Vol 78, No 6 (2023)

Among many versions of methods for the chromatographic separation of substances, to date, insufficient attention has been paid to their continuous separation. Among a few exceptions is a review by Maryutina and Spivakov published in 2001 [4]. Our paper deals with a more detailed consideration of the attempts made for the continuous chromatographic separation of substances and the assessment of the efficiency of the solutions found. The aim of this review was to draw more attention to this promising direction for solving two interrelated problems. First, to creating systems for the continuous analytical control of complex multicomponent samples of the composition changing with time, and, second, to solving preparative and technological problems of the separation of substances with similar chemical properties. In the first case, the method ensures studies of the dynamics of changes in the composition of complex multicomponent mixtures in studying fast chemical processes, and, when used for technological purposes, it opens up a possibility of the continuous chemical-analytical monitoring of their course from the standpoint of economic efficiency and safety. In the second case, methods of continuous chromatographic separation ensure an increase in the efficiency and productivity of obtaining valuable high-purity substances.

A procedure for determining concentrations of lignin, cellulose, and hemicellulose in plant materials using Fourier-transform IR spectroscopy in the middle spectral region was developed and tested. The procedure is based on the use of calibration functions reflecting the dependence of the intensity of analytical absorption bands on the concentration of lignin (1512 cm–1) and cellulose (1450 cm–1) in model samples; for hemicellulose, indirect correlations were used. The model samples were ternary mixtures consisting of lignin, bacterial cellulose, and hemicellulose in various proportions. The proposed method was tested on a wide range of plant biomass samples; it demonstrated adequate precision (RSD no more than 4%). The accuracy of the procedure for determining the main components of plant biomass (lignin, cellulose, and hemicellulose) was demonstrated using the standard addition method.

Specific features of chromatographic determination of xanthophyll esters are studied using an example of marigold flower lutein diesters under reversed-phase HPLC conditions. The developed two-column method made it possible to establish that, in samples with a low solubility of carotenoids in the used solvent and on a chromatography column in using a mobile phase with a low solubility of carotenoids, the precipitation of diesters is possible, which detrimentally affects the accuracy of the chromatographic determination. A critical factor in this case isì temperature: the storage of samples (solutions) in a refrigerator is not always advisable, because freezing of the main components is possible. It was shown that the use of a mobile phase containing from 0 to 10 vol % acetonitrile in acetone at a temperature not lower than 20°C is acceptable for the separation of all-trans-lutein diesters from cis-derivatives of lutein and zeaxanthin derivatives on “monomeric” C18-phases.

A rapid procedure for the determination of phenol and cresol isomers in drinking, sea, and polluted domestic wastewater is developed based on a single-stage extraction of analytes by extractive freezing-out under sample centrifugation conditions. In combination with gas chromatography, the procedure provides the minimum detection limits for each of phenols in 10 mL of water at a level of 0.0005 µg/mL. The duration of sample preparation does not exceed 30 min; the consumption of the ethoxyethane extractant is 1.4 mL. In comparison with liquid–liquid and solid-phase extraction traditionally used at the stage of sample preparation, the proposed procedure is simpler and more environmentally friendly. The stages of filtering samples and dehydrating extracts are excluded; the amount of chemical glassware is minimized.

The reactivity of coulometric titrants (bromine, iodine, and hexacyanoferrate(III) ions) with respect to the antioxidants (AOs) of beer is evaluated. It is shown that electrogenerated iodine interacts with ascorbic acid and sulfur-containing compounds, but does not oxidize phenolic AOs. The stoichiometric coefficients of reactions of phenolic AOs with electrogenerated bromine and hexacyanoferrate(III) ions are found. A comprehensive assessment of the antioxidant properties of beer is carried out through overall antioxidant parameters (total antioxidant capacity (TAC) according to the reaction with electrogenerated bromine, ferric reducing power (FRP) according to the reaction with electrogenerated hexacyanoferrate(III) ions, and oxidation by). Sixteen samples, differing in the type of fermentation, variety, and style, are considered. A statistically significant difference between the parameters for individual samples is shown. The TAC and FRP of beer correlate with the total concentration of phenolic compounds and antioxidant activity (r = 0.7175–0.8703 at rcrit = 0.4973), which confirms the correctness of the results obtained using coulometric titration. Differences in the overall antioxidant parameters of the top-fermented and bottom-fermented beers, as well as filtered and unfiltered light and dark beers, are statistically insignificant (p = 0.10–0.82). The change in the overall antioxidant parameters of beer during storage in air is evaluated.