Related Experiment Video
Updated: Oct 17, 2025

Qualitative Identification of Carboxylic Acids, Boronic Acids, and Amines Using Cruciform Fluorophores
Published on: August 19, 2013
Colorimetric detection of fluoride ions in aqueous medium using thiourea derivatives: a transition metal ion assisted
Rituraj Das1, Dhrubajyoti Talukdar1, Plaban J Sarma1
1Department of Chemical Sciences, Tezpur University, Tezpur-784028, Assam, India. samahanta@gmail.com.
Abstract:
This work explores the position of the hydroxyl moiety and its participation in intramolecular H-bonding towards dictating the fluoride selective colorimetric response in functionalized thiourea derivatives. The study reveals the pivotal aspect of the hydroxyl moiety in C2 towards attaining selectivity for fluoride over acetate and dihydrogenphosphate ion. Furthermore, a methodology employing stabilization of deprotonated thiourea through metal ion (Ni2+ and Cu2+) coordination is proposed for the colorimetric sensing of fluoride in water medium. The mechanism of interaction is thoroughly studied by UV-Vis, 1H NMR, ESR spectroscopy, electrochemical techniques and further validated by DFT calculations. This study reveals the formation of an in situ Ni2+ complex that shows greater stability in aqueous medium. The methodology is applied in the detection of fluoride in groundwater samples.
Related Concept Videos
Precipitation Titration: Endpoint Detection Methods
In the Volhard method, a standard excess of AgNO3 is first added to the...
Effects of EDTA on End-Point Detection Methods
In the visual method, metal-ion indicators (metallochromic dyes), which have distinct colors in their free and complex forms, are added to the mixture to signal the titration's end point. They form stable complexes with metal ions, but these complexes are weaker than the corresponding metal–EDTA complexes. As a...
EDTA: Direct, Back-, and Displacement Titration
Direct titration involves buffering the metal ion solution to the desired pH and directly titrating with standard EDTA until the endpoint. The optimum pH ensures a large conditional formation constant of metal−EDTA and visibility of the free indicator color in the solution. In addition, auxiliary complexing reagents are used to prevent the precipitation of metal hydroxides...
Photoluminescence: Applications
Complexometric Titration: Overview
EDTA: Indirect and Alkalimetric Titration

