On-line pervaporation separation process for the potentiometric determination of fluoride in “dirty” samples

A selective method for the determination of fluoride in contaminated samples based on pervaporation of a volatile derivative and potentiometric monitoring of the anion after collection in a basic solution has been developed. Fluoride was converted to volatile trimethylfluorosilane by reaction with hexamethyldisilazane, and absorbed in dilute NaOH solution. Both the continuous and stopped-flow modes were used in order to accomplish a variable efficiency of the separation process thus enlarging the determination range which was established between 5 and 100 mg l−12, the precision ranging between 2.60 and 3.58%. The determination of the analyte in samples from different sources (i.e., tap water, well water, fertilizers and ceramic industry wastewater) testifies to its usefulness.