Flow analysis data of the response of an aluminum wire electrode to fluoride into which A13+ is added is modeled assuming a logarithmic response of the electrode to F-and reaction of F-with aluminum ions to give a series ofcomplexes [A1F,](3-9)f when q = 1,2,3,4,5,6. The solutions were maintained at pH 5.0 with acetic acid/acetate buffer. Other species modeled were the hydroxo complexes of aluminum [Al,(OH),]'3"-"'+ when m = I, n = 1,2,3,4; m = 2, n = 2; m = 3, n = 4; m = 13, n = 32, and the acetate complex [A12(0H),OAc]'+. Protonation of F-to H F and HFF was also considered. Three coefficients were required to fit the data, a constant and slope of the response of the electrode to free fluoride and a dispersion factor in the flow analysis. Published stability constants were used and no account was taken of ionic strength. The model may be used to predict optimum analysis conditions given an approximate aluminum concentration.