Sensitive Optical Detection of Cyanide and Al(III) Ions and Development of a Simple Colourimetric Method for Estimation of Cyanide in Cassava Flour.

Abstract

This endeavour's novel Schiff base VDP3 is a fruitful candidate for colourimetric/fluorometric detection of cyanide and fluorometric detection of Al(III) ions in a 50% aqua-organic medium. The prompt naked eye colour change (yellow to orange) and noteworthy fluorescence enhancement of VDP3 in the presence of CN^- avowed that VDP3 was an exemplary probe for detecting CN^- with a low detection limit of 0.4 µM. The NMR studies infer that deprotonation followed by nucleophilic addition is the probable sensing mechanism for detecting CN^- by VDP3. The faint fluorescence of VDP3 was owing to the photoinduced electron transfer (PET), and the nucleophilic addition of CN^- intervenes with the PET and consequently enhances the fluorescence significantly. The VDP3 selectively detects Al(III) by forming the chelate octahedral complex [Al(VDP3)(H₂O)₃] as witnessed by the ²⁷Al-NMR, ¹H-NMR, and mass spectral studies with a LOD of 0.14 µM. The striking fluorescent enhancement for VDP3 + Al(III) was ascribed to the collective impacts of PET-CHEF mechanisms (PET-OFF/CHEF-ON). The experimental findings and expected sensing mechanism for detecting CN^- and Al(III) were upheld by the computational studies, and they provide robust evidence for the PET ON and PET OFF mechanisms to explain the fluorescence enhancement behaviour further. The VDP3 was proficiently applied for quantitatively estimating CN^- and Al(III) in real-world samples. Additionally, VDP3 was effectively utilised for the qualitative and quantitative assessment of cyanide in cassava flour through a simple and convenient colourimetric method without any complex instruments.