Spectrophotometric Determination of Microconcentrations of Zinc(II) and Copper(II) in Water and Industrial Alloys Using a New Chromogenic Reagent [۴-Amino-۵-hydroxy-۶-[(۵-methyl-۲-pyridyl)azo]-۳-sulfo-۱-naphthyl]sulfonyloxysodium

The present study aimed to develop a new spectrophotometric method for the determination of zinc(II) and copper(II) using a new chromogenic reagent, [۴-amino-۵-hydroxy-۶-[(۵-methyl-۲-pyridyl)azo]-۳-sulfo-۱-naphthyl]sulfonyloxysodium (HR). The complexation of Zn(II) and Cu(II) with HR was studied spectrophotometrically at absorption maxima of ۵۶۵ nm (Δλ=۵۵ nm) and ۵۹۵ nm (Δλ=۹۰ nm) for Zn-HR and Cu-HR, respectively. The HR reagent interacts with Zn(II) and Cu(II) instantaneously at pH ۶.۵ and pH ۴.۰, respectively, and the absorbance of the solution is stable for ۷۰ and ۱۴۴۰ minutes, respectively. Using isomolar series, Asmus straight line, equilibrium shift and spectrophotometric titration methods, the stoichiometries of the complexes were found to be ۱:۲ metal-to-ligand ratios for Zn and Cu. To determine the charge of the complex, the solution was passed through columns containing the cations KU-۲ and KRS-۱۰ and the anions AB-۱۶-GS and AN-۲FN. In this case, one proton is released from the reagent molecule, and a chelate cycle is formed mainly through the atoms of the oxygen-OH group, the nitrogen of the pyridine ring and the N=N group. The dilute Babko method was used to estimate the stability constant (Kstab) values, which were found to be on the order of ۱.۴۴∙۱۰۲۱ (lgβ=۲۱.۱۶) and ۲.۹۷∙۱۰۱۷ (lgβ=۱۷.۴۷) for the Zn and Cu complexes, respectively. The proposed spectrophotometric methodology established that the concentrations of zinc(II) and copper(II) could be estimated to be ۱.۰-۱۸.۰ and ۰.۵۰-۶.۵۰ ppm, respectively, corresponding to molar absorptivities of ۴.۲∙۱۰۴ and ۲.۰∙۱۰۴ l/mol∙cm, respectively (εHR=۳.۳∙۱۰۲, Kdis., HR=۲.۹۵∙۱۰-۸, pK=۷.۵۳). Likewise, the formed complexes were stable at different pH values, allowing the simultaneous estimation of the two metals. The suggested spectrophotometric method of definition was applied in the analysis of model mixtures, industrial alloys based on aluminum and natural water, and the obtained results were metrologically evaluated (Sr=۰.۰۴۳)

Keywords:

[۴-Amino-۵-hydroxy-۶-[(۵-methyl-۲-pyridyl)azo]-۳-sulfo-۱-naphthyl]-sulfonyloxysodium , zinc(II) ions , Copper ions , Spectrophotometry , Water samples , Alloys