Field-based comparison of platinum and wax impregnated graphite redox electrodes

Abstract

An inert electrode was constructed using wax-impregnated graphite (WIG) as an alternative to Pt for permanent installation in the regolith. The performance of WIG electrodes has not previously been systematically evaluated by using data from field trials, although Pt and WIG measure similar Eh values in laboratory solutions. We compared the performance of the WIG electrode when installed adjacent to Pt redox electrodes in the A, B and C horizons of duplex soils in a X-eralf-Aqualf toposequence near Mount Crawford in the Mt Lofty Ranges, South Australia. Lower potentials, commonly in the order of 200 mV, were measured from WIG electrodes, relative to Pt electrodes. Measurements of potential from adjacently installed WIG and Pt electrodes did not show significant correlation. Generally oxidizing redox potentials were measured in all soils in which electrodes were installed due to below average rainfall during the sampling period. Further testing of WIG electrodes in reduced regolith is needed. Interpretation of Eh trends, measured using Pt electrodes, between the A, B and C horizon are presented.