The series of mixed-mode stationary phases with varying polyelectrolyte hydrophilicity and attachment density to poly(styrene-divinylbenzene) surfaces was synthesized. The influence of resins hydrophilicity and substrate shielding degree on the chromatographic properties of obtained phases in ion chromatography (IC), hydrophilic interaction liquid chromatography (HILIC), and reversed-phase high-performance liquid chromatography (RPHPLC) modes was investigated. The stationary phase with more hydrophilic amine, namely N-methylethanolamine, in polyelectrolyte structure allowed simultaneous separation of highly polarizable anions and standard inorganic ones in IC mode, various polar analytes in HILIC mode, and nitro- and chloro-phenols as well as alkylbenzenes in RP-HPLC mode. Covering the substrate surface with polyethyleneimine prior to polyelectrolyte attachment turned out to be the most effective way to increase the hydrophilicity and shielding degree. The application of this approach resulted in growing the separation ability toward nucleosides and nucleobases as compared to previously obtained mixed-mode stationary phases based on the same substrate. The retention mechanism of phenols on polymer-based polyelectrolyte-grafted resins was studied for the first time.

A set of covalently-bonded poly(styrene-divinylbenzene)-based stationary phases with linear polyelectrolyte layers was obtained by one-step epoxy-amine polymerization and examined. The influence of synthesis conditions, such as temperature, duration of the synthesis and quantity of reagents, on ion-exchange capacity and selectivity toward inorganic anions and organic acids was investigated using hydroxide eluent in suppressed ion chromatography (IC) mode. Obtained stationary phases packed in 10-cm long columns allowed the separation of up to 21 anions in 45 min, including mono-, di-, and trivalent organic acids, as well as inorganic anions. For the first time the possibility of using PS-DVB-based polyelectrolyte-grafted stationary phase for separation of watersoluble vitamins, sugars, nucleosides and nitrogenous bases in hydrophilic interaction liquid chromatography (HILIC) mode and alkylbenzenes in reversed phase high performance liquid chromatography (RP HPLC) mode was demonstrated. The obtained phases showed beneficial performance as compared to previously reported mixed-mode adsorbents based on the same substrate.

Two methods for increasing the degree of hydrophilization and shielding of a resin substrate based on a styrene–divinylbenzene copolymer with attached polyethylenimine quaterinized with glycidol are proposed. The first method is the polymerization of glycidol in a functional layer by varying the pH of the reaction medium, and the second one is the modification of the substrate by oxidizing double bonds on its surface to form anchor epoxy groups. It is demonstrated that, in the first case, the optimal approach is to add glycidol twice before and after adding an alkali, because, in this case, the first addition of glycidol is consumed for the quaternization of the polyamine, and the second addition—for the polymerization in ion-exchange centers. The novel method of substrate modification in combination with the developed method for creating hydrophilic layers made it possible to significantly reduce the retention of oxohalides, haloacetic acids, and polarizable anions in the suppressed ion chromatography mode and amino acids in hydrophilic interaction liquid chromatography mode up to a change in the elution order. The obtained stationary phases are suitable for the simultaneous determination of standard inorganic anions, oxohalides, and haloacetic or alkylphosphonic acids in an ion chromatography mode, and also for the separation of amino acids, sugars, and vitamins in a hydrophilic interaction liquid chromatography mode.

Two methods for increasing the degree of hydrophilization and screening of the sorbent matrix based on a copolymer of styrene and divinylbenzene grafted with polyethyleneimine quaternized with glycidol are proposed. The first method involves the polymerization of glycidol in the functional layer by varying the pH of the reaction medium, and the second method involves modifying the matrix by oxidizing the double bonds on its surface to obtain anchor epoxy groups. It was demonstrated that in the first method, the optimal approach is the twofold addition of glycidol before and after the addition of alkali, as in this case, the first addition of glycidol is consumed for the quaternization of polyamine, and the second for polymerization in ion-exchange centers. The new method of matrix modification, combined with the developed method of creating hydrophilic layers, significantly reduced the retention of oxyhalides, haloacetic acids, and polarizable anions in ion chromatography with suppressed background conductivity and amino acids in hydrophilic chromatography up to the point of changing the elution order. The obtained stationary phases are suitable for the simultaneous determination of standard inorganic anions, oxyhalides, and anions of haloacetic or alkylphosphonic acids in ion chromatography, as well as for the separation of amino acids, sugars, and vitamins in hydrophilic chromatography.

