N-doped graphene quantum dots are carbonaceous smart nanomaterials that play a promising role in analytical chemistry methods, especially as sensors, high-performance liquid chromatography, and gas chromatography stationary phases. However, their application in electromigration methods was limited to the role of absorbing probes for indirect detection or a pseudostationary phase, while their high surface area and functionality present broader opportunities to increase analytical capabilities of the capillary electrochromatography method. The current work explores their ability to form a stationary phase on the inner walls of a fused-silica capillary for the capillary electrochromatography alone and with the following surfactant modification. It reports stability, the working pH range, efficiency, and selectivity of the novel capillary coating obtained with its further surfactant modification using imidazolium ionic liquids. The stationary phase was applied to separate a mixture of neutral and charged analytes, namely aromatic amino acids and steroid hormones, and the coating applicability to real samples was demonstrated with the food supplement analysis.

GABA tea is a relatively new type of tea produced through fermentation in an oxygen-free environment, which leads to increased levels of gamma-aminobutyric acid (GABA). This study represents the first investigation into the development of GABA tea production technology using Russian raw materials, specifically the 'Colchida' cultivar, known for its high yield and exceptional quality. Various anaerobic conditions were applied to produce GABA tea samples, and a key focus of the research was to monitor the content of GABA and other amino acids (AAs) at different stages of the tea processing. A novel, sensitive HPTLC method using microcrystalline cellulose plates was developed for profiling AAs and quickly assessing GABA levels in tea products. Additionally, an HPLC-DAD method with pre-column derivatization using dansyl chloride was optimized and validated for the quantitative determination of AAs in GABA tea. Both HPLC and HPTLC methods yielded comparable results. Based on the findings, optimal conditions for further refinement of the GABA tea production process were identified. Elevated levels of other amino acids, particularly alanine and theanine, were also observed. The developed analytical methods are effective for routine AA analysis in tea products and hold promise for further optimization of GABA tea production technology.

Smart materials-based polyfunctional capillary coatings used as stationary or pseudostationary phases significantly increase the capabilities of the capillary electromigration methods and provide separation, analysis, and on-line concentration of ionic, hydrophilic, hydrophobic, and neutral analytes in one analytical cycle while implementing different separation mechanisms of the individual capillary electromigration methods. The review covers such topics as the use of micellar polymers, ionic liquids, oligosaccharides, metal-organic and covalent organic frameworks, molecularly imprinted polymers, nanoparticles, and other smart materials for the synthesis of capillary electrochromatography stationary phases and summarizes and comprehends existing approaches to the development of smart materials for electromigration techniques. The unique properties of smart materials are discussed in terms of implementing various modes of hydrophilic capillary electrochromatography and micellar electrokinetic chromatography, which significantly expands method's analytical limits. Particular attention is paid to the synergistic effect exhibited by the joint use of two or more smart materials in electrophoretic analysis. A special section is devoted to chiral electrophoretic and electrochromatographic separations in bioanalysis involving smart materials.

New polymeric modifiers of electrophoretic systems have been synthesized. These are cationic polyelectrolytes with micellar properties: poly-11-acryloyloxyundecyl-1,4-diazobicyclo[2.2.2]octanium bromide and a chiral copolymer based on acylated quinine and N-(11-acryloyloxydecyl)-N-methylpiperidinium bromide. The electrophoretic capabilities of these polymers have been studied in the separation of model mixtures of steroid hormones and biogenic amines by capillary micellar electrokinetic chromatography and capillary electrochromatography methods. It has been found that the new polyelectrolytes serve as multifunctional modifiers of the bare fused silica capillary wall and background electrolyte, allow for the implementation of various mechanisms of electrophoretic and chromatographic separation, generate an anodic electroosmotic flow, and influence the separation efficiency and selectivity. It was discovered that the copolymer with quinine acting as a chiral label in the composition of two-phase chiral systems promotes the separation of the enantiomers of β-blockers propranolol and carvedilol.

New comb-like polyelectrolytes with triethylammonium (pAUTEA-Br), N-methyl-piperidinium (pAUMP-Br), N-methyl-morpholinium (pAUMM-Br) and pyridinium (pAUPy-Br) cation groups were first used to separate steroid hormones, biogenic amines and amino acids under capillary electrophoresis conditions. The polymers acted as modifiers of electrophoretic systems and were used as dynamic coatings of inner surface of fused-silica capillary and additives to background electrolyte to perform capillary electrochromatography and micellar electrokinetic chromatography regimes, leading to increase in separation selectivity and efficiency, and as reagents for indirect spectrophotometric detection of amino acids. New materials also showed activity during on-line preconcentration of biogenic amines and reduced their limits of detections by 10 times. Thus, new comb-like polyelectrolytes were demonstrated to act as multifunctional materials for capillary electrophoresis. This study discusses the features of the influence of the polyelectrolytes on electrophoretic separation capabilities and their possibilities in separation of model biologically active substances. Modifiers of this type significantly expand the analytical capabilities of the capillary electrophoresis method.

