Abstract
We describe a new approach for high sensitivity and real-time online measurements to monitor the kinetics in the processing of nuclear materials and other chemical reactions. Mid infrared (Mid-IR) quantum cascade laser (QCL) high-resolution spectroscopy was used for rapid and continuous sampling of nitrates in aqueous and organic reactive systems, using pattern recognition analysis and high sensitivity to detect and identify chemical species. In this standoff or off-set method, the collection of a sample for analysis is not required. To perform the analysis, a flow cell was used for in situ sampling of a liquid slipstream. A prototype was designed based on attenuated total reflection (ATR) coupled with the QCL beam to detect and identify chemical changes and be deployed in hostile environments, either radiological or chemical. The limit of detection (LOD) and the limit of quantification (LOQ) at 3σ for hydroxylamine nitrate ranged from 0.3 to 3 and from 3.5 to 10 g·L−1, respectively, for the nitrate system at three peaks with wavelengths between 3.8 and 9.8 μm.
Highlights
The monitoring of chemical processing in hazardous or extreme conditions challenges methods that rely on sampling followed by offline analysis
For attenuated total reflection (ATR)-FTIR spectroscopy, the effective path length is equal to the number of reflections of the quantum cascade laser (QCL) beam in the ATR crystal times the penetration depth
We have developed an approach for high sensitivity and realtime online measurements to monitor chemical processes in aqueous systems
Summary
The monitoring of chemical processing in hazardous or extreme conditions challenges methods that rely on sampling followed by offline analysis. Resonance Raman has been used to study nitrate and nitrite in wastewater treatment processes, with detection limits of 7 μg [21] This method depends on far UV excitation; this method becomes unfeasible for use in applications involving high concentrations of nitrate because self-absorption becomes problematic at concentrations above 3.5 mM. We have developed a new method of in situ or online measurement in aqueous solution, which can be used to effectively monitor key species such as NO3− and HNO2 involved in the redox process chemistry of actinides. This prototype can be incorporated into the reaction system for continuous monitoring of the reaction progress to provide rapid quantitative and qualitative analysis. The QCL spectroscopic method was employed online to observe simultaneously the spectral signatures of NH3OH+ and HNO2
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