SORPTION-LUMINESCENT DETERMINATION OF MARKS OF TEA PRODUCTS QUALITY

Natural organic polyphenolic compounds are essential components of the diet. Determination of the presence and amount of dominant phenolic and polyphenolic components in food objects allows to assess the quality of products, which is important in food expertise. Luminescent sensors based on Ln(III) ion complexes are widely used for the highly sensitive determination of biologically active substances. The spectral and luminescent properties of polyphenolic substances – catechols, which are quality markers of tea products, have been studied. The diversity of isomers and the similarity of the structure of all catechols due to the presence of a chromium nucleus make it impossible to use the absorption spectra of individual isomers as a characteristic feature. The intrinsic luminescence of catechols is insignificant. When excited by UV light (λexcitation=365 nm) in the presence of catechols, a sensitized luminescence of Tb(III) ions is observed. In a thin layer of sorbent on TLC Aluminium oxide 60 plates and on the surface of Sephadex G-75, Tb(III) ion forms a complex with catechols that exhibits intense luminescence. The effect of Tb (III) ion concentration, acidity of the medium, surface-active and donor-active substances on the luminescent signal was studied. The optimal conditions for complexation were found. Polytopic coordination ligands cause an increase in the luminescent signal of the complex sorbate. The greatest influence on the luminescent properties of sorbates is exerted by 1,10-phenanthroline. The luminescence intensity increases 30-fold. In the presence of Phen, a change in the nature of the luminescence spectrum of the sorbate of the Tb(III) complex with Catechol is observed, which confirms the change in the symmetry of the complex, which occurs due to the entry of the Phen molecule into the internal coordination sphere with the formation of a multiligand complex. 1,10-Phenanthroline, due to the presence of chromophore groups, acts as a “photoantenna” and can participate in the transfer of excitation energy from triplet levels of ligands to the resonant level of the terbium ion. In the medium of nonionic surfactant Twin-80, an increase in the illumination of the sorbate complex is observed. In the micellar medium, the degree of radiation-free decontamination in the complex decreases due to an increase in the rigidity of its structure. On the basis of the conducted studies, new analytical forms in the form of multiligand complexes of Tb (III) ion with catechol and 1,10-Phen in the Twin-80 medium were obtained and a method for solid-phase luminescent determination of the amount of catechols in tea products was developed.