The chapter describes the implementation of ion chromatography in the analysis of anions and cations. The ion-exchange processes and factors influencing the retention of ionic species are covered. Detection systems utilized for the determination of anions and cations, as well as eluents that are compatible with these detectors are presented. The main types of anion and cation exchangers and areas of their application are demonstrated. The most significant examples of using anion-exchange chromatography include the determination of inorganic anions, carboxylic acids, organophosphates, organosulfates, and carbohydrates. The application of cation-exchange chromatography is demonstrated in the example of alkali and alkaline-earth metals, ammonium, alkylamines, biogenic amines, and transition metals analysis.

In the pharmaceutical industry, the need for analytical standards is a bottleneck for comprehensive evaluation and quality control of intermediate and end products. These are complex mixtures containing structurally related molecules. In this regard, chromatographic peak annotation, especially for critical pairs of isomers and closest structural analogs, can be supported by using a Quantitative Structure Retention Relationship (QSRR) approach. In our study, we investigated the fundamental basis of the reversed-phase (RP) retention mechanism for 1141 isomeric compounds from the METLIN SMRT dataset. Nine different descriptor calculation tools combined with different feature selection methods (genetic algorithm (GA), stepwise, Boruta) and machine learning (ML) approaches (support vector machine (SVM), multiple linear regression (MLR), random forest (RF), XGBoost) were applied to provide a reliable molecular structure-based interpretation of RP retention behaviour of the isomeric compounds. Strict internal and external validation metrics were used to select models with the best predictive capabilities (rtest > 0.73, order of elution > 60 %). For the developed models, mean absolute errors were in the range of 60 to 110 s. Stepwise and GA showed the most suitable performance as descriptor selection methods, while SVM and XGBoost modeling gave satisfactory predictive characteristics in most cases. Validation performed on the published experimental data for structurally related pharmaceutical compounds confirmed the best accuracy of MLR modeling in combination with GA feature selection of general physico-chemical properties. The resulting models will be useful for the prediction of separation and identification of structurally related compounds in pharmaceutical analysis, providing a simultaneous understanding of the interaction mechanisms leading to their retention under RP conditions.

The aim of this work was to the obtaining novel mixed-mode stationary phases with increased hydrophilicity and applying them in ion and hydrophilic interaction liquid chromatography. The resins were obtained by the sequential covalent attachment of branched polyethylenimine and polyelectrolytes synthesized from diepoxide and a secondary amine on the surface of epoxidized polystyrene–divinylbenzene. To increase the shielding degree of the polymer substrate, an additional polymerization of glycidol was carried out in the functional layer of the sorbent at an increased pH of the reaction medium. The synthesized phases possessed increased hydrophilicity compared to most resins based on a styrene–divinylbenzene copolymer with covalently attached layers. This was evidenced in the ion chromatography mode by a decrease in the relative retention of polarizable anions, weakly hydrated oxyhalides (up to a change in the elution order of the bromate), and haloacetic acids. In the hydrophilic interaction liquid chromatography mode, an increased hydrophilicity of the phases was confirmed by an increase in the retention factors of polar analytes, as well as by the reversal of the elution order of ascorbic and nicotinic acids as compared to the phases based on polystyrene–divinylbenzene presented in the literature. The low efficiency of the obtained stationary phases in the ion chromatography mode was noted, which is associated with slow mass transfer in the bulk polymer functional layer. The negative impact of the polymer layer on efficiency in hydrophilic interaction liquid chromatography is less pronounced due to the presumably smaller thickness of the part of the functional layer involved in this mode. The proposed method for the synthesis of resins ensures an increase in the efficiency, selectivity, and separation ability of sorbents in the hydrophilic interaction liquid chromatography mode as compared to phases based on a styrene–divinylbenzene copolymer described previously in the literature. The resulting highly hydrophilic resins makes it possible to separate a mixture of 9 nitrogenous bases and nucleosides in 18 min, 6 vitamins in 24 min, and 8 sugars in 11 min. Thus, the method of substrate hydrophilization proposed in this work is promising for improving the chromatographic characteristics of phases in the hydrophilic interaction liquid chromatography mode and can be used to create sorbents with increased selectivity and efficiency.

