Solid-state reduction at a platinum microelectrode in relation to measurement of oxygen flux in soil

Abstract

In acidic soils (pH < 5.5) saturated with water the polarogram measured with a platinum microelectrode between applied potentials - 0.1 to - 0.9 V (versus a saturated calomel electrode) corresponds to an oxygen reduction polarogram from - 0.1 to - 0.4 V but deviates markedly at more negative potentials. As the pH of the soil decreases the extent of the deviation increases, but at pH values as low as 3.5 there is no material effect on the current reading at - 0.4 V. Evidence is presented which suggests that interference to the oxygen reduction polarogram occurs over and above the liquid phase effect by solid-state reduction of at least carboxyl groups within the soil. It is recommended that the maximum negative potential to be applied to a platinum microelectrode to measure oxygen flux in a saturated soil should be -0.4 V (v. S.C.E.).