This review provides an overview of recent works focusing on the determination of amino acids (AAs) and peptides using capillary electrophoresis with contactless conductivity detection and ultraviolet (UV) detection, which is the most widespread detection in capillary electromigration techniques, without pre-capillary derivatization. Available options for the UV detection of these analytes, such as indirect detection, complexation with transition metal ions, and in-capillary derivatization are described. Developments in the field of direct detection of UV-absorbing AAs and peptides as well as progress in chiral separation are described. A separate section is dedicated to using on-line sample preconcentration methods combined with capillary electrophoresis-UV.

The review considers the main trends in actively developing methods of solid-phase and liquid–liquid microextraction for the extraction, purification, and preconcentration of analytes from medicinal plants and plant materials, the use of new extractants and approaches to the preparation of samples of plant origin, and their compatibility with mass-spectrometric detection. Particular attention is paid to the analytical capabilities, advantages, and limitations of each of the approaches to extracting analytes from plant materials for the subsequent analysis of the obtained extracts by chromatography–mass spectrometry.

Versions of the electrophoretic determination of neutral carbohydrates by a method of indirect detection using acridone acetic and folic acids as absorbing additives (AA) are proposed. The effects of the nature and concentration of AA, alkali, and various modifiers (cetyltrimethylammonium bromide, CTAB) and ionic liquids (1-dodecyl-3-methylimidazolium chloride and 1-hexadecyl-3-methylimidazolium chloride) on the electrophoretic parameters of the migration of analytes are studied. The lowest limits of detection for carbohydrates are achieved in a background electrolyte containing 2.5 mM acridone acetic acid, 75 mM KOH, 0.5 mM CTAB, and 5 vol

INTRODUCTION:Deep eutectic solvents (DESs) are promising extractants with tuneable properties. However, there is a lack of reports about the influence of the nature of the original DES on obtaining the metabolomic profile of a plant.OBJECTIVE:The aim of this study is to investigate the possibility of obtaining Iris sibirica L. chromatographical profiles with DESs based on various hydrogen bond donors and acceptors as extraction solvents.METHODOLOGY:DESs were prepared by mixing choline chloride or tetrabutylammonium bromide with various hydrogen bond donors and investigated for the extraction of bioactive substances from biotechnological raw materials of I. sibirica L. The obtained extracts were analysed by HPLC with diode array detector (DAD) and Q-MS.RESULTS:Chromatographic profiles for I. sibirica L. extracts by eight choline chloride DESs and six tetrabutylammonium DESs have been obtained. It has been found that selective recovery of bioactive substances can be achieved by varying the composition of DESs. Eleven phenolic compounds were identified in I. sibirica L. using HPLC-MS. Phase separation was observed with acetonitrile for four DESs. New flavonoid derivatives have been found in DES extracts compared with methanol extracts.CONCLUSION:The results showed the possibility of DES usage for extraction without water addition. Selectivity of DESs varies depending on the chemical composition of hydrogen bond donors and acceptors. Choline chloride is a more suitable hydrogen bond acceptor for the flavonoid extraction. Choline chloride-lactic acid (1:1) DES has demonstrated a metabolic profile that was the closest to the methanol one and enhanced the extraction up to 2.6-fold.

In this study, we developed physically adsorbed multi-layer coatings using poly-l-lysine or poly(diallyldimethylammonium chloride) and gold nanoparticles, which were functionalized with bovine serum albumin for the chiral separation in electrochromatography. The approach involves sequentially depositing positively charged polymers and negatively charged citrate-stabilized gold nanoparticles. By repeating this modification cycle, we created two- and four-layer coatings, which were sequentially functionalized with albumin forming three- and five-layer coatings that were finally applied for the separation of enantiomers of dl-tryptophan. The formed coatings exhibit stability across a pH range of 2-10 and feature a dense, uniform surface, as confirmed by scanning electron microscope images. The number of layers impacted nanoparticle deposition density, with five-layer coatings being denser than three-layer ones. Five-layer coatings enable baseline separation of dl-tryptophan enantiomers, whereas three-layer coatings require the presence of albumin in the background electrolyte for separation. Therefore, increasing the number of layers and gold nanoparticles density enhances albumin active center concentration on capillary walls, improving the separation of dl-tryptophan enantiomers. The five-layer coatings can be easily fabricated and possess good repeatability of analytes migration time.

