Water-Based Microwave-Assisted Digestion Method for Electrochemical and Chromatographic Determination of Total Fluoride Ions in Toothpaste Samples

Fluoride ions are the major constituents of dental products because they prevent cavities through bacterial growth inhibition. However, excessive consumption of fluoride ions results in fluorosis, thereby causing tooth staining and roughness. Therefore, there is a crucial need to develop rapid and effective methods for monitoring fluoride levels in dental products. The current study describes a greener water-based microwave-assisted digestion (WB-MAD) prior to fluoride-ion-selective electrode (F-ISE) measurement for the determination of fluoride ions in various toothpaste products. The optimum conditions of the developed WB-MAD method were 180 °C digestion temperature, 60 min digestion time, 0.05 g toothpaste amount and 10 mL distilled water. Under the optimum conditions, the method detection limit (MDL) of 0.00302 µg/kg and the method quantification limit (MQL) of 0.01007 µg/kg obtained were favorably comparable with the literature reports. The proposed WB-MAD method was both accurate (99.2 to 101%) and precise (≤0.75%) for the quantitative determination of F⁻ in toothpaste samples using F-ISE. Furthermore, the newly developed WB-MAD method showed better accuracy (97–100%) than the traditional microwave-assisted acid digestion methods (71–92%). It is worth indicating that since water was used as the only digestion reagent, it was possible to validate the F-ISE results with ion chromatography (IC). The percentage recoveries obtained from IC (91–104%) and F-ISE (93–100%) were statistically insignificant. In view of the validation data, the proposed WB-MAD method can be considered as an alternative to the conventional microwave-assisted acid digestion (MAAD) methods for the determination of F⁻ in toothpaste samples containing sodium monofluorophosphate.