New simple and sensitive spectrophotometric determination of fluoride in drinking groundwater has been developed using aluminium-resorcin blue complex. The method is based on the reaction of fluoride with the coloured complex to produce colourless aluminium fluoride complex and releasing of the free ligand. The relationship of the reaction of flu-oride with the complex is sixth-order polynomial function. The reaction reaches equilibrium at fluoride concentration of 0.054 mM. The equilibrium constant (Keq) was calculated as 1.12 × 1014. Beer-Lambert law is obeyed in the range 0.0 - 0.024 mM of fluoride (0.0 - 1.0 mg·L-1). The molar absorptivity at 502 nm is 6.45 × 103 L·mol-1·cm-1. Fluoride concentration higher than 1.0 mg·L-1 can be measured after proper dilution. The sensitivity, detection limit, quantitation limit, and the percentage recovery of 0.75 mg·L-1 fluoride for the method were found to be 0.357 μg·ml-1., 0.07 mg·L-1, 0.2 mg·L-1, and 101.1 respectively.
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