Vol 80, No 11 (2025)

Miniaturized methods for sorptive isolation and preconcentration of organic compounds include micro-solid-phase extraction (μ-SPE) and solid-phase microextraction (SPME). These methods are characterized by reduced amounts of sorbents, analyzed samples, and organic solvents, high preconcentration factors, and the integration of preconcentration and sample introduction into a single device. Since the emergence of μ-SPE (1989) and SPME (1990), numerous variants of these methods have been developed, differing in sample preparation techniques, the nature of the sorbents used, and their integration with subsequent determination methods. The popularity of these methods is evidenced by the large number of reviews summarized in this publication.

Medicinal plants are an important source of biologically active compounds used in medicine for the prevention and treatment of various diseases. The main classes of such compounds—alkaloids, glycosides, flavonoids, essential oils, tannins, polyphenols, and polysaccharides—exhibit a wide range of pharmacological activities (antimicrobial, anti-inflammatory, antiseptic, antioxidant, etc.). Phytochemical screening of plant extracts is essential for identifying these compounds and developing new highly active therapeutic agents. Spectrophotometric phytochemical screening was conducted for alkaloids, tannins, flavonoids, phenolic compounds, steroidal cardiac glycosides, and polysaccharides, along with the determination of antioxidant activity in extracts of three medicinal plants from different families: milky ripe oats (Avena sativa L.), madder root (Rubia tinctorum L.), and common heather (Calluna vulgaris L.). High-performance liquid chromatography was employed for a more detailed analysis of the extracts. Both traditional solvents (methanol, ethanol, water-ethanol mixture, water, acetonitrile) and a new class of solvents—deep eutectic solvents—were used as extractants. Extraction of biologically active compounds was performed using ultrasound at 40–80 °C for 10–60 minutes. Optimal extraction conditions for the main compound groups were established: 80 °C and 60 minutes for traditional solvents; 50°C for 30 minutes (heather) and 60°C for 30 minutes (madder root and oats) when using deep eutectic solvents. Deep eutectic solvents enable the extraction of target bioactive compounds under milder conditions, demonstrating their potential as environmentally friendly extractants in phytochemical studies.

The features of planar (thin-layer) chromatography of several linear non-ionic polysaccharides (amylose, pullulan), their visualization by post-chromatographic derivatization with iodine, and the factors influencing this process are described. It is shown that the coloration of pullulan results from the formation of pseudoclathrate complexes of molecular iodine–iodide–pullulan in short helical segments of the polysaccharide, as well as iodine absorption in the bends of the polymer chain. It was established that the shift of the spectral absorption maximum of amylose (λ_max ~ 600 nm, blue coloration) to the shorter wavelength region (λ_max = 560 nm, red-brown coloration) is associated with specific interactions of starch with silica and the formation of a molecular iodine–iodide-anion–amylose–silica gel complex. It was demonstrated that the intensity of iodine staining of high-molecular-weight polysaccharides does not depend on their degree of polymerization, and polysaccharide visualization by the iodine reaction in thin-layer chromatography is possible only on neutral forms of silica sorbents.

The chromatographic retention features of alkali and alkaline earth metal cations on poly(styrene-divinylbenzene) cation exchangers with grafted carboxylic groups were investigated. It was found that the retention of metal cations with the same charge is directly proportional to their polarizability. The retention patterns of metal and ammonium cations were studied in relation to the nature and concentration of the eluent, and the contribution of secondary processes to retention and peak shape was determined. It was shown that increasing eluent concentration improves the symmetry of chromatographic peaks. Van’t Hoff dependencies were constructed, and the enthalpy values (ΔH°) of adsorption were calculated. It was noted that column efficiency increases with temperature. The possibility of simultaneous determination of alkali, alkaline earth metal, and ammonium cations by ion chromatography using carboxylic cation exchangers and two variants of conductometric detection was demonstrated. Practical applications of the sorbents are discussed.

The features of gas chromatographic identification of 80 common low-boiling organic solvents based on retention indices on standard non-polar polydimethylsiloxane stationary phases were examined. It was shown that one-dimensional analytical parameters, such as retention indices, cannot provide unambiguous identification of all compounds in this group, as the informativeness criterion R(RI) for this group is only about 29, which is less than the number of compounds. To address this issue, supplementing chromatographic data with independent characteristics, such as refractive indices (n_D²⁰), is recommended, as their determination requires minimal time and sample amounts. However, about 10% of the solvents cannot be distinguished even by combining RI and n_D²⁰. For comparison, the potential use of dynamic viscosity values as an additional analytical parameter was considered. The provided table of retention indices for the most common organic solvents is of independent value for analytical practice.

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