Dynamic light scattering has been employed to investigate aqueous Pluronic P123 solutions at different temperatures and in the presence of different solvents and quercetin additives. Significant changes have been revealed in the average particle size and polydispersity index depending on the conditions. The effect of temperature on micellization of the block copolymer in aqueous solutions has been studied in a range T = 15–45°C, which is most often considered when using P123 in the sol–gel synthesis of silica. The most pronounced effect of temperature on the micellization of the studied surfactant has been observed at T = 15–20°C. In this temperature range, the scattered light intensity distribution over particle sizes has a polymodal character, which indicates the presence of macromolecules, micelles, and their aggregates in the system. A further increase in temperature up to 45°C causes no significant changes in the particle size. In aqueous solutions, micelles with a narrow size distribution (minimum polydispersity index) are formed within temperature ranges of 21–25 and 35–40°C. Substantial effects have been found when adding alkanols and polyphenolic substances as solubilizers capable of influencing the structure of micelles both in their bulk and on the surface of polar moieties of the surfactant. It has been shown that, in the presence of butanol-1, micelles are stabilized at temperatures of 15–20°C. At T > 30°C, the structure of micelles is transformed. As the fraction of butanol-1 in the solution increases, its influence is manifested at lower temperatures. It has been noted that ethanol has a destructive effect on micelles. Additives of quercetin exhibit an opposite effect of micelle stabilization, which leads to the formation of a homogeneous surfactant structure. It has been shown that, by varying solvent composition, the flavonoid–micelle binding can be controlled due to changes in the solvation. The greatest influence of quercetin on the structure formation of P123 has been observed at a solvent composition corresponding to ethanol-to-block copolymer molar ratio of n(EtOH) : n(P123) = 80 : 1.

The application of nanostructured adsorbents in sample preparation (extraction and preconcentration) of multicomponent mixtures in the solid-phase extraction of organic compounds is gaining significant interest. This study examines the adsorption properties of ordered mesoporous analogues of SBA-15, synthesized in the presence of quercetin as a potential adsorbate. The work explores the specific features of the adsorption-based recovery and preconcentration of quercetin, dihydroquercetin, naringin, and rutin under dynamic conditions from acetonitrile solutions using the breakthrough curve method. The use of the generalized optimization criterion of adsorption preconcentration CE, within the framework of the Venitsianov–Tsysin model of dynamic adsorption preconcentration, taking into account the limiting (mixed-diffusion) stage of adsorption kinetics, enabled the evaluation of the efficiency of the adsorption preconcentration of flavonoids on the studied adsorbents. The results demonstrate that the use of ordered silica synthesized in the presence of a potential adsorbate significantly enhances concentration efficiency compared to nonstructured silicas or unmodified SBA-15 analogue samples.

In this brief review, we consider various characterizations of “monomeric” reversed phases for elucidating the interactions governing adsorbate retention in liquid chromatography. Conventional methods related to the assessment of retention capacity and hydrophobicity (specifically methylene selectivity) using single mobile phase compositions are discussed with a focus on dispersion interactions, along with their inherent strengths and limitations. An alternative approach involving separation maps through relative retention analysis is proposed. It is noted that, in real reversed-phase adsorbents, the density of the attached alkyl chains is typically one half of that of solid n-alkanes. In this case, adsorbate molecules to penetrate into the attached phase, and the process depends on the molecular shape. Consequently, conventional “monomeric” reversed phases exhibit specific selectivity towards substances with specific structures. The review also notes that current analytical methods often do not pay sufficient attention to the difference between the substance retention mechanisms, absorption and adsorption, because the predominant parameters of these mechanisms are quite different. Moreover, in the two most widely used very interesting and informative methods, linear solvation energy relationships (LSERs) and the hydrophobic-subtraction model, this characteristic has not received due attention. Taking into account that the method does not distinguish adsorbates retained by different mechanisms, absorptive versus adsorptive, to the obtained significant discrepancies between the calculated and experimental data do not seem extraordinary. The interpretation of the results of an LSER analysis is also complicated by uncertainties in the contributions of partial properties of adsorbates in both mobile and stationary phases to the total solvation energy, as only their difference is typically calculated. Nonetheless, a comparison of different columns in identical mobile phases can yield informative insights. A drawback of the second approach is the necessity of using multiple columns with substantial qualitative differences in the adsorbate retention among them. Furthermore, a possibility of the decomposition of all interactions into distinct types seems questionable, because the method does not involve any orthogonal (independent of the applied calculation method) properties.

