Determination of the Oxidative Redox Capacity of Aquifer Sediment Material BySpectrochemical Coulometric Titration

摘要

Methodology was developed for determination of the oxidative redox capacity ofaquifer sediment material by the method of spectroelectrochemical coulometric titration. This method involves the measurement of absorbance of sediment particles slurries at the maximum absorption wavelengths of the optically detectable mediator-titrant (reporter) molecules resorufin and methyl viologen as a function of the charge passed in a constant-potential coulometric titration. Titration was carried out on diluted, dry-sieved Columbus Air Force Base material of particle size smaller than 75 micrometers diameter. Resorufin was reduced first, followed by methyl viologen. There was no perceptible delay between completion of titration of resorufin and the initiation of titration of methyl viologen. Based on the uncertainties of measurement, it could be estimated that the upper limit of oxidative redox capacity of the Columbus aquifer material was ca. 3 microequivalents per gram-of solid material. More precise determination of oxidative redox capacity will require use of methods such as fluorescence which are more immune to the effects of scattered light than absorption spectrophotometry, and will allow higher loading of suspended solids than the current absorbance based method.