One of the most important directions of the development of pharmacological science is the development and introduction into clinical practice of medicines of natural and synthetic origin. A striking representative of domestic cytoprotectors is malic acid salt. 3-hydroxy-6-methyl-2-ethylpyridine, patented under the trade name "Ethoxidol". It is not inferior, and sometimes surpasses similar drugs in its pharmacological activity. Only one work has been found in the literature devoted to the determination of ethoxidol in medicinal preparations by voltammetry. Sensitivity is not sufficient for its determination in blood plasma. It was necessary to develop a more sensitive and selective method. Microemulsions are often used in variants of capillary electrokinetic chromatography or sample preparation, but the method of microemulsion liquid chromatography (MLC) has not been so widely used. The method has certain advantages over HPLC. In this work, the determination of ethoxidol in blood plasma was carried out by high-performance microemulsion chromatography with fluorimetric detection. 300 mm3 microemulsions were added to 300 mm3 of plasma and thoroughly mixed to precipitate plasma proteins. The addition of microemulsion prevents the co-deposition of ethoxidol together with proteins. The filler fluid was taken and injected into a chromatograph. The degree of extraction was controlled chromatographically by adding a known amount of ethoxidol to the extract from the blank plasma. In a micellar medium, substances can be solvated differently than in aqueous methanol/acetonitrile solutions. Changes in the spectral characteristics of substances are caused by the presence of oil in the composition of the microemulsion, the introduction of substances into a drop of which leads to a spectral shift. When determining ethoxidol, the excitation and detection wavelengths of λex 287 nm and λem 399 nm, respectively, were selected. It should be emphasized separately that the microemulsion additionally allows you to stabilize the components being determined. Thus, in the case of determination of ethoxidol in blood plasma, standard methods of sample preparation (liquid and solid-phase extraction, precipitation of proteins with organic solvents, acids, metal ions) did not lead to the desired result. In the case of dilution of the sample with microemulsion, the extraction was quantitative. The calibration dependence was linear in the concentration range 0.1-10 mg/dm3. The graph is described by the linear equation S=23.97C-1.257. The correlation coefficient R2=0.998. The detection limit is 50 micrograms/dm3. The relative standard deviation of S(r) is 0.08 (n=3). Thus, a new chromatographic method for determining ethoxidol in human blood plasma is proposed. It is shown that the use of microemulsion as an eluent leads to the stabilization of the drug in solutions and a significant increase in the extraction of ethoxidol from real samples.

