Monofluorophosphate: Its analysis, preparation and stability with regard to its use in toothpaste.

Abstract

A study has been carried out on aspects of monofluorophosphate chemistry, with consideration for its use in toothpaste, A survey of techniques available for the analysis of mono- fluorophosphate was carried out. Conditions were established for the complete separation of monofluorophosphate and its major impurities by ion exchange chromatography. A detector based on heats of sorption and desorption was investigated as a means of automating the monitoring of species eluting from the chromatographic column. Procedures for determining monofluorophosphate and free fluoride ions using the fluoride ion electrode were devised. The methods were based on the determination of fluoride ion present in solution both with and without a preliminary acid hydrolysis step. Methods of preparing pure monofluorophosphate were investigated. Direct synthesis by heterogeneous gas-solid reactions on disodium hydrogen orthophosphate were attempted. Thionyl fluoride, sulphur tetrafluoride and hydrogen fluoride were the gaseous reagents investigated. A pure product vas not obtained in any of these reactions. Various chromatographic techniques, including preparative-layer and column chromatography were used in attempts to purify monofluorophosphate. A successful isolation of the pure ammonium salt was achieved using ion exchange chromatography followed by precipitation with ethanol and prolonged drying under high vacuum. Attempts to convert the pure compound to the sodium salt without decomposition were unsuccessful. The stability of the anion in glycerol-water mixtures was studied by investigating the kinetics of its hydrolysis in these media. The rates were studied at varying hydroxyl ion concentrations. The individual rate constants for the water and the hydroxyl ion reactions were determined for the various solvent compositions. Attempts were made to correlate the rate constants with certain solution parameters.

Date of Award	1974
Original language	English
Awarding Institution	University of Bath