Archive / Volume LXXVIII 2025

Yustyna REDKEVYCH, Petro RYDCHUK, Roman LYTVYN, Oleksandr TYMOSHUK

Ivan Franko Lviv National University, Kyryla and Mefodiya Str., 6, 79005 Lviv, Ukraine
e-mail: oleksandr.tymoshuk@lnu.edu.ua

N-[PHENYL(PYRIDIN-2-YL)METHYLIDENE]HYDROXYLAMINE – A REAGENT FOR SPECTROPHOTOMETRIC DETERMINATION OF IRON

This study investigates the spectrophotometric properties of N-[phenyl(pyridin-2-yl)methylene]hydroxyl¬amine as a novel analytical reagent for the quantitative determination of iron ions in aqueous solutions. In its solid state, the compound is a white crystalline substance, readily soluble in both aqueous and alcoholic media, and does not exhibit absorption in the visible region of the electromagnetic spectrum. Upon interaction with Fe2+ ions, the reagent forms a red-colored complex, which displays a distinct absorption maximum at 528 nm. In contrast, Fe3+ ions form a yellow complex with a maximum at 430 nm. The addition of ascorbic acid as a reducing agent to Fe(III) solutions containing the reagent, or to Fe(III) solutions followed by reagent addition, results in the formation of red-colored complexes identical in both spectral and quantitative characteristics to those of the Fe(II) complex.
Given the reagent’s ability to selectively interact with Fe(II), the study explores its use for determining both Fe(II) directly and total iron after reduction. Among various tested reductants (ascorbic acid, hydroxylamine, zinc powder, and stannous chloride), ascorbic acid demonstrated the highest effectiveness and stability over time, making it the optimal choice. Hydroxylamine and zinc required prolonged interaction times, and the use of stannous chloride was hindered by hydrolysis under experimental conditions. The complex exhibits stability over a wide pH range. Maximum absorbance is achieved in the pH range 5.5–7.0, with pH 6.5 chosen as optimal for further studies. The absorption maximum at 528 nm remains constant regardless of pH. The effect of ionic strength was assessed using NaCl, NaNO3, and Na2SO4 at concentrations from 0.005 to 2.0 mol/L. Absorbance fluctuations within this range were below 2%, indicating negligible impact of ionic strength on complex formation.
The stoichiometry of the Fe(II)–reagent complex was established using the methods of continuous variations and mole-ratio, showing a 1:2 (metal:ligand) ratio. Based on this, a tentative structure of the complex is proposed. The conditional stability constant of the complex was calculated.
Studies revealed that Cu(I), Co(II), Pd(II), Ag(I), Ru(IV), Ir(IV), and Rh(III) form yellow complexes with absorption maxima in the range of 385–425 nm, while Ni(II) and Mn(II) form poorly soluble precipitates. Some lower oxidation states of platinum-group metals such as Ru(II), Ir(II), and Rh(I) form pink to red complexes absorbing at 480–500 nm. However, Cu(II), Zn(II), Cd(II), Pb(II), Al(III), and alkaline/alkaline-earth metals do not react with the reagent and their solutions remain colorless. Given the strong spectral contrast (Δλ > 100 nm) between the Fe(II) complex and potential interferences, the method allows for selective iron determination in complex matrices without separation or masking.
The complex obeys Beer’s law in the concentration range of 2.0–30.0 μmol/L, with a molar absorptivity (ε) of 1.80 × 10⁴ L mol⁻¹ cm⁻¹, detection limit of 0.80 μmol/L, and correlation coefficient of 0.9994. The linear regression equation was A = 0.014 + 0.18·C×10⁵.
The developed method was successfully applied to the determination of iron in real soil samples collected from different environments in Volyn region, Ukraine. After appropriate sample preparation including acid digestion and organic matter decomposition, the iron content was measured using the described spectrophotometric procedure. The results confirmed the method’s accuracy, sensitivity, and applicability for real sample analysis. Thus, N-[phenyl(pyridin-2-yl)methylene]hydroxylamine presents a highly selective and effective reagent for the spectrophotometric determination of iron in environmental and complex matrices, offering advantages of simplicity, reliability, and low detection limits.

Keywords: spectrophotometric determination, complex formation, iron, analytical reagent.

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How to Cite

REDKEVYCH Yu., RYDCHUK P., LYTVYN R., TYMOSHUK O. N-[PHENYL(PYRIDIN-2-YL)METHYLIDENE]HYDROXYLAMINE – A REAGENT FOR SPECTROPHOTOMETRIC DETERMINATION OF IRON. Proc. Shevchenko Sci. Soc. Chem. Sci. 2025. Vol. 78. P. 33-43.