The sorption of triterpene saponins is studied on different brands of active carbon under equilibrium conditions. The effect the surface activity of glycosides has on the course of the curves is established. Sorption isotherms are assessed using a formal approach based on selecting the sorption equations (Langmuir, Freundlich, BET, Redlich–Peterson) that describe the obtained dependences as closely as possible. Thermodynamic characteristics of the given process (energy of sorption, enthalpy, and entropy) are calculated using sorption curves in the coordinates of the Langmuir equation.

A rapid method is developed for the determination of bisphenol A (BPA) in ethanolic extracts by gas chromatography–mass spectrometry (GC–MS). The GC–MS method has acquired reference status in accredited analytical laboratories in identifying contaminant impurities in food and alcohol products. Bisphenol A is used as a monomer in the production of a number of plastics and epoxy resins; in its free form, it can be contained in quantities exceeding the permissible level in food containers. Bisphenol A can accumulate in a human body and cause harmful health effects. The studies were performed on an Agilent 8890 gas chromatograph equipped with a mass selective detector model 5977B and a 30 m long Ultra ALLOY®-5 UA5-30M-0.25F capillary column. Optimal modes for the determination of bisphenol A in ethanolic extracts were selected. The direct determination of BPA in ethyl solutions without derivatization using GC–MS can be recommended for the development of procedures for monitoring the quality and safety of food packaging, monitoring BPA in alcohol-containing liquids, as well as in forensic medical examination as a reference procedure to confirm the reliability of BPA identification.

The dynamic light scattering method was used to investigate the aqueous solutions of Pluronic P123 under different temperature, solvent, and quercetin additives. Significant changes in the average particle size and polydispersity index were revealed depending on the conditions. The effect of temperature on micelle formation of block copolymer in aqueous solution in the range T=15–45°C, the most commonly considered in the use of P123 in sol-gel synthesis of silica, was studied. The formation of micelles of the studied surfactant was greatly influenced by temperature, especially at T=15–20°C. In this temperature range, the size distribution of the scattering intensity has a polymodal character, which indicates the presence of macromolecules, micelles and their aggregates in the system. Further increase in temperature up to 45°C does not result in a significant change in particle size. In aqueous solutions, micelles with a narrow size distribution (minimum polydispersity index) are formed in the temperature ranges 21–25 and 35–40°C. Significant influence of alkanols and polyphenolic substances additives as solubilizers and able to influence the structure of micelles both in their volume and on the surface of polar parts of surfactants was noted. It is shown that in the presence of butanol-1 the stabilization of micelles at temperatures 15–20°C is observed. At T30°C rearrangements of the mesophase structure occur. As the proportion of butanol-1 in the solution increases, its influence is manifested at lower temperatures. It was noted that ethanol has a destructive effect on micelles. Quercetin additives exhibit the opposite micelle stabilizing effect, leading to the formation of a homogeneous surfactant structure. It is shown that by varying the solvent composition, it is possible to control the binding of flavonoid to micelle by changing the solvation. The greatest influence of quercetin on the structure formation of P123 was observed at the solvent composition corresponding to the molar ratio of ethanol and block copolymer n(EtOH):n(P123)=80:1.

The article provides a brief overview of chromatographic methods for the determination of free bisphenol A in technical and food products. Bisphenol A (BPA) is used as a monomer in the production of some plastics and epoxy resins. Free BPA may be present in quantities exceeding acceptable levels in plastic food containers and in food products packaged in these containers. Maximum permissible concentration (MPC) of BPA in the air of the working area is 5 mg/m3, which in terms of liquid is 5 µg/dm3. Maximum permissible concentration for the content of BPA in water, in water bodies for domestic, drinking and community water use is 0.1 mg/dm3. In European countries for plastics in contact with food, the BPA migration value is 0.6 mg/kg. Despite the relatively low toxicity of BPA, it can accumulate in the human body and cause harmful effects. To determine BPA in plastic, food products, and biological fluids, gas chromatography with preliminary derivatization by silylation or acylation of the analyte is most often used. Gas chromatographic techniques for direct chromatography on heat-resistant columns have also been developed. A fluorometric detector and a mass spectrometric detector are used as detection devices, along with a flame ionization detector. An alternative method for determination of BPA is HPLC with optical and mass spectrometric detection methods. The TLC method was also developed for the determination of BPA. For the preparation of BPA samples, solid-phase extraction (SPE), liquid-liquid extraction (LLE), dispersive liquid-liquid microextraction (DLLME), combined extraction method with acetonitrile separation (QuEChERS) are used.

