Comparison of two indigo dye derivatives in the spectrophotometric detection of copper in aqueous media.
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Copper is an essential element in the human body, playing a role in redox reactions and substrate activation reactions. Several diseases, including Menkes disease and Wilson’s disease, are associated with copper metabolism in the body. Copper primarily enters the body through our diet (by consuming foods like meat, bread, and beans) and through drinking water. Copper compounds can enter drinking water sources through copper pipes in plumbing infrastructure and through runoff from insecticides and fertilizers. The World Health Organization recommends that the amount of copper in drinking water does not exceed 2 ppm; for this reason the accurate detection of copper in aqueous media is needed. The objective of this investigation is to investigate the binding constants and thermodynamic parameters for two detection methods using indigo dye derivatives and spectrophotometric analysis. Copper cations (Cu2+(aq)) form a 1:1 complex with both indigo carmine (IC) and potassium indigotrisulfonate (KItS) in aqueous solutions. Both dyes selectively form a complex with copper and do not form a complex with other metal (II) cations like cadmium, magnesium, lead, or calcium. The Cu-KItS system in water was found to be the most favorable reaction because it had the highest binding constants and highest magnitude negative Gibb’s free energy. The detection limit of copper cations in water was found to be 0.031 ppm using the Cu-KItS system in water compared to 0.076 ppm using the Cu-IC system in water.
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