Vol 73, No 8 (2018)

A review of methods of surface molecular imprinting using micro- and nanodimensional inorganic materials, including nanostructured ones, as substrates and methods of their application to analysis for increasing the selectivity and sensitivity of the determination. Molecularly imprinted polymers play an increasingly important role in the development of methods for the separation and preconcentration of organic substances and inorganic ions. Their main advantage over traditional adsorbents used in analytical chemistry consists in a combination of adsorption properties with the selective recognition of template molecules or related compounds. Recently much attention has been paid to surface molecular imprinting as a technology ensuring not only an increase in the efficiency of the selective preconcentration of analytes, but also in the sensitivity of their subsequent determination in complex matrixes, and also the reduction of the cost of the adsorbent material using substrates for preparing thin films of molecularly imprinted polymers on their surface.

The results of model experiments on the effect of transition elements (iron, manganese) and sulfide ions on the values of chemical (COD) and biochemical oxygen demand (BOD) are presented. It is shown that, in the presence of transition elements in water, BOD is overestimated. In the presence of 100 mg/L of iron(II) and >0.05 mg/L of sulfides in water, the BOD values exceed those of COD.

A procedure is developed for the detection of ricin in plant extracts and soil based on its hydrolysis with trypsin and chymotrypsin with the formation of specific peptides and their determination by HPLC with high-resolution tandem mass spectrometric detection. The conditions for the sample preparation of plant extracts and soil samples, mass spectrometric detection in the mode of selected reaction monitoring and gradient elution of specific peptides are optimized. The limit of detection of ricin in extracts is 5 μg/mL. The developed procedure is tested on real samples of plant extracts containing natural ricin.

Voltammetric characteristics of vanillin are determined using electrodes modified with tin dioxide nanoparticles dispersed in surfactants of various nature in the Britton–Robinson buffer solution. The best characteristics are observed for a glassy carbon electrode modified by a dispersion of SnO₂ nanoparticles in cationic cetylpyridinium bromide (SnO₂–CPB/GCE). The electrode is characterized by cyclic voltammetry and electrochemical impedance spectroscopy. A fourfold increase in the effective surface area of SnO₂–CPB/GCE and a significant decrease in charge transfer resistance are shown in comparison with a GCE. The electrooxidation of vanillin proceeds irreversibly with the participation of two electrons and two protons and is controlled by the diffusion of the analyte. A sensor based on a SnO₂–CPB/GCE was developed to determine vanillin; it functions under conditions of differential pulse voltammetry. The analytical ranges for vanillin are 0.10–100 and 100–500 µM with the limits of detection and quantification 20 and 67 nM, respectively. The developed sensor is selective to vanillin in the presence of inorganic ions, saccharides, ascorbic acid, and a number of phenolic compounds. The sensor is used for the determination of vanillin in perfumes for household chemicals and vanilla essential oils. The results are in good agreement with the data of gas chromatography.

The poly(L-arginine)–graphene modified glassy carbon electrode (GCE) was fabricated and the electrochemical behavior of carmine and amaranth on this electrode was studied by cyclic voltammetric method. Compared with poly(L-arginine)/GCE and GCE, the poly(L-arginine)–graphene modified GCE improved the sensitivity for the determination of carmine and amaranth. The experimental results indicated that the oxidation peaks of carmine and amaranth were separated at 121 mV in phosphate buffer solution at pH 2.5. The linear range for the simultaneous determination of carmine and amaranth were 7.5 × 10^–7–7.5 × 10^–5 M. The detection limits were 7 × 10^–8 M for carmine and 2.5 × 10^–7 M for amaranth. The method has been applied to the simultaneous determination of carmine and amaranth in drinks with satisfactory results.

A procedure is developed for the determination of technical polymethylene naphthalene sulfonates (TPNS) in concrete by HPLC. The presence of 9.8–18.8% of a fraction with a low adsorption activity in TPNS is detected. A correlation is found between the initial slump of the concrete mix cone and the refined amount of oligomers of polymethylene naphthalene sulfonic acids with n ≥ 11, contained in TPNS.