An innovative device to determine the partial pressure of volatile components via substrate-integrated hollow waveguide infrared spectroscopy with integrated microfluidics

C. Penisson, J. Theisen, V. Kokoric, A. Wilk, G. Bernard, T. Zemb, B. Mizaikoff, J.-C.P. Gabriel
CEA,
France

Keywords: chemical activity, partial pressure, microsystem, FTIR, iHWG, sensor

Summary:

A microfluidic system combined with substrate-integrated hollow waveguide (iHWG) vapor phase infrared spectroscopy has been developed for evaluating the chemical activity of volatile compounds dissolved in complex fluids [1]. Chemical activity is an important yet rarely exploited parameter in process analysis and control. However following chemical activity could lead to an increase of industrials plants yields by tuning more precisely processes and preventing industrials failures. Indeed easy access to chemical activity parameters could enable systematic studies on phase diagrams of complex fluids which is very time consuming nowadays. In particular, chemical processes associated with any separation plant, reactors, or purification/recycling [2] systems would benefit from such capabilities. Surprisingly, to the best of our knowledge, following chemical activities to study complex fluid behaviour has yet to be performed and exploited routinely and in real time. We attribute the lack of reports on this highly relevant aspect to the technical difficulties of the presented experimental setup. Direct and (near) real-time measurement of chemical activity of volatile components remains challenging. In order to measure chemical activity, the most straightforward approach is to measure vapor partial pressures of all chemicals above liquid, and to follow their changes as a function of time and concentration. Indeed Raoult’s law states that partial pressures are correlated to chemical activity inside the liquid phase. Thus following partial pressure enable to follow chemical activity inside the liquid phase. The instrumental approach developed here uniquely enables controlled evaporation from a liquid sample solution into a hollow waveguide structure, and analyses the partial pressures of volatile constituents in equilibrium with the liquid phase. Fourier transform infrared spectroscopy (FTIR) technic is used to follow partial pressures by measuring absorbance of the different gas molecules. Such an assembly only requires few micro litters of liquid by using jointly microfluidic cartridge and vapor cell based on iHWG [3] technology in combination with an FTIR spectrometer for rapid equilibration compare to bulky system (e.g White cells or Herriott cells). This assembly allow measurements in the absence of any perturbations provoked by injection operations, which is unavoidable using state-of-the-art analytical techniques such as headspace gas chromatography. Moreover using microsystems make easier the integration on industrial processes. Such analyses would be a major breakthrough in advancing fundamental understanding and modelling of complex fluids, as well as real-time process monitoring. The global architecture together with proof of concept measurements demonstrating the utility of the device for future process analysis-and-control applications will be presented. [1] Vjekoslav Kokoric, Johannes Theisen, Andreas Wilk, Christophe Penisson, Gabriel Bernard, Boris Mizaikoff and Jean-Christophe P. Gabriel, “Determining the Partial Pressure of Volatile Components via Substrate-Integrated Hollow Waveguide Infrared Spectroscopy with Integrated Microfluidics” (submitted); Patent pending. [2] Thomas Zemb et al., “Recycling Metals by Controlled Transfer of Ionic Species between Complex Fluids: En Route to ‘ienaics,’” Colloid and Polymer Science 293, (January 2015) [3] Andreas Wilk et al., “Substrate-Integrated Hollow Waveguides: A New Level of Integration in Mid-Infrared Gas Sensing,” Analytical Chemistry 85, (December 3, 2013)