The possibility of using a new graphene-based carbon monolith for searching new oil deposits or branches adjacent to the already registered oilfields by areal geochemical survey is demonstrated. The material has been developed at the Faculty of Chemistry of M. V. Lomonosov Moscow State University. Sorption of volatile organic compounds (VOCs) from soil air at the oilfield was carried out using two sorbents (carbon adsorbent and Tenax-TA traditionally used for such analyses) with subsequent determination by gas chromatography with mass spectrometric detection and thermal desorption as a way of sample injection (TD/GC/MS). The new material absorbs more hydrocarbons (n-alkanes and monoaromatics) in the range from C8 to C16 than Tenax-TA, the intensities of the chromatographic peaks of the compounds also being higher. The phenomenon of irreversible sorption from carbon materials is observed for VOCs from C17 and more. However, the concentration of such substances in the soil air is rather low due to the low pressure of saturated vapors of these compounds under normal conditions. Hence, the chromatogram of carbon monolith reflects the macro-characteristics of this oil deposit better than Tenax-TA. To increase the sensitivity of the determination, a preliminary optimization of thermal desorption conditions was carried out. The values of the helium flow rate through the sorbent sample and the desorption time of the compounds are chosen to get the largest peak area. The regeneration of sorbent samples is carried out to provide the possibility of their reusage. Tenax-TA decomposes at lower temperatures compared to carbon sorbent and thus cannot be purified completely unlike the new monolith. The graphene-based sorbent is reusable and much cheaper in the manufacture than imported polymer Tenax-TA since it is made of domestic materials.

Four amino phases representing 3-aminopropyl silica gel batches with different numbers of grafted functional groups are compared. To evaluate the chromatographic properties of the adsorbents, the Tanaka test for hydrophilic stationary phases is used and the retention of polar substances of various classes in the HILIC (hydrophilic) mode is studied. It is shown that even small changes in the nitrogen content between different batches of 3-aminopropyl silica gel have a significant effect on the retention of polar analytes. The hydrophilicity of a substrate is shown to have the greatest effect on its chromatographic behavior, and its evaluation using the Tanaka test is the basis for selecting a batch to separate specific classes of polar substances or for further modification to obtain new phases.

Adsorbents based on various substrates—silica and a copolymer of styrene with divinylbenzene—are developed for the determination of amino acids by hydrophilic interaction liquid chromatography—mass spectrometry. The optimal version of the structure of the functional layer in two series of the obtained stationary phases was chosen, which provides the best hydrophilization for each substrate. Retention mechanisms were studied and the conditions for the mass-spectrometric detection, separation, and determination of 16 amino acids were chosen. The applicability of the obtained adsorbents and a method for determining amino acids for the analysis of soil extracts were estimated.

This study offers a theoretical rationale and experimental validation of extraction of 22 polychlorinated biphenyls (PCBs) having various degrees of chlorination (including five dioxin-like ones: PCB-105, PCB-118, PCB -156, PCB-157, and PCB-167) from waters of various salinity levels by dispersive liquid-liquid microextraction (DLLME) using various extractants and mixtures of aliphatic alcohols for additional dispersion, with subsequent identification by gas chromatography coupled with mass spectrometry. To optimize the conditions of DLLME and of concentrating PCBs of various degrees of chlorination, the experiment was planned via the three-factor Box-Behnken design (response surface methodology). Composition and ratios of components were found for the extractant mixture, and composition of the dispersive agent was optimized. Effective recovery of the 22 congeners from waters with salinity ranging between 1%o and 22%o was ensured by an extractant mixture consisting of chloroform, dichloromethane, and carbon tetrachloride and by a dispersive agent composed of acetone, ethyl acetate, ethyl alcohol, and isopropyl alcohol. The newly developed sample preparation scheme is compatible with gas chromatography coupled with mass spectrometry, and limits of detection and quantitation varied as follows: 0.0075-0.0150 and 0.025-0.050 mu g/L, respectively. The newly developed assay allows to quantify the analytes at concentrations of 0.025-15 mu g/L in waters, with recovery 90-105% and relative standard deviation 4-8%.

