DETERMINATION OF FREE AND TOTAL FLUORIDE IN RAIN WATER USING A CONTINUOUS-FLOW SYSTEM EQUIPPED WITH A FLUORIDE ION-SELECTIVE ELECTRODE DETECTOR

A continuous-flow system equipped with a fluoride ion-selective electr ode (F- ISE) detector was constructed for the determination of free an d total amounts of fluoride in rain water The buffer system proposed w as a mixture of p-alanine (2-aminopropionic acid) and HCl with and wit hout CDTA(1,2-cyclohexanediamine tetraacetic acid). Only one calibrati on graph is needed to calculate the free and total fluoride concentrat ions. The detection limit is 1 x 10(-8) mol dm(-3). The precision of f ive independent measurements was within 7.3% for 3 x 10(-8) -1 x 10(-6 ) mol dm(-3) standard fluoride solutions. About 50-70% of the fluoride in rain water samples was found to be in free form. (C) 1998 Elsevier Science B.V.