A quercetin based fluorescent chemical sensor for ultra-sensitive determination and speciation of tungsten species in water.

The current study explores the use of quercetin for developing a highly selective spectrofluorimetric methodology for trace determination, speciation and thermodynamic characterization of tungstate (WO42-) species in water. The study relies on the principle of chelate formation between WO42- and quercetin with subsequent increase in the emission intensity. The developed method could be applied successfully in a wide linear range (1.0-400.0 μg L-1) with a detection limit of 0.28 μg L-1 and quantification limit of 0.92 μg L-1 at λex/em = 400/492 nm. The developed method was successfully applied in real tap and waste water samples. The suitability of the proposed method was further validated by inductively coupled plasma-optical emission spectrometry (ICP-OES) in terms of student's t and F tests at 95% confidence. Characterization (NMR, FTIR and electronic spectra), stoichiometry, stability constant, fluorescence mechanism and thermodynamic parameters (ΔH, ΔS, and ΔG) of the produced complex species were evaluated and properly assigned. The fluorescence quenching mechanism of tungstate quercetin complex by Triton X-100 was also evaluated for computing Stern-Volmer quenching constant and approximating quenching sphere. The method showed a clear significance over most of the reported methods for tungsten in literature in terms of good accuracy, robustness, ruggedness, short analytical time and cost-effectiveness.