Smartphone-based colorimetric determination of fluoride anions using polymethacrylate optode

We developed a new transparent polymer optode based on polymethacrylate with Zr(IV) and alizarin red complex immobilized into it for digital colorimetric and solid-phase spectrophotometric determination of fluoride anions. The matrix changes its colour from purple to yellow after it contacts fluoride anion. We developed a processing algorithm for coloured images which helps calculate mean value for the RGB colour-coordinate system in a selected optode image and translates it into a fluoride concentration value. The analytical signal of the suggested method has a linearity range of 0.1-30 mg⋅L^-1 with the detection limit 0.03 mg⋅L^-1. Compared to other methods, the modified polymethacrylate matrix is actually a ready-to-use colorimetric system offering rapid results for drinking water quality control.