Abstract
This work is devoted to a detailed study of the complex formation of iron(II) and iron(III) ions with a series of alkyl- and phenyl-substituted salts of 6,7-dihydroxybenzopyrylium (R). Such complexes are of interest due to their potential application as analytical reagents for photometric determination of trace amounts of metals in aqueous systems, particularly in drinking water. The optimal conditions for the reactions in the studied chemical systems have been established: pH range of 3–7 and the analytical signal observed at λ = 550–580 nm. Under these conditions, the maximum color intensity of the complexes is achieved, which indicates their stability and reproducibility.
Using the methods of molar ratios and Bent – French analysis, it was shown that under optimal conditions the complex formation proceeds stepwise with the formation of stable compounds with a metal-to-ligand ratio of 1:3. This confirms the ability of iron cations to form polynuclear and multicoordinated structures with R. To characterize the spectrophotometric properties of the complexes, the molar absorption coefficient was determined, and the logarithm of the stability constant (lgβ) was calculated using the Komar method, which allowed a quantitative evaluation of the stability level of the obtained complexes.
Special attention was given to the study of the metrological characteristics of the proposed technique: the linearity intervals of the calibration curves, as well as the limits of detection and quantification of iron ions, were established. The practical application of the method was demonstrated on samples of tap water. The obtained results showed that the iron content complies with hygienic standards according to DSANPIN 2.2.4–171.10 and statistically agrees with the results obtained by an independent ICP-OES method, which confirms the reliability and reproducibility of the developed approach.
Thus, the conducted research not only expands the understanding of the complex formation of iron with 6,7-dihydroxybenzopyrylium derivatives but also demonstrates the practical applicability of these systems in drinking water quality control and environmental monitoring.
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