Combined effort: Microreactors under UV

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  • Published: Dec 1, 2013
  • Author: David Bradley
  • Channels: UV/Vis Spectroscopy
thumbnail image: Combined effort: Microreactors under UV

Segmented and multiphase

Microreactors with integrated UV/Vis spectroscopic detection for online process analysis under segmented flow. Credit: Royal Society of Chemistry/LoC

The combination of reaction and detection in a single lab-on-a-chip, or microfluidic, device could lead to viable microreactor systems that exploit multiphase flow. A team in The Netherlands has now coupled UV/Vis spectroscopy to such a microreactor system for online process analysis under segmented flow conditions.

Jun Yue, Jaap Schouten and Alexander Nijhuis of the Laboratory of Chemical Reactor Engineering, at Eindhoven University of Technology, and Floris Falke of LioniX BV, in Enschede, The Netherlands, explain how during the last ten years or so microreactors have become an important component of the modern laboratory bench. They have facilitated novel synthetic schemes through their nuanced means of mixing reagents in ways that are essentially off-limits to conventional flask chemistry. They add that their full potential is yet to be realised and that there are many advantages waiting to be tapped with respect to their "well-defined flow pattern, uniform temperature distribution, fast response, and increased safety and substantial process intensification through enhanced mass transport and improved chemistry," the team suggests.

Clear principles

One issue that has slowed their widespread adoption for flow reactions is finding a simple and effective means to integrate an analytical function for quality control on such micro devices. However, Yue and colleagues reason that ultraviolet-visible spectroscopy might provide a solution this problem. Integrating UV/Vis might allow processes to be monitored in real-time, inline and so allow optimisation to be carried out so that any given reaction within the micro device can produce the best yield possible with minimal by-products. Moreover, most work has focused on homogeneous, liquid-phase reactions at the microreactor scale with offline analysis, but the team hopes that their approach will enable multiphase reactions to be monitored inline.

The team points out that an additional obstacle is the fact that integrating a spectroscopic system is not a trivial task it requires a "clear understanding of the interplay between hydrodynamics in microreactors and the spectroscopic measurement principles." However, many reactions of commercial or industrial interest are not homogeneous and involve immiscible reagents and might involve liquids or liquids and gases, thus they involve segmented flow in the microreactor setup.

Embedded solutions

In one of the first pieces of research to address the issues surrounding real-time analysis in microreactors, the team explain in the journal "Lab on a Chip" how they have successfully coupled UV/Vis spectroscopy at the microfluidics scale with a microreactor. Indeed, they investigated two approaches to integration. The first uses a cross-type flow-through cell placed in the out-stream of a capillary microreactor; this allows detection in the transmission mode. The second approach uses embedded waveguides on a microfluidic chip for detection.

They carried out model experiments to look at the capabilities of each approach in a microreactor gold nanoparticle synthesis. They were able to successfully obtain liquid-phase concentrations and data on the segmented flow from their 2-millisecond resolution UV/Vis spectra.

"The next steps in the research will be to use the on-line real time spectroscopic information that we collect for process control purposes," NIjhuis told SpectroscopyNOW. "In the example of gold nanoparticle production, you can use the spectroscopy to collect information on the gold particle size that you are producing and use this information to tune the process condition so that you will be producing the desired particle size. At a later stage, we will also want to scale up the system to multichannel applications. Since we are doing spectroscopy with visible light and optical fibres, it will be possible to use a single light source and spectrometer and multiplex these to do measurements in different channels."

Related Links

Lab Chip , 2013, 13, 4855: "Microreactors with integrated UV/Vis spectroscopic detection for online process analysis under segmented flow"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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