Vol 74, No 12 (2019)

Along with traditional methods for the determination of environmental pollution, biosensors have become widely used in recent years. The review surveys modern microbial biosensors for determining pesticide residues in the environment. A microbial biosensor is a complex analytical device in which a microorganism is a sensitive element that responds to the presence of a pesticide in the test sample and the analytical signal depends on the concentration of the compound to be determined. The basic principles of the formation of these biosensors and their advantages and disadvantages are described. Methods of the immobilization of microorganisms as the constituents of a biosensor and various types of signal transducers are presented. The future prospects for this line of inquiry are considered.

A new method for preconcentration of trace Cu(II) in beverages before determination by spectrophotometry is presented. The method is based on the ternary complex formation of Cu(II) with Safranin T in presence of pyrogallol at pH 5.5 followed by its extraction into the micellar phase of Triton X-114. The ternary complex was monitored by spectrophotometry at 532 nm. Variables affecting extraction efficiency were evaluated and optimized. Under the optimal conditions, the detection limit was 0.6 µg/L in the range of 2–300 µg/L with sensitivity enhancement of 55 after preconcentration from 15 mL of the sample, and precision was in the range of 2.5–3.9%. The accuracy was verified by the analysis of two certified samples and recovery studies of the spiked samples. The intra- and inter-day precision varied in the ranges of 3.7–4.6 and 3.9–5.2%, respectively. The method was successfully applied to determination of trace Cu(II) in beverages.

We investigated 53 coniferous wood samples and 77 deciduous wood samples of trees in the central Russia by single-reflection attenuated total reflection IR spectroscopy. The characteristic absorption bands in the IR spectra of the samples are described, and the regions of absorption bands characteristic of coniferous and deciduous wood are identified. Characteristic differences in the spectra of coniferous and deciduous wood species suitable for their identification are found. Wood species of three archaeological materials were identified using these characteristic differences.

A procedure is developed for the quantitative determination of 1,2,4-trithiolane in oils and petroleum products by gas chromatography with flame photometric detection. The analytical range is 2‒100 mg/kg, relative standard deviations are 2‒5%. A possibility of using the developed procedure for establishing the fact of using formaldehyde-containing absorbers of hydrogen sulfide in the preparation of oil is shown.

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The glassy carbon electrode was modified by gold nanoparticles (AuNps)–Fe₃O₄ beads/multiwalled carbon nanotubes (MWCNTs). Surface morphology characterization of the bare and modified electrodes was characterized by scanning electron microscopy technique. This modified glassy carbon electrode was applied for electro-catalytic determination of loratadine. The modified electrode lowered the reduction overpotential of loratadine with the enhancement of its peak current; this behavior was attributed to the electro-catalytic activity of the modified electrode toward loratadine electro-reduction. Various parameters, such as pH of the working solution, amounts of MWCNTs, Fe₃O₄ beads and AuNps affecting the electrochemical performance of the modified electrode toward loratadine determination were optimized. The linear response of the modified electrode toward loratadine concentration using hydrodynamic amperometry method was between 0.05–5 μM with a detection limit of 0.04 μM (S/N = 3). The modified electrode figures of merit were high repeatability, reproducibility, long-term life time and low response time (<3 s). The practicability of this proposed method was examined by loratadine content quantification in commercial pharmaceutical samples, human blood serum and urine samples and satisfactory results were obtained.

A method is proposed for the determination of methionine by stripping voltammetry on a carbon-containing electrode modified by vitamin B₁₂. The procedure is based on the reaction of methionine reduction to homocysteine. The preparation of the electrode consists in the formation of a vitamin B₁₂ film on the surface of a carbon-containing electrode modified with carbon nanotubes by cyclic voltammetry with a potential sweep from –1.4 to +1 V. The conditions of analysis are optimized: accumulation potential, accumulation time, and sweep rate. The limit of detection for methionine is 1 × 10^–7 M.

The results of a study of sensors based on thin semiconductor films of Cd_xPb_1 – xS solid solutions intended for the determination of nitrogen dioxide in air are described. For a comparative assessment of the composition, morphology, and functional properties of the films, they were synthesized from reaction mixtures containing various cadmium salts. It was found that the maximum response is provided by layers obtained using cadmium acetate, in which the composition of the solid solution differs in the maximum supersaturation level in CdS. The films were formed of crystallites with average sizes of ~200 nm. When the concentration of nitrogen dioxide in air was 0.05‒200 mg/m³, the relative change in the ohmic resistance of sensors ranged from 8 to 80%. It was shown that the threshold concentration of NO₂ in air was about 0.02 mg/m³. The reversible nature of the gas adsorption process opens a possibility for the creation of reusable chemical sensors based on Cd_xPb_1 – xS films, differing in a relatively low threshold concentration of NO₂ detection and selective response in the presence of significantly higher concentrations of O₂, CO₂, and H₂.