Thermometric Sensing of Fluoride by Adsorption on Ceramic Hydroxyapatite Using Flow Injection Analysis

Abstract

A thermometric method for detection of fluoride has been developed that relies on the specific interaction of fluoride with hydroxyapatite. The detection principle is the measurement of the enthalpy change upon adsorption of fluoride onto the ceramic hydroxyapatite by temperature monitoring using a thermistor-based flow injection calorimeter. The detection limit for fluoride was 5 µM (0.1 ppm) which is in the same range as that of a commercial ion-selective electrode. The method could be applied to fluoride in aqueous solution as well as in cosmetic preparations. The system yielded highly reproducible results over at least 6 months without the need for replacing or regenerating the ceramic hydroxyapatite column. The ease of operation of thermal sensing and the ability to couple the system to flow injection analysis provides a versatile, low-cost and fast detection method for fluoride.