Optical spectroscopy is a valuable tool for online monitoring of a variety of processes. Ultraviolet–visible (UV–vis) spectroscopy can monitor the concentration of analytes as well as identify the speciation and oxidation state. However, it can be difficult or impossible to employ UV–vis-based sensors in chemical systems that are very dark (i.e., have a high optical density), requiring exceedingly short path lengths (for transmission approaches) or an effective means of backscattering (for reflectance approaches). Examples of processes that produce highly absorbing solutions and that would benefit significantly from the diagnostic potential of optical sensors include used nuclear fuel recycling and molten salt systems with high concentrations of dissolved uranium. Utilizing an attenuated total reflectance (ATR) UV–vis approach can overcome these challenges and allow for the measurement of solutions orders of magnitude more concentrated than transmission UV–vis. However, determining ideal sensor specifications for various processes can be time-consuming and expensive. Here, we evaluate the ability of a novel ATR–UV–vis probe to measure very concentrated solutions of Co(II) and Ni(II) nitrate as well as organic dyes (methylene blue, acid red 1, and crystal violet). This sensor design provides a modular method for exploring possible “path lengths” by altering the length of the ATR fiber that was submerged within solution during spectral measurements. Measurements within the ATR sensor cell were compared to measurements gathered by transmission UV–vis of samples within a commercially available 1 cm optical cuvette. The ATR–UV–vis probe was capable of measuring absorbance of solutions with a chromophore concentration 600 times greater than that in the 1 cm cuvette. Advanced data analysis in the form of multivariate curve resolution (MCR) was used to analyze the speciation of methylene blue over a large concentration range. The application of this novel ATR–UV–vis probe to the investigation of dark solutions is a promising avenue for use in online monitoring of nuclear processes.

中文翻译：

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开发用于暗溶液在线监测的衰减全反射-紫外-可见光探头


光谱学是在线监测各种过程的宝贵工具。紫外-可见 （UV-Vis） 光谱可以监测分析物的浓度，并确定形态和氧化态。然而，在非常暗（即具有高光密度）、需要极短光程（对于透射方法）或有效的反向散射方法（对于反射方法）的化学系统中使用基于 UV-Vis 的传感器可能很困难或不可能。生产高吸收性溶液并将从光学传感器的诊断潜力中受益匪浅的工艺示例包括废核燃料回收和具有高浓度溶解铀的熔盐系统。利用衰减全反射 （ATR） UV-vis 方法可以克服这些挑战，并允许测量比透射 UV-vis 更集中几个数量级的溶液。然而，为各种过程确定理想的传感器规格可能既耗时又昂贵。在这里，我们评估了新型 ATR-UV-vis 探针测量非常浓的 Co（II） 和 Ni（II） 硝酸盐溶液以及有机染料（亚甲蓝、酸性红 1 和结晶紫）的能力。这种传感器设计提供了一种模块化方法，通过改变光谱测量期间浸没在溶液中的 ATR 光纤的长度来探索可能的“路径长度”。将 ATR 传感器池内的测量值与通过市售 1 cm 光学比色皿内样品的透射紫外-可见光收集的测量值进行了比较。ATR-紫外-可见光探针能够测量发色团浓度比 1 cm 比色皿高 600 倍的溶液的吸光度。 采用多变量曲线分辨率 （MCR） 形式的高级数据分析来分析亚甲基蓝在大浓度范围内的形态。这种新型 ATR-UV-vis 探头应用于暗溶液的研究是用于在线监测核过程的有前途的途径。