Turmeric, naturally available colorimetric receptor for quantitative detection of fluoride and iron

• Turmeric, a natural material is used for the first time for the F− and iron ions detection.
• Simple, reusable, cheap device is developed for the colorimetric detection of F−.
• The detection is based on the intramolecular charge transfer mechanism.

Turmeric (Curcuma longa) an important food ingredient has been used from ancient times for various biological applications, but to date it has not been considered for the colorimetric detection of anions and cations. In this work, the application of turmeric solution for the colorimetric detection of F− and iron ions was demonstrated. Results showed a significant colour change from yellow to blue and yellow to orange upon addition of F− and iron ions respectively. The detection mechanism was investigated using curcumin, a major component of turmeric powder. The change in colour and fluorescence quenching was attributed to the formation of receptor complex with F− and iron ions which resulted in intramolecular charge transfer transition. The mechanism of binding has been confirmed by UV–vis, 1H NMR and fluorescence titrations. The present detection concept was further explored to develop a low cost, reusable F− detection kit, which showed its ability to detect F− ions in both aqueous and organic medium at a very low concentration such as 1 ppm.