Detection of copper ions in arid and semi-arid lands using UV-visible and fluorescence spectrophotometry

Generally arid soils are calcareous and prone to contamination of copper due to the usage of high-intensity agriculture and copper-based pesticides which leads to toxicity of organisms present in the soil resulting in fertility loss and crop diseases. We synthesised a sensor R, having a rhodanine scaffold for sensitive and selective detection of Cu2+ ions available in the soil. The sensor exhibited characteristic UV-Visible spectral properties and fluorometric “turn-off” emission properties towards Cu2+ ions. As a practical application detection of Cu2+ ions by the Sensor R adsorbed on a test filter paper system is also reported. The UV–Vis spectrum of sensor R, exhibited an absorption band at 308 nm due to the presence of a thioamide group in the rhodanine moiety and a quantitative intensity enhancement is observed only in presence of Cu2+ ions. In the fluorescence spectra an emission band around 380 nm was observed upon the addition of copper ions and the fluorescence intensity gradually decreased with the increasing Cu2+ concentration indicating the formation of a complex. Nuclear Magnetic Resonance (1H-NMR) analysis indicated that methylene protons signal at δ 4.79 disappeared and shifted up field to appear as a broad peak at δ 3.62. Filter paper strips were dipped into the solution R and dried and subjected to FTIR analysis. On binding with Cu2+ ions the -COOH band appeared with reduced intensity whereas the carbonyl group completely disappeared. The results showed that our method would be suitable to routinely analyse the Cu2+ content in real samples.