The ease of varying the conditions of electrophoretic separation and the possibility of using a wide variety of chiral selectors make the capillary electrophoresis method a promising alternative to high-performance liquid chromatography for the separation of racemic drugs. This review summarizes the main directions of development of electrophoretic methods for enantiomeric analysis of biologically active compounds, including the use of various modifiers of the quartz capillary walls and background electrolyte (cyclodextrins, nanoparticles, ionic liquids, etc.), formation of multilayer coatings, and combining of enantiomeric analysis with online derivatization and preconcentration of analytes.

Approaches to the highly sensitive determination of low-molecular-weight fatty acids and amino acids in blood serum samples of patients diagnosed with endometriosis by gas chromatography with mass spectrometric detection (GC–MS) and HPLC with a diode array detector were proposed. Conditions for the selective determination of 23 amino acids in the form of dansyl chloride derivatives by reversed-phase HPLC with spectrophotometric detection were found, and the main factors influencing the separation parameters (pH of the mobile phase, the solvent and the buffer solution, and the gradient profile) were identified. It was shown that the traditional GC determination of metabolites in the form of silyl derivatives did not provide the required sensitivity: the high volatility of derivatives already at the stage of sample preparation led to significant losses and, as a consequence, to irreproducible results. Conditions for the determination of organic acids without derivatization using GC–MS on a polar stationary phase were optimized. A procedure for preparing blood serum for analysis (precipitation of proteins and removal of lipids) and conditions for the selective separation of analytes (temperature gradient, 70−230°C) were proposed. The developed approaches made it possible to obtain characteristic profiles of organic acids in the blood serum samples of patients with endometriosis and uterine myoma (as a comparison reference group).

The conditions for the formation of physically adsorbed three-layer coatings of quartz capillary walls in capillary electrophoresis (CE) with successively deposited oppositely charged layers of polydiallyldimethylammonium chloride (PDADMAC) modifiers and citrate-stabilized gold nanoparticles (GNPs) are proposed. It was shown that three-layer PDADMAC–GNP–PDADMAC coatings favorably differ from monolayer coatings with PDADMAC by greater stability in a wide range of pH (2–10). The formed coatings were characterized by scanning electron microscopy, and the presence of a uniform dense layer of nanoparticles on the capillary surface was confirmed. The applicability of the modified capillaries under CE conditions was demonstrated by the separation of a mixture of 16 carboxylic acids. An increase in the separation selectivity achieved with the use of three-layer coatings based on GNPs was explained by the reversible exchange of citrate anions on the GNP surface with negatively charged analytes in the course of electrophoretic analysis.

Combination of properties of gold nanoparticles and bovine serum albumin is promising for the formation of chiral stationary phases enabling high enantioselectivity due to developed surface of coatings and increased chiral selector concentration on the capillary walls. In this work we proposed and compared two approaches to the formation of physically adsorbed multilayer coatings based on citrate-stabilized gold nanoparticles (cGNP) and bovine serum albumin (BSA) for the chiral separation in capillary electrophoresis. In the first approach pre-synthesized cGNP modified with BSA were immobilized on the capillary coated by poly(diallyldimethylammonium chloride) (PDADMAC). PDADMAC polymer was used as a binding layer promoting sorption of the nanoparticles on the capillary surface. It was shown that cGNP-BSA was poorly adsorbed on the capillary surface due to low zeta potential and could not be used for the formation of dense coatings. The second approach included sequential layer-by-layer deposition of PDAMAC and cGNP, resulting in the formation of a dense layer of nanoparticles. The main stage included in-capillary functionalization of cGNP with BSA. Scanning electron microscopy confirmed that the layer-by-layer deposition of modifiers ensured the formation of dense layer of nanoparticles on the capillary surface. The coating was stable in the entire range of pH studied (2–10). The application of such coating allowed reduction of BSA concentration (to 5 μM) in the background electrolyte required for the tryptophan enantiomers separation. It confirms the prospectiveness of combining nanoparticles and chiral selectors for the increase of specific surface area of the capillary inner walls.

