Direct determination of phosphate in soil extracts by potentiometric flow injection using a cobalt wire electrode

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 1.0×10−5 – 5.0×10−3 M with a detection limit of 1×10−6 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.