Keywords
Chemical analysis
Cobalt
Spectrophotometry
Method validation
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Abstract
Objective: To develop, optimize, and validate a spectrophotometric method for the determination of Co2+ in aqueous matrices using 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) as a chromogenic reagent. Methods: Experimental conditions were optimized using a 22 central composite design to evaluate the effects of pH and the metal-to-ligand molar ratio on complex formation. Analytical validation was performed according to the Eurachem and Inmetro guidelines, including the evaluation of linearity, precision, accuracy, and limits of detection and quantification. Results: The experimental design established the optimum conditions as pH 5.36 and a Co2+:5-Br-PADAP molar ratio of 1:3.4, with maximum absorbance at 590 nm. The method showed linearity over the concentration range of 0.005–0.500 µg mL–1 (R2 = 0.9996), coefficients of variation below 13%, recoveries ranging from 88.8% to 115.1%, and limits of detection and quantification of 0.004 and 0.005 µg mL–1, respectively. Application to surface water samples demonstrated satisfactory analytical performance for the determination of trace levels of Co2+. Conclusion: The proposed method exhibited sensitivity, precision, and accuracy consistent with analytical validation requirements, representing a simple and low-cost alternative for the spectrophotometric determination of cobalt(II) in aqueous matrices, under the evaluated conditions. However, additional selectivity studies involving other metal ions are required to further validate the methodology for more complex environmental matrices.
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