Mixed-mode stationary phases based on epoxidized copolymer of styrene and divinylbenzene have been obtained by amination with methylamine, further alkylation with 1,4-butanediol diglycidyl ether and opening the terminal oxirane rings with dimethylethanolamine. To evaluate the effect of the number of anchor amino and diol groups on the degree of hydrophilization of resins, the quantity of reagents was varied. Polymerization of glycidol in the functional layer at an increased pH of the reaction medium was carried out for additional shielding of the substrate. It was found that increasing the number of anchor amino groups is promising for increasing hydrophilicity in suppressed ion chromatography and hydrophilic interaction liquid chromatography modes, while polymerization of glycidol increases the degree of substrate shielding. The applicability of the most hydrophilic adsorbent in three HPLC modes was demonstrated. Novel mixed-mode stationary phase allows the separation of six nucleosides and nitrogenous bases by hydrophilic interaction liquid chromatography, 7 alkylbenzenes by reversed phase liquid chromatography, and 20 organic and inorganic anions by suppressed ion chromatography.

To expand the field of application of anion exchangers based on a copolymer of styrene and divinylbenzene with attached polyethyleneimine, quaternized with glycidol, the following conditions for their synthesis were varied: the amount of the added glycidol, temperature, and duration of synthesis. The influence of these factors on the capacity, selectivity, and efficiency of the resins in the mode of suppressed ion chromatography was studied; in addition, the stationary phases were studied in the mode of hydrophilic interaction liquid chromatography using the Tanaka test. It was shown that the synthesis conditions under study ensure the control of the capacity and selectivity of anion exchangers, while their hydrophilicity changes insignificantly. The behavior of oxoanions on covalently attached resins in the ion chromatography mode was studied for the first time, and the applicability of phases with quaternized polyethyleneimine in the hydrophilic interaction liquid chromatography mode to the separation of sugars, amino acids, water-soluble vitamins, nucleosides, and nitrogenous bases was demonstrated for the first time.

A domestic composite material based on silicon carbide and nitrile butadiene rubber was used to identify volatile substances of banana, banana flavor, and creamy chewing candies by passive adsorption in combination with thermal desorption GC–MS. This method can be used to determine a wide range of compounds, for example, esters of carboxylic acids, terpenoids, aldehydes, aromatic hydrocarbons, alkanes, heterocyclic compounds, phenols, glycerides, and fatty acids. The obtained chromatographic profiles of the samples were compared. In the chromatogram of “Banana” flavor, five peaks (out of eight) corresponded to the compounds that form the aroma of a banana, and in the chromatogram of “Love is” candies with banana flavor, three corresponding peaks (out of 21) were found.

A novel enantioselective adsorbent was obtained by hybridization of microspherical polystyrene-divinylbenzene (PS-DVB) macroporous particles with eremomycin-stabilized gold nanoparticles (GNPs). Macrocyclic antibiotic eremomycin was used as a stabilization agent to obtain GNPs which were then characterized by transmission electron microscope. The average diameter of obtained nanoparticles is about 16.6 nm. Eremomycin-stabilized nanoparticles were successfully embedded into the porous polymer structure with a resulting chiral selector content of 37.5 pmol/g. The obtained PS-DVB composite containing GNPs with immobilized eremomycin was studied by scanning electron microscopy and diffuse reflectance spectroscopy. The values of the specific surface area (500 m2/g) and porosity of the adsorbent (0.39 cm3/g) are measured using nitrogen adsorption at low temperatures. The obtained composite material was used as a chiral stationary phase of liquid chromatography. A good separation enantio-selectivity to amino acids, their derivatives and beta-blockers under RPC (reversed-phase) and HILIC (Hidrophilic Interaction Liquid Chromatography) mode is demonstrated. The results obtained revealed that the prepared Eremo@GNP@PS-DVB composite is promising for use as a stationary phase in HPLC.