In this work the study of adsorption immobilization of inulinase on super-crosslinked macroporous sorbents based on styrene and divinylbenzene: low-base anion exchanger A100, high-base anion exchanger A500R, strong acid cation exchanger C100H was carried out. The influence of the duration of the sorption process, the value of the concentration of hydrogen ions and the concentration of protein in solution on the amount of immobilized enzyme and the activity of the obtained heterogeneous biocatalysts is considered. It was revealed that adsorption reaches its maximum value on average after 4 h at pH of 4.7-5.0 for the sorbents under consideration. The activity of the obtained heterogeneous biocatalysts is 64.8-83.5% of the activity of free inulinase. Although the activity of inulinase during adsorption on the polymer carriers used in the work decreases, the integral amount of the resulting product will be higher than for the native catalyst. The isotherms of inulinase adsorption on super-crosslinked polymers have been studied. The high stability of the obtained heterogeneous biocatalysts is explained by the high sorption capacity of super-crosslinked sorbents. It was revealed that immobilized inulinase can be used during 8-11 consecutive cycles of the substrate hydrolysis reaction. Using the BET adsorption theory, the enzyme sorption isotherms were analyzed and the equilibrium sorption parameters were calculated: the maximum amount of sorbed inulinase, the constants characterizing the sorbate-sorbent and sorbate-sorbate interaction. Among the considered carriers, the highest value of the sorption equilibrium constant (KL=4.25 +/- 0.04 l/mmol) corresponds to the inulinase-cation exchanger biocatalyst, the sorption capacity of which is also the largest. The data obtained is of interest for evaluating the effectiveness of the use of sorbents as inulinase carriers in subsequent technological operations of processing of inulin-containing raw materials.

ЗД-37 ПРИМЕНЕНИЕ МЕТОДА ДИНАМИЧЕСКОГО РАССЕИВАНИЯ СВЕТА (ФОТОННОЙ КОРРЕЛЯЦИОННОЙ СПЕКТРОСКОПИИ) ДЛЯ ОПРЕДЕЛЕНИЯ РАДИУСА АССОЦИАТОВ ПОВЕРХНОСТНО

The regularities of changes in structural characteristics during the formation of associates in micellar aqueous solutions of triterpene saponins Quillaja Saponin and Sapindus Mukorossi are considered. The dependence of surface tension and adsorption on the concentration of an aqueous saponin solution is analyzed, and the values of surface activity and parameters of the adsorption layer are calculated. The average values of diffusion coefficients for spherical and cylindrical micelles are determined based on the measurement of the solution viscosity. The effect of the electrolyte solution on the surface tension and viscosity of glycoside solutions is studied: when the electrolyte is introduced into the saponin solution, the surface tension decreases, which leads to a shift in the critical concentration of micelle formation towards lower concentrations. The introduction of potassium chloride electrolyte reduces the degree of ionization and, as a result of suppressing the electroviscosity effect, leads to a decrease in the viscosity of the solution. The dynamic light scattering method is used to determine the size of glycoside aggregates. It is established that there are aggregates of several sizes in an aqueous solution of saponin. The size and shape of aggregates were calculated using the concepts of micelle packing parameters. In the region of very low concentrations of glycoside solutions, when approaching the critical concentration of micelle formation in the solution, there are spherical micelles. A further increase in the saponin concentration in the solution leads to a decrease in the content of structures with a hydrodynamic radius of 50-80 nm and the appearance of larger agglomerates with sizes greater than 100 nm. It was found that micelles acquire a less hydrated and more densely packed cylindrical shape in the concentration range of 1.7-2.6 mmol/dm3. Compaction of associates leads to an increase in the content of particles with a hydrodynamic radius of 150-250 nm and larger ones, and their presence predicts the appearance of larger agglomerates. Analyzing the data obtained using the dynamic light scattering method, it can be concluded that aggregates of several sizes co-exist in the volume of aqueous saponin solutions at certain concentrations.

