

Industrial sediments of calcium sulfate semihydrate obtained from industrial extraction phosphoric acid and containing 0.3–4.5 wt % of impurity La−Sm are investigated by energy-dispersive X-ray fluorescence analysis (XRFA) and a procedure for the quantitative determination of cerium lanthanides in the sediments is developed. The use of linear regression analysis of X-ray fluorescence spectra of multielement industrial samples and models of individual compounds NaLn(SO₄)₂ · H₂O (cp grade) allowed us to resolve overlaps of spectral L-series lines for La–Sm, eliminate the background, and perform the regression assessment of line intensities of these elements. On this basis, we developed a procedure for the determination of La, Ce, Pr, Nd, and Sm in CaSO₄ · 0.5H₂O sediments with limits of detection (wt %): 0.022, 0.013, 0.011, 0.008, and 0.008, respectively. In concentration ranges (wt %) La (0.05–0.99), Ce (0.1–4.9), Pr (0.005–0.49), Nd (0.02–0.99), and Sm (0.005-0.19), the relative standard deviation RSD (n = 10, P = 0.95) was 18−27, 9−18, 20−31, 17−26, and 19−31%, respectively. A comparison of the results of XRFA with the data of inductively coupled plasma mass spectrometry confirms the accuracy of the results obtained according to OST (Branch Standard) 41-08-221-04.

Organosilica materials containing λ-carrageenan on their surface are synthesized. The conditions for the immobilization of the polysaccharide, such as phase contact time and pH and concentration of solutions, are optimized. It is shown that the chemisorption of the polysaccharide passes through ion exchange multipoint immobilization, which provides a high hydrolytic stability of the prepared organosilica. The rate of washing of λ-carrageenan to the solution does not exceed 0.5%. The physical and chemical characteristics of the new material are studied. In particular, it is shown that the material is completely stable up to 200°C and reversibly desorbs water at 120°C; it well adsorbs 1,4-dioxane from the gas phase and desorbs it under heating to 70°C. This ensures the use of the prepared carrageenan-containing material as an adsorbent for a solid-phase cartridge designed for the adsorption preconcentration of 1,4-dioxane in its headspace gas chromatographic determination in samples of nonionic surfactants. The developed procedure ensures the determination of 1,4-dioxane by gas chromatography with a flame ionization detector in the concentration range 0.012–3.750 mg/L with a limit of detection of 0.0014 mg/L. Preconcentration lowers the limit of detection in the determination of 1,4-dioxane by 50 times.

An approach to the detection and determination of chitosan aggregates in acetic acid solutions is proposed using pressure-assisted capillary zone electrophoresis. Processes of chitosan aggregation are studied depending on the composition of dispersion medium and storage time. The presence of several species of positively charged chitosan aggregates is revealed for the first time. Particle sizes in the range 20–2500 nm are determined by scanning electron microscopy and static and dynamic light scattering. The dependence of the shape of electropherograms on particle size distribution obtained under the same conditions is found. A trend to changing electrophoretic mobility depending on the size of the aggregate is observed, which enables the approximate evaluation of the polydispersity of chitosan solutions. Chitosan is used for the effective dynamic modification of capillaries, which does not require the introduction of a modifier into the background electrolyte.

Chemical sensors for determining lead in aqueous solutions are developed based on hydrochemically deposited lead sulfide (PbS) films; their composition and surface morphology are studied. The sensors are sensitive to lead to 31.5–32.5 mV/pc_Pb with the limit of detection of the metal 1.5 × 10^–8 M. The role of photoactivation and doping of films in increasing the sensitivity of the film sensor to lead is determined. The studied chemical sensors can be relatively easily regenerated by soaking in distilled water for 10–30 min; they have sufficiently high selectivity to lead in the presence of sodium, nickel, zinc, and cadmium salts in solution.

A procedure for the determination of Phenolic compounds in extracts from the medicinal plants of the Lamiaceae family—garden sage (Salvia officinalis L.), creeping thyme (Thymus serpyllum L.), wild marjoram (Origanum vulgare L.), and common balm (Melissa officinalis L.)—obtained under different extraction conditions was developed. The identification of the extracted compounds was performed and their qualitative and quantitative composition was established by HPLC with diode array and mass-spectrometric detection with consideration for the obtained characteristics of the standard samples of individual components. The test samples of medicinal herbs contained caffeic acid (0.19–0.62 mg/g) and rosmaric acid (4–23 mg/g); the highest rosmaric acid content (23 mg/g) was found in wild marjoram, and the lowest content (4 mg/g), in creeping thyme. The extracts of wild marjoram contained the greatest amounts of Phenolic compounds; rosmaric acid and luteolin-7-O-β-D-glucuronide were major components, whereas protocatechuic, 3-O-caffeoylquinic, and caffeic acids were minor components.