The Determination of Fluoride in Milk and Milk Products

A literature survey was carried out concerning the function and determination of Fluoride with respect to biological materials. As a result two methods of fluoride determination, the Fluoride Ion-selective Electrode (FISE) and a solvent extraction/GLC method were selected for detailed investigation.
Studies using the FISE revealed that cationic species e.g. calcium and magnesium ions removed fluoride ions from solution, thus rendering them indeterminable, an effect partially reversible by the presence of carboxylic acids. Individual amino acids were shown not to be capable of removing fluoride ions from solution whilst milk proteins were so, their degree of success being dependent on the completeness of their three-dimensional structure. The possibility of two protein binding sites for fluoride ions is discussed.
The solvent extraction/GLC method for the determination of fluoride was critically examined and shown to accurately and repeatably determine total fluoride, depending on the conditions used, in full—cream and skimmed milks up to concentrations of 100 μg ml-1. The use of cyclohexane as organic solvent has been examined and it has been shown to be equally efficient as benzene. No association between fluoride ions and milk proteins was determinable using Gel Filtration studies of fluoridated milk due to the mechanism of separation entailed.
19 F NMR studies of fluoride ions in solution confirmed the findings using the FISE with respect to the removal of fluoride ions from solution. The effects of pH and temperature on the resonance shifts observed relative to the proton shift of water were also investigated.
Electro-Optic studies using milk proteins and fluoride ions showed that ‘primary micelles’ are capable of binding more fluoride than milk protein alone. The site of binding of fluoride ions was discussed in connection with the existence of two binding sites.