Spectroelectrochemical Sensing Based on Multimode Selectivity Simultaneously Achievable in a Single Device. 11. Design and Evaluation of a Small Portable Sensor for the Determination of Ferrocyanide in Hanford Waste Samples

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 μL, 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 × 10-5 to 5 × 10-3 M ferrocyanide with electrochemical modulation by scanning at 20 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. A value for the ferrocyanide concentration in the sample of 0.61 mM was determined by FTIR spectroscopy.