Abstract
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 (Figure 1). Chemical activity is an important yet rarely exploited parameter in process analysis and control. Access to chemical activity parameters enables systematic studies on phase diagrams of complex fluids, the detection of aggregation processes, etc.. The instrumental approach developed herein uniquely enables controlled evaporation/permeation from a sample solution into a hollow waveguide structure, and analyzing the partial pressures of volatile constituents. For the example of a binary system, it was shown that the chemical activity may be deduced from partial pressure measurements at thermodynamic equilibrium conditions. The combined microfluidic-iHWG mid-infrared sensor system (µFLUID-IR) allows realizing such studies in absence of any perturbations provoked by sampling operations, which is unavoidable using state-of-the-art analytical techniques such as headspace gas chromatography. We will present our results on various complex fluids proving perturbation-free measurements, response time and recovery times, which substantiates the utility of µFLUID-IR for future process analysis-and-control applications.