This article describes an optical reagent-mediated sensor for copper, where the ligand 1-(2-pyridylazo)-2-naphthol (PAN) is immobilized in a sensor cation-selective Nafion film. Cu2+ is detected optically by partitioning into the film and complexing with the film-immobilized PAN to form the intensely colored complex ion CuPAN+. While most optical sensors rely on a conventional transmittance configuration to measure absorbance, we employ attenuated total reflectance (ATR) at 550 nm to detect CuPAN+ formed in situ in the Nafion film. This experiment offers students exposure to the cutting edge analytical technique of optical ATR sensing, as well as to classical topics such as generation of a standard curve, UV–vis spectroscopy, volumetric characterization of inorganic complex ion stoichiometry via microtitration, determination of isosbestic point, and manipulation of thin films.
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