Micro-Raman Technology to Interrogate Two-Phase Extraction on a Microfluidic Device

Abstract

Microfluidic devices provide ideal environments to study solvent extraction. When droplets form and generate plug flow down the microfluidic channel, the device acts as a microreactor in which the kinetics of chemical reactions and interfacial transfer can be examined. Here, we present a methodology that combines chemometric analysis with online micro-Raman spectroscopy to monitor biphasic extractions within a microfluidic device. Among the many benefits of microreactors is the ability to maintain small sample volumes, which is especially important when studying solvent extraction in harsh environments, such as in separations related to the nuclear fuel cycle. In solvent extraction, the efficiency of the process depends on complex formation and rates of transfer in biphasic systems. Thus, it is important to understand the kinetic parameters in an extraction system to maintain a high efficiency and effectivity of the process. This monitoring provided concentration measurements in both organic and aqueous plugs as they were pumped through the microfluidic channel. The biphasic system studied was comprised of HNO as the aqueous phase and 30% (v/v) tributyl phosphate in n-dodecane comprised the organic phase, which simulated the plutonium uranium reduction extraction (PUREX) process. Using pre-equilibrated solutions (post extraction), the validity of the technique and methodology is illustrated. Following this validation, solutions that were not equilibrated were examined and the kinetics of interfacial mass transfer within the biphasic system were established. Kinetic results of extraction were compared to kinetics already determined on a macro scale to prove the efficacy of the technique.

Microfluidic In-Situ Spectrophotometric Approaches to Tackle Actinides Analysis in Multiple Oxidation States

“…Additional solutions containing uranyl nitrate (98.0–102%, Spectrum Chemical Manufacturing Corporation) and U(IV) with sodium nitrate (>99%, Sigma Aldrich) and nitric acid (70%, Sigma Aldrich) were made and measured on a fused silica microfluidic chip using Raman spectroscopy. The Raman setup has been described previously as have solution preparation approaches in Lines et al 3 and Nelson et al 21,30,31…”

Quantitative electrolysis of droplet contents in microfluidic channels. Concept and experimental validation

“…Despite the powerful detection methods used today, analytical techniques are still needed to improve detection performance and to expand the application fields [15]. Methods have been implemented like absorbance and fluorescence spectroscopy [16], laser-induced fluorescence [17], mass spectrometry [18], and Raman spectroscopy [19]. They provide selective, sensitive and accurate quantifications but their coupling with miniaturized systems for on-site applications remain unsuitable due to bulky and expensive instrumentations.…”

Experimental Methodology for Kinetic Acquisitions Using High Velocities in a Microfluidic Device

“…Some authors are now using microfluidics to study mass transfer in the nuclear field [9][10][11][12] and fewer attempts exist to determine the intrinsic constants governing it [13,14]. They are characterized by the absence of a diffuse layer [15].…”