A system is described for the direct potentiometric flow injection analysis of phosphates using a cobalt wire electrode. It is proposed that the electrode response to phosphate is a result of CO3(PO)(2) precipitate formation at the electrode surface. The electrode response to phosphate was found to be depend on the phthalate concentration, carrier pH, flow rate and injected volume. A linear response with a slope of -41+/-0.5 mV/decade was obtained in the concentration range of 1.0x10(-5) -5.0x10(-3) M with a detection limit of 1x10(-6) M, using a carrier solution containing 25 mM potassium hydrogen phthalate at pH 4.0. The proposed method was used for the determination of soil extracts with a fast analysis, low cost, high sensitivity and selectivity. (C) 1998 Elsevier Science B.V.