Direct Potentiometric Determination of Fluoride Species by Using Ion-Selective Fluoride Electrode

A novel approach and method for potentiometric determination of acid dissociation constant (K-a) of hydrofluoric acid are described. Proposed method is based on using commercial fluoride ISE (FISE) as very inexpensive, simple and reasonably fast method for determination of fluoride species. We are proposing a usage a direct potentiometric method for determination of fluoride species and K-a of hydrofluoric acid in water solutions for 1.01 <= pH <= 7.01 and 1.0x10(-1) <= c(T)(F-) <= 1.0x10(-6) mol L-1. Found acid dissociation constant of hydrofluoric acid (pK(a) = 3.24 +/- 0.02, K-a = 5.75x10(-4) L mol(-1)) and formation constant of HF2- (log beta = 0.600, beta = 3.98 L mol(-1)) are in very good agreement with literature ones.