A novel approach for the separation of ketorolac enantiomers by capillary electrophoresis is presented. A cationic beta-cyclodextrin derivative based on imidazole was synthesized and used as a chiral selector in the background electrolyte. The influence of pH and ionic strength of background electrolyte, as well as cationic beta-cyclodextrin derivative concentration on the resolution of ketorolac enantiomers, was investigated. The highest value of the resolution for ketorolac enantiomers was 1.46 when the background electrolyte consisted of 25 mM NaH2PO4 (pH 6.4) with 1 mM 1-butyl-3-beta-cyclodextrinimidazolium tosylate. Additionally, the possibilities of cationic derivatives for the separation of ketoprofen enantiomers were shown (peak resolution 1.06). The two-step preconcentration mode was developed to reduce the limit of detection of individual enantiomers. The proposed approach was successfully applied to determine ketorolac enantiomers in tablet "Ketorol express" and human plasma. The calibration range of ketorolac enantiomers for plasma samples was 0.25-2.50 mu g/ml with coefficients of determination >= 0.99. The relative standard deviation both of the peak area and migration time was less than 15%, as well as the accuracy ranged from 90.1% to 110.2% for both analytes. The limits of detection were 44 and 55 ng/ml for R- and S-ketorolac. The quantity of ketorolac in plasma was verified with high-performance liquid chromatography.

The paper presents various theoretical and practical aspects of sample preparation of blue ballpoint pen ink applied on paper for subsequent quantitative analysis using reverse-phase high-performance liquid chromatography (RP HPLC). Estimation of analytical characteristics of a variant of cutting out a paper fragment containing applied ink for reproducibility of analysis results is discussed; composition of the extraction system and extraction conditions were evaluated. Qualitative and quantitative characterization of the extracts was performed by RP HPLC with the diode array detection. Using a scalpel as a tool for cutting out sample fragments and an acidified mixture of solvents as an extractant with performing extraction in an ultrasonic bath at the room temperature for 2 minutes is recommended. It was shown that the influence of different degree of pressure on a ballpoint pen when applying ink to the paper can be minimized by using normalized peak areas of individual dyes. The proposed sample preparation conditions were tested when studying the processes of changes in the composition of applied ink during artificial aging under the influence of constant ultraviolet (UV) irradiation.

Biomedicine is one of the most rapidly evolving fields in medicine with a strong focus on diagnostics. Capillary electrophoresis (CE) is a separation technique widely used for determining concentrations of biologically active compounds, pharmaceuticals, microorganisms, and their metabolites in biological fluids. Today, CE is widely employed in the diagnosis of various diseases. Additionally, it has become an important tool in the pharmaceutical industry, especially for assessing the enantiopurity of drugs. The main advantages of CE include an ability of the automation and miniaturization of an analysis, compatibility with mass-spectrometric detection, use of small sample volumes (nanoliters), and the availability of the equipment and consumables. This review summarizes the key areas of CE application to biomedicine, including proteomic and metabolomic studies, and examines its prospects for the ultra-miniaturization and automation of enantiomeric analysis, including the use of microelectronics and microfluidic systems.

Предложены подходы к высокочувствительному определению низкомолекулярных жирных кислот методом газовой хроматографии с масс-спектрометрическим детектированием ( ГХ-МС ) и аминокислот методом ВЭЖХ с применением диодно-матричного детектора в образцах сыворотки крови больных с диагнозом эндометриоз. Найдены условия селективного определения 23 аминокислот методом обращенно-фазовой ВЭЖХ со спектрофотометрическим детектированием в виде производных с дансилхлоридом и выявлены основные факторы, влияющие на параметры их разделения (рН подвижной фазы, природа растворителя и буферного раствора, профиль градиентного режима). Показано, что традиционное ГХ-определение метаболитов в форме силильных производных не обеспечивает требуемой чувствительности: высокая летучесть производных уже на стадии пробоподготовки приводит к значительным потерям и, как следствие, к невоспроизводимым результатам. Оптимизированы условия определения органических кислот без дериватизации методом ГХ-МС на полярной неподвижной фазе. Предложена схема подготовки сыворотки крови к анализу (осаждение белков и очистка от липидов) и условия селективного разделения аналитов (температурный градиент 70−230°C). Разработанные подходы обеспечили получение характеристических профилей органических кислот в образцах сыворотки крови больных с эндометриозом и миомой матки (в качестве группы сравнения).

The review discusses the advantages and limitations of chromatographic and electrophoretic approaches to the determination of neutral carbohydrates in various samples with complex matrices, the possibility of implementing a variety of liquid chromatography and capillary electrophoresis modes (in zone and micellar versions), and their combinations with various derivatization, detection, and sample preparation techniques. Conditions for the indirect detection of sugars upon the introduction of various absorbing additives into a mobile phase or supporting electrolyte, ligand-exchange capillary electrophoresis, and intracapillary complexation and the determination of carbohydrates by anion-exchange and hydrophilic chromatography are discussed.