Colorimetric sensing of fluoride ion by a Chlorophosphonazo III-based Al3+ complex in aqueous media via indicator displacement approach

Abstract

We have developed a colorimetric chemosensor for fluoride ion in pure aqueous solution using an Al3+ complex of Chlorophosphonazo III (CPA) via indicator displacement approach. CPA can form a complex with Al3+ in a 1:1 M ratio (CPA-Al3+), resulting in the change of the solution color from red to purple. The CPA-Al3+ complex showed a selective response to fluoride ion with a hypsochromic shift in absorption spectra with the clear color change from purple to red through the regeneration of CPA by the binding of fluoride ion to Al3+ in a 3:1 M ratio. Moreover, the recognition of fluoride ion was not hampered by the presence of other anions. Hence, CPA-Al3+ is efficient in the highly selective and sensitive colorimetric detection of fluoride ion in 100 % aqueous media.