Spectrophotometric determination of copper (II) ions in samples of modeled waters

ISSN: 2582-4686 SJIF 2021-3.261, 2022-2.889, 20235.384, 2024-6.875 ResearchBib IF: 9.948 / 2024 VOLUME-5, ISSUE-12 292 Spectrophotometric determination of copper (II) ions in samples of modeled waters Jumayeva E. Sh., Makhamatova S.B., Ruziqulova M.F., Soliboyeva S.V. Navoi State University Annotation: The work examines the features of photometric determination of copper (II) ions in wastewater from several industrial facilities in the Navoi region. Xylene orange, which forms a stable colored complex compound with Cu (II), was used as an analytical reagent. Complex formation conditions, including pH of the medium and reagent concentration, have been optimized. The obtained results allowed for the development of a methodology for the quantitative determination of copper in the concentration range characteristic of real industrial wastewater. Wastewater samples were analyzed and the contamination level based on copper content was assessed. Keywords: Miss (II); wastewater; spectrophotometry; complex formation; reagent. Introduction. The intensive development of industrial complexes in the Navoi region is accompanied by an increase in the volume of wastewater containing elevated concentrations of heavy metals. Among them, copper (II) ions stand out for their high toxicity, bioaccumulativity, and ability to disrupt the hydrochemical balance of aquatic ecosystems. According to environmental observations, copper is among the priority pollutants requiring regular monitoring in industrial wastewater [1]. Controlling the Cu (II) content is particularly relevant for regions with developed metallurgical, chemical, and electrochemical industries, as exceeding permissible concentrations reflects not only the state of natural waters but also the effectiveness of local treatment plants [2]. Among the instrumental methods for analyzing copper compounds, spectrophotometric approaches attract attention due to their ease of implementation, affordability of equipment, and the ability to determine low concentrations of metals, including trace levels [3-4]. The use of organic chromogenic reagents allows for increased selectivity and sensitivity of analysis due to the formation of stable colored complexes with Cu (II). Such reagents include xylene orange, which forms intensely colored complexes with a number of transition metals, making it a promising analytical reagent in wastewater research [5-6]. Considering the environmental significance of heavy metal monitoring and the need of regional enterprises for operational analytical methods, the development and optimization of a spectrophotometric method for determining copper (II) ions in wastewater is a pressing task. Materials and methods. Objects of research. Simulated solutions with wastewater simulations were used for the study. Reagents and Equipment. As a device base in the work, a dual-beam spectrophotometer UVVis 755 was used, which ensures the registration of optical density in a wide range of wavelengths and allows for measurements with high reproducibility. To construct the graduation dependence and verify the accuracy of the methodology, a standard solution of copper (II) ions prepared from a certified state standard sample was used. xylene orange, capable of forming a colored complex compound with Cu (II) under strictly defined acid-base conditions, was chosen as the organic reagent. To maintain a stable pH value during the complexation process, buffer solutions of the corresponding composition were used, which ensured the consistency of the analytical signal and minimized matrix influences. Determination method. Quantitative determination of copper (II) ions was carried out using a spectrophotometric approach based on the formation of a colored complex compound of Cu (II) with ISSN: 2582-4686 SJIF 2021-3.261, 2022-2.889, 20235.384, 2024-6.875 ResearchBib IF: 9.948 / 2024 VOLUME-5, ISSUE-12 293 xylene orange in a controlled acid-base environment with a pH value of 3.8. To prepare the analytical series, standard copper solutions were pre-prepared from the initial certified solution, after which their concentrations were brought to working values by sequential dilution. A certain volume of dissolved xylenic orange was added to each measuring flask, after which a universal buffer solution was added, ensuring a stable pH value of 3.8. Maintaining optimal acidity was a key condition for the reproducible formation of the complex, as the intensity of the reagentmetal coloration significantly depends on the protonation of the indicator's functional groups and the degree of coordination of the copper ion. After introducing the reagent and buffer solution, a specified volume of standard or analytical Cu (II) solutions was added to the test samples, and the volume was brought to the mark with distilled water. It has been established that the complex acquires a stable optical characteristic immediately after mixing the components, and the subsequent change in signal intensity remains insignificant throughout