Improvement on the microdiffusion technique for the determination of ionic and ionizable fluoride in cows' milk.

Different microdiffusion techniques for the determination of ionic and ionizable fluoride in milk have been evaluated for measurement with a fluoride-selective sensor. This work culminated in a modified version of the hexamethyldisiloxane-acid diffusion technique where an increased amount of perchloric acid and sodium hydroxide seemed to be a prerequisite for accurate and precise results. The configuration of the fluoride-selective electrode was also modified by using an adapted microanalytical procedure to determine fluoride in small volumes (50 microliters each) and to avoid contamination between successive milk samples. The resultant procedure is free of interferences and is capable of measuring fluoride in milk at concentrations from 0.02 to 10.00 mg dm-3 with improved accuracy and precision compared with earlier work.