A study is performed of features of sorption by heterogeneous ion-exchange membranes of aliphatic and aromatic amino acids with various side groups from individual solutions and solutions containing different mineral salts. One of the most important factors that determines membrane capacity in the sorption of amino acid and mineral salt ions from mixed solutions is the volume of the amino acid side groups, a rise in which reduces of the amount of the sorbed ampholyte. The quantity of amino acid sorbed by a cation exchange membrane from a mixed solution is lower than from the individual solution. The larger the radius of the hydrated cation of the mineral salt, the greater the amount of amino acid sorbed by the membrane from the mixed solution. The change in the hydration of membranes that sorb amino acids is established. The highest content of strongly bound water in the membrane phase is observed for the sorption of the most hydrated amino acid in a solution. The moisture content of the membrane and the hydrophilicity of its surface fall during the sorption of the amino acid with more hydrophobic side group.

Возрастающее с каждым годом число синтетических препаратов не снижает перспективу использования природных соединений.Благодаря широкому спектру биологической активности (адаптогенное, антиоксидантное, противомикробное, диуретическое, гемолитическое, гипогликемическое и др.действия) лидирующее положение среди подобных веществ занимают тритерпеновые сапонины [1-

Molecularly imprinted polymers were synthesized as selective coatings of piezoelectric sensors for determination of carboxylic acids in the intermediate fractions of rectified ethanol. Molecularly imprinted polymers were obtained by reorganizing and imidizing polyamic acid chains in N,N-dimethylformamide in the presence of a template by the non-covalent imprinting method. The ability of molecularly imprinted polymers to recognize the target templates was evaluated by studying their sorption properties in comparison with non-imprinted polymers using direct conductometry in static mode. The equilibrium time of polyimide and molecularly imprinted polymers for acetic, propionic, butyric acids is in the range of 40 - 80 min. The type of sorption isotherm of acetic acid is characteristic of polymeric materials with micropores. During the sorption of acetic acid at low concentrations, the solvent-ethanol strongly competes with the adsorbed substance due to the close molecular sizes and the presence of group -OH. The type of sorption isotherms of propionic and butyric acids refers to the monomolecular adsorption. The sorption of carboxylic acids by molecularly imprinted polyimide is carried out mainly due to the formation of hydrogen bonds between carboxyl groups of adsorbent and adsorbate. According to the sorption data, the degrees of extraction, distribution coefficients, and imprinting factor values were calculated (IF = 3.0-15.1). It is shown that the molecularly imprinted polymers for carboxylic acids have better sorption ability to acid molecules than their non-imprinted polymers. At the same time, the molecularly imprinted polymer for butyric acid has the highest sorption capacity. Thus, the possibility of using molecularly imprinted polymers for carboxylic acids based on polyimide as selective coatings of piezosensors has been established.

A complex consisting of a model carbon nanotube and L-alanine located on its outer side surface, inside it, and at its end is simulated by quantum-chemical means using density functional theory, including dispersion corrections. The mechanism of interaction between amino acids and nanotubes is analyzed, and the energies of the van der Waals interactions in the sorbent–sorbate are assessed. Adsorption isotherms of L‑alanine on MKN-MWCNT-P5000 multi-walled carbon nanotubes (Canada) from aqueous solution are constructed and explained.

The mechanism of phenylalanine absorption by a shaped sulfonic acid cation-exchange membrane with a styrene-divinylbenzene matrix was studied by IR spectroscopy. An analysis of the results of the IR spectroscopic studies showed that the interaction in the sorbent–sorbate system is based on ion-exchange sorption via protonation with addition of the hydrogen counterion to the carboxyl group of amino acid and ion exchange with displacement of the hydrogen ion into the equilibrium solution. The occurrence of nonexchange sorption due to the additional interparticle interactions characteristic of the aromatic amino acid of phenylalanine was proven by sorbate association in the polymer material.

Piezoelectric sensors based on molecularly imprinted polymers (MIPs) for sensing oleic (MIP-Oleic) and palmitic (MIP-Palmitic) acids were tested in the analysis of vegetable oils. When creating the MIP sensors, electrodes were modified with the PM polyimide (dianhydride of 1,2,4,5-benzenetetracarboxylic acid and 4,4′-diaminodiphenyl oxide). Values of the imprinting factor and selectivity coefficients of the molecularly imprinted polymers for sensing fatty acids were compared. Chromatography mass spectrometry was used as a comparison method. The difference between the results of the determination of acids by using a piezoelectric sensor and by chromatography mass spectrometry does not exceed 10%. It is established that sensors modified with molecularly imprinted polymers are selective to the acid that served as a template for the polymer synthesis.