the measurement time. The optical density of the analyzed solutions was recorded on a UV-Vis 755 spectrophotometer at a wavelength corresponding to the maximum light absorption of the copper-xylene orange complex (Figure 1). Based on the absorption values of standard solutions, a graduation dependence was constructed, characterizing the linear relationship between the analytical signal and the metal concentration. The Cu (II) concentration in wastewater samples was determined by the regression line equation, taking into account dilution factors. To eliminate matrix influences, the studied samples were pre-filtered and, if necessary, mineralized. Comparison of the analysis results of model and real samples confirmed the correctness of the methodology and its suitability for use in the monitoring of industrial and domestic wastewater. Fig.1. Absorption spectra of the xylene orange solution (1) and the xylene orange-ion copper (II) complex (2). Figure 1 shows the absorption spectra of a solution of xylene orange (1) and its complex compound with copper (II) ions (2). The spectral curves demonstrate a fundamental change in the nature of the reagent's absorption after the formation of a coordination compound, which confirms the participation of the functional groups of xylene orange in the complex formation. ISSN: 2582-4686 SJIF 2021-3.261, 2022-2.889, 20235.384, 2024-6.875 ResearchBib IF: 9.948 / 2024 VOLUME-5, ISSUE-12 294 For the xylene orange solution spectrum, an intense light absorption maximum in the region of about 395 nm is typical, which is due to π→π* transitions in the aromatic system of the reagent. Spectral band 2 characterizes the Cu (II) -xylene orange complex spectrum. In the spectrum, a shift of the absorption maximum to the long-wavelength region is observed - approximately 490 nm, which is related to the redistribution of electron density in the reagent molecule after the coordination of the copper ion. Such a bathochromic shift is a characteristic feature of the formation of chelate or ionic metal associates with organic indicators. The increase in optical density at the absorption maximum also indicates an increase in transition intensity due to a change in the energy state of the chromophore groups. The difference in spectral bands confirms that the interaction of Cu (II) with xylene orange is accompanied by a deep restructuring of the electron spectrum, making the system convenient for spectrophotometric determination. The clearly expressed peak of the complex in the visible region provides the possibility of analytical measurement at a wavelength corresponding to the maximum absorption of the complex, where the contribution of the free reagent is minimal. Results and discussion. Investigation of the spectral characteristics of free xylene orange and its complex compound with copper (II) ions allowed us to establish optical parameters that determine the analytical capabilities of the method. The obtained data allow us to conclude that the formation of the Cu (II) -xylene orange complex is accompanied not only by a change in the spectral pattern, but also by a pronounced change in the color of the solution, which facilitates the identification of the analytical signal. The maximum absorption of the complex in the region of about 490 nm provides high sensitivity during spectrophotometric measurements, since in this zone the contribution of free reagent absorption is minimal. Thus, the chosen wavelength is optimal for the quantitative determination of copper (II) ions. Comparison of the spectra also confirms that the formation of the complex occurs completely and quantitatively under given pH conditions and the concentration ratio of the reagent. The absence of additional peaks or blurred bands indicates the absence of side reactions or competing forms of complex compounds. The use of a buffer solution ensures the stability of the optical characteristics throughout the entire measurement time, which positively affects the reproducibility of the results. Overall, the analysis of spectral data demonstrates the prospects of using xylene orange as a chromogenic reagent for the determination of copper (II) ions in wastewater. The significant shift of the absorption maximum and the high intensity of the complex's coloring create conditions for sensitive and selective photometric determination of the metal even in the presence of accompanying organic and inorganic components. References 1. Babel, S., Kurniawan, T. A. "Low-cost adsorbents for heavy metals uptake from contaminated water: A review." Journal of Hazardous Materials, 97 (1-3), 2003. 2. Nriagu, J. O. Copper in the Environment. Wiley, 1980.</2] 3. Skoog, D. A., Holler, F. J., Crouch, S. R. Principles of Instrumental Analysis. Cengage Learning, 2014. 4. Marczenko, Z., Balcerzak, M. Separation, Preconcentration and Spectrophotometry in Inorganic Analysis. Elsevier, 2000. 5. Fu, F., Wang, Q. "Removal of Heavy Metal Ions from Wastewater: A Review." Journal of Environmental Management, 92 (3), 2011. 6. Alloway, B. J. Heavy Metals in Soils. Springer, 2013.