Phosphate ion sensor using a cobalt phosphate coated cobalt electrode.

Phosphorous is one of three major nutritional elements for plants and usually exists as phosphate ions in nature. For hydroponic culturing and wastewater treatment, the development of a high-performance phosphate sensor would be very helpful. A novel phosphate ion-selective electrode was constructed using a cobalt phosphate surface coated cobalt electrode. The potential response seems to be caused by the formation of Co(H 2 PO 4 ) 2 in the coexistence of CoO and Co(OH) 2 . The sensor exhibited a linear response to H 2 PO 4 − in the concentration range from 1.0 × 10 −5 to 1.0 × 10 −1  mol L −1  at a pH range from 4.0 to 6.5 with a slope of −39 mV dec −1 . The sensor was unaffected by common anions, such as chloride, carbonate, and sulfate. The electrode maintained stability for at least 4 weeks in a live hydroponics system when sufficient Co 3 (PO 4 ) 2 ·8H 2 O was deposited on the Co electrode. [ABSTRACT FROM AUTHOR]