PNNL

Abstract

A portable spectroelectrochemical sensor has been designed, evaluated, and demonstrated on a complex sample of radioactive waste. The sensor consisted of a black delrin sample compartment with a total internal sample volume of 800 ?L, attached to an indium tin oxide coated glass multiple internal reflection optical element. Detection was by total internal reflection of light from a blue light emitting diode source. After a 10 min uptake for each standard, the sensor showed a linear response in absorbance change for 5 x 10-5 to 5 x 10-3 M ferrocyanide with electrochemical modulation by scanning at 25 mV/s from ? 0.30 V to + 0.55 V vs. a Ag/AgCl reference electrode. Due to the complex nature of Hanford radioactive tank waste samples containing ferrocyanide, a standard addition method was developed for analysis. The spectroelectrochemical sensor determined a concentration of 9.2 mM ferrocyanide for U-Plant-2 simulant solution containing 9.38 mM ferrocyanide that was prepared according to Hanford process flowsheets. A radioactive tank waste sample from Hanford Tank 241-C-112 was determined to be 1.0 mM in ferrocyanide using the spectroelectrochemical sensor. The accepted value for ferrocyanide concentration in the sample is 0.61 mM as determined by IR spectroscopy.