Volume 80, Nº 7 (2025)

One of the actual fields of application of paper-based microfluidic systems (µPADs) is the determination of biologically active substances in various objects, including pharmaceuticals. Often such determination is carried out as a variant of screening analysis to identify samples that should be investigated in more detail by highly informative but relatively expensive methods. In this work, an original method for the colorometric determination of quercetin using microfluidic analytical systems based on paper modified with gold and silver nanoparticles of different morphologies is proposed. It is based on the reduction of silver(I) ions to metallic silver under the action of quercetin, which leads to a contrast color change of the BMFS detection zones. The possibility of using a monitor calibrator and a smartphone camera to record the analytical signal was demonstrated. Optimal conditions of the analysis have been selected. It is shown that the type of nanoparticles affects the sensitivity coefficient of quercetin detection, which is promising for the creation of multisensor systems for discrimination of samples of complex composition. The limits of quercetin detection under the selected conditions are 70-120 ng depending on the nature of the analytical reagent and the method of analytical signal registration. The range of detectable contents is 2-10 µg. Sufficient sample volume for analysis does not exceed 25 µl. The selectivity of the proposed method for the determination of quercetin in relation to a series of common inorganic ions and organic substances was evaluated. The applicability of the developed approach for the determination of quercetin in three pharmaceutical preparations is shown.

The technique of acid decomposition of 1000 mg black shale samples in an open system has been developed. The procedure involves the destruction of the mineral matrix with a fivefold excess of ammonium bifluoride at 230°C for 6 h, followed by the reagent removal through distillation and the subsequent treatment of the residue with a mixture of perchloric and nitric acids to achieve the complete dissolution. The resulting solution remains stable over time and serves as the basis for the direct determination of more than 60 elements using a combination of ICP–MS and ICP–AES techniques. The method enables the quantification of gold, silver, and rhodium directly in the post-decomposition solution with the computational correction of spectral interferences. The method was tested on reference black shale materials from the Baikal–Vitim province SLg-1 and SChS-1 (Sukhoi Log deposit, Irkutsk region, Russia). The study also presents analytical results for their updated counterparts, SLg-1A and SChS-1A.

A selective technique for the determination of 20 beta-adrenostimulants in muscle tissue and liver by chromatography-mass spectrometry has been developed. The limit of quantitative determination of the technique is 0.1-0.25 (0.5) µg/kg (depending on the compound to be determined). The technique is based on hydrolysis of research objects followed by extraction of the determined compounds with acetic acid acetonitrile, obtaining the organic fraction by salting, its purification on aluminum oxide layer and dispersive purification with C₁₈, further purification by liquid-liquid extraction with hexane. Data on promising ion-transitions of some determined compounds are given; detection parameters of bambuterol, formoterol, phenylethanolamine A are established. Data on optimization of hydrolysis, extraction and purification of extracts are given. Information on stage-by-stage losses of the determined compounds is given; data on the analysis of reference material are obtained. The validation of the developed method shows that the relative expanded uncertainty ranges from 7 to 24 %.

A voltammetric sensor based on a glassy carbon electrode (GCE) modified with tin dioxide nanoparticles dispersed in N-hexadecylpyridinium bromide (NPs SnO₂₎ was developed for the determination of taxifolin. Modification of the electrode surface provides an increase in the reversibility of the electrode reaction, as well as a significant increase in the redox currents compared to GCE (2.3 and 3.3 times for the anodic and cathodic peaks, respectively). The morphology of the electrode surface according to scanning electron microscopy data is represented by uniformly distributed on the electrode surface SnO₂ NPs of spherical shape with a diameter of 20-40 nm, which leads to a 3.9-fold increase in the effective area of the electrode and a 143-fold increase in the heterogeneous electron transfer rate constant. The electrooxidation of taxifolin was found to proceed with the participation of protons. Mixed control with diffusion and adsorption contributions was confirmed for the electrode reaction. In differential pulse mode against Britton-Robinson buffer with pH 6.0, the range of determined taxifolin contents is 0.075-25 μM with a detection limit of 70.7 nM. The obtained characteristics are comparable to other electrochemical approaches, but the proposed approach is simpler and more rapid, and does not require complex modification of the electrode. The developed sensor was successfully applied in the analysis of dihydroquercetin (taxifolin) based bioadditives. The results obtained were compared with the data of coulometric titration by electrogenerated bromine.

New modifiers of electrophoretic systems – cationic polyelectrolytes with micellar properties poly-11-acryloyloyloxyundecyl-N-methylpiperidinium bromide (pAUMP-Br), poly-11-acryloyloxyundecylpyridinium bromide, poly-11-acryloyloxyundecyl-1,4-diazobicyclo[2. 2.2.2.2]octan-1-ium bromide and a chiral copolymer based on acylated quinine and N-(11-acryloyloyloyloxyundecyl)-N-methylpiperidinium bromide (pAUMP-AQin). The electrophoretic capabilities of these polymers were studied in the separation of model mixtures of biologically active substances: steroid hormones, biogenic amines and amino acids in the modes of micellar electrokinetic chromatography and capillary electrochromatography. It was found that new polyelectrolytes are polyfunctional modifiers of quartz capillary walls and background electrolyte and allow to realize different modes of electrophoretic separation of biologically active substances, indirect detection in the presence of chromophoric group in the polymer composition, generate anodic electroosmotic flow, influence the efficiency and selectivity of analytes separation. Field-amplified sample stacking was performed on a quartz capillary modified with pAUMP-Br, providing a 15-fold concentration of biogenic amines and lowering the detection limits. The chiral labeled pAUMP-AQin copolymer was found to facilitate the separation of tryptophan enantiomers.