ONLINE PERVAPORATION SEPARATION PROCESS FOR THE POTENTIOMETRIC DETERMINATION OF FLUORIDE IN DIRTY SAMPLES

A selective method for the determination of fluoride in contaminated s amples based on pervaporation of a volatile derivative and potentiomet ric monitoring of the anion after collection in a basic solution has b een developed. Fluoride was converted to volatile trimethylfluorosilan e by reaction with hexamethyldisilazane, and absorbed in dilute NaOH s olution. Both the continuous and stopped-now modes were used in order to accomplish a variable efficiency of the separation process thus enl arging the determination range which was established between 5 and 100 mg l(-1), the precision ranging between 2.60 and 3.58%. The determina tion of the analyte in samples from different sources (i.e., tap water , well water, fertilizers and ceramic industry wastewater) testifies t o its usefulness.