Nanosized cation exchanger for the electrophoretic separation and preconcentration of catecholamines and amino acids

The first example of application of nanosized polystyrene-based cation exchanger (NSCE) with sulfo groups as a dynamic coating of capillary walls was demonstrated. The conditions of dynamic coating formation were optimized and ensured the long-term stability of the coating. Capillary-to-capillary and day-to-day repeatabilities were 4% and 3%, correspondingly. The NSCE coating stability at various pH and influence of pH on the EOF mobility were investigated. The developed NSCE-modified coated capillaries provided improved resolution (R_s = 0.9–3.2 for catecholamines and R_s = 1.7–2.8 for amino acids) and efficiencies (330–520 ×10³ t.p./m) of basic analytes, which are 1.5 times higher compared to untreated capillary. The optimized conditions were as follows: 50 mM phosphate buffer solution at pH 2.2 with 5 μM NSCE. The effect of the NSCE concentration in BGE on the electrophoretic mobilities of the analytes was investigated. The various online concentration techniques were tested in order to decrease the LODs. The simultaneous application of NSCE capillaries and field-amplified sample stacking provided the lowest LODs of catecholamines and amino acids and allowed to determine these analytes in human urine.     

Tuning the morphology and magnetic properties of single-domain SrFe8Al4O19 particles prepared by a citrate auto-combustion method

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Generation of characteristic profiles of steroid hormones by reversed-phase HPLC

A method for the determination of steroid hormones by reversed-phase HPLC has been applied to the analysis of biological fluids from healthy individuals and patients with endocrine systems diseases. The obtained chromatographic profiles were processed by the method of principal component analysis and method of soft independent modeling of class analogy. The principle possibility of using the results of chemometric processing of the chromatographic profiles as an additional diagnostic criterion for the treatment of some endocrine pathologies has been shown.     

Factors Responsible for the Electrophoretic Behavior of Carboxylic Acid and Triazine Derivatives under Conditions of Capillary Zone Electrophoresis and Micellar Electrokinetic Chromatography

The effects of the pH, nature, and ionic strength of the running buffer; temperature; and surfactants, organic solvents, and macrocyclic compounds added to the buffer solution on the electrophoretic separation parameters of anionic, cationic, and neutral components of complex mixtures of organic compounds under the conditions of capillary zone electrophoresis and micellar electrokinetic chromatography. Pesticides from the series of chlorophenoxycarboxylic acids and triazines, as well as amino acids and substituted benzoic acid derivatives, were used as model systems. The predominant role of the addition of macrocyclic reagents, in particular, -cyclodextrin, as buffer electrolyte components was noted.     

Ligand-exchange capillary electrophoresis

The fundamentals of ligand-exchange capillary electrophoresis are discussed, and the potential of the method in solving major problems, such as the separation of enantiomers and the determination of biologically active compounds poorly absorbing in the UV region (sugars, amines, and amino acids) is considered.     

Synthesis of substituted thiazolo[4,5-b]pyridines and other annulated heterocycles via SN2→Thorpe-Ziegler→Thorpe-Guareschi domino reactions

A new combinatorial method for the preparation of substituted thiazolo[4,5-b]pyridines, which utilizes cyanoacetamide, heterocumulenes (isothiocyanates, carbon bisulfide), and ethyl-4-chloroacetoacetate in a new S_N2→Thorpe-Ziegler→Thorpe-Guareschi domino reactions has been developed. The obtained thiazolo[4,5-b]pyridines were then used together with aldehydes and malononitrile in another Knoevenagel reaction→Michael reaction→hetero-Thorpe-Ziegler domino reaction for the synthesis of substituted 4,6-dihydro-5H-pyrano[2,3-d]thiazolo[4,5-b]pyridines.     

Determination of mitomycin C in urinary bladder tissue by reversed-phase high-performance liquid chromatography

A procedure was developed for the determination of an anticancer drug of mitomycin C (MMC) in urinary bladder tissue samples by reversed-phase high-performance liquid chromatography with spectrophotometric (365 nm) and mass-spectrometric detection with detection limits of 50 and 10 ng/mL, respectively (signal-to-noise ratio = 3). The tissue samples were homogenized and solid-phase extraction was performed on a DSC-18 cartridge. The procedure was used for comparing the effectiveness of the MMC penetration into the urinary bladder tissue by passive diffusion and by intravesical drug electrophoresis. EDMA increases the rate of mitomycin penetration into urinary bladder walls by 3 to 5 times with respect to passive diffusion.     

Determination of endo- and exogenous corticosteroids by cyclodextrin-modified micellar electrokinetic chromatography with the use of on-line preconcentration

A method was proposed for the simultaneous determination of steroids of the endo- and exogeneous origin with the use of micellar electrokinetic chromatography, which provides the determination of residual medicines in biological fluids and the control of medication efficiency at different steroidogenesis abnormalities. The introduction of a macrocyclic addition of β-cyclodextrin (from 1 to 6 mM) into a buffer electrolyte solution (25 mM phosphoric acid, 20 mM sodium dodecyl sulfate, 4.5 mM urea, pH 2.5) or into a sample solution decreases the detection limit by a factor of 20–200.