Determination of inorganic phosphate in a soil extract using a cobalt electrode

Abstract

In soil and environmental science, a sensitive and accurate phosphate sensor would constitute a very useful tool. Several designs, mainly potentiometric and amperometric, have been published, but no commercial sensor exists. Recently, a cobalt electrode has been shown to respond to phosphate in solution. This electrode is extremely simple and robust. In this work, the cobalt electrode applicability to the measurement of phosphate in ammonium lactate-acetic acid (AL) extracts of soils was investigated. The slope of the calibration curve was -30 mV/decade; the linear part corresponded well with the concentration range usually encountered in AL extracts. Dissolved organic substances caused the electrode potential to drift and the extracts were therefore shaken with carbon black prior to measurement. Iron was shown to interfere, most likely by participating in the cathodic electrode reaction.