Review—Potentiometric Determination of Phosphate Using Cobalt: A Review

Inorganic phosphorus (orthophosphate) determination is crucial within environmental applications. Conventional accredited measurement methods of orthophosphate provide accurate measurements for a limited number of samples due to cost, time, and labor involved with laboratory analysis and are insufficient to characterize phosphate variability within environmental applications. Precise electrochemical sensing has the potential to provide accurate phosphate measurements and has the advantage of being inexpensive to produce and portable. Cobalt is a robust metal that has shown a unique selectivity towards phosphate in potentiometric sensors. In this manuscript, we reviewed the cobalt phosphate ion-selective electrodes with cobalt matrices in the form of pure metal, microelectrode, thin-film, and heterogeneous metal membrane in building integrated probes for determining phosphate concentrations in aqueous solutions. We reviewed different proposals of the cobalt-phosphate chemical reactions on the electrode surface, the factors affecting the stability of the phosphate measurement, and the success stories in the form of the limit of detection, linear range, and sensitivity. With strong progress in recent decades, we restricted ourselves at the time between 1995 and 2018. We discussed future opportunities of cobalt sensors towards more reliable phosphate sensing using novel approaches like cobalt alloys, three in one cobalt phosphate sensors, and external interference elimination methods.