PNNL

Abstract

A ferrocyanide spectroelectrochemical sensor has been evaluated on Hanford U-Plant-2 simulant solution. The sensor consists of an indium tin oxide optically transparent electrode coated with a thin film of porous silica containing immobilized PDMDAAC as an anion exchanger. Ferrocyanide is quantified by the absorbance change at 420 nm that accompanies electrochemical modulation of ferrocyanide that partitions into the film. Hanford U-Plant-2 simulant mimics the contents of tanks in which radioactive waste is stored. A solution of the simulant is a complex mixture of high pH (10) and high ionic strength that contains ferrocyanide. Systematic evaluation of the species in the simulant solution showed the only significant interference to be competition by the anions in the simulant with the preconcentration of ferrocyanide into the sensing film. Deterioration of the sensing film by the high ionic strength and alkaline conditions restricted its useful lifetime to about 40 min. Analysis of simulant with a sensor calibrated at high ionic strength gave 8.0 mM ferrocyanide compared to 8.2 mM obtained by FTIR.