Phosphate And Fluoride Error Of Ph Glass Electrodes. Erroneous Potentials Caused By A Component Of Some Membrane Glasses

Two errors in pH glass electrodes, the phosphate error and the fluoride error, are reported. They are exhibited by electrodes with lanthanum-containing membranes in phosphate and fluoride solutions, in which the electrode potential first shows the constant correct value during an induction time, and then suddenly drifts by -4 to -18mV, depending on the membrane glass, for an even longer drift period, finally attaining a constant erroneous value.