Synthesis of 2-(2-Hydroxy-4-Methoxybenzylideneamino)-4, 5, 6, 7-Tetrahydrobenzo[b] Thiophene-3-Carboxamide and Application of This New Sensor for Determination of Fluoride in Toothpaste by Spectrofluorometric Methods

In this work, we synthesized a new thiophene derivative Schiff base as new luminophore. The aim of this study was determination of fluoride using 2-[(E)-(2-Hydroxy-4-methoxybenzylidene) amino] -4, 5, 6, 7- tetrahydro-1-benzothiophene-3-carboxamide [Ligand L] as new and intense fluorescence sensor by spectrofluorometric method. In this method, we optimized all reagents concentrations such as ionic, pH, luminophore concentration. Afterwards, we used a new fluorimetric method for determination of fluoride ion based on quenching effect of fluoride ion on fluorescence of thiophene derivative schiff base, as new luminophore. Despite previous methods, that had less selectivity and sensitivity, in this work we presented a new sensitive fluorimetric sensor for determination of fluoride with good selectivity, sensitivity and reproducibility. A linear calibration range was obtained from 4.31×10-6 – 4.70×10-4. The relative standard deviation was very good (1.098% for 10-4 M of F- and n=5) and the detection limit was acquired 2.1×10-6 M. In addition, interference of some anions and cations were investigated. The proposed method was successfully applied for the determination of fluoride in toothpaste samples.