The experimental design methodology based on central composite design of experiments was applied to compare the retention mechanisms in supercritical fluid chromatography (SFC) and non-aqueous hydrophilic interaction liquid chromatography (NA-HILIC). The selected set consists of 26 compounds that belong to imidazoline and serotonin receptor ligands. The different chemometric tools (multiple linear regression, principal component analysis, parallel factor analysis) were used to examine the retention, as well as to identify the most significant retention mechanisms. The retention mechanism was investigated on two different stationary phases (diol, and mixed-mode diol). In NA-HILIC, the mobile phase contains acetonitrile as a main component, and methanolic solution of ammonium formate (+ 0.1% of formic acid) as a modifier. The same mobile phase modifier was used in SFC, with a difference in the main component of the mobile phase which was CO2. The retention behaviour differs significantly between HILIC and SFC conditions. The retention pattern in HILIC mode was more partition-like, while in SFC the solute-sorbent interactions allowed retention. The retention mechanism between mixed-mode diol and the diol phases varies depending on the applied chromatographic mode, e.g., in HILIC the type of stationary phase significantly affects the elution order, while in SFC this was not the case. The HILIC retention behaviour was influenced by the number of tertiary amines-aliphatic, and N atom-centred fragments in tested compounds. On the other hand, the number of pyrrole and pyridine rings in the structure of the compound showed correlation with their SFC retention, simultaneously increasing the molecular weight and rapid elution of larger compounds. It was found that temperature surprisingly plays a major role in SFC mode. The increase in temperature reduces the relative contribution of enthalpy factors to total retention, so the separation in SFC was more entropy-controlled. For further pharmaceutical research and optimization, the SFC would be considered more beneficial compared to HILIC since it gives good selectivity in separation of chosen impurities.

In phytotherapy, Echinacea purpurea L. is generally used in the form of water-alcohol extracts, which contain phenylpropanoids exhibiting anti-inflammatory, hypoglycemic and moderate antiproliferative effects. The relevance of using plants of the genus Echinacea as a phytomaterial is due to the high demand of consumers; nowadays, the level of sales of water-alcohol extracts in the world is quite high. Considering the importance of using these plants, the present work aimed to determine phenolic compounds in water-alcohol extracts of echinacea obtained by various extraction methods. The biological activity of echinacea is related to hydroxycinnamic acids and their derivatives (chlorogenic, caftaric and chicoric acids). In this study, conditions for the identification and determination of phenolic compounds using such chromatographic methods as HPLC-DAD-MS and GC-MS allowing to expand the range of target analytes in water-alcohol extracts of echinacea have been proposed. A number of unknown compounds of phenolic nature and monosaccharides have been identified in water extracts of echinacea by implementing the SPAD technique on a sorbent for solid-phase extraction -Strata C18-E. The effectiveness of various extraction methods and their influence on the composition of extracted phenolic compounds from plant raw materials was studied. Subcritical extraction at 120 degrees C was established to provide maximum extraction of rutin, caffeic and caftaric acids. Chlorogenic and chicoric acids are most effectively extracted by traditional methods described in the Pharmacopoeia. The influence of growing conditions on the total content of phenolic compounds in echinacea was studied; the increase in the altitude above sea level results in higher contents of phenolic compounds. The assessment of the content of phenolic compounds in industrially manufactured preparations based on echinacea was carried out. The possibility of using the ratio of chicoric to caftaric acids as an indicator of the quality and authenticity of extracts and preparations based on them was shown.

The silicon carbide and poly(butadiene-acrylonitrile) rubber (NBR) composite material was used for the first time as adsorbent for gas-phase preconcentration of volatile hydrocarbons. The possibility of the preconcentration of n -alkanes and polyaromatic hydrocarbons from the air by using passive sampling on cartridges packed with this sorbent following by thermal desorption - gas chromatographic determination was demonstrated. The sorption rate of model substances from the air at room temperature and atmospheric pressure was studied. The optimum material for the storage and transportation of the collected samples was selected. The desorption efficiency of model compounds from the adsorbent was investigated. The result of thermo gravimetric analysis of the composite to provide the choice of temperature for the regeneration was given. Soil air at the oil field was analyzed using the developed method. The possibility of multiple use of the composite sorbent